Plant-mediated biosynthesis of metallic nanoparticles: A review of literature, factors affecting synthesis, characterization techniques and applications

Accepted Manuscript Title: Plant-mediated biosynthesis of metallic nanoparticles: A review of literature, factors affecting synthesis, characterization techniques and applications Authors: K. Vijayaraghavan, T. Ashokkumar PII: DOI: Reference:

S2213-3437(17)30464-5 http://dx.doi.org/10.1016/j.jece.2017.09.026 JECE 1874

To appear in: Received date: Revised date: Accepted date:

21-4-2017 11-9-2017 13-9-2017

Please cite this article as: K.Vijayaraghavan, T.Ashokkumar, Plant-mediated biosynthesis of metallic nanoparticles: A review of literature, factors affecting synthesis, characterization techniques and applications, Journal of Environmental Chemical Engineeringhttp://dx.doi.org/10.1016/j.jece.2017.09.026 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

1

Plant-mediated biosynthesis of metallic nanoparticles: A review of literature, factors affecting synthesis, characterization techniques and applications

K. Vijayaraghavan1,2,* and T. Ashokkumar1,*

1

Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai-

600036, India 2

Sino-Forest Applied Research Centre for Pearl River Delta Environment, Hong Kong

Baptist University, Kowloon Tong, Hong Kong

*Corresponding authors: K. Vijayaraghavan: Tel: +91-44-22575156; Fax: +91-44-22570509; E mail: [email protected]; [email protected]; [email protected]; T.

Ashokkumar:

Tel:

+91-44-22575156;

Fax:

+91-44-22570509;

E

mail:

[email protected]

Highlights 

Phytomolecules act as reducing and stabilizing molecules for metal nanoparticles



Various instrumental techniques to characterize nanoparticles were discussed



Factors influencing bioreduction potential were highlighted



Application of biosynthesized nanoparticles in different fields was discussed

Abstract Nanoparticles exhibit unique properties that enable them to find potential applications in various fields. Accordingly, significant research attention is being given to the

2

development of novel strategies for the synthesis of nanoparticles. Among these, biological route of nanoparticle synthesis has been portrayed as an efficient, low-cost and environmental friendly technique. Biological materials such as bacteria, fungi, yeast, algae and plant have been reported to possess high bioreduction ability to synthesize various size and shape of metallic nanoparticles. Of these biomaterials, this review focuses on plant-mediated biosynthesis of metallic nanoparticles. The biomolecules present in the plants such as terpenoids, flavones, ketones, aldehydes, proteins, amino acids, vitamins, alkaloids, tannins, phenolics, saponins, and polysaccharides play a vital role in reduction of metals. A systematic comparison of literature, based on the bioreduction capacity of various plant biomass/extract towards various metals under different experimental conditions, is also provided. Various instrumental techniques utilized to characterize nanoparticles are also discussed. Finally, this review also highlights the application of biosynthesized nanoparticles in different fields such as medicine, agriculture, catalytic, cosmetic and food. Thus, this article reviews the achievements and current status of plant-mediated biosynthesis, and hopes to provide insights into this exciting research frontier.

Keywords: biosynthesis; nanotechnology; green chemistry; biosorption; plant biotechnology

1. Introduction Nanoscience is a multidisciplinary field that involves the design and engineering of functional systems at the molecular scale. It is a field of applied science focused on the synthesis, characterization and application of materials and devices on the nanoscale. In general, nanoscience can be defined as the art and science of manipulating matter at the nanoscale to create new and unique materials. Nanoscaled materials are usually categorized as materials having structured components with at least one dimension less than 100 nm. The

3

emergence of nanoscience has provided promising results in recent years by intersecting with various other branches of science and forming impact on all forms of life. There are two basic approaches to attain nanostructures, viz. top-down and bottom-up methods [1]. Top-down approach involves break down of bulk material into fine particles through size reduction using various lithographic techniques e.g. grinding, milling, sputtering and thermal/laser ablation [2]. In bottom-up approach, the nanoparticles are fabricated from smaller entities, for example by joining atoms, molecules and smaller particles [3]. The bottom-up synthesis mostly relies on chemical and biological methods of production. An important benefit of bottom-up approach is the increased possibility of preparing metallic nanoparticles with relatively lesser defects and more homogeneous chemical composition [4]. Nanoparticles are of great interest owing to their extremely small size and high surface to volume ratio, which alter their physical and chemical properties (such as mechanical properties, biological and satirical properties, catalytic activity, thermal and electrical conductivity, optical absorption and melting point) compared to bulk of the same chemical composition [5]. Due to these beneficial properties, nanomaterials have found potential applications in electronics, photonics, catalysis, information storage, chemical sensing and imaging, environmental remediation, drug delivery, biological labelling, cosmetics, biomedical, mechanics, optics, chemical industries, space industries, energy science, light emitters, single electron transistors and nonlinear optical devices [6]. Functionalization facilitates targeted delivery of these nanoparticles to various cell types, bioimaging, gene delivery, and other therapeutic and diagnostic applications [7]. Generally, nanoparticles are synthesized through three different kinds of methods: physical, chemical, and biological [8,9]. Physical methods used for synthesis of nanoparticles include thermal decomposition, laser irradiation and electrolysis. For example, in thermal decomposition method, the synthesizing process was carried out at very high temperature

4

[10]. The general disadvantages of physical methods are that they usually are energy intensive and require costly vacuum systems or equipment to prepare nanoparticles. The most often used method for the chemical synthesis of nanoparticles is the chemical reduction method using chemical like sodium borohydride or sodium citrate as reducing agents [5]. Even though chemical syntheses have several advantages, the use of toxic chemicals on the surface of nanoparticles and non-polar solvents in the synthesis procedure limits their applications in clinical fields [11]. Therefore, several researchers attempted to develop clean, biocompatible, non-toxic and eco-friendly methods for nanoparticles synthesis [12]. This intensive research leads to development of biological synthesis route for nanoparticle production. The biological synthesis of nanoparticles are being carried out using different biomaterials such as bacteria [13], fungi [14], yeast [15], virus [16], microalgae [17], macroalgae [18] and plant biomass/extract [19]. The use of various biological organisms in this area is rapidly developing due to their growing success and ease of formation of nanoparticles. Recently, the biosynthesis of metallic nanosized rods, wires, flowers, tubes, triangles, spherical, hexagonal, tetragonal and pentagonal were reported successfully [20]. These biological synthesized nanomaterials have potential applications in different areas such as treatment, diagnosis, development surgical nanodevices and commercial product manufacturing [21]. Of various biological materials, plant biomass/extract possesses several inert advantages over other microscopic organisms in nanoparticle synthesis. Plant-mediated biosynthesis of metallic nanoparticles occurs through biomolecules (such as proteins, vitamins, amino acids, enzymes, polysaccharides and organic acids such as citrates) present in the plant biomass [2]. Thus, the aim of present review paper is to highlight the recent trends and developments in plant-mediated biosynthesis of metallic nanoparticles. The application of nanoparticles in medical and other sectors will also be highlighted.

5

2. Synthesis of nanoparticles 2.1. Physical methods Physical methods for synthesis of metallic nanoparticles include evaporationcondensation, laser ablation, electrolysis, diffusion, plasma arcing, sputter deposition, pyrolysis and high energy ball milling [5]. Evaporation-condensation is generally carried out using a tube furnace at atmospheric pressure. The source material within a boat centred at the furnace is vaporized into a carrier gas. Nanoparticles of various materials such as Ag, Au and indium tin oxide (In2O5Sn) have been synthesised using evaporation-condensation technique [22]. However, synthesis of nanoparticles using a tube furnace at atmospheric pressure has some disadvantages; for example, tube furnace occupies a large space, consumes a great amount of energy while raising the environmental temperature around the source material, and requires a lot of time to achieve thermal stability [23]. The laser ablation method is typically designed to produce colloidal nanoparticles in a variety of solvents. The pulse laser ablation process takes place in the chamber under vacuum and in the presence of some inert gases [24]. One important advantage of laser ablation technique compared to other methods for production of metal colloids is the absence of chemical reagents in solutions [5]. In plasma-arcing, the very high temperatures associated with the formation of an arc or plasma is used to effectively separate the atomic species of feedstock, which quickly recombine outside the plasma to form nanosized particles [25]. In recent years, significant advances have been made in the field of spray pyrolysis for the synthesis of nanoparticles and several investigators demonstrated its versatility in producing particles of a variety of compositions, shapes, and sizes [26]. In high energy ball milling, high impact collisions are used to reduce macroscale or microscale materials down into nano-crystalline structures without chemical change. 2.2. Chemical methods

6

Chemical methods for synthesis of nanoparticles include chemical reduction, microemulsion/colloidal, electrochemical and thermal decomposition. Chemical reduction by inorganic and organic reducing agents is one of the most common methods to synthesize colloidal metal particles because of ease in operation and equipment needed. Commonly used reducing agents are sodium borohydride (NaBH4) [27], potassium bitartrate (KC4H5O6) [28], methoxy polyethylene glycol (CH3O(CH2CH2O)nH) [29], trisodium citrate dihydrate (Na3C6H9O9) [30], ascorbate [5] and elemental hydrogen [31].The aforementioned chemical agents reduce metallic ions and lead to the formation of corresponding metallic nanoparticles, which is followed by agglomeration into oligomeric clusters. Turkevich et al. [32] described for the first time the reduction of Au(III) ions to Au(0) using citric acid and further suggested that the method can also be stabilized to form monodispersed nanoparticles and could be exchanged to other ligand. Subsequently in 1994, Brust et al. [33] produced Au nanoparticles using sodium borhydride as reducing agent to produce monodispersed nanoparticles which was easy to disperse in organic solvent and to reisolate as pure powders. Micro-emulsion method is one of a versatile and reproducible method which enables control of particle properties such as size, morphology, geometry, homogeneity and surface area [34]. As discussed in the review by Ganguli et al. [35], micro-emulsion process takes place in the aqueous cores of the reverse micelles which are dispersed in an organic solvent and are stabilized by a surfactant. The dimensions of these aqueous cores are in the nanoregime and are thus being referred to as nanoreactors. The product obtained after the reaction is homogeneous. Several authors successfully attempted to control the shape and size of the nanoparticles through micro-emulsion technique [36]. In the electrochemical method for the synthesis of nanoparticles, electricity is used as a controlling force. The method involves passing an electric current between two electrodes separated by an electrolyte and the nanoparticle synthesis occurs at the electrode/electrolyte interface [37]. Rodríguez-Sánchez et

7

al. [38] used electrochemical procedure, based on the dissolution of a metallic anode in an aprotic solvent, to prepare Ag nanoparticles ranging from 2 - 7 nm. The authors also demonstrated that it was possible to obtain different Ag particle sizes by changing the current density. Furthermore, Ma et al. [39] synthesized spherical Ag nanoparticles (10 - 20 nm) with narrow size distributions in an aqueous solution through electrochemical method. Thermal decomposition is one of the most common chemical techniques to produce stable monodisperse suspensions with the ability of self-assembly [40]. Nucleation occurs when the precursor metal is added into a heated solution in the presence of surfactant, while the growth stage takes place at a higher reaction temperature [41]. The composition and the size of the formed particles depend on parameter such as the reaction time, the temperature and the surfactant molecule length [40]. Even though chemical synthesis route has several benefits, the usage of excessive solvents, surfactants and other chemicals hinder the application aspects of synthesized nanoparticles. 2.3. Biological methods In an attempt to develop low-cost and eco-friendly route, researchers have utilized the potential of biological materials for the synthesis of metallic nanoparticles. Biological (green) synthesis involves the reduction of metal ions using biological mass/extract as a source of reductants either extra-cellularly or intra-cellularly. Apart from cost-effectiveness and ecofriendliness, the advantages of biological approach over traditional physical and chemical methods include effectiveness of the process to catalyze reactions in aqueous media at standard temperature and pressure as well as flexibility of the process as it can be implemented in nearly any setting and at any scale [42]. The constituents of biological materials are responsible for reduction and the process is often triggered by several compounds present in the cell such as phenolic, carbonyl, amine, amide groups, proteins,

8

pigments, flavonones, terpenoids, alkaloids and other reducing agents [43]. More than one of these groups/agents may be responsible for the production of metallic nanoparticles. Considering the composition of these groups/agents vary with each type of biomaterial, elucidation of exact mechanism associated with biosynthesis of nanoparticles may be difficult and has not been completely understood as yet. Bacteria, fungi, yeast, virus, microalgae, macroalgae and plant biomass/extract are some of the important biological materials used in synthesis of metallic nanoparticles. Even though, the ability of biological materials to synthesize nanoparticles is a recent technique, the interactions between metal ions and micro/macro-organism have been known for decades such as the ability of microorganisms to extract or accumulate metals in processes of bioleaching and bioaccumulation [44]. Bacteria are a major group of unicellular living organisms belonging to the prokaryotes, which are ubiquitous in soil and water, and as symbionts of other organisms [45,46]. Bacteria are known to produce inorganic materials either intra-cellularly or extracellularly [47]. Some of the important bacteria studied for biosynthesis come under the following genus: Bacillus [48], Pseudomonas [49]. Husseiny et al. [50] studied extra-cellular synthesis of Au nanoparticles using Pseudomonas aeruginosa. On the other hand, Kalimuthu et al. [51] synthesized Ag nanoparticles of around 50 nm size using Bacillus licheniformis, isolated from sewage collected from municipal wastes. Nair and Pradeep [52] synthesized nanocrystals of Au, Ag and their alloys by reaction of the corresponding metal ions within cells of lactic acid bacteria present in buttermilk. Platinum and palladium metal nanoparticles were produced by sulfate-reducing bacterium, Desulfovibrio desulfuricans [53]. There were reports on potential of Stenotrophomonas malophilia [54], E. coli [55], Geobacillus sp.[56], Pseudomonas proteolytica [57] and Salmonella typhirium [58] to extra-cellularly synthesize various metallic nanoparticles. It is interesting to note that even dead/inactive bacterial

9

biomasses shown potential to reduce metal ions to nanoparticles owing to the presence of certain organic functional groups on cell wall [59]. Fungi are non-phototrophic and eukaryotic microorganisms comprising of a rigid cell wall. The fungal cell wall comprises glycoproteins and polysaccharides, which mainly include glucan and chitin [60]. Fungi, when challenged with aqueous metal ions lead to the formation of nanoparticles both intra- and extra-cellularly [3]. Extra-cellular synthesis is much rapid compared to the intra-cellular route; however the synthesised nanoparticles are much bigger through extra-cellular route [11]. Yadav et al. [60] explained that this difference in size could be possibly due to the nucleation of particles inside the fungus. Extra-cellular syntheses of nanoparticles by fungi such as Penicilium fellutanum [61], Fusarium solani [62], Phoma glomerata [9], Aspergillus oryzae [63], Aspergillus terreus [64] and Rhizopus nigricans [65] have been reported. On the other hand, only limited studies have been carried out on the intra-cellular synthesis of nanoparticles using fungal species [3,66]. Few investigators also explored the possibility of nanoparticle formation using macrofungi [67]. Yeast, which belongs to the class ascomycetes of fungi, has shown good potential for the synthesis of nanoparticles. As a result, several research reports highlighted potential of yeasts such as Yarrowia lipolytica [68] and Saccharomyces cerevisiae [69] in synthesis of nanoparticles. Algae are simple plants; however they lack many distinct organs and structures that characterize terrestrial plants. Some algae are microscopic and are able to float in surface waters (phytoplankton) due to their lipid content, while others are macroscopic and attach to rocks or other structures (seaweeds) [70]. Comparably, there is very little literature supporting the use of algae in nanoparticle synthesis. Only few reports highlighted the potential of microalgae in formation of nanoparticles [71,72]. The brown marine algae (Sargassum wightii) showed potential to synthesize Au nanoparticles extra-cellularly in the

10

size range of 8 – 12 nm. Other brown seaweeds such as Turbinaria conoides [73] green seaweeds [74] and red seaweeds [75] also investigated for nanoparticle formation. Few researchers highlighted the involvement of biosorption followed by bioreduction in nanoparticle

synthesis

by seaweeds

[76,77].

During

Au

nanoparticle

synthesis,

Vijayaraghavan et al. [77] observed two phases: (1) rapid biosorption phase which lasted about 1h in which sorption of Au(III) ions onto the surface of seaweed occurs and (2) slow bioreduction phase which involves reduction of Au(III) ions to Au(0). Of the different biomaterials, the utilization of plant biomass/extracts has been considered more reliable as well as eco-friendly method for the biosynthesis of nanoparticles. The advantages of plant-mediated biosynthesis over other biomaterials include [2,78], 

Easy availability



Safe to handle



Cost-effective



One-step simple process



Composed of various metabolites that may aid in reduction



Elimination of elaborate maintenance of cell cultures



Rapid rate of synthesis



More environmental friendly



More stable nanoparticles



Better control over size and shape of nanoparticles



Suitable for large-scale synthesis

Owing to these advantages, several researchers aimed to explore different plant species for their potential to synthesize nanoparticles. Thus, the present review specifically focus on plant-mediated biosynthesis of metal and metal oxide nanoparticles and their characterization, influencing factors and applications in various fields in subsequent sections.

11

3. Plant-mediated biosynthesis of nanoparticles For biosynthesis of nanoparticles, plants can be used in their live form or dead/inactive form. Several plants are known for their metal accumulation property and these accumulated metals later reduce to nanoparticles intra-cellularly [79]. Gold nanoparticles with a size range of 2 – 20 nm have been synthesized using the live alfalfa plants [80]. Bali and Harris [81] observed that metallophytes (Brassica juncea and Medicago sativa) initially accumulated Au from aqueous KAuCl4 solution and later stored Au as nanoparticles throughout the epidermis, cortex and vascular tissue of both species. The authors also determined the particle sizes ranged between 2 nm - 2 μm in B. juncea and 2 nm - 1 μm in M. sativa. However, recently much work has been done using inactive plant parts as reductant for synthesis of nanoparticles. The biomolecules present in the plants such as terpenoids, flavones, ketones, aldehydes, proteins, amino acids, vitamins, alkaloids, tannins, phenolics, saponins, and polysaccharides play a vital role in reduction of metals [47]. Plant biomass can either be used in powder form or as extracts [82]. In general, the plant biomass particle/extract is mixed with a solution of the metal salt at room temperature and desired pH with or without agitation. In a short span of time, synthesis of nanoparticles will be completed. The experimental protocol for nanoparticle synthesis using plant biomass is depicted in Figure 1. Plant parts such as stem, leaf, flower, fruit, root, latex, seed and seed coat are being used for synthesis of metal nanoparticles. Bhati-Kushwaha and Malik [83] prepared leaf and stem extracts of Verbesina encelioides for biosynthesis of Ag. The authors confirmed that both extracts successfully synthesized Ag nanoparticles; however the rate of synthesis was faster in stem extracts. Similarly, Paulkumar et al. [84] observed the differences in synthesis of Ag nanoparticles while using leaf and stem extracts of Piper nigrum. The authors noted that reaction started at 10 min and ended at 2 h for leaf and 4 h for

12

stem extracts. In addition, the size of the stem-derived Ag nanoparticles was 9 – 30 nm, whereas, small (4 – 14 nm) and large (20 – 50 nm) sized nanoparticles were observed in TEM images of Ag nanoparticles synthesized leaf (Piper nigrum) extracts. On the other hand, Umadevi et al. [85] synthesized Ag nanoparticles using fruit extract of Solanum lycopersicums (tomato) plant. The authors indicated that citric acid present in S. lycopersicums fruit extract acted as reducing agent and malic acid was responsible for capping of the bioreduced Ag nanoparticles. Sneha et al. [86] investigated Au nanoparticles using cumin seed powder. The authors observed polydispersed Au nanoparticles at pH 3 and 30 °C. Noruzi et al. (2011) [87] studied synthesis of Au nanoparticles using rose petals. The authors determined that the flower extract medium contains abundant sugars and proteins and thereby responsible for reduction of tetrachloroaurate salt into Au nanoparticles. Some other important results obtained in biosynthesis of nanoparticles by different plant parts include, fenugreek seed extract for Se nanoparticles [88]; Hevea brasiliensis latex for Ag nanoparticles [89]; mango peel extract for Au nanoparticle [90] and bark extracts of Ficus benghalensis and Azadirachta indica for Ag nanoparticles [91]. Analysing the literature, we understand that much attention was focussed towards noble metals such as Ag, Au, Pt and Pd. These metals come under “precious metal” category and nanoparticles of these metals are widely used in emerging interdisciplinary field of nanomedicine and nanotechnology. Literature on other metal/metal-oxide nanoparticles is scare. In the subsequent sections, we have described the use of plant biomass or their extracts in the synthesis of various metal and metal-oxide nanoparticles. 3.1. Silver nanoparticles Of all the metals, Ag has been studied extensively for plant-mediated biosynthesis and it proved easier and more rapid method than the tedious and time-consuming microbial synthesis processes [92]. Furthermore, synthesis of Ag nanoparticles is of much interest to

13

the scientific community because of their wide range of applications including spectrally selective coating for solar energy absorption [93], surface enhanced Raman scattering for image [94] and many other biomedical applications [42]. Several plants and their respective portions had been utilized for the preparation of Ag nanoparticles. Table 1 lists some of the important results of plant-mediated biosynthesis of Ag nanoparticles. Plant biosynthesis basically involves contacting silver nitrate salt (AgNO3) with extract/biomass of plants. The appearance of brownish yellow colour after short span of contact confirms the formation of Ag nanoparticles according to the following reaction: Ag+NO3- + Plant molecule (OH, C=H, etc.) → Ag0 nanoparticles

(1)

Among earlier reports on Ag nanoparticle synthesis using plants, Shankar et al. [95] conducted Geranium (Pelargonium graveolens) leaf assisted extracellular synthesis of Ag nanoparticles. Upon contacting leaf extract with AgNO3 solution, the authors observed rapid reduction of the Ag ions leading to the formation of highly stable, crystalline Ag nanoparticles (16 – 40 nm) in solution. The authors also proved that the rate of reduction of the Ag ions by the geranium leaf extract was faster than that observed for a fungal species, Fusarium oxysporum. Few years later, Huang et al. [6] showed that triangular or spherical shaped Ag nanoparticles (55 – 80 nm) could be produced using sundried Cinnamomum camphora leaf extract. The authors identified polyol components and the water-soluble heterocyclic components in the leaf extract were mainly responsible for the reduction of Ag ions. In 2008, Leela and Vivekanandan [96] compared leaf extracts of different plant species (Basella alba, Helianthus annus, Oryza sativa, Sorghum bicolar, Saccharum officinarum and Zea mays) for synthesis of Ag nanoparticles and concluded that H. annus exhibited highest potential and rapid reduction of Ag ions. Ahmad et al. [97] prepared broth of popular medicinal plant, basil (Ocimum sanctum) to synthesize Ag nanoparticles. The authors observed highly stable Ag nanoparticles in the size range of 10 ± 2 and 5 ± 1.5 nm. Jeyaraj et

14

al. (2013b) [98] have reported synthesis of Ag nanoparticles from leaf extract of Podophyllum hexandrum. The authors observed complete reduction of Ag ions within 2.5 h of contact at 60 °C and pH 4.5, and process results in spherical shaped particles size ranged from 12 - 40 nm. 3.2. Gold nanoparticles Gold nanoparticle also attracted several researchers in the field of plant-mediated biosynthesis owing to their unique properties and applications in nanoelectronics, biomedical, nonlinear optics, nanodevices and catalysis [99]. In particular, Au nanoparticles provide promising scaffolds for drug and gene delivery [100]. Their unique features such as tunable core size, monodispersity, large surface to volume ratio, and easy functionalization with virtually any molecule or biomolecule allow targeting, transport, and tuning of delivery processes [101]. For most of the above applications, Au nanoparticles synthesized through eco-friendly as well as chemical-free route is preferred. Table 1 lists some of the important results achieved in green synthesis of Au nanoparticles using plant biomasses. In general, bioreduction of chloroauric acid (HAuCl4) to Au nanoparticles follows the below reaction, H+Au3+4Cl-.4H2O + Plant molecule (OH, COOH, etc.) → Au0 nanoparticles

(2)

The above reaction generally turns the suspension to ruby red color, which confirms formation of Au nanoparticles in the solution. Shankar et al. [102] firstly reported the possibility of Au nanoparticle formation using geranium leaves (Pelargonium graveolens). They noted that terpenoids in the leaves acted as reducing and capping agents for rapid reduction of chloroaurate ions to stable Au nanoparticles of variable size. In subsequent years, the same research group demonstrated synthesis of Au nanoparticles using different plant species such as lemon grass plant extract [103] and Neem (Azadirachta indica) leaf extract [78]. Begum et al. [104] produced sphere-, trapezoid-, prism- and rod-shaped Au nanoparticles using black tea leaf extract. The authors identified that extremely efficient

15

reduction potential of leaf extract was due to the presence of tea polyphenols, including flavonoids. Song et al. [105] reported that Magnolia kobus and Diospyros kaki leaf broths were capable of eco-friendly extracellular production of metallic Au nanoparticles (5 – 300 nm) with different triangular, pentagonal, hexagonal and spherical shapes within few minutes (up to 90 % conversion at a reaction temperature of 95 °C). Due to the presence of flavonoids and phenol compounds, Babu et al. [106] noted that ethanolic extract of Mentha arvensis leavesproduced hexagonal- and spherical-shaped Au nanoparticles with an average size of 39 ± 15 nm. Pear fruit extract was used at room-temperature to biosynthesize triangular- and hexagonal-shaped Au nanoparticles (200–500 nm) [107]. Due to the presence of phytochemicals such as organic acids, peptides, proteins, saccharides and amino acids, pear fruit extract when exposed to chloroaurate ions resulted in Au nanoparticles with plate-like morphologies in a highly productive state. In 2014, the extract of Garcinia combogia fruit was used for the production of Au nanoparticles in spherical and anisotropic shapes [108]. The authors indicated that shape of the Au nanoparticles depended on the extract quantity and reaction temperature. Islam et al. [109] reported the leaf galls extract of Pistacia integerrima to reduce ions to Au nanoparticles. Hydroxyl and carboxylic acid groups of polyphenols were responsible for the reduction. Polyphenols capping the nanoparticles makes them stable in different pH solutions as well as at extreme of temperature and also showed significant potential in enzyme inhibition, antibacterial, antifungal, antinociceptive, muscle relaxant and sedative activities. 3.3. Platinum nanoparticles Platinum nanoparticles are widely used as catalysts as well as in many biomedical applications [92]. Compared to Ag and Au, the reports on Pt nanoparticles are significantly limited. The interaction between platinum solution and plant biomass usually leads to the following reaction:

16

H2Pt+6Cl-.6H2O + Plant molecule (OH, COOH, etc.) → Pt0 nanoparticles

(3)

The first report on Pt nanoparticle synthesis using a plant extract was by Song et al. [110], where the authors employed leaf extract of Diopyros kaki as a reducing agent for extracellular synthesis of Pt nanoparticles (2 – 12 nm) from an aqueous chloroplatinic acid hexaydrate (H2PtCl6.6H2O) solution. They achieved 90 % conversion of Pt ions into nanoparticles at reaction temperature of 95 °C and a leaf broth concentration >10 %. With the aid of Cacumen platycladi extract, Zheng et al. [111] biologically synthesized Pt nanoparticles measuring 2.4±0.8 nm obtained under the following conditions: reaction temperature, 90 °C; plant extract percentage, 70 %; initial Pt(II) concentration, 0.5 mM; and reaction time, 25 h. The authors also pointed out that reducing sugars and flavonoids played a vital role in reduction of Pt ions than proteins. Similarly, Soundarrajan et al. [112] used leaf extract of Ocimum sanctum as a reducing agent for the synthesis of Pt nanoparticles (23 nm) from aqueous H2PtCl6·6H2O solution. Through several instrumental techniques, the authors identified that plant compounds such as ascorbic acid, gallic acid, terpenoids, certain proteins and amino acids acted as reducing agents for Pt reduction. Kumar et al. [113] demonstrated simple one step green synthesis of Pt nanoparticles (< 4 nm) using naturally occurring plant polyphenols obtained from an aqueous extract of Terminalia chebula. They identified that reduction of Pt(IV) to Pt(0) and subsequent stabilization was due to oxidised polyphenols in the plant extract. Other important results of Pt nanoparticle synthesis using plant materials are summarized in Table 1. 3.4 Palladium nanoparticles Palladium nanoparticles are widely used as catalysts in various reactions and plasmonic wave guiding as well in chemiresistor-type sensing devices [42].The reduction of palladium chloride (PdCl2) to nanoparticles by plant biomass follows the below equation: Pd+Cl2- + Plant molecule (–C=C, –C=O, etc.) → Pd0 nanoparticles

(4)

17

Nadagouda and Varma [114] reported formation of Pd nanocrystals using coffee and tea extract at room temperature. The authors indicated that the obtained nanoparticles were in the size range of 20-60 nm and crystallized in face centered cubic symmetry. Subsequently, Cinnamom zeylanicum bark extract mediated synthesis of Pd nanoparticles (15 – 20 nm) has been reported by Sathishkumar et al. [115]. Even though the authors were unclear on the exact mechanism, they believed that terpenoids played an important role in biosynthesis of Pd nanoparticle. Similarly, Yang et al. [116] used Cinnamomum camphora leaf extract as bioreductant for the formation of Pd nanoparticles. The authors observed the mean size of Pd nanoparticles as 3.2 - 6.0 nm and they believed that the polyols and the heterocyclic components were responsible for the reduction of Pd ions and the stabilization of Pd nanoparticles. Recently, Kora and Rastogi [117] synthesized Pd nanoparticles from PdCl2 using plant polymer, gum ghatti (Anogeissus latifolia). The authors confirmed the formation of Pd nanoparticles from the appearance of intense brown colour in the solution and the produced Pd nanoparticles were spherical in shape, polydisperse with average particle size of 4.8 ± 1.6 nm. 3.5. Other metals and metal-oxides Other metal and metal-oxide nanoparticles through plant-mediated biosynthesis are represented by a considerably fewer number of reports (Table 2). Copper (Cu) nanoparticles were biosynthesized using Magnolia leaf extract [118]. When aqueous solution of copper (II) sulphate pentaydrate (CuSO4·5H2O) treated with the leaf extract, stable copper nanoparticles (37–110 nm) were formed. In another study, Cu nanoparticles were synthesized extracellularly using stem latex of a medicinally important plant, Euphorbia nivulia. The synthesized Cu nanoparticles were stabilized and subsequently capped by peptides and terpenoids present within the stem latex. Copper oxide nanoparticles were synthesized by Sivaraj et al. [119] using leaf extract of Tabernaemontana divaricate. Highly stable and

18

spherical CuO nanoparticles (48 ± 4 nm size) were synthesized using 50 % concentration of leaf extract. Zinc oxide (ZnO) nanoparticle is an attractive semiconductor material for photonic and nano-electronic application. Highly stable and spherical ZnO nanoparticles (25 – 40 nm) were produced by Sangeetha et al. [120] using Aloe barbadensis miller leaf extract. The authors reported more than 95 % conversion to nanoparticles using aloe leaf broth concentration greater than 25 %. It was also shown that the ZnO nanoparticles were poly dispersed and particle size could be controlled by varying the concentrations of leaf broth solution. Rajiv et al. [121] prepared highly stable, spherical and hexagonal ZnO nanoparticles using leaf extracts of Parthenium hysterophorus L. On the other hand, Vijayakumar et al. [122] synthesized ZnO nanoparticles using the leaf extract of Plectranthus amboinicus. Titanium dioxide (TiO2) is an important metal-oxide nanoparticle and is widely used in paints, printing ink, rubber, paper, cosmetics, sunscreens, car materials, cleaning air products, industrial photocatalytic processes and decomposing organic matters in wastewater due to their unique physical, chemical, and biological properties [123]. Sundrarajan and Gowri [124] synthesized TiO2 nanoparticles (100 - 150 nm) from titanium isopropoxide solution using Nyctanthes arbor-tristis leaf extract. Alternatively, TiO2 nanoparticles (25 100 nm) have been synthesized using 0.3 % aqueous extract prepared from latex of Jatropha curcas L. [125]. The authors have identified curcain (enzyme) and cyclic peptides [such as curcacycline A (an octapeptide) and curcacycline B (a nonapeptide)] as possible reducing and capping agents present in the latex of J. curcas L. Other important metal and metal-oxide nanoparticles synthesized using plants are summarized in Table 2.

4. Characterization of plant-mediated biosynthesis of nanoparticles

19

Nanoparticles are typically characterized by their size, shape, surface area and dispersity nature. The common techniques of characterizing nanoparticles are as follows: UV–visible spectrophotometry, Fourier transform infrared spectroscopy (FTIR), powder Xray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). 4.1. UV–visible spectrophotometry The formation of various metallic nanoparticles from their respective metallic salts gives characteristic peaks at different absorptions that can be monitored using UV-visible spectrophotometry. In particular, noble metallic nanoparticles such as Ag and Au possess strong absorption in the visible region with the maximum in the range of 400 - 450 nm and 500 - 550 nm, respectively, due to the surface plasmon resonance (SPR) phenomenon which occurs in metallic nanoparticles [126]. SPR in the UV-Vis region of the spectrum originates from the resonant collective oscillations of the conduction electrons along the transversal direction of the electromagnetic field [127]. SPR band intensity maximum and band width are influenced by the particle shape, dielectric constant of the medium and temperature [128]. Hence, UV–vis spectrophotometry analysis is usually the first technique used in characterization of metallic nanoparticles and several authors used this technique to confirm the formation of nanoparticles [126]. On contacting the noble metal salt with plant biomass/extract, the color of the suspension changes and the color change was due to excitation of surface plasmon vibrations in the metal nanoparticles. Analysing the suspension using UV-vis spectrophotometer method usually reveals a band from which adsorption peak can be determined and the respective metal can be confirmed. A progressive increase in the characteristic peak with increase in reaction time and concentration of plant biomass/extract with metallic ion is a clear indicator

20

of nanoparticle formation [129]. Narayanan and Sakthivel [130] observed that addition of coriander leaf extract to aqueous HAuCl4 resulted in the color change to pink-ruby red after 12 h of reaction due to the production of Au nanoparticles. In addition, they determined Au SPR band was centered at about 536 nm and the intensity increases with increase in contact time. Similarly, Ashokkumar and Vijayaraghavan [131] confirmed the formation of Au nanoparticles by observing the color change of reaction mixture from brown to ruby red and surface plasmon resonance centered at 525 nm (Figure 2). During synthesis of Ag nanoparticles, Gurunathan et al. [132] visualized color change from pale green to deep brown on contacting Allophylus cobbe leaf extract and AgNO3. Using UV-vis spectrophotometer, the authors determined strong and broad peak at about 420 nm confirming the formation of Ag nanoparticles. On the other hand, Yang et al. [116] reported that the color of the solution gradually turned from brownish yellow into dark brown in 12 h and the absence of the absorption peaks above 300 nm in the sample indicated the generation of Pd nanoparticles. There was also a report by Venu et al. [133], which indicates the color of the Pt reduced solutions gradually turned from yellow to black and absorbance dominates near 200 nm wavelength confirms the generation of Pt nanostructures. 4.2. Fourier transform infrared (FTIR) spectroscopy Fourier transform infrared (FTIR) spectroscopy is a surface chemical analytical technique, which measures the infrared intensity versus wavenumber (wavelength) of light. The nature of the functional groups and their involvement during bioreduction can be approximately evaluated using the FTIR spectroscopy. The identification of these plant components is vital to develop new routes in synthesis of nanoparticles. In general, FTIR spectrum of virgin plant biomass/extract and that of synthesized nanoparticles will be compared to gather information about functional groups responsible for bioreduction. Several researchers used FTIR technique to elucidate various plant biomolecules responsible for

21

metal bioreduction as depicted in Table 3. As discussed previously, the important plant biomolecules that acts as reducing and capping agents are polysaccharides, proteins, terpenoids and flavonoids. Analysing the Table 3, it can be inferred that significant absorption bands have observed in the region of 1000 – 1800 cm-1, which confirm the role of above biomolecules in bioreduction. It should also be noted that stretching vibrations of N-H and O-H groups appear in the range of 3200 – 3500 cm-1. A typical FTIR spectrum of T. ornata extract and synthesized gold nanoparticles using T. ornata extract is shown in Figure 3. 4.3. X-ray diffraction (XRD) The X-ray diffraction (XRD) technique is used to study structural information about crystalline metallic nanoparticle. The energetic X-rays can penetrate deep into the materials and provide information about the bulk structure [6]. If the nanoparticles are produced in an amorphous structure, no diffraction peak is observed and this technique cannot help to identify the sample [126]. The broadening of the peaks in XRD confirms the formation of particles in nano size. The size of nanoparticle can be calculated by means of the Debye– Scherrer equation [134]. The Debye–Scherrer equation was used to derive the particle size from the XRD data by determining the width of the (1 1 1) Bragg reflection according to the following equation: d

K  cos 

(5)

where d is the particle size (nm), K is the Scherrer constant, βis the full width half maximum, θ is half of Bragg angle and λ is the wavelength of X-ray [135]. Gao et al. [136] observed XRD pattern of newly synthesized Au nanoparticles showed intense peaks of (111), (200), (220), (311) and (222), which confirmed the monophasic nature of pure Au with face centered cubic symmetry. In addition, the peaks are broad with fair intensity indicating the nanocrystalline nature of Au powder. Khazaei et al. [137] reported that the XRD pattern

22

showed three characteristic peaks at (1 1 1), (2 0 0) and (3 1 1). These characteristic peaks indicated crystallographic planes of the Pd (0) nanoparticles. From the XRD pattern, the size and structure of ZnO nanoparticles synthesized from leaf extract of Tamarindus indica was determined by Elumalai et al. [138]. The authors identified that synthesized ZnO nanoparticles were 16 – 37 nm and crystalline in nature owing to the strong and narrow diffraction peaks. For illustration purpose, the XRD pattern of gold nanoparticles synthesized using leaf extract of Portulaca grandiflora is presented in Figure 4. 4.4 Electron microscope Scanning electron microscopy (SEM) provides information about the topography and morphology of the nanoparticles. In addition, electron microscopy techniques can also be used to measure the average size of nanoparticles using statistical software. Through SEM images, Anand et al. [139] confirmed that Au nanoparticles synthesized by Moringa oleifera flower extracts were in spherical shape with the size of 100 nm. Similarly, Rajiv et al. [121] distinguished spherical and hexagonal-shaped ZnO nanoparticles synthesized using Parthenium hysterophorus extract through SEM images. Figure 5 shows SEM images of synthesized nanoparticles using the green seaweed extract of star like Ag-Au bimetallic NPs (data not published). Few researchers also used atomic force microscopy (AFM) to analyse morphology of nanoparticles. Das et al. [140] studied the surface morphology of the Sesbania grandiflora-synthesized Ag nanoparticles using AFM. Through two- and three- dimensional topography of the Ag nanoparticles provided by AFM, the authors determined Ag nanoparticles were spherical in shape and 10 – 25 nm in size. Through AFM images, Bhat et al. [141] demonstrated that Au nanoparticles were irregular in shape with organic shell over it. The average size of the Au nanoparticles from the AFM data was found to be 12–15 nm. To study surface morphology and shape of nanoparticles, many researchers preferred transmission electron microscopy (TEM). TEM technique has greater magnification and

23

resolution than SEM and the images provide more accurate information regarding size, shape and crystallography of the nanoparticles [142]. Philip [20] observed triangular, hexagonal, dodecahedral and spherical shaped Ag and Au nanoparticles with average size 13 - 14 nm in TEM images after bioreduction of Ag and Au ions by Hibiscus rosa-sinensis leaf extract. Similarly, Dhayananthaprabhu et al. [143] conducted Cassia auriculata flower extractmediated biosynthesis of Au nanoparticles and noticed spherical, hexagonal and triangular shaped Au nanoparticles with size ranging from 10 – 55 nm through TEM images. Another advantage of TEM analysis over SEM images is that TEM images can be used to distinguish amorphous structures from crystalline structures using the selected area electron diffraction technique [126]. Figure 6 shows TEM images of gold nanoparticles synthesized using leaf extract of Portulaca grandiflora. Elemental composition of metal nanoparticles can be established using energy dispersive X-ray spectroscopy (EDX) [144]. Each element has a unique atomic structure making a unique set of peaks on its X-ray spectrum which, in turn, leads to the characterization of the elements [126]. Figure 7 shows EDAX spectrum of synthesized gold nanoparticles using T. ornata extract. Sathishkumar et al. [145] synthesized Au nanoparticles using Illicium verum and the EDX spectrum confirmed the presence of Au in the measured sample. The authors assigned the peak at 2keV to Au nanoparticles. With the aid of EDX spectrum, Dipankar and Murugan [146] confirmed synthesis of Ag nanoparticles using Iresine herbstii leaf extract. The authors observed a sharp signal peak of Ag, which in turn indicated the reduction of AgNO3 to Ag nanoparticles.

5. Factors influencing biosynthesis of nanoparticles Several factors affect the synthesis, characterization and application of nanoparticles during plant-mediated biosynthesis. Some of the important factors are summarized below.

24

5.1. Solution pH The solution pH plays an important role in plant-mediated biosynthesis of nanoparticles. Several reports indicated that pH of the solution medium influences the size, shape and rate of the synthesized nanoparticles [147]. This phenomenon is due to the formation of nucleation centres, which increases with increase in pH. As the nucleation centre increases, the reduction of metallic ion to metal nanoparticles also increases. At the same instance, the solution pH also influences the activity of the functional groups in the plant extract/biomass and also influences the rate of reduction of a metal salt [81]. Armendariz et al. [147] identified that the size of Au nanoparticle produced by Avena sativa was strongly dependent on the solution pH. They determined that large size Au nanoparticles (25 – 85 nm) were formed at pH 2, in small quantities. On the other hand, smaller sized nanoparticles were formed at pH 3 and 4 in large quantities. They speculated that at low pH (pH 2), the Au nanoparticles prefer to aggregate to form larger nanoparticles rather than to nucleate and form new nanoparticles. In contrast, at pH 3 and 4, more functional groups (carbonyl and hydroxyl) were available for Au binding; thus a higher number of Au(III) complexes bounded to the plant biomass at the same time. Zhan et al. [148] studied influence of pH on biosynthesis of Au nanoparticles by leaf extracts of Cacumen platycladi. The authors observed that the size of the Au nanoparticles decreased whereas the intensity of absorbance peaks increased with increase in pH. They also noted that high pH leads to rapid reduction rate of the chloroaurate ions, boosts the homogenous nucleation, and decreases the anisotropy growth. In contrast, slow reduction rate occurred under acidic condition resulted in heterogeneous nucleation and secondary nucleation of small Au seeds. Moreover, Jacob et al. [149] studied the reduction rates of Au and Ag ions at pH 3.3 and 10.8. Their work revealed that at pH 3.3, Ag ions reduced very slowly compared to Au ions and the resulting nanoparticles precipitated in 2 days. Nevertheless, at pH 10.8, simultaneous reductions

25

occurred for both metal ions and a single SPR band was observed. The TEM image showed homogenous electron density, suggesting that alloyed nanoparticles were formed. They further stated that high pH value also contributed to the formation of AgO- and AgO which strongly interact with hydroxyl groups in plant extracts hence effectively covered the surface of nanoparticles. 5.2. Temperature Temperature is another important factor that influences the size, shape and rate of nanoparticles. Similar to pH, formation of nucleation centres increase with increase in temperature, which in turn increase the rate of biosynthesis. Sneha et al. [59] studied the effect of temperature on biosynthesis of Au nanoparticles by Piper betle leaf extract. Through TEM images, the authors visualized mainly nanotriangles at 20 ○C, whereas nanoplatelets and nanoparticles ranging in size from 5 - 500 nm were observed at 30 – 40 ○C. Further at 50 and 60 °C, the authors noticed the size and morphology of the formed nanoparticles were reasonably consistent since the density of the spherical nanoparticles dominated the nanotriangles and octahedral platelets. Sheny et al. (2011) [150] compared the reduction processes of Au and Ag ions by leaf extract of Anacardium occidentale at different temperature values to determine the optimum condition for bimetallic Au-Ag synthesis. The authors determined that a greater amount of leaf extract was required to synthesize stable nanoparticles at low reaction temperature than at high temperature. To be precise, only 0.6 mL of leaf extract was required for biosynthesis at 100 °C while as much as 2.5 mL of leaf extract was required for synthesis at 27 °C. Also, the authors observed that nanoparticles formed at high temperature were not only more stable but also larger in size. In an attempt to investigate the effect of temperature, Iravani and Zolfaghari [151] heated the reaction mixture (Pinus eldarica bark extract and AgNO3) to different temperatures (25, 50, 100 and 150 °C).

26

By increasing reaction temperature, the authors observed an increase in absorbance and decrease in size of Ag nanoparticles. 5.3. Reaction time The size, shape and extent of nanoparticle synthesis using plant-based biomaterials also greatly influenced by the length of reaction time the suspension medium is incubated. Nazeruddin et al. [152] observed rapid synthesis of Ag nanoparticles by seed extract of Coriandrum sativum within 1 – 2 h as compared to 2 – 4 days required by microorganisms. Similarly, Noruzi et al. [87] reported that the Rosa hybrid petal mediated synthesis of Au nanoparticles reaction was rapid and completed within 5 min. Even though plant-mediated biosynthesis of nanoparticles is usually rapid compared to microorganism, several authors observed efficient production rate at high reaction times [153]. Dwivedi and Gopal [154] observed that Chenopodium album leaf mediated synthesis of Ag and Au nanoparticles started within 15 min of the reaction. In addition, they found that an increase in contact time strongly influenced the sharpening of the peaks in both Ag and Au nanoparticles. Few reports also indicated that size and shape of the nanoparticles alter with the extent of reaction time [155,59]. During Ag nanoparticles synthesis using Capsicum annuum L. extract, Li et al. [155] identified five hours reaction time led to spherical and polycrystalline shaped nanoparticles (10±2 nm). With increase in reaction time to 9 h and 13 h, the size of the nanoparticles was increased to 25±3 nm and 40±5 nm, respectively. 5.4. Plant extract/biomass dosage The concentration of plant biomass/extract often decides the efficiency of nanoparticle synthesis. Several investigators identified that increase in biomass dosage enhances the production of nanoparticles as well as alter the shape of nanoparticles [111,156]. Hence, it is often essential to determine optimum biomass dosage for the process. Chandran et al. [157] used the Aloe vera leaf extract to modulate the shape and the size of the

27

synthesized Au nanoparticles. Most of the Au nanoparticles were triangular in the size range of 50 – 350 nm, which depended on the extract quantity. The addition of low amounts of the extract to HAuCl4 solution resulted in the formation of nanogold triangles in larger sizes. Also, when the extract quantity was increased, the ratio of nanotriangles to spherical nanoparticles decreased.

6. Applications of nanoparticles Due to their unique properties, nanoparticles are widely used in different fields such as medicine, agriculture, cosmetic industry, drug delivery, catalysis and wastewater treatment. Figure 8 illustrate applications of nanopartilces in various fields. In particular, biosynthesized metallic nanoparticles are much preferred especially in medical-based applications. The nanoparticles exhibit high differential uptake efficiency in the target cells over normal cells through preventing them from prematurely interacting with the biological environment, enhanced permeation and retention effect in disease tissues and improving their cellular uptake, resulting in decreased toxicity [158]. The use of nanoparticles for cancer therapy has been gaining popularity in recent years. Several researchers explored the cytotoxic effects of various metallic nanoparticles on different cell lines synthesized using plant biomass/extracts [139, 145, 159]. Raghunandan et al. [160] synthesized Au and Ag nanoparticles using guava and clove plant extracts and subsequently examined their anticancer

efficacy against

different

cancer

cell

lines

including

human

colorectal

adenocarcinoma, human kidney, human chronic myelogenous, leukemia, bone marrow, and human cervix. The authors proved that these nanoparticles as potential anti-cancer agents. Multi-functional Au nanoparticles have been demonstrated to be highly stable and versatile scaffolds for drug delivery due to their unique size, coupled with their chemical and physical properties [101]. The ability to tune the surface of the particle provides access to cell-specific

28

targeting and controlled drug release. Yallappa et al. [161] synthesized Au nanoparticles using Mappia foetida leaves extract and subsequently conjugated Au nanoparticles with activated folic acid and doxorubicin complex to deliver the drug to human cancer cells. The authors determined that the maximum amount of drug released was at pH 5.3, which was toxic to human cancer cells viz., MDA-MB-231, HeLa, SiHa and Hep-G2. In addition, Au and Ag nanoparticles have been commonly found to have wide spectrum of antimicrobial activity against pathogens [109,162,163]. The antimicrobial activity of metallic nanoparticles recommend its possible application in the food preservation field and also as a potent sanitizing agent for disinfecting and sterilizing food industry equipment and containers against the attack and contamination with foodborne pathogenic bacteria [164]. Au nanoparticles synthesized from Cassia fistula (stem bark) extract have also exhibited antidiabetic activity [165]. Praveenkumar et al. [166] described the blood compatibility of Au nanoparticles synthesized with ginger (Zingiber officionale) extract. Zargar et al. [167] reported that Ag/V. negundo films have a biocompatible and rough surface used for special biological applications, such as cell immobilization. The application of nanoparticles as catalysts is also receiving increased research attention. Compared to bulk materials, nanoparticles have high surface-area-to volume ratio and thus found to exhibit higher turnover frequencies. The catalytic activity of Au, Ag Pd and Pt in the decomposition of H2O2 to oxygen is well known [47]. Ghosh et al. [168] reported that Au nanoparticles synthesized using Gnidia glauca flower extract exhibited remarkable catalytic properties in a reduction reaction of 4-nitrophenol to 4-aminophenol by NaBH4 in aqueous phase. In addition, Trigonella foenum-graecum bioreduced Ag nanoparticles exhibited remarkable size dependent catalytic properties in a reduction reaction of organic dyes such as methyl orange, methylene blue and eosin Y [169].

29

The nanosized metal nanoparticles such as Au, Ag and Pt are broadly being applied for various commercial personal care products such as shampoo, soap, detergent, anti-ageing creams and perfumes [129]. Applications of nanoparticles are emerging in crop protection and agriculture. Several types of nanoparticles have also been shown to reduce the microbial loads in treated wastewater effluent as well [170].

7. Conclusions and future directions In recent years, the biological synthesis of metal nanoparticles garnered significant attention and has emerged as an important scientific field. A wide number of biological materials, including bacteria, fungi, yeast, micro-algae, seaweeds and plant parts have shown potential to synthesize various metal and metal oxide nanoparticles such as Ag, Au, Pd, Pt, Cu, ZnO, CuO and TiO2. Of these biomaterials, the plant extract/biomass has gained great importance in nanoparticles synthesis due to the fact that plant-mediated biosynthesis is generally inexpensive, more environmental friendly, simple one-step process and safe to handle. It was understood that the reaction rate strongly depends on pH, temperature, reaction time and plant dosage. Biosynthesized nanoparticles have been characterized using FTIR, SEM, TEM, EDX, AFM, XRD and UV-spectrophotometry. Several studies also pointed out that plant synthesized metallic nanoparticles found usage in many fields in particular medicine and catalysis. Although several research reports highlighted potential of various plant species in nanoparticle synthesis, the exact mechanism is yet to be understood. Some researchers hypothesized involvement of certain chemical agents/functional groups in plant biomass during synthesis of nanoparticles. However considering the diversity of plants and their varied chemical composition, more efforts should be made to elucidate mechanism through experimental techniques. Also additional steps should be taken to determine potential

30

application of biosynthesized nanoparticles in fields other than medicine and catalysis. Hence, more research investment and an interdisciplinary team work are therefore required to elevate the plant-biosynthesis method to successfully compete with chemical and physical syntheses of nanoparticles.

Acknowledgements This work was financially supported by Ramalingaswami Re-entry Fellowship (Department of Biotechnology, Ministry of India, India).

31

References [1] S. Sepeur, Nanotechnology: technical basics and applications, (2008) Hannover: Vincentz. [2] S. Iravani, Green synthesis of metal nanoparticles using plants, Green Chem. 13 (2011) 2638–2650. [3] P. Mukherjee, A. Ahmad, D. Mandal, S. Senapati, S.R. Sainkar, M.I. Khan, Fungus mediated synthesis of silver nanoparticles and their immobilization in the mycelia matrix: a novel biological approach to nanoparticle synthesis, Nano Lett. 1 (2001) 515519. [4] K.N. Thakkar, S.S. Mhatre, R.Y. Parikh, Biological synthesis of metallic nanoparticles, Nanomedicine: Nanotechnology, Biology and Medicine 6 (2010) 257-262. [5] S. Iravani, H. Korbekandi, S.V. Mirmohammadi, B. Zolfaghari, Synthesis of silver nanoparticles: chemical, physical and biological methods, Res. Pharmaceutical Sci. 9 (2014) 385–406. [6] J. Huang, Q. Li, D. Sun, Y. Lu, Y. Su, X. Yang, Biosynthesis of silver and gold nanoparticles by novel sundried Cinnamomum camphora leaf, Nanotechnology 18 (2007) 105104-105114. [7] P.M. Tiwari, K. Vig, V.A. Dennis, S.R. Singh, Functionalized gold nanoparticles and their biomedical applications, Nanomaterials 1 (2011) 31-63. [8] S.P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad, M. Sastry, Synthesis of gold nanotriangles and silver nanoparticles using Aloe vera plant extract, Biotechnol. Prog. 22 (2006) 577-583. [9] S.S. Birla, V.V. Tiwari, A.K. Gade, A.P. Ingle, A.P. Yadav, M.K. Rai, Fabrication of silver nanoparticles by Phoma glomerata and its combined effect against Escherichia

32

coli Pseudomonas aeruginosa and Staphylococcus aureus, Lett. Appl. Microbiol. 48 (2009) 173–179. [10] N. Yang, K. Aoki, Voltammetry of the silver alkylcarboxylate nanoparticles in suspension, Electrochimca Acta 50 (2005) 4868-4872. [11] K.B. Narayanan, N. Sakthivel, Biological synthesis of metal nanoparticles by microbes, Adv. Coll. Interf. Sci. 156 (2010) 1-13. [12] P. Dauthal, M. Mukhopadhyay, Noble metal nanoparticles: plant-mediated synthesis, mechanistic aspects of synthesis, and applications, Ind. Eng. Chem. Res. 55 (2016) 9557–9577. [13] N.I. Hulkoti, T.C. Taranathm, Biosynthesis of nanoparticles using microbes—A review, Coll. Surf. B: Biointerf. 121 (2014) 474–483. [14] G.S. Dhillon, S.K. Brar, S. Kaur, M. Verma, Green approach for nanoparticle biosynthesis by fungi: Current trends and applications, Crit. Rev. Biotechnol. 32 (2012) 49-73. [15] A.B. Moghaddam, F. Namvar, M. Moniri, P.M. Tahir, S. Azizi, R. Mohamad, Nanoparticles biosynthesized by fungi and yeast: A review of their preparation, properties, and medical applications, Molecules 20 (2015) 16540-16565. [16] E. Dujardin, C. Peet, G. Stubbs, J.N. Culver, S. Mann, Organization of metallic nanoparticles using tobacco mosaic virus templates, Nano Lett. 3 (2003) 413–417. [17] A. Schrofel, G. Kratosova, M. Krautova, E. Dobrocka, I. Vavra, Biosynthesis of gold nanoparticles using diatoms–silica-gold and EPS-gold bionanocomposite formation, J. Nanoparticle Res. 13 (2011) 3207-3216. [18] G. Singaravelu, J.S. Arockiamary, V. Ganesh Kumar, K. Govindaraju, A novel extracellular synthesis of monodisperse gold nanoparticles using marine alga, Sargassum wightii Greville, Coll. Surf. B: Biointerf. 57 (2007) 97-101.

33

[19] A.K. Mittal, Y. Chisti, U.C. Banerjee, Synthesis of metallic nanoparticles using plant extracts, Biotechnol. Adv. 31 (2013) 346-356. [20] D. Philip, Green synthesis of gold and silver nanoparticles using Hibiscus rosasinensis, Physica E 42 (2010) 1417-1424. [21] P. Kuppusamy, M.M. Yusoff, S.J.A. Ichwan, N.R. Parine, G.P. Maniam, N. Govindan, Commelina nudiflora L. edible weed as a novel source for gold nanoparticles synthesis and studies on different physical–chemical and biological properties, J. Ind. Eng. Chem. 27 (2015) 59-67. [22] S.J. Hong, J.I. Han, Synthesis and characterization of indium tin oxide (ITO) nanoparticle using gas evaporation process, J. Electroceramics 17 (2006) 821-826. [23]

H.

Korbekandi,

S.

Iravani,

Silver

nanoparticles,

Nanotechnology

and

Nanomaterials, The Delivery of Nanoparticles, book edited by Abbass A. Hashim, (2015) ISBN 978-953-51-0615-9. [24] B. Khodashenas, H.R. Ghorbani, Synthesis of copper nanoparticles : An overview of the various methods, Korean J. Chem. Eng. 31 (2014) 1105-1109. [25] M.G. Lines, Nanomaterials for practical functional uses, J. Alloys Compounds 449 (2008) 242-245. [26] Z. Hongwang, M.T. Swihart, Synthesis of tellurium dioxide nanoparticles by spray pyrolysis, Chem. Mater. 19 (2007) 1290-1301. [27] J.S. Kim, E. Kuk, K.N. Yu, J.H. Kim, S.J. Park, H.J. Lee, Antimicrobial effects of silver nanoparticles, Nanomedicine NBM 3 (2007) 95-101. [28] Y. Tan, Y. Dai, Y. Li, D. Zhua, Preparation of gold, platinum, palladium and silver nanoparticles by the reduction of their salts with a weak reductant-potassium bitartrate, J. Mater. Chem. A 13 (2003) 1069-1075.

34

[29] K. Mallick, M.J. Witcomb, M.S. Scurell, Polymer stabilized silver nanoparticles: a photochemical synthesis route, J. Mater. Sci. 39 (2004) 4459-4463. [30] L. Rivas, S. Sanchez-Cortes, J.V. Garcia-Ramos, G. Morcillo, Growth of silver colloidal particles obtained by citrate reduction to increase the raman enhancement factor, Langmuir 17 (2001) 574-577. [31] G. Merga, R. Wilson, G. Lynn, B. Milosavljevic, D. Meisel, Redox Catalysis on “naked” silver nanoparticles, J. Phys. Chem. C 111 (2007) 12220-12206. [32] J. Turkevich, P.C. Stevenson, J. Hillier, A study of the nucleation and growth processes in the synthesis of colloidal gold, Discussions of the Faraday Society (1951) 55–75. [33] M. Brust, M. Walker, D. Bethell, D.J. Schiffrin, R. Whyman, Synthesis of thiol derivatised gold nanoparticles in a two-phase liquid/liquid system, J. Chem. Soc. Chem. Comm. 7 (1994) 789-912. [34] M.A. Malik, M.Y. Wani, M.A. Hashim, Microemulsion method: A novel route to synthesize organic and inorganic nanomaterials: 1st Nano Update, Arabian J. Chem. 5 (2012) 397-417. [35] A.K. Ganguli, T. Ahmad, S. Vaidya, J. Ahmed, Microemulsion route to the synthesis of nanoparticles, Pure Appl. Chem. 80 (2008) 2451-2477. [36] R.A. Martínez-Rodríguez, F.J. Vidal-Iglesias, J. Solla-Gullón, C.R. Cabrera, J.M. Feliu, Synthesis of Pt nanoparticles in water-in-oil microemulsion: Effect of HCl on their surface structure, J. American Chem. Soc. 136 (2014) 1280-1283. [37] M. Starowicz, B. Stypuła, J. Banas, Electrochemical synthesis of silver nanoparticles, Electrochem. Comm. 8 (2006) 227-230. [38] L. Rodriguez-Sanchez, M.C. Blanco, M.A. Lopez-Quintela, Electrochemical synthesis of silver nanoparticles, J. Phys. Chem. B 104 (2000) 9683-9688.

35

[39] H. Ma, B. Yin, S. Wang, Y. Jiao, W. Pan, S. Huang, S. Chen, F. Meng, Synthesis of silver and gold nanoparticles by a novel electrochemical method, Chem. Phys. Chem. 24 (2004) 68-75. [40] K. Simeonidis, S. Mourdikoudis, M. Moulla, I. Tsiaoussis, C. Martinez-Boubeta, M. Angelakeris, C. Dendrinou-Samara, O. Kalogirou, Controlled synthesis and phase characterization of Fe-based nanoparticles obtained by thermal decomposition, J. Magnetism Magnetic Mater. 316 (2007) e1-e4. [41] S. Navaladian, B. Viswanathan, R.P. Viswanath, T.K. Varadarajan, Thermal decomposition as route for silver nanoparticles, Nanoscale Res. Lett. 2 (2007) 44-48. [42] A. Schrofel, G. Kratosova, I. Safarik, M. Safarikova, I. Raska, L.M. Shor, Applications of biosynthesized metallic nanoparticles - A review, Acta Biomaterialia 10 (2014) 4023-4042. [43] N. Asmathunisha, K. Kathiresan, A review on biosynthesis of nanoparticles by marine organisms, Coll. Surf. B: Bionterf.103 (2013) 283-287. [44] A.T. Lombardi, O. Garcia Jr., An evaluation into the potential of biological processing for the removal of metals from sewage sludges, Crit. Rev. Microbiol. 25 (1999) 275288. [45] K. Vijayaraghavan, Y.S. Yun, Bacterial biosorbents and biosorption, Biotechnol. Adv. 26 (2008) 266-291. [46] K. Vijayaraghavan, R. Balasubramanian, Is biosorption suitable for decontamination of metal-bearing wastewaters? A critical review on the state-of-the-art of biosorption processes and future directions, J. Environ. Manage. 160 (2015) 283-296. [47] D. Nath, P. Banerjee, Green nanotechnology - A new hope for medical biology, Environ. Toxicol. Pharmacol. 36 (2013) 997-1014.

36

[48] K. Kalishwaralal, V. Deepak, S. Ram Kumar Pandian, S. Gurunathan, Biological synthesis of gold nanocubes from Bacillus licheniformis, Bioresour. Technol. 100 (2009) 5356-5358. [49] M. Phadke, J. Patel, Biological synthesis of silver nano particles using Pseudomonas aeruginosa, J. Pure Appl. Microbiol. 66 (2012) 1917-1924. [50] M.I. Husseiny, M.A. El-Aziz, Y. Badr, M.A. Mahmoud, Biosynthesis of gold nanoparticles using Pseudomonas aeruginosa, Spectrochimica Acta-Part A: Molecular and Biomolecular Spectroscopy 67 (2007) 1003-1006. [51] K. Kalimuthu, R.S. Babu, D. Venkataraman, M. Bilal, S. Gurunathan, Biosynthesis of silver nanoparticles by Bacillus licheniformis, Coll. Surf. B Biointerf. 65 (2008) 150153. [52] B. Nair, T. Pradeep, Coalescence of nanoclusters and formation of submicron crystallites assisted by Lactobacillus strains, Crystal Growth Design 2 (2002) 293-298. [53] P. Yong, N.A. Rowson, J.P.G. Farr, I.R. Harris, L.E. Macaskie, Bioreduction and biocrystallization of palladium by desulfovibrio desulfuricans NCIMB 8307, Biotechnol. Bioeng. 80 (2002) 369-379. [54] Y. Nangia, N. Wangoo, N. Goyal, G. Shekhawat, C.R. Suri, A novel bacterial isolate Stenotrophomonas maltophilia as living factory for synthesis of gold nanoparticles, Microbial Cell Factories 8 (2009) 1-7. [55] S.K. Srivastava, R.Yamada, C. Ogino, A. Kondo, Biogenic synthesis and characterization of gold nanoparticles by Escherichia coli K12 and its heterogeneous catalysis in degradation of 4-nitrophenol, Nanoscale Res. Lett. 8 (2013) 70. [56] D.N. Correa-Llantén, A. Sebastian, M. Ibacache, M. E. Castro, P.A. Muñoz1, J. M. Blamey1, Gold nanoparticles synthesized by Geobacillus sp. strain ID17 a thermophilic

37

bacterium isolated from Deception Island, Antarctica , Microbial Cell Factories 12 (2013) 75. [57] S. Shivaji, S. Madhu, S. Singh, Extracellular synthesise of antibacterial silver nanoparticles using psychrophilic bacteria, Process Biochemistry 49 (2011) 830-837. [58] H.R. Ghorbani, Biosynthesis of silver nanoparticles using Salmonella typhirium, J. Nanostructure Chem. 3 (2013) 29. [59] K. Sneha, M. Sathishkumar, S. Kim, Y.S. Yun, Counter ions and temperature incorporated tailoring of biogenic gold nanoparticles, Proc. Biochem. 45 (2010) 14501458. [60] A.Yadav, K. Kon, G. Kratosova, N. Duran, A.P. Ingle, M. Rai, Fungi as an efficient mycosystem for the synthesis of metal nanoparticles: progress and key aspects of research, Biotechnol. Lett. 37 (2015) 2099-2120. [61] K. Kathiresan, S. Manivannan, M.A. Nabeel, B. Dhivya, Studies on silver nanoparticles synthesized by a marine fungus, Penicillium fellutanum isolated from coastal mangrove sediment, Coll. Surf. B: Bionterf.71 (2009) 133-137. [62] A. Ingle, M. Rai, A. Gade, M. Bawaskar, Fusarium solani: a novel biological agent for the extracellular synthesis of silver nanoparticles, J. Nanoparticles Res. 11 (2009) 2079–2085. [63] A.R. Binupriya, M. Sathishkumar, S.I. Yun, Myco-crystallization of silver ions to nanosized particles by live and dead cell filtrates of Aspergillus oryzae var. viridis and its bactericidal activity toward Staphylococcus aureus KCCM 12256, Ind. Eng. Chem. Res. 49 (2010) 852-858. [64] G. Baskar, J. Chandhuru, K. Sheraz Fahad, A.S. Praveen, Mycological synthesis, characterization and antifungal activity of zinc oxide nanoparticles, Asian J. Pharmacy Technol. 3 (2013) 142-146.

38

[65] B.K. Ravindra, A.H.A. Rajasab, A comparative study on biosynthesis of silver nanoparticles using four different fungal species, Int. J. Pharmacy Pharmaceutical Sci. 6 (2013) 372-376. [66] Z. Sheikhloo, M. Salouti, Intracellular biosynthesis of gold nanoparticles by the fungus Penicillium chrysogenum, Int. J. Nanosci. Nanotechnol. 7 (2011) 102-105. [67] S.U. Ekar, Y.B. Khollam, P.M. Koinkar, S.A. Mirji, R.S. Mane, M. Naushad, S.S. Jadhav, Biosynthesis of silver nanoparticles by using Ganoderma -mushroom extract, Modern Phys. Lett. B 29 (2015) 1540047. [68] M. Agnihotri, S. Joshi, A.R. Kumar, S. Zinjarde, S. Kulkarni, Biosynthesis of gold nanoparticles by the tropical marine yeast Yarrowia lipolytica NCIM 3589, Materials Lett. 63 (2009) 1231–1234. [69] S.J.G. Mala, C. Rose, Facile production of ZnS quantum dot nanoparticles by Saccharomyces cerevisiae MTCC 2918, J. Biotechnol. 170 (2014) 73-78. [70] L.E. Graham, J.E. Graham, L. Wilcox, W. Algae, 2nd ed.; Benjamin-Cummings Publishing: Menlo Park, CA, 2008; ISBN: 0321559657. [71] S.S. Sudha, K. Rajamanickam, J. Rengaramanujam, Microalgae mediated synthesis of silver nanoparticles and their antibacterial activity against pathogenic bacteria, Indian J. Exp. Biol. 51 (2013) 393-399. [72] J. Jena, N. Pradhan, R.R. Nayak, B.P. Dash, L.B. Sukla, P.K. Panda, B.K., Mishra, Microalga Scenedesmus sp.: A potential low-cost green machine for silver nanoparticle synthesis, J. Microbiol. Biotechnol. 24 (2014) 522-533. [73] S. Rajeshkumar, C. Malarkodi, G. Gnanajobitha, K. Paulkumar, M. Vanaja, C. Kannan, G. Annadurai, Seaweed-mediated synthesis of gold nanoparticles using Turbinaria conoides and its characterization, J. Nanostructure Chem. 3 (2013) 44.

39

[74] N. Sangeetha, K.S. Priyenka Devi, K. Saravanan, Synthesis and characterization of silver nanoparticles using the marine algae Ulva lactuca, Poll. Res. 32 (2013) 135-139. [75] R.I. Priyadharshini, G. Prasannaraj, N. Geetha, P. Venkatachalam, Microwave-mediated extracellular synthesis of metallic silver and zinc oxide nanoparticles using macro-algae (Gracilaria edulis) extracts and its anticancer activity against human PC3 Cell Lines, Appl. Biochem. Biotechnol. 174 (2014) 2777-2790. [76]

M.

Sathishkumar,

A.

Mahadevan,

K.

Vijayaraghavan,

S.

Pavagadhi,

R.

Balasubramanian, Green recovery of gold through biosorption, biocrystallization, and pyro-crystallization Ind. Eng. Chem. Res. 49 (2010) 7129-7135. [77]

K.

Vijayaraghavan,

A.

Mahadevan,

M.

Sathishkumar,

S.

Pavagadhi,

R.

Balasubramanian, Biosynthesis of Au(0) from Au(III) via biosorption and bioreduction using brown marine alga Turbinaria conoides, Chem. Eng. J. 167 (2011) 223-227. [78] S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, Rapid synthesis of Au, Ag, and bimetallic Au core-Ag shell nanoparticles using Neem (Azadirachta indica) leaf broth, J. Coll. Interf. Sci. 275 (2004) 496-502. [79] R. Bali, N. Razak, A. Lumb, A.T. Harris, The synthesis of metal nanoparticles inside live plants, In: International Conference on Nanoscience and Nanotechnology (ICONN ‘06) (2006) 224-227. [80] J.L. Gardia-Torresday, J.G. Parsons, E. Gomez, J. Peralta-Videa, H.E. Troian, I.P. Santiago, M.J. Yacaman, Formation and growth of Au nanoparticles inside live alfa alfa plant, Nanoletters 2 (2002) 397-401. [81] R. Bali, A.T. Harris, Biogenic synthesis of Au nanoparticles using vascular plants, Ind. Eng. Chem. Res. 49 (2010) 12762-12772. [82] N.A.N. Mohamad, N.A. Arham, J. Jai, A. Hadi, Plant extract as reducing agent in synthesis of metallic nanoparticles: A review, Adv. Mater. Res. 832 (2014) 350-355.

40

[83] H. Bhati-Kushwaha, C.P. Malik, Biopotential of Verbesina encelioides (stem and leaf powders) in silver nanoparticle fabrication, Turkish J. Biol. 37 (2013) 645-654. [84] K. Paulkumar, G. Gnanajobitha, M. Vanaja, S. Rajeshkumar, C. Malarkodi, K. Pandian, G. Annadurai, Piper nigrum leaf and stem assisted green synthesis of silver nanoparticles and evaluation of its antibacterial activity against agricultural plant pathogens, Sci. World J. 829894 (2014) 1-9. [85] M. Umadevi, M.R. Bindhu, V. Sathe, A Novel synthesis of malic acid capped silver nanoparticles using Solanum lycopersicums fruit extract, J. Mater. Sci. Technol. 29 (2013) 317-322. [86] K. Sneha, M. Sathishkumar, S.Y. Lee, M.A. Bae, Y.S. Yun, Biosynthesis of Au nanoparticles using cumin seed powder extract, J. Nanosci. Nanotechnol. 11 (2011) 1811-1814. [87] M. Noruzi, D. Zare, K. Khoshnevisan, D. Davoodi, Rapid green synthesis of gold nanoparticles using Rosa hybrida petal extract at room temperature, Spectrochimica Acta Part A 79 (2011) 1461– 1465. [88] C.H. Ramamurthy, K.S. Sampath, P. Arunkumar, M.S. Kumar, V. Sujatha, K. Premkumar, C. Thirunavukkarasu, Green synthesis and characterization of selenium nanoparticles and its augmented cytotoxicity with doxorubicin on cancer cells, Bioproc. Biosys. Eng. 36 (2013) 1131-1139. [89] E.J. Guidelli, A.P. Ramos, M.E.D. Zaniquelli, O. Baffa, Green synthesis of colloidal silver nanoparticles using natural rubber latex extracted from Hevea brasiliensis, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 82 (2011) 140-145.

41

[90] N. Yang, L. Weihong, L. Hao, Biosynthesis of Au nanoparticles using agricultural waste mango peel extract and its in vitro cytotoxic effect on two normal cells, Mater. Lett. 134 (2014) 67-70. [91] D. Nayak, S. Ashe, P.R. Rauta, M. Kumari, B. Nayak, Bark extract mediated green synthesis

of

silver

nanoparticles:

Evaluation

of

antimicrobial

activity and

antiproliferative response against osteosarcoma, Materials Science and Engineering C 58 (2016) 44-52. [92] M.S. Akhtar, J. Panwar, Y.S. Yun, Biogenic synthesis of metallic nanoparticles by plant extracts, ACS Sustainable Chem. Eng. 1(2013) 591-602. [93] J.R. Cole, N.J. Halas, Optimized plasmonic nanoparticles distributions for solar spectrum harvesting, Appl. Phys. Lett. 89 (2006) 153120. [94] S. Yomamoto, H. Watarai, Surface Enhanced Raman Spectroscopy of dodecanethiolbound silver nanoparticles at the liquid/liquid interface, Langmuir 22 (2006) 65626569. [95] S.S. Shankar, A. Ahmad, M. Sastry, Geranium leaf assisted biosynthesis of silver nanoparticles, Biotechnology Progress 19 (2003a) 1627-1631. [96] A. Leela, M. Vivekanandan, Tapping the unexploited plant resources for the synthesis of silver nanoparticles, African Journal of Biotechnology 7 (2008) 3162-3165. [97] N. Ahmad, S. Sharma, M.K. Alam, V. N. Singh, S. F. Shamsi, B. R. Mehta, A. Fatma, Rapid synthesis of nanoparticles using medicinal particles of basil, Coll. Surf. B: Bionterf. 81(2010) 81-86. [98] M. Jeyaraj, M. Rajesh, R. Arun, D. MubarakAli, G. Sathishkumar, G. Sivanandhan, G. Kapildev, M. Manickavasagam, N. Thajuddin, K. Premkumar, N. Thajuddin, A. Ganapathi, An investigation on the cytotoxicity and caspase-mediated apoptotic effect

42

of biologically synthesized silver nanoparticles using Podophyllum hexandrum on human cervical carcinoma cells, Coll. Surf. B: Bionterf. 102 (2013b) 708-717. [99] Q. Huo, J.G. Worden, Monofunctional gold nanoparticles: Synthesis and applications, Journal of Nanoparticle Research 9 (2007) 1013-1025. [100] K.S. Siddiqi, A. Husen, Recent advances in plant-mediated engineered gold nanoparticles and their application in biological system, Journal of Trace Elements in Medicine and Biology, 40 (2017) 10-23. [101] G. Han, P. Ghosh, M. De, V.M. Rotello, Drug and gene delivery using gold nanoparticles, Nanobiotechnology 3 (2007) 40-45. [102] S.S. Shankar, A. Ahmad, R. Pasricha, M. Sastry, Bioreduction of chloroaurate ions by geranium leaves and its endophytic fungus yields gold nanoparticles of different shapes, Journal of Materials Chemistry 13 (2003b) 1822–1826. [103] S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, Controlling the optical properties of lemongrass extract synthesized gold nanotriangles and potential application in infraredabsorbing optical coatings, Chemistry of Materials 17 (2005) 566-572. [104] N.A Begum, S. Mondal, S. Basu, R.A. Laskar, D. Mandal, Biogenic synthesis of Au and Ag nanoparticles using aqueous solutions of black tea leaf extracts, Coll. Surf. B: Bionterf. 71 (2009)113-118. [105] J.Y. Song, H.K. Jang, B.S. Kim, Biological synthesis of gold nanoparticles using Magnolia kobus and Diopyros kaki leaf extracts, Process Biochemistry 44 (2009) 11331138. [106] P.J. Babu, P. Sharma, B.B. Borthakur, R.K. Das, P. Nahar, U. Bora, Synthesis of gold nanoparticles using Mentha arvensis leaf extract, International Journal of Green Nanotechnology: Physics and Chemistry 2 (2010) 62-68.

43

[107] G.S. Ghodake, N.G. Deshpande, Y.P. Lee, E.S. Jin, Pear fruit extract-assisted roomtemperature biosynthesis of gold nanoplates, Coll. Surf. B: Bionterf.75 (2010) 584-589. [108] A. Rajan, M. Meena,Kumari, D. Philip, Shape tailored green synthesis and catalytic properties of gold nanocrystals, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 793-799. [109] N.U. Islam, K. Jalil, M. Shahid, N. Muhammad, A. Rauf, Pistacia integerrima gall extract mediated green synthesis of gold nanoparticles and their biological activities, Arabian J. Chem. (2015) In Press http://dx.doi.org/10.1016/j.arabjc.2015.02.014. [110] J.Y. Song, E.Y. Kwon, B.S. Kim, Biological synthesis of platinum nanoparticles using Diopyros kaki leaf extract, Bioprocess and Biosystems Engineering 33 (2010) 159-164. [111] B. Zheng, T. Kong, X. Jing, T. Odoom-Wubah, X. Li, D. Sun, F. Lu, Y. Zheng, J. Huang, Q. Li, Plant-mediated synthesis of platinum nanoparticles and its bioreductive mechanism, Journal of Colloid and Interface Science 396 (2013) 138-145. [112] C. Soundarrajan, A. Sankari, P. Dhandapani, S. Maruthamuthu, S. Ravichandran, G. Sozhan, N. Palaniswamy, Rapid biological synthesis of platinum nanoparticles using Ocimum sanctum for water electrolysis applications,

Bioprocess and Biosystems

Engineering 35 (2012) 827-833. [113] K.M. Kumar, B.K. Mandal, S.K., Tammina, Green synthesis of nano platinum using naturally occurring polyphenols, RSC Advances 3 (2013) 4033-4039. [114] M.N. Nadagouda, R.S. Varma, Green synthesis of silver and palladium nanoparticles at room temperature using coffee and tea extract, Green Chem. 10 (2008) 859-862. [115] M. Sathishkumar, K. Sneha, I.S. Kwak, J. Mao, S.J. Tripathy, Y.S. Yuna, Phytocrystallization of palladium through reduction process using Cinnamom zeylanicum bark extract, Journal of Hazardous Materials 171 (2009) 400-404.

44

[116] X. Yang, Q. Li, H. Wang, J. Huang, L. Lin, W. Wang, D. Sun, Y. Su, J.B. Opiyo, L. Hong, Y. Wang, N. He, L. Jia, Green synthesis of palladium nanoparticles using broth of Cinnamomum camphora leaf, Journal Nanoparticles Research 12 (2010) 1589-1598. [117] A.J. Kora, L. Rastogi, Green synthesis of palladium nanoparticles using gum ghatti (Anogeissus latifolia) and its application as an antioxidant and catalyst, Arabian J. Chem. (2015) In Press https://doi.org/10.1016/j.arabjc.2015.06.024. [118] H.J. Lee, J.Y. Song, B.S. Kim, Biological synthesis of copper nanoparticles using Magnolia kobus leaf extract and their antibacterial activity, J. Chem.Technol. Biotechnol. 88 (2013) 1971-1977. [119] R. Sivaraj, P.K.S.M. Rahman, P. Rajiv, H.A. Salam, R. Venckatesh, Biogenic copper oxide nanoparticles synthesis using Tabernaemontana divaricate leaf extract and its antibacterial activity against urinary tract pathogen, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 133 (2014) 178-181. [120] G. Sangeetha, G., Rajeshwari, R. Venckatesh, Green synthesis of zinc oxide nanoparticles by Aloe barbadensis Miller leaf extract: Structure and optical properties, Materials Research Bulletin 46 (2011) 2560-2566. [121] P. Rajiv, S. Rajeshwari, R. Venckatesh, Bio-fabrication of zinc oxide nanoparticles using leaf extract of Parthenium hysterophorus L. and its size-dependent antifungal activity against plant fungal pathogens, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 112 (2013) 384-387. [122] S. Vijayakumar, G. Vinoj, B. Malaikozhundan, S. Shanthi, B. Vaseeharan, Plectranthus amboinicus leaf extract mediated synthesis of zinc oxide nanoparticles and its control of methicillin resistant Staphylococcus aureus biofilm and blood sucking mosquito larvae, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 137 (2015) 886-891.

45

[123] G. Rajakumar, A. Rahuman, C. Jayaseelan, T. Santhoshkumar, S. Marimuthu, A. Bagavan, A.A. Zahir, A.V. Kirthi, G. Elango, P. Arora, R. Karthikeyan, S. Manikandan, S. Jose,

Solanum trilobatum extract-mediated synthesis of titanium dioxide

nanoparticles to control Pediculus humanus capitis, Hyalomma anatolicum anatolicum and Anopheles subpictus, Parasitology research 113 (2013) 469-479. [124] M. Sundrarajan, S. Gowri, Green synthesis of titanium dioxide nanoparticles by Nyctanthes arbor-tristis leaves extract, Chalcogenide Lett. 8 (2011) 447-451. [125] M. Hudlikar, S. Joglekar, M. Dhaygude, K. Kodam, Green synthesis of TiO2 nanoparticles by using aqueous extract of Jatropha curcas L. latex, Mater. Lett. 75 (2012) 196-199. [126] M. Noruzi, Biosynthesis of gold nanoparticles using plant extracts, Bioprocess and biosystems engineering 38 (2015) 1-14. [127] C.F. Bohren, D.R. Huffman, Absorption and Scattering of Light by Small Particles; Wiley: New York, NY, USA, 1983. [128] A.C. Templeton, J.J. Pietron, R.W. Murray, P. Mulvaney, Solvent refractive index and core charge influences on the surface plasmon adsorbance of alkanethiolate monolayerprotected gold clusters, Journal of Physical Chemistry B 104 (2000) 564-570. [129] V. Kumar, S.K. Yadav, Plant-mediated synthesis of silver and gold nanoparticles and their applications, Journal of Chemical Technology and Biotechnology 84 (2009) 151157. [130] K.B. Narayanan, N. Sakthivel, Coriander leaf mediated biosynthesis of gold nanoparticles, Mater. Lett. 62 (2008) 4588-4590. [131] T. Ashokkumar, K. Vijayaraghavan, Brown seaweed-mediated biosynthesis of gold nanoparticles, Journal of Environment & Biotechnology Research, 2 (2016) 45-50.

46

[132] S. Gurunathan, J.W. Han, D.N. Kwon, J.H. Kim, Enhanced antibacterial and antibiofilm activities of silver nanoparticles against Gram-negative and Gram-positive bacteria, Nanoscale Res. Lett. 9 (2014) 373. [133] R. Venu, T.S. Ramulu, S. Anandakumar, V.S. Rani, C.G. Kim, Bio-directed synthesis of platinum nanoparticles using aqueous honey solutions and their catalytic applications, Colloids and Surfaces A: Physicochemcal Engineering Aspects 384 (2011) 733-738. [134] L. Alexander, H.P. Klug, Determination of crystalline size with the Xray spectrometer, Journal of Applied Physics 21 (1950) 137-142. [135] T.C. Prathna, N. Chandrasekaran, A.M. Raichur, A. Mukherjee, Biomimetic synthesis of silver nanoparticles by Citrus limon (lemon) aqueous extract and theoretical prediction of particle size, Coll. Surf. B: Bionterf. 82 (2011) 152-159. [136] Z. Gao, R. Su, R. Huang, Q. Wei, Z. He, Glucomannan-mediated facile synthesis of gold nanoparticles for catalytic reduction of 4-nitrophenol, Nanoscale Res. Lett. 9 (2014) 404. [137] A. Khazaei, S. Rahmati, Z. Hekmatian, S. Saeednia, A green approach for the synthesis of palladium nanoparticles supported on pectin: Application as a catalyst for solvent-free Mizoroki–Heck reaction, Journal of Molecular Catalysis A Chemical 372 (2013) 160-166. [138] K. Elumalai, S. Velmurugan, S., Ravi, V., Kathiravan, S. Ashokkumar, Facile, ecofriendly and template free photosynthesis of cauliflower like ZnO nanoparticles using leaf extract of Tamarindus indica (L.) and its biological evolution of antibacterial and antifungal activities, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 1052-1057.

47

[139] R. Anand, M. Gengan, A. Phulukdaree, A. Chuturgoon, Agro forestry waste Moringa oleifera petals mediated green synthesis of gold nanoparticles and their anti-cancer and catalytic activity, J. Ind. Eng. Chem. 21 (2015) 1105–1111. [140] J. Das, M. Paul Das, P. Velusamy, Sesbania grandiflora leaf extract mediated green synthesis of antibacterial silver nanoparticles against selected human pathogens, Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 265-270. [141] R. Bhat, V.G. Sharanabasava, R. Deshpande, U. Shetti, Ganesh Sanjeev, A. Venkataraman,

Photo-bio-synthesis

of

irregular

shaped

functionalized

gold

nanoparticles using edible mushroom Pleurotus florida and its anticancer evaluation, Journal of Photochemistry and Photobiology B: Biology 125 (2013) 63–69. [142] B. Schaffer, U. Hohenester, A. Trugler, F. Hofer, High-resolution surface plasmon imaging of gold nanoparticles by energy-filtered transmission electron microscopy, Phys. Rev. B 79 (2009) 041401. [143] J. Dhayananthaprabhu, R. Lakshmi Narayanan, K. Thiyagarajan, Facile synthesis of gold (Au) nanoparticles using Cassia auriculata flower extract, Adv. Mater. Res. 678 (2013) 12-16. [144] P. Strasser, S. Koh, T. Anniyev, J. Greeley, K. More, C. Yu, Lattice-strain control of the activity in dealloyed core–shell fuel cell catalysts, Nature Chem. 2 (2010) 454-460. [145] M. Sathishkumar, S. Pavagadhi, A. Mahadevan, R. Balasubramanian, Biosynthesis of goldnanoparticles and related cytotoxicity evaluation using A549 cells, Ecotoxicology and Environmental Safety 114 (2015) 232-240. [146] C. Dipankar, S. Murugan, The green synthesis, characterization and evaluation of the biological activities of silver nanoparticles synthesized from Iresine herbstii leaf aqueous extracts, Coll. Surf. B: Bionterf.98 (2012) 112-119.

48

[147] V. Armendariz, I. Herrera, J.R. Peralta-Videa, M. Jose-yacaman, H. Troiani, P. Santiago, J.L. Gardea-Torresdey, Size controlled gold nanoparticle formation by Avena sativa biomass: use of plants in nanobiotechnology, Journal of Nanoparticle Research 6 (2004) 377–382. [148] G. Zhan, J. Huang, L. Lin, W. Lin, K. Emmanuel, Q. Li, Synthesis of gold nanoparticles by Cacumen Platycladi leaf extract and its simulated solution: Toward the plant-mediated biosynthetic mechanism, J. Nanoparticle Res. 13 (2011) 4957-4968. [149] J. Jacob, T. Mukherjee, S. Kapoor, A simple approach for facile synthesis of Ag, anisotropic Au and bimetallic (Ag/Au) nanoparticles using cruciferous vegetable extracts, Mater. Sci. Eng.: C 32 (2012) 1827-1834. [150] D.S. Sheny, J. Mathew, D. Philip, Phytosynthesis of Au, Ag and Au–Ag bimetallic nanoparticles using aqueous extract and dried leaf of Anacardium occidentale, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 79 (2011) 254262. [151] S. Iravani, B. Zolfaghari, Green synthesis of silver nanoparticles using Pinus eldarica bark extract, BioMed Research International (2013) 639725. [152] G.M. Nazeruddin, N.R. Prasad, S.R. Prasad, Y.I. Shaikh, S.R. Waghmare, P. Adhyapak, Coriandrum sativum seed extract assisted in situ green synthesis of silver nanoparticle and its anti-microbial activity, Ind. Crops Prod. 60 (2014) 212-216. [153] M. Darroudi, M.B. Ahmad, R. Zamiri, A. Zak, A.H. Abdullah, N.A. Ibrahim, Timedependent effect in green synthesis of silver nanoparticles, Int. J. Nanomedicine 6 (2011) 677–681. [154] A.D. Dwivedi, K. Gopal, Biosynthesis of silver and gold nanoparticles using Chenopodium album leaf extract, Colloids and Surfaces A: Physicochemcal Engineering Aspects 369 (2010) 27–33.

49

[155] S. Li, Y. Shen, A. Xie, X. Yu, L. Qiu, L. Zhang, Q. Zhang, Green synthesis of silver nanoparticles using Capsicum annuum L. extract, Green Chem. 9 (2007) 852-885. [156] M. Balamurugan, N. Kandasamy, S. Saravanan, N, Ohtani, Synthesis of uniform and high-density silver nanoparticles by using Peltophorum pterocarpum plant extract, Japanese J. Appl. Phys. 53 (2014) 05FB19 1-7. [157] S.P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad, M. Sastry, Synthesis of gold nanotriangles and silver nanoparticles using Aloe vera plant extract, Biotechnol. Prog. 22 (2006) 577-583. [158] S. Wang, R. Su, S. Nie, M. Sun, J. Zhang, D. Wu, N.M. Moussa, Application of nanotechnology in improving bioavailability and bioactivity of diet-derived phytochemicals, Journal of Nutritional Biochemistry, 25 (2014) 363-376. [159] P. Kuppusamy, M.M. Yusoff, G.P. Maniam, N. Govindan, Biosynthesis of metallic nanoparticles using plant derivatives and their new avenues in pharmacological applications – An updated report, Saudi Pharmaceutical J. 24 (2016) 473-484. [160] D. Raghunandan, B. Ravishankar, G. Sharanbasava, D.B. Mahesh, V. Harsoor, M.S. Yalagatti, M. Bhagawanraju, A. Venkataraman, Anti-cancer studies of noble metal nanoparticles synthesized using different plant extracts, Cancer Nanotechnol. 2 (2011) 57-65. [161] S. Yallappa, J. Manjanna, B.L. Dhananjaya, U. Vishwanatha, B. Ravishankar, H. Gururaj, Phytosynthesis of gold nanoparticles using Mappia foetida leaves extract and their conjugation with folic acid for delivery of doxorubicin to cancer cells, J. Mater. Sci. Mater. Med. 26 (2015) 235. [162] B. Sadeghi, Zizyphus mauritiana extract-mediated green and rapid synthesis of gold nanoparticles and its antibacterial activity, J. Nanostructure Chem. 5 (2015) 265-273.

50

[163] M. Khatami, S. Pourseyedi, M. Khatami, H. Hamidi, M. Zaeifi, S. Lida, Synthesis of silver nanoparticles using seed exudates of Sinapis arvensis as a novel bioresource, and evaluation of their antifungal activity, Bioresour. Bioproc. 2 (2015) 19. [164] A.T. Ahmed, F.E. Wael, M. Shaadan, Antibacterial action of ZnO nanoparticles against foodborne pathogens, Journal of Food Safety 31 (2010) 211–218. [165] P. Daisy, K. Saipriya, Biochemical analysis of Cassia fistula aqueous extract and phytochemically synthesized gold nanoparticles as hypoglycemic treatment for diabetes mellitus, International Journal of Nanomedicine 7 (2012) 1189–1202. [166] K. Praveen Kumar, W. Paul, C.P. Sharma, Green synthesis of gold nanoparticles with Zingiber officinale extract: Characterization and blood compatibility, Process Biochemistry 46 (2011) 2007-2013. [167] M. Zargar, K. Shameli, G.R. Najafi, F. Farahani, Plant mediated green biosynthesis of silver nanoparticles using Vitex negundo L. extract, J. Ind. Eng. Chem., 20 (2014) 41694175. [168] S. Ghosh, S. Patil, M. Ahire, R. Kitture, D.D. Gurav, A.M. Jabgunde, S. Kale, K. Pardesi, V. Shinde, J. Bellare, D.D. Dhavale, B.A. Chopade, Gnidia glauca flower extract mediated synthesis of gold nanoparticles and evaluation of its chemocatalytic potential, J. Nanobiotechnol. 10 (2012) 17. [169] V.K. Vidhu, D. Philip, Catalytic degradation of organic dyes using biosynthesized silver Nanoparticles , Micron 56 (2014) 54-62. [170] N. Duran, P.D. Marcato, G.I.H. De Souza, O.L. Alves, E. Esposito, Antibacterial effect of silver nanoparticles produced by fungal process on textile fabrics and their effluent treatment, Journal of Biomedical Nanotechnology 3 (2007) 203–208. [171] C. Krishnaraj, P. Muthukumaran, R. Ramachandran, M.D. Balakumaran, P.T. Kalaichelvan, Acalypha indica Linn: Biogenic synthesis of silver and gold nanoparticles

51

and their cytotoxic effects against MDA-MB-231, human breast cancer cells, Biotechnology Reports 4 (2014) 42- 49. [172] A. Baghizadeh, S. Ranjbar, V.K. Gupta, M. Asif, S. Pourseyedi, M.J. Karimi, R. Mohammadinejad, Green synthesis of silver nanoparticles using seed extract of Calendula officinalis in liquid phase, Journal of Molecular Liquids 207 (2015) 159– 163. [173] R. Sankara, A. Karthika, A. Prabua, S. Karthika, K.S. Shivashangari, V. Ravikumara, Origanum vulgare mediated biosynthesis of silver nanoparticles for its antibacterial and anticancer activity, Coll. Surf. B: Bionterf.108 (2013) 80-84. [174] V. Vignesh, K.F. Anbarasi, S. Karthikeyenia, G. Sathiyanarayanan, P. Subramanian, R. Thirumurugan, A superficial phyto-assisted synthesis of silver nanoparticles and their assessment on hematological and biochemical parameters in Labeo rohita (Hamilton, 1822), Colloids and Surfaces A: Physicochemcal Engineering Aspects 439 (2013) 184-192. [175] J.P.S. Jacob, J.S. Finub, A. Narayanan, Synthesis of silver nanoparticles using Piper longum leaf extracts and its cytotoxic activity against Hep-2 cell line, Coll. Surf. B: Bionterf. 91(2012) 212– 214. [176] R. Sukirtha, K.M. Priyanka, J.J. Antony, S. Kamalakkannana, R. Thangam, P. Gunasekaran, M. Krishnan, S. Achiramana, Cytotoxic effect of Green synthesized silver nanoparticles using Melia azedarach against in vitro HeLa cell lines and lymphoma mice model, Process Biochemistry 47 (2012) 273-279. [177] R. Vivek, R. Thangam, K. Muthuchelian, P. Gunasekaran, K. Kaveri, S. Kannana, Green biosynthesis of silver nanoparticles from Annona squamosa leaf extract and its in vitro cytotoxic effect on MCF-7 cells, Process Biochemistry 47 (2012) 2405–2410.

52

[178] M. Jeyaraj, G. Sathishkumar, G. Sivanandhan, D. MubarakAli, M. Rajesh, R. Arun, G. Kapildev, M. Manickavasagam, N. Thajuddin, K. Premkumar, N. Thajuddin, A. Ganapathi, Biogenic silver nanoparticles for cancer treatment: An experimental report, Coll. Surf. B: Bionterf.106 (2013a) 86-92. [179] Zhang, Y., Cheng, X., Zhang, Y., Xue, X., Fu, Y. Biosynthesis of silver nanoparticles at room temperature using aqueous aloe leaf extract and antibacterial properties (2013) Colloids and Surfaces A: Physicochemcal Engineering Aspects, 423, 63-68. [180] K.L. Niraimathi, V. Sudha, R. Lavanya, P. Brindha, Biosynthesis of silver nanoparticles using Alternanthera sessilis (Linn.) extract and their antimicrobial, antioxidant activities, Coll. Surf. B: Bionterf.102 (2013) 288-291. [181] U.B. Jagtap, V.A. Bapat, Green synthesis of silver nanoparticles using Artocarpus heterophyllus Lam. seed extract and its antibacterial activity, Industrial Crops and Products 46 (2013) 132– 137. [182] U. Suriyakalaa, J.J. Antony, S. Suganya, D. Siva, R. Sukirtha, S. Kamalakkannan, P.B.P. Tirupathi, S. Achiraman, Hepatocurative activity of biosynthesized silver nanoparticles fabricated using Andrographis paniculata, Coll. Surf. B: Bionterf.102 (2013) 189-194. [183] V. Chaturvedi, P. Verma, Fabrication of silver nanoparticles from leaf extract of Butea monosperma (Flame of Forest) and their inhibitory effect on bloom-forming cyanobacteria, Bioresources and Bioprocessing 2:18 (2015) 1-8. [184] A. K. Mittal, J. Bhaumik, S. Kumar, U. C. Banerjee, Biosynthesis of silver nanoparticles: Elucidation of prospective mechanism and therapeutic potential, Journal of Colloid and Interface Science 415 (2014) 39–47.

53

[185] R. Geethalakshmi, D.V.L. Sarada, Characterization and antimicrobial activity of gold and silvernanoparticles synthesized using saponin isolated from Trianthema decandra L., Industrial Crops and Products 51 (2013) 107-115. [186] K. Gopinath, K.S. Venkatesh, R. Ilangovan, K. Sankaranarayanan, A. Arumugam, Green synthesis of gold nanoparticles from leaf extract of Terminalia arjuna, for the enhanced mitotic cell division and pollen germination activity, Industrial Crops and Products 50 (2013) 737-742. [187] K. Mohan Kumar, B. Kumar Mandal, S. Madhulika, V. Krishnakumar, Terminalia chebula mediated green and rapid synthesis of gold nanoparticles, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 86 (2012) 490– 494. [188] M.F. Zayed, W.H. Eisa, Phoenix dactylifera L. leaf extract phytosynthesized gold nanoparticles; controlled synthesis and catalytic activity, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 121 (2014) 238-244. [189] M. Guo, W. Li, F. Yang, H. Liu, Controllable biosynthesis of gold nanoparticles from a Eucommia ulmoides bark aqueous extract, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 142 (2015) 73–79. [190] M.M.H. Khalil, E.H. Ismail, F. El-Magdoub, Biosynthesis of Au nanoparticles using olive leaf extract, Arabian Journal of Chemistry 5 (2012) 431-437. [191] R.M. Ganesan, H. Gurumallesh Prabu, Synthesis of gold nanoparticles using herbal Acorus calamus rhizome extract and coating on cotton fabric for antibacterial and UV blocking

applications,

Arabian

J.

Chem.

(2015)

In

Press,

https://doi.org/10.1016/j.arabjc.2014.12.017 [192] B. Sadeghi, M. Mohammadzadeh, B. Babakhani, Green synthesis of gold nanoparticles using Stevia rebadiauna leaf extracts: Characterization and their stability, Journal of Photochemistry and Photobiology B: Biology 148 (2015a) 101-106.

54

[193] P. Khademi-Azandehi, J. Moghaddam, Green synthesis, characterization and physiological stability of gold nanoparticles from Stachys lavandulifolia Vahl extract, Particuology 19 (2015) 22-26. [194] N. Muniyappan, N.S. Nagarajan, Green synthesis of gold nanoparticles using Curcuma pseudomontana essential oil, its biological activity and cytotoxicity against human ductal breast carcinoma cells T47D (2014) Journal of Environmental Chemical Engineering, 2, 2037–2044. [195] M.V. Sujitha, S. Kannan, Green synthesis of gold nanoparticles using Citrus fruits (Citrus limon, Citrus reticulata and Citrus sinensis) aqueous extract and its characterization, Spectrochimica Acta

Part

A: Molecular

and

Biomolecular

Spectroscopy 102 (2013)15–23. [196] P. Karuppaiya, E. Satheeshkumar, W.T. Chao, L.Y. Kao, E.C. Fun Chen, H.S. Tsay, Anti-metastatic activity of biologically synthesized gold nanoparticles on human fibrosarcoma cell line HT-1080, Coll. Surf. B: Bionterf.110 (2013) 163-170. [197] N. Basavegowda, A. Idhayadhulla, Y.R. Lee, Phyto-synthesis of gold nanoparticles using fruit extract of Hovenia dulcis and their biological activities, Industrial Crops and Products 52 (2014) 745– 751. [198] M. Nasrollahzadeh, S. Mohammad Sajadi, M. Maham, Green synthesis of palladium nanoparticles using Hippophae rhamnoides Linn leaf extract and their catalytic activity for the Suzuki–Miyaura coupling in water, Journal of Molecular Catalysis A: Chemical 396 (2015) 297-303. [199] A. Bankar, B. Joshi, A. Ravi Kumar, S. Zinjarde, Banana peel extract mediated novel route for the synthesis of palladium nanoparticles, Mater. Lett. 64 (2010) 1951–1953. [200] A. Kalaiselvi, S.M. Roopan, G. Madhumitha, C. Ramalingam, G. Elango, Synthesis and characterization of palladium nanoparticles using Catharanthus roseus leaf extract

55

and its application in the photo-catalytic Degradation, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 135 (2015) 116-119. [201] K. Mohan Kumar, B.K. Mandal, K. Siva Kumar, P. Sreedhara Reddy, B. Sreedhar, Biobased green method to synthesise palladium and iron nanoparticles using Terminalia chebula aqueous extract, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 102 (2013) 128-133. [202] D.S. Sheny, D. Philip, J. Mathew, Synthesis of platinum nanoparticles using dried Anacardium occidentale leaf and its catalytic and thermal applications, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 114 (2013) 267-271. [203] R.W. Raut, A.S.M. Haroon, Y.S. Malghe, B.T. Nikam, S.B. Kashid, Rapid biosynthesis of platinum and palladium metal nanoparticles using root extract of Asparagus racemosus Linn, Adv. Mater. Lett. 4 (2013) 650-654. [204] S. Shende, A.P. Ingle, A. Gade1, M. Rai, Green synthesis of copper nanoparticles by Citrus medica Linn. (Idilimbu) juice and its antimicrobial activity, World J. Microbiol. Biotechnol. 31 (2015) 865-873. [205] K. Cheirmadurai, S. Biswas, R. Murali, P. Thanikaivelan, Green synthesis of copper nanoparticles and conducting nanobiocomposites using plant and animal sources, Royal Society of Chemistry 4 (2014) 19507–19511. [206] D.K. Vasudev, S.K. Pramod, Green synthesis of copper nanoparticles using Ocimum sanctum leaf extract, International J. Chem. Stud. 1 (2013) 1-4. [207] V. Vellora, T. Padil, M. Cerník, Green synthesis of copper oxide nanoparticles using gum karaya as a biotemplate and their antibacterial application, International Journal of Nanomedicine 8 (2013) 889-898.

56

[208] G. Jayakumarai, C. Gokulpriya, R. Sudhapriya, G. Sharmila, C. Muthukumaran, Phytofabrication and characterization of monodisperse copper oxide nanoparticles using Albizia lebbeck leaf extract, Appl. Nanosci. 5 (2015) 1017-1021. [209] S.C.G. Kiruba Daniel, G. Vinothini, N. Subramanian, K. Nehru, M. Sivakumar, Biosynthesis of Cu, ZVI, and Ag nanoparticles using Dodonaea viscosa extract for antibacterial activity against human pathogens, J. Nanoparticle Res. 15 (2013) 1319. [210] V. Madhavi, T.N.V.K. Prasad, A.V. Bhaskar Reddy, B. Ravindra Reddy, G. Madhavi, Application of phytogenic zerovalent iron nanoparticles in the adsorption of hexavalent chromium, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 116 (2013) 17–25. [211] T. Wang, X. Jin, Z. Chen, M. Megharaj, R. Naidu, Green synthesis of Fe nanoparticles using Eucalyptus leaf extracts for treatment of eutrophic wastewater, Sci. Total Environ. 466 (2014) 210–213. [212] S. Venkateswarlu, Y. Subba Rao, T. Balaji, B. Prathima, N.V.V. Jyothi, Biogenic synthesis of Fe3O4 magnetic nanoparticles using plantain peel extract, Mater. Lett. 100 (2013) 241-244. [213] S. Marimuthu, A. Rahuman, C. Jayaseelan, A.V. Kirthi, T. Santhoshkumar, K. Velayutham, A. Bagavan, C. Kamaraj, G. Elango, M. Iyappan, C. Siva, L. Karthik, K.V.B. Rao, Acaricidal activity of synthesized titanium dioxide nanoparticles using Calotropis gigantea against Rhipicephalus microplus and Haemaphysalis bispinosa, Asian Pacific J. Tropical Med. (2013) 682-688. [214] S.M. Roopan, A. Bharathi, A. Prabhakarn, A. Abdul Rahuman, K. Velayutham, G. Rajakumar, R.D. Padmaja, M. Lekshmi, G. Madhumitha, Efficient phyto-synthesis and structural characterization of rutile TiO2 nanoparticles using Annona squamosa peel

57

extract, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 86–90. [215] R.P. Singh, V.K. Shukla, R.S. Yadav, P.K. Sharma, P.K. Singh, A.C. Pandey, Biological approach of zinc oxide nanoparticles formation and its characterization, Adv. Mater. Lett. 2 (2011) 313-317. [216] A.J. Kora, R.B. Sashidhar, J. Arunachalama, Aqueous extract of gum olibanum (Boswellia serrata): A reductant and stabilizer for the biosynthesis of antibacterial silver nanoparticles, Proc. Biochem. 47 (2012) 1516-1520. [217] R. Amooaghaie, M.R. Saeri, M. Azizi, Synthesis, characterization and biocompatibility of silver nanoparticles synthesized from Nigella sativa leaf extract in comparison with chemical silver nanoparticles, Ecotoxicol. Environ. Safe. 120 (2015) 400-408. [218] V. Gopinath, D. MubarakAli, S. Priyadarshini, N. Meera Priyadharsshini, N. Thajuddin, P. Velusamy, Biosynthesis of silver nanoparticles from Tribulus terrestris and its antimicrobial activity: A novel biological approach, Coll. Surf. B: Bionterf. 96 (2012) 69-74. [219] T. Ashokkumar, D. Prabhu, R. Geetha, K. Govindaraju, R. Manikandan, C. Arulvasu, G. Singaravelu, Apoptosis in liver cancer (HepG2) cells induced by functionalized gold nanoparticles. Coll. Surf. B: Biointerf. 123 (2014) 549-556. [220] R. Geetha, T. Ashokkumar, S. Tamilselvan, K. Govindaraju, M. Sadiq, G. Singaravelu, Green synthesis of gold nanoparticles and their anti-cancer activity, Cancer Nanotechnol. 4 (2013) 91-98. [221] T. Ashokkumar, J. Arockiaraj, K. Vijayaraghavan, Biosynthesis of gold nanoparticles using green roof species Portulaca grandiflora and their cytotoxic effects against C6 glioma human cancer cells, Environ. Prog. Sustain. Energ. 35 (2016) 1732–1740.

58

Whole plant or plant parts were added to solvent

Solvent

The suspension was left to equilibrate or slightly agitated

Metal solution

Formation of Nanoparticle

UV-spectrophotometry FTIR SEM/TEM/AFM/EDX XRD

Figure 1. Experimental protocol for plant-mediated biosynthesis of nanoparticles.

Characterization

Plant

Plant extract was then filtered and added to metal solution

59

3.5 3 Absorbance

2.5 2

525 nm

1.5 1 0.5 0 300

400

500 600 Wavelength (nm)

700

800

Figure 2. UV–visible spectra of synthesized gold nanoparticles using seaweed extract of T. ornata Reprinted from Ashokkumar and Vijayaraghavan [131] with permission from Vinanie Publishers copyright (2016).

60

T. ornata extract synthesized gold nanoparticles using T. ornata extract

4000

3500

3000

2500

2000

1500

1000

Wavenumber cm-1 Figure 3. FTIR spectra of T. ornata extract and synthesized gold nanoparticles using T. ornata extract Reprinted from Ashokkumar and Vijayaraghavan [131] with permission from Vinanie Publishers copyright (2016).

61

4000

(111)

3500

(220)

2000

(311)

2500

(200)

1500

(222)

Intensity (Counts)

3000

1000 500 0 30

40

50

60

70

80

90

2Ɵ

Figure 4. XRD pattern of crystalline gold nanoparticles synthesized using leaf extract of Portulaca grandiflora. Reprinted from Ashokkumar et al. [221] with permission from American Institute of Chemical Engineers copyright (2016).

62

Figure 5. SEM images of synthesized nanoparticles using the green seaweed extract of star like Ag-Au bimetallic NPs. (data not published)

63

A Pentagonal Hexagonal Triangle Rhombus

B Spherical Rod

Figure 6. TEM images of gold nanoparticles synthesized using leaf extract of Portulaca grandiflora. Reprinted from Ashokkumar et al. [221], with permission from American Institute of Chemical Engineers copyright (2016).

64

Figure 7. EDAX spectrum of synthesized gold nanoparticles using T. ornata extract Reprinted from Ashokkumar and Vijayaraghavan [131] with permission from Vinanie Publishers copyright (2016).

65

Biology

Physics



   

Food package Pesticide Elements removal Fertilizer

Optics

Chemistrty

 

Catalyst Paints

Diagnosis Therapy Prevention

        

Anticancer Antiviral Antidiabetic Antimicrobial Cardioprodective Drug delivery

Figure 8. Various applications of nanoparticles.

Engineering

   

Nanosensor Nanochips Nanocoatings Nanosemiconductors

Environmental

  

Water purification Removal of soil contaminates Antifouling

66

Table 1. Green synthesis of various noble metal nanoparticles by different plant species

Experimental conditions Metals

Plant species pH

Contact time

Temperature

Functional molecule

Shape and size

Applications

Reference

Ag

Acalypha indica Linn

Neutral pH

30 min

Room temperature

-

Spherical; 20–30 nm

Cytotoxicity activity

[171]

Ag

Chenopodium leaf

2.0 - 10.0

15 min

Different temperatures

Carbonyl and carboxylate groups

Spherical; 10 – 30 nm

-

[154]

7.2 - 8.5

-

-

Amine and carboxylate groups

Spherical; 13 nm

-

[20]

3.0 - 9.0

-

30 and 60 °C

Amide group and groups

Spherical; 7.5 nm

-

[172]

Spherical; 2 - 10 nm

-

album

Hibiscus rosa sinensis Ag Leaf Ag

Calendula seed

officinalis

Antibacterial and

Allophylus cobbe Ag

8.0

6h

60 °C

Amide II, amino and carboxylate groups

-

10 min

60 – 90 °C

Amide, nitrile and aromatic groups

leaf

Ag

Origanum vulgare

amino acid

Anti-biofilm activities Cytotoxic and antimicrobial activities

[132]

[173]

Antibacterial, Ag

Ocimum tenuiflorum leaf extract

-

10 min

Room temperature

Hydroxyl, carbonyl polysaccharides groups

and

Spherical and ovoid; 7 – 15 nm

anti-protease and myeloperoxidase activities

[174]

67 Room Ag

Piper longum leaf

-

temperature

Alkenes, polyols amines groups

and aliphatic

-

cytotoxicity activity

[175]

Ag

Melia azedarach

-

-

35 - 95 °C

Carbonyl group of proteins, amines and polyphenolics groups

-

In vitro and In vivo cytotoxicity

[176]

Ag

Annona squamosa leaf

-

-

Room temperature

Carboxylic, phenols and hydroxyl groups

Spherical; 20 - 100 nm

In vitro cytotoxicity

[177]

Ag

Sesbania leaf

-

24 h

Room temperature

Carboxylic, carbonyl and amine groups

-

In vitro anticancer activity

[178]

Ag

Aloe leaf

-

20 min

Room temperature

Free amino, carboxylic and amide groups

Spherical; 20 nm

Antimicrobial activity

[179]

[180]

grandiflora

-

10 min

-

Polyphenols and aliphatic amines groups

-

Anti-microbial and free radical scavenging activities

Lam.

-

5 min

Autoclave (15 psi and 121 ◦C)

Amides, carboxyl, amino acid groups

Irregular; 3 - 25 nm

Antibacterial activity

[181]

Ag

Trigonella foenumgraecum seed

-

5 min

-

Phenolic hydroxyl, amides and carboxyl groups

Spherical; 17 nm

Catalytic degradation activity

[169]

Ag

Andrographis paniculata

-

-

30 - 95 °C

Carbonyl, ketones and groups

Spherical; 13 - 27 nm

Ag

Alternanthera Linn.

Ag

Artocarpus heterophyllus seed

sessilis

amino

and

hydroxyl

In vitro antioxidant and protective effect

[182]

68 on liver injury

20 - 60 °C

Aromatic, amide III and II, polyphenols, alkanes and carbonyl groups

Spherical; 12 - 40 nm

In vitro anticancerous activity

-

25 °C

Carboxyl, hydroxyl and amine groups

Spherical; 1 - 35 nm

Antifungal activity

-

-

Amide I and II groups

Spherical; 20 - 30 nm

Anti-algal property

2h

Room temperature

Spherical; 5 – 20 nm

Cytotoxic antioxidant activity

-

Room temperature

Hydroxyl, amide amines groups

Rectangular and triangular; 55.2 – 98.4 nm

Diabetes mellitus

[165]

-

Spherical; 37.7 nm and hexagonal; 79.9 nm

Antimicrobial activity

[185]

5 min

Hydroxyl, carbonyl and aldehyde groups

60 min

Room temperature

Hydroxyl groups

Triangular, hexagonal and spherical; 5 nm

Catalytic cytotoxicity activities

Ag

Podophyllum hexandrum leaf

4.5 - 10.0

30 - 150 min

Ag

Sinapis arvensis seed extract

-

Ag

Butea monosperma leaf

-

Aromatic Ag

Syzygium cumini fruit

7.0 – 9.0

Au

Cassia fistula stem bark

-

Au

Trianthema L.

-

Au

Moringa flower

decandra

oleifera

-

and aliphatic amines, carbonyl flavonoids and phenolic groups

and

and aliphatic

carboxylic

acid

[98]

[163]

[183]

and [184]

and [139]

69

Au

Illicium verum

2 - 11

15 min

25 - 50 °C

Triangular and hexagonal; 20 - 50 nm

Cytotoxicity activity

[145]

Amines and carboxylic acid groups

Spherical; 20 – 50 nm

Pollen germination activity

[186]

Polyphenols group

Au

Terminalia arjuna leaf

-

15 min

Room temperature

Au

Zingiber officinale

7.4

20 min

37 and 50 °C.

Alkane and carboxylic acid groups

Spherical; 5 – 10 nm

Blood compatibility

[166]

Au

Rosa hybrida petal

-

5 min

Room temperature

Amine, hydroxyl groups

Spherical, triangular and hexagonal; 10 nm.

-

[87]

Au

Terminalia seed

-

20 sec

Room temperature

Hydroxyl, aliphatic and groups

Triangular, pentagonal and spherical; 6 – 60 nm.

Antimicrobial activity

[187]

Phoenix dactylifera L. leaf

Room

Hydroxyl

Au

-

-

Catalytic activity

[188]

temperature

and carbonyl groups

Triangular, tetragonal and rod; 32 - 45 nm

Eucommia bark

5 - 13

30 - 60 °C

Hydroxyl, amines and carboxylic acid groups

Spherical

Catalytic activity

[189]

-

Hydroxyl, carboxylic amines groups

-

[190]

Au

chebula

ulmoides

30 min

and carbonyl

carbonyl

Triangular, hexagonal, Au

Olive leaf

2.3 - 9.6

30 min

acid and and spherical; 50 to 100 nm

70

Au

Acorus rhizome

calamus

4 - 9.2

-

At room temperature

Amide I and amine groups

20 - 80 °C

Polyphenols, hydroxyl carboxylic acids groups

Amines, amide and groups

Spherical; 10 nm

Antibacterial activity

[191]

Antibacterial and Au

Pistacia integerrima

4.0 - 13.0

Au

Stevia rebadiauna leaf

6.0 - 12.0

-

-

Au

Stachys Vahl

7.4

20 min

80 °C

lavandulifolia

and

carbonyl

Flavonoids and monoterpenes groups

-

antinociceptive activities

[109]

Spherical; 5 - 20 nm

-

[192]

Spherical and triangular; 34 - 80 nm

-

[193]

-

Antibacterial and antioxidant activities

[21]

Hexagonal and triangular

-

[105]

[194]

[195]

Au

Commelina nudiflora

5.0 - 8.0

-

30 - 60 °C

Amide, phenolic acids, sugar moieties and aliphatic amine groups

Au

Magnolia kobus and Diopyros kaki leaves

-

-

25 - 95 °C

Amines, alcohols, ketones, aldehydes and carboxylic acids groups

Au

Curcuma pseudomontana root

-

30 min

Room temperature

Carbonyl and hydroxyl groups

Spherical shape; 20nm

Antioxidant, antibacterial and anti-inflammatory activities

Au

Citrus limon, Citrus reticulata and Citrus sinensis

-

10 min

Room temperature

-

Spherical and triangular; 15 - 80 nm

-

71

Au

Dysosma rhizome

pleiantha

Anti-metastatic -

20 min

30 - 60 °C

Amide, amine and carbonyl groups

Spherical; 127 nm

[196] Activity

Zizyphus Au

-

10 min

mauritiana

Room temperature

Hydroxyl and carboxylic groups

Spherical; 20 – 40 nm

Antimicrobial activity

[162]

Hydroxyl and carbonyl groups

Spherical and hexagonal; 10 - 20 nm

In antioxidant activity

[197]

vitro

Au

Hovenia dulcis fruit

-

30 min

Pd

Hippophae rhamnoides Linn leaf

-

25 min

80 °C.

Polyphenols and carbonyl groups

2.5 - 14 nm

Catalytic activity

[198]

1.0 - 11.0

72 h

30 °C

-

Spherical; 15 – 20 nm

-

[137]

2.0 - 5.0

3 min

40- 100 °C

50 nm

-

[199]

Quasi-spherical and irregular; 3.6 – 9.9 nm

-

[116]

Spherical; 38 nm

Dye degradation

[200]

-

-

[201]

Room temperature

Cinnamom Pd zeylanicum bark extract Carboxyl, hydroxyl and amide Pd

Banana peel extract

groups Cinnamomum Pd

-

12 h

Room temperature

-

2h

60 °C

camphora leaf

Pd

Pd

Catharanthus leaf extract Terminalia fruit

roseus

Carbonyl, aldehyde, ketones, carboxylic acid groups and aromatic rings Carboxyl and hydroxyl groups

chebula

-

40 min

Room temperature

Polyphenols of carboxyl and hydroxyl

72 groups

Pd

Anogeissus latifolia

-

30 min

-

-

Pt

Anacardium occidentale leaf

6.0 - 8.0

-

Room temperature

Amide II and I, carboxylate ions of amino acid, hydroxyl groups

Pt

Cacumen platycladi

-

25 h

30 - 90 °C

Aldehyde groups

Pt

Asparagus racemosus root extract

-

5 min

-

-

Catalytic activity antibacterial activities

[117]

Catalytic activity

[202]

Spherical; 2 - 2.9 nm

-

[111]

1.0 - 6.0 nm

-

[203]

Spherical; 2.3 - 7.5 nm

and

carboxylic

acid

Irregular rod shaped

73

Table 2. Green synthesis of various metal/metal-oxide nanoparticles by different plant species Methodology importance Metals

Plants/Microbes pH,

Contact time

Temperature

Functional molecule

Shape and size

Applications

Reference

Cu

Citrus medica Linn

-

-

60 – 100 °C

-

-

Antimicrobial activity

[204]

Cu

Lawsonia inermis leaf

11.0

-

-

Hydroxyl and carboxylic groups

Spherical; 83 nm

-

[205]

Cu

Magnolia kobus leaf

-

24 h

25–95 °C

-

Spherical; 50 – 250 nm

Antibacterial activity

[118]

-

Room temperature

-

-

[206]

Cu

Ocimum sanctum leaf

-

Terpenoids, alcohols, ketones, aldehydes and carboxylic acid groups

CuO

Gum karaya

-

1h

75 °C

Hydroxyl and carboxylate groups

Spherical; 2 - 10 nm

Antimicrobial activity

[207]

CuO

Albizia lebbeck leaf

-

24 h

37 °C

-

Spherical; 100 nm

-

[208]

Fe

Dodonaea viscosa

-

-

-

Carbonyl, polyols , hydroxyl, and amide I groups

Spherical; 50 - 60 nm.

Antibacterial effect

[209]

Fe

Eucalyptus globules leaf extract

-

-

-

Hydroxyl phenol

-

-

[210]

Fe

Eucalyptus leaf extract

-

-

Room temperature

Phenols, amines, carboxyl and carbonyl groups

-

Treatment swine wastewater

groups

of

of [211]

74

Fe3O4

Plantain peel extract

-

2h

70 °C

Polyphenolic, carbohydrates , carboxylic acids and amine groups

TiO2

Calotropis gigantean

-

2h

90 °C

Primary amines, amides, carbonyl and hydroxyl groups

-

Acaricidal activity

TiO2

Annona squamosa fruit peel

-

6h

Room temperature

-

Spherical; 23 ± 2 nm

-

[214]

TiO2

Jatropha curcas L. latex

-

12 h

50 °C

Amide II, amide III, carboxylic acid and amines groups

Spherical; 25 - 50 nm

-

[125]

TiO2

ZnO

ZnO

Solanum trilobatum L. leaf

Calotropis latex

procera

Aloe barbadensis Miller leaf extract

-

2h

5–6h

[212]

[213]

-

Room temperature

-

Spherical; 5 - 40 nm

-

[215]

150 °C

Phenolic compounds, terpenoids, proteins, free amino and carboxylic groups

Spherical and hexagonal; 25 - 55nm

-

[120]

6h temperature

12

-

Hydroxyl, alkanes, monosubstituted alkynes, vinyl ethers, aldehydes, beta lactones, and aliphatic amines groups

Room -

Spherical; > 50 nm

Pediculocidal and larvicidal

[123]

Activities

75

Table 3. Exemplary stretching frequencies observed in FTIR spectra during plant-mediated biosynthesis of metal nanoparticles in some important studies. Metal

Type of plant Wavenumber (cm-1) biomass Native Biomass biomass after metal reduction

Surface functional groups identified

References

Ag

Boswellia serrata

3435

-OH groups

[216]

2963,2925

Methylene groups

3395

extract of gum 2963,2926 olibanum 2858

2855

2145

2014

1651,1520

1630,1537

1605,1420

1454,1398

C-C groups Amide I and II

C=O groups

1383

Ag

Ag

Ag

1261,1093

1261,1093

1022

1026

Nigella sativa 3397 leaf extract 2939

3394

-NH groups

-

-

1605

1608

-C=C groups

1413

1389

-C-H groups

Sesbania 3397 grandiflora leaf 1646 extract

3394

N-H groups

1646

C=C groups

1397

1406

C-O groups

1070

1070

C-O-C groups

3488

3419

-OH groups

Tribulus terrestris L. fruit

C-O groups

[217]

[140]

[218]

76

Au

Au

2811,2727

2726

C-H groups

2164

2171

C=C groups

-

1613

C-C groups

1348,1124

1348,1125

C-N groups

Cajanus cajan 3433 seed coat 2924

3434

-OH groups

2924

C-H groups

2161

2142

C= C groups

1614

1629

C=O groups

1415

1419

C-H groups

1089

-

C-O groups

1031,947, 903,819

1031

Ester groups

3414

3615,3547

-OH groups

-

2924,2855

C-H groups

2133

2402,2129

C= C groups

1648

-

C=C groups

-

1744

C=O groups

1383

1378

C-N groups

1288

-

C-O groups

1073

1071

C-N groups

3390

3378

Amide groups

2848,2916

-

-OH groups

1641

1635

C=O groups

1108

-

C-O groups

3415

3398

-OH groups

Couroupita guianensis

[219]

[220]

flower extract

Au

Moringa oleifera

[139]

flower extract

Au

Phoenix dactylifera

[188]

77

Au

Au

Pd

Pd

Terminalia chebula

1632

1651,1613

-C=O groups

-

3145

-OH groups

2922

C-H groups

1720

C=O groups

1613

C=C groups

1445

C-N groups

1384

C-O groups

1205

C-O-H groups

1020

C-O-C groups

1638, 515

C=C groups

1275,1151 ,1033

C=O groups

Zingiber officinale extract

Hippophae rhamnoides Linn leaf extract

Terminalia chebula fruit

1603,1190 ,935,850, 813,723

heterocyclic

3375

3387

-OH groups

1722

1714

-C=O groups

1674

-

-

1522

1462

C=C groups

1396

1381

C-OH groups

1122

1074

-

3400

3430

OH groups

[187]

[166]

compounds such as alkanoids, flavoinds and alkaloids, [198]

[201]

78

Pt

1610

1620

-C=C groups

1040

1040

C-O-C groups

3200

-OH groups

1720,1641

C=O groups

-

Amide groups

Anacardium 3400 occidentale dried leaf 1720,1641 powder 1519

1448

1448

1222

1222

C-OH groups Polyols

[202]

II