Green synthesis of Ag nanoparticles using Tamarind fruit extract for the antibacterial studies

Accepted Manuscript Green synthesis of Ag nanoparticles using Tamarind fruit extract for the antibacterial studies

N. Jayaprakash, J. Judith Vijaya, K. Kaviyarasu, K. Kombaiah, L. John Kennedy, R. Jothi Ramalingam, Murugan A. Munusamy, Hamad A. Al-Lohedan PII: DOI: Reference:

S1011-1344(17)30151-3 doi: 10.1016/j.jphotobiol.2017.03.013 JPB 10764

To appear in:

Journal of Photochemistry & Photobiology, B: Biology

Received date: Revised date: Accepted date:

2 February 2017 14 March 2017 14 March 2017

Please cite this article as: N. Jayaprakash, J. Judith Vijaya, K. Kaviyarasu, K. Kombaiah, L. John Kennedy, R. Jothi Ramalingam, Murugan A. Munusamy, Hamad A. Al-Lohedan , Green synthesis of Ag nanoparticles using Tamarind fruit extract for the antibacterial studies. The address for the corresponding author was captured as affiliation for all authors. Please check if appropriate. Jpb(2017), doi: 10.1016/j.jphotobiol.2017.03.013

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Green synthesis of Ag nanoparticles using Tamarind fruit extract for the antibacterial studies N. Jayaprakash1,2, J. Judith Vijaya1*, K. Kaviyarasu3,4, K.Kombaiah1, L. John Kennedy5,

Catalysis and Nanomaterials Research Laboratory, Department of Chemistry, Loyola College,

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Chennai 600 034, India. 2

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R. Jothi Ramalingam6, Murugan A. Munusamy7, Hamad A. Al‐Lohedan6

Department of Chemistry, SRM Valliammai Engineering College, Chennai 603 203, India.

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UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology Laboratories, College of

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Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, P O Box 392, Pretoria, South Africa.

Nanosciences African network (NANOAFNET), Materials Research Group (MRG),

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iThemba LABS-National Research Foundation (NRF), 1 Old Faure Road, 7129, P O Box 722, 5

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Somerset West, Western Cape Province, South Africa. Materials Division, School of Advanced Sciences, VIT University, Chennai Campus,

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Chennai 600 048, India.

Surfactant Research Chair, Chemistry Department, College of Science, King Saud University,

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Riyadh 11451, Saudi Arabia

Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia.

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* Corresponding author: Tel: +91-44-28178200, Fax: +91-44-28175566 E-mail: [email protected], [email protected] (J. Judith Vijaya)

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ABSTRACT In the present study, first time we report the microwave-assisted green s ynt hesi s of silver nanoparticles (AgNPs) using Tamarindus indica natural fruit extract. The plant extract plays a dual role of reducing and capping agent for the synthesis of AgNPs. The formation of spherical shape AgNPs is confirmed by XRD, HR-SEM, and HR-TEM. The presence of face-

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centered cubic (FCC) silver is confirmed by XRD studies and the average crystallite size of

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AgNPs is calculated to be around 6-8 nm. The average particle diameter is found to be around

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10 nm, which is identified from HR-TEM images. The purity of AgNPs is confirmed by EDX analysis. The presence of sigmoid curve in UV-Visible absorption spectra suggests that the

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reaction has complicated kinetic features. To investigate the functional groups of the extract and their involvement in the reduction of AgNO3 to form AgNPs, FT-IR studies are carried out. The redox peaks are observed i n c y c l i c v o l t a m m e t r y in the potential range of -1.2 to +1.2

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V, due to the redox active components of the T. indica fruit extract. In photoluminescence spectroscopy, the excited and emission peaks were obtained at 432 nm and 487 nm,

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respectively. The as-prepared AgNPs showed good results towards antibacterial activities. Hence, the

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present approach is a facile, cost- effective, reproducible, eco-friendly, and green method. Keywords: Silver nanoparticles; Green synthesis; UV-Visible spectroscopy; Electron

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microscopy; Antibacterial activity. 1. Introduction

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Recently, nanomaterials have attracted researchers among the scientific world, because of their most important and peculiar properties which are different when compared with their bulk

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materials. Among them, noble metal nanoparticles, such as Ag, Au, Pt, and Pd nanoparticles are used in physical, chemical and biological applications. [1,2]. AgNPs represents a good candidate to carry out the nanostructured part of antibacterial and anticancer applications [3-7]. The properties of the nanomaterials are controlled by their shape, size and nature. AgNPs are highly in demand, because of its various applications in medicine, water treatment and catalysis. In general, colloidal dispersions lead to the formation of AgNPs and their morphology differ, based on the methods adopted for the synthesis [8-10]. The size and shape of AgNPs can be controlled by different synthesis methods, for example, are discharge, 2

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lazer CVD, physical adsorption and emulsion polymerization are used as common methods to prepare AgNPs. But, because of the usage of the toxic chemicals or solvents or non-biodegradable agents, these methods should be avoided. Without using the above said toxic chemicals as reducing or stabilizing agents , AgNPs cannot be prepared. Since, these methods are potential threats to the environment and biological systems;

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there is a need for a green synthesis to prepare eco-friendly AgNPs. The use of capping agents is

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also important. Since, as per thermodynamics, oxidation of AgNPs is not a favorable one,

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because of its higher positive reduction potential, which will lead to a stable condition in both aqueous and alcoholic medium.

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Recently, green synthesis has gained importance over other physical and chemical methods, since, it offers environmental friendly, cheap, biocompatible, shape, and size controlled nanoparticles. The key aspect of nanotechnology is primarily aimed at the

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development of suitable and reliable synthesis routes, which in turn governs the size and shape, chemical composition and large scale production with better monodispersion for the

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synthesis of nanomaterials. Various synthesis methods are available in literature including green

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routes based on using plants, bacteria, and fungi, and they are given importance because of their non-toxic, economical and eco-friendly method of preparation and bio-compatible nature. Also,

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AgNPs prepared by using the above mentioned methods donot/less use of toxic chemicals, which makes them to be used in medical and pharmaceutical applications[11-13] . Also, AgNPs based

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antimicrobial packaging is a promising form of active food packaging, which plays an important role in extending shelf-life of foods and reduce the risk of pathogens. Also, the use of AgNPs as

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antimicrobial agents in food packaging is a mature technology, which concerns on the risks associated with the potential ingestion of the Ag ions migrated into food and drinks. This leads to a prudent attitude of food safety authorities [14]. There are reports available on the formation of AgNPs using plant extracts like Murraya koenigii leaf [15], Mangosteen leaf [16], Mangifera indica leaf [17], Jatropha curcas [18], Cinnamomum zeylanicum leaf [19], Camellia sinensis [20], Aloe vera [21], mushroom [22], and honey [23]. There are few reports on the preparation of AgNPs using fruit extract, such as papaya [24], tansy [25], pear [26], lemon [27] and

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goose berry [28]. The advantage of using plant and fruit extract includes the formation of stable nanoparticles without molecular aggregation even if they are stored for a longer time. In our study, we have synthesized AgNPs using T. indica fruit, which is commonly known as Tamarind fruit. In general, Tamarind is sweet and sour in taste and has tartaric acid,

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sugar and vitamins. In traditional medicine and food, it is used as the main ingredient in general.

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Hence we have explained the synthesis of AgNPs using T. indica fruit extract without the addition of any external surfactant, capping agent or template. Thus, we have attempted a simple,

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non-toxic, eco-friendly and economically viable green synthesis of AgNPs, which stands stable for more than six months in the liquid form.

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2. Experimental 2.1. Materials & Methods

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Silver nitrate (AgNO3) was obtained from Qualigens Fine Chemicals, Mumbai, India, and was used without any further purification. The T. indica fruit was collected from

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Tamarind tree in Kanchipuram, Tamil Nadu, India. De-ionized water was used in the whole process.

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2.2. Preparation of T. Indica Fruit Extract

A small piece (approximately 2 g) of the T. indica fruit was kept in 50 mL of hot de-

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ionized water for 5 min. Then this tamarind was squeezed well. The extract of T. indica fruit was then filtered using Whatman 41 paper and stored for future use.

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2.3. Green synthesis of AgNPs

A microwave irradiation was used for the synthesis of AgNPs. 5mM/100 ml silver

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nitrate solution was taken in 250 mL conical flask and 10 mL of T. indica fruit extract was added into the above silver nitrate solution. The above mixed solution was kept in the microwave oven (model: MS- 2049 UW) (input power 230 V, 50 Hz) for 180 s. The solution finally shows yellowish brown color, which in turn affirms the formation of AgNPs. Fig. 1 shows the digital photo of the AgNPs colloidal solutions prepared at different time intervals of 30, 60, 90, 120, 150, 180, and 210 s respectively. 2.4. Characterization Techniques The UV-Visible spectra were recorded by a Shimadzu 1800 spectrophotometer. Emission 4

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spectrum of the AgNPs was recorded by using VARIAN CARY ECLIPSE fluorospectrometer. The X-ray diffraction pattern was studied using XPERT-PRO diffractometer with Cu Kα (λ = 1.540 Å). A Bruker, Alpha T mode, Fourier Transform Infrared (FTIR) spectrometer was used to record FTIR spectra with 4 cm -1 resol ut i on and 2o m / s scanning speed. The m orphol ogy and size of AgNPs were found using a TECHNAI, FEI G2 model T-30, S-

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twin, 300 kV, High-resolution transmission electron microscope (HR-TEM) and a FE-I Quanta FEG 200 High-resolution scanning electron microscope (HR-SEM). The purity of the samples

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were analysed by energy dispersive X-ray analysis (EDX). Electrochemical measurements were carried out with a CHI 600A electrochemical workstation attached with a personal computer.

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0.1 M KNO3 was used as an electrolytic solution. A platinum wire, glassy carbon electrode (GCE) and a saturated calomel electrode (SCE) were used as the counter, working, and

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reference electrode respectively. 2.5 Antibacterial Assay

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The AgNPs were tested in the sterilized de-ionized water for their antibacterial activity by the agar d i f f u s i o n m e t h o d . Nine b a c t e r i a l s t r a i n s , B a c i l l u s c e r e u s ,

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S t a p h y l o c o c c u s a u r e u s , Micrococcus Luteus, Bacillus Subtilis and Enerococcus Sp. as gram positive bacteria and pseudomonas aeruginosa, Salmonella typhi, Escherichia coli and

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Klebsiella pneumonia as Gram-negative bacteria were used for the antibacterial activity analysis. The bacterial strains used in the p r e s e n t study were obtained from the

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Department of Medical Microbiology, Taramani Campus, University of Madras, India. These bacteria were grown on liquid nutrient agar media for 24 h prior to the experiment, and were

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seeded in agar plates by the pour plate technique. Different trails were carried out by preparing different plates for each and every bacterial strain. In each petri plate, three cavities were made using a cork borer at an equal distance. In each cavity, 50 µL of AgNPs, T. indica fruit extract, and AgNO3 solutions were filled. The plates were incubated for 24 h at 35 ºC. The reproducibility of the results was analyzed by repeating the antibacterial experiments for 3 times.

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Results and Discussion 3.1. UV-Visible Spectral studies of AgNPs The solution of AgNO3, T. indica f r u i t e x t r a c t a n d s y n t h e s i z e d AgNPs were taken and their respective UV-Visible absorption spectra were studied (Fig. 2). The presence of an intense peak at 432 nm confirms the formation of AgNPs [29-31]. The UV-Visible spectrum

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of AgNPs colloidal solution is similar with that of Ag nanoparticles prepared by using triton X

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100 [32]. As per the Mie’s theory [33], spherical AgNPs will show a single symmetric

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absorption peak, whereas anisotropic AgNPs will give two or more bands. Also, the UV-Visible spectrum of the as-synthesized AgNPs is symmetrical with sphere-like morphology.

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The UV-Visible absorption spectra of AgNPs solutions were studied at different time intervals as shown in Fig. 3. The sufficient peaks are formed at 180 s which in turn shows the

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formation of AgNPs at 180 s. Fig. 4 displays the absorbance versus time plot at 5 mM of AgNPs. It shows that the curve is sigmoid in nature, which suggests that the reaction has complicated kinetic features [34].

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The plot of ln[a/(1-a)] against time is shown in Fig. 5, where a = At/A∞, and At and A∞

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are the absorbance at time (t) and infinite (∞) time respectively. This figure is helpful in confirming the autocatalytic reaction paths involved during the formation of AgNPs. The first

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step is the formation of Ag nucleation centre, which will reduce other Ag+ ions in the solutions and thus lead to autocatalytic reaction towards the formation of AgNPs [34].

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3.2. Photoluminescence (PL) Spectroscopy of AgNPs The AgNPs were excited at 432 nm, and the emission peak was obtained at 487 nm as shown in Fig. 6. The stabilization of AgNPs by [poly(styrene)]-dibenzo-18-crown-6[poly(styrene)] with the emission band at 486 nm is reported [35]. The emission band at 491 nm

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upon excitation at 416 nm for PVP capped AgNPs is also reported [36]. Due to the promotion of d-band electrons of the AgNPs by absorbing the incident radiation to higher electronic states in the sp-band the origin of fluorescence occurs. 3.3. Fourier Transform Infrared Spectral studies of AgNPs To investigate the functional groups of the extract and their involvement in the reduction of AgNO3 to form AgNPs, FT-IR studies are carried out (Fig. 7a-b). FT-IR spectrum of colloidal AgNPs and T. indica fruit extract is similar with a slight shift in the band positions. T. indica 6

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fruit extract shows the bands at 3398 cm-1, 2940 cm-1, 1740 cm-1, 1632 cm-1, 1415 cm-1, and 1075 cm-1. The peak at 1740 cm-1 corresponds to the stretching vibration of =C=O (carbonyl group) [28]. The peaks at 1632 cm-1 and 1415 cm-1 are assigned to the stretching vibrations of C=C (aliphatic) and stretching vibration of -C=C (aromatic ring) respectively. The peak at 1075 cm-1 is because of the stretching vibrations of -C=O (ester). These peaks confirm the presence of

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active components of T. indica fruit extract, such as, heterocyclic compounds (alkanoids,

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flavonoids, and alkaloids), which act as the capping agent during the synthesis of AgNPs. The

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band positions of T. indica fruit extract capped AgNPs at 3424 cm-1, 1753 cm-1, 1627 cm-1, and 1042 cm-1 are slightly shifted to lower wave number than in the FT-IR spectra of pure T. indica fruit extract. The weak bands appearing at 1,074 and 1,042 cm−1 in the spectra of leaf extract and

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AgNPs, respectively, was due to –C–C– stretching and it corresponds to the interface between silver/ Tamarindus fruit extract [37].

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The above mentioned shift confirmed that the intensity of –OH vibration is decreased because of the formation of AgNPs. At the same time, the intensity of bands due to C=O group is

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increased. These two bands are primarily reproducible for the formation of AgNPs.

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The various functional groups in the final AgNPs are because of the heterocyclic compounds present in the T. indica fruit. They are responsible for the reduction and stabilization

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of AgNPs and they are soluble in water [38]. Hence, these water soluble compounds (alkanoids, flavonoids, and alkaloids) play the role of a capping and stabilizing agent in the synthesis of

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AgNPs.

3.4 XRD Analysis of AgNPs

The X-ray diffraction pattern of AgNPs produced by using the extract of T. indica fruit is

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shown in Fig. 8. The presence of face-centered cubic (FCC) silver which corresponds to (111), (200), (220), (311) and (222) planes with the corresponding diffraction peaks at 38.8°, 45.0°, 65.1°, 77.9° and 82.2° is confirmed by comparison with JCPDS Card No. 96-900-8460. Inter planar spacing (dcalculated) values for the above mentioned planes are 2.3169 Å, 2.0127 Å, 1.4325 Å, 1.2251 Å and 1.1722 Å respectively. It also agrees to the standard values [39]. The size of the crystallites of AgNPs is calculated to be around 6-8 nm from the full-width at half maximum (FWHM) of the high intense diffraction peak using well-known Scherrer’s formula [40]. 7

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3.5 Morphological Analysis of AgNPs The morphology of the AgNPs was examined by using HR-SEM and HR-TEM. The HRSEM image of AgNPs is shown in Fig. 9 (a-d) and Fig. 9 (e-h) shows the typical HR-TEM images of the as-synthesized AgNPs. It confirms that the particles are relatively uniform in diameter and almost spherical in shape. The presence of biomolecules that act as a capping agent

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is shown in Fig. 9 (b, d, f, h). The advantage of the present green synthesized AgNPs is that they

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are highly stay stable for more than 6 months. Thus, it is confirmed that the T. indica fruit extract

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is effective and suitable to synthesize stable AgNPs. The graphical representation of the formation of AgNPs is shown in Scheme 1.

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3.6 Energy Dispersive X-ray Analysis (EDX)

The EDX spectrum (Fig. 10a) was analyzed to determine the purity of the as-synthesized AgNPs. It shows the peaks for the presence of Ag, O and C. The Ag peak could be originated

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from AgNPs, and other peaks of O and C from the heterocyclic compounds of the T. indica fruit extract. Due to the surface plasmon resonance, metallic silver nanocrystals show an optical

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absorption peak approximately at 3 keV [41]. Fig. 10b shows the histogram of the particle size

range of AgNPs is 5-12 nm.

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3.7 Cyclic Voltammetry studies

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distribution and the average particle diameter is found to be 10 nm. It confirms that the size

Cyclic voltammograms (CV) of pure T. indica fruit extract and AgNPs at the scan rate of

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0.05 Vs-1 shows that the CV of AgNPs is similar to that of the pure T. indica fruit extract. Because of the presence of redox active components of the T. indica fruit extract, AgNPs show the redox peaks in the potential range of -1.2 to +1.2 V (Fig. 11). Since, T. indica fruit extract

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gains the electron, it shows the oxidation peak and the reduction peak arises because of the oxidation when the electric field is applied. The oxidation of Ag(0) into Ag+ is confirmed by the presence of a sharp peak at 0.13 V [42]. Hence, the present study confirms that the assynthesized AgNPs could be used as electrochemical sensors [43]. 3.8 Antibacterial activity studies of AgNPs In order to study the antibacterial effect of AgNPs towards Bacillus cereus, Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, Enterococcus species (Grampositive bacteria) and Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, and 8

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Klebsiella pneumonia (Gram-negative bacteria). Agar diffusion method is used which usually shows the inhibition zone around the holes with the increase in bacteria growth. Fig. 12 shows the results of inhibition zones of antibacterial activity. The diameter of the inhibiting zones of AgNPs against Bacillus cereus, Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, and Enterococcus sp. are 15, 16, 14, 18, and 16 mm respectively and

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Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, and Klebsiella pneumonia are 22,

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15, 15, and 10 mm respectively. The diameter of the inhibiting zones of AgNO3 against Bacillus

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cereus, Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, and Enterococcus sp. are 14, 15, 13, 16, and 15 mm respectively and Pseudomonas aeruginosa, Salmonella typhi,

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Escherichia coli, and Klebsiella pneumonia are 20, 13, 13, and 10 mm respectively. The inhibition zone is absent in the cavities having T. indica fruit extract. The above mentioned values are taken as the mean values after conducting the experiments for three times. From the

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results, it is found that the inhibition zone of AgNPs was slightly better than AgNO3 against the bacterial strains and the respective inhibition zone is represented in Fig. 13.

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Antibacterial activity is a well-known property of AgNPs. The mechanism of

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antibacterial activity is shown in Scheme 2. (i) AgNPs get attached and penetrate into the cell membrane of bacteria to disrupt the permeability and respiration functions of the cell, and thus

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kill the cells [44-46]. (ii) Reactive oxygen species (ROS) or oxygen radical species, which could be generated by the gaining of electrons from AgNPs has caused the damage of DNA by the help

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of oxidative stress [47]. (iii) Ag+ produced from AgNPs might also cause the disruption of ATP production and DNA replication [48, 49]. (iv) Phosphate and thiols in nucleic acids and amino Ag+.

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acids containing nitrogen, oxygen and sulphur (electron donor groups) forms a complex with

It is a well-known fact that silver salts have a good antibacterial activity. If taken in higher concentration, it is toxic to microbes and consumers. Therefore, AgNPs of smaller concentration in nano-regime is in demand for a better antimicrobial activity and the present green synthesis of AgNPs pave a way for the same. Conclusions Green synthesis of highly stable AgNPs by a simple microwave method is proposed. The use of T. indica fruit extract avoids the use of extra reducing and capping agent. The as9

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synthesized AgNPs are characterized by UV-Visible, FT-IR, XRD, CV, HR-SEM and HR-TEM and the obtained results confirm the formation of cubic Ag-phase with spherically-shaped particles at the nanoscale. Another advantage of this method is that the AgNPs formed are stable without any oxide formation for more than six months.

Hence, this green method shows

reproducible results, eco-friendly, less reaction time, cost effective and straight forward method

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that leads to the formation of highly stable nanoparticles with better antibacterial activity. Also,

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the as-synthesized AgNPs in the present study could be used in the field of medicine, food

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industries and sensors. Acknowledgements

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The authors duly acknowledge the Loyola college management for the funding through LOY-TOI project [Project Code: 2LCTOI14CHM003, dated 25.11.2014] and King Saud University, Vice Deanship of Research Chairs for the support rendered in completing the present

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work. The first author thanks SRM University, and SRM Valliammai Engineering College,

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[29] R.A. de Matos, L.C. Courrol, Saliva and light as templates for the green synthesis of silver nanoparticles, Colloids and Surfaces A: Physicochem. Eng. Aspects 441 (2014) 539-543. [30] V.K. Vidhu, D. Philip, Spectroscopic, microscopic and catalytic properties of silver nanoparticles synthesized using Saraca indica flower, Spectrochim. Acta A 117 (2014) 102-108. [31] N. Jayaprakash, J. Judith Vijaya, L. John Kennedy, K. Priadharsini, P. Palani, Antibacterial

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Fig. 2 UV-Visible absorption spectra of the solutions containing synthesized AgNPs, tamarind fruit extract, and AgNO3 Fig. 3 UV-Visible absorption spectra of the solutions containing synthesized AgNPs at different time intervals of 30, 60, 90, 120, 150, 180, and 210 s Fig. 4 Plot of absorbance versus microwave irradiation time

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Fig. 5 Plot of ln[a/(1-a)] against microwave irradiation time

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Fig. 6 Emission spectrum of AgNPs

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Fig. 7 FT-IR spectrum of a) pure Tamarindus indica fruit extract, and b) AgNPs stabilized by the Tamarindus indica fruit extract

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Fig. 8 XRD pattern of AgNPs produced by the Tamarindus indica fruit extract Fig. 9 HR-SEM images of AgNPs at (a, b) 30 µm (c, d) 10 µm and HR-TEM images of the synthesized AgNPs with magnification of (e, f) 100 nm (g, h) 50 nm

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Fig. 10 a) EDX spectrum of the synthesized AgNPs

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Fig. 11 Cyclic voltammogram of (a) pure Tamarindus indica fruit extract and (b) AgNPs

Fig. 12 Results of inhibition zones of antibacterial activity (1. AgNO3, 2. AgNPs and 3. pure

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Tamarindus indica fruit extract). (a) Bacillus cereus, (b) Staphylococcus aureus, (c) Pseudomonas aeruginosa, (d) Salmonella typhi, (e) Micrococcus luteus, (f) Escherichia coli, (g)

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Klebsiella pneumoniae, (h) Bacillus subtilis, and (i) Enterococcus sp Fig. 13 Bar diagram of inhibition zones of antibacterial activity of AgNPs

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Scheme Captions:

Scheme-1: Graphical representation for the formation mechanism of AgNPs Scheme-2: A schematic showing the various possibilities of antibacterial activities by AgNPs

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RESEARCH HIGHLIGHTS

 Highly stabilized colloidal silver nanoparticles (AgNPs) are produced.

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 Tamarindus indica (Tamarind) fruit extract is first time used to synthesize AgNPs.  Microwave oven is used for faster heating to synthesize AgNPs.

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 A detailed study of antibacterial activities is discussed.

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