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Green synthesis of gelatin-noble metal polymer nanocomposites for sensing of Hg2+ ions in aqueous media
Nano-Structures & Nano-Objects 13 (2018) 132–138
Contents lists available at ScienceDirect
Nano-Structures & Nano-Objects journal homepage: www.elsevier.com/locate/nanoso
Green synthesis of gelatin-noble metal polymer nanocomposites for sensing of Hg2+ ions in aqueous media Rudzani Muthivhi, Sundararajan Parani, Bambesiwe May, Oluwatobi Samuel Oluwafemi * Department of Applied Chemistry, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa Centre for Nanomaterials Science Research, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa
highlights
graphical abstract
• Gelatin stabilized Ag, Au, Pt nanopar-
• •
• •
ticles were synthesized via green method. Maltose was used as a green reducing agent. Metal nanoparticles were investigated for optical sensing of various metal ions. Ag NPs are highly selective to Hg2+ ions. Ag NPs were used for the determination of Hg2+ ion in lake water.
article
info
Article history: Received 19 August 2017 Received in revised form 27 November 2017 Accepted 30 December 2017 Keywords: Gelatin Green synthesis Metal nanoparticles Optical sensing Heavy metal detection
a b s t r a c t We herein report a greener method for the synthesis of silver (Ag), gold (Au) and platinum (Pt) nanoparticles (NPs) using gelatin and maltose as non-toxic, capping and reducing agents respectively. The formation of these noble metal NPs was monitored and confirmed by UV–visible absorption spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy. The as-synthesized metal NPs were investigated for optical sensing of various metal ions in aqueous solutions by monitoring their surface plasmon resonance. The results showed that Ag NPs showed selective response to mercury (Hg2+ ) ions, though all the metal NPs are sensitive to all the metal ions investigated. Taking this advantage, Ag NPs were then employed for quantitative detection of Hg2+ ions in a local lake water and this was found to be 4.73 × 10−6 ppm. The proposed method is simple, cost-effective and ecofriendly to prepare Ag NPs sensor in assessing the quality of real water samples. © 2018 Elsevier B.V. All rights reserved.
1. Introduction Noble metal nanoparticles such as silver nanoparticles (AgNPs), gold nanoparticles (Au-NPs) and platinum nanoparticles
*
Corresponding author at: Department of Applied Chemistry, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa. E-mail addresses: [email protected], [email protected] (O.S. Oluwafemi). https://doi.org/10.1016/j.nanoso.2017.12.008 2352-507X/© 2018 Elsevier B.V. All rights reserved.
(Pt-NPs) have attracted researcher’s attention greatly in the past years due to their unique properties and possible applications in environmental and biological fields [1–4]. These nanoparticles have led to various aspects of applications which include colorimetric sensing [5,6], catalysis [7], bioimaging [8] and optical devices [9]. The special application roles for Ag-NPs include antibacterial treatment [10] and wounds treatment [11]. Au-NPs is advantageous in disease diagnostics [12], drug delivery [13], cancer
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treatment [14], while Pt-NPs have been used for catalysis [15] degradation of dyes [16] and fuel cells [17]. These nanoparticles are usually synthesized via the ‘‘bottom-up’’ method employing conventional chemicals such as sodium borohydrides, dimethylformamide, trisodium citrates, which are used as reducing agents with the drawbacks of polluting environment and affecting human health [18–20]. This concern has led to the emergence of new synthetic route based on green chemistry principles with maximum safety and minimum impact on the environment [20–22]. According to Raveendran et al., [23], there are three factors that need to be considered for the green synthesis of metal nanoparticles. These include (i) the use of green solvent, (ii) use of environmental friendly reducing agent, and (iii) use of non-toxic capping agent. In line with this, he reported the first completely green synthesis of Ag-NPs by using water, starch and D-glucose as solvent, capping and reducing agent respectively [23]. The use of water and starch replaced the use of organic solvents and toxic chemicals in the synthesis. In another development, Philip et al., synthesized anisotropic Au-NPs using honey as both capping and reducing agent without any accelerator [24] while Panigrahi et al. [25] synthesized Pt-NPs using fructose as both reducing and capping agent. Metal ions such as Hg2+ , Pb2+ , Cd2+ and Cr3+ have been reported as pollutant to environment as many of them are toxic even at trace level concentrations. Therefore, it is essential to monitor these metals in biological and environmental fields. Different analytical techniques such as atomic absorption spectroscopy (AAS), inductive coupled plasma optical emission spectroscopy (ICP-OES), ion-selective electrode (ISE) [26] have been used for qualitative and quantitative detection of these metal ions. Although these techniques have been successful, they are associated with some drawbacks which include, time consuming procedures, presence of skilled personnel for operation and high cost. An alternative to this, is the use of colorimetric sensor which is quick to use, inexpensive and shows good response to a wide range of analytes. With the added advantages of nanotechnology, a typical nanosensor works in the same way, in addition it can be able to detect up to part per billion (ppb) levels. This makes nanomaterials promising potential candidate for the detection of elements in trace levels in both biological and chemical systems [27]. In line with this, Annadhasan et al., [28] reported the detection of Hg2+ , Pb2+ and Mn2+ ions with the naked eye by using L-tyrosine stabilized Ag-NPs and Au-NPs. Farhadi et al. [29] also reported the detection of Hg2+ using unmodified Ag-NPs via green synthesis. Recently, Vasileva et al. [30] reported the starch stabilized Ag-NPs for colorimetric sensing of Hg2+ ions. Natural polymers like alginate, chitosan, dextran and gelatin with good biocompatibility and biodegradability have been widely investigated for biological applications such as drug delivery and tissue applications. Among them, gelatin forms a versatile group of naturally occurring biopolymer that it is widely used in food and pharmaceutical industries as a binder because of its gelling nature [31]. It is a denatured form of collagen which has been used to stabilize nanoparticles of Ag and Au [32]. In this present investigation, we herein report a facile and green synthesis of Au, Ag and Pt-NPs by using gelatin as capping agent and maltose, a disaccharide sugar as the reducing agent. To the best of our knowledge, we report first time maltose reduced Au and Pt NPs. The as-synthesized noble metal nanoparticles were tested for colorimetric sensing application. Among these metal nanoparticles, Ag-NPs offered an excellent colorimetric sensor for the detection of Hg2+ ions in aqueous solution and hence it was applied to detect the Hg2+ ions in lake water.
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2. Experimental 2.1. Materials Silver nitrate (AgNO3 ), gold (III) chloride hydrate (HAuCl4 . xH2 O) and chloroplatinic acid hydrate (H2 PtCl6 . xH2 O) were obtained from Sigma-Aldrich, USA. Gelatin and maltose were obtained from Merck, Germany. All reagents were of analytical-grade and used as received without further purification. Deionized water was used throughout the synthesis and analysis. The reactions were carried out in the dark to avoid any photochemical reactions. 2.2. Green synthesis of metal nanoparticles The metal NPs were synthesized based on the previous reported method [5]. In a typical experiment, 1 g of gelatin was added to 100 ml of water and the resulting solution was heated under continuous stirring at 40 ◦ C for some time. This was followed by addition of either AgNO3 (5 mL, 0.1 M) or HAuCl4 .xH2 O (40 mL, 0.4507 mM) or H2 PtCl6 .H2 O (5 mL, 0.01 M) to the hot gelatin solution to obtain a corresponding metal ions–gelatin mixture. Afterwards, maltose solution was added to these mixtures under continuous stirring. The solutions were maintained at 75 ◦ C, 80 ◦ C and 95 ◦ C for Ag-NPs, Au-NPs and Pt-NPs respectively and allowed to react for several hours. Aliquots were taken at different time intervals to monitor the growth of the nanoparticles. 2.3. Characterization The absorption spectra of the samples were obtained in the wavelength range of 200–900 nm using Perkin Elmer Lambda 25 UV–visible (UV–Vis) spectrophotometer. Fourier transform infrared spectroscopy (FTIR) spectra were recorded with universal ATR sampling accessory using a Perkin Elmer Spectrum Two FTIR spectrophotometer. Transmission electron microscopy (TEM) measurements were carried out using JEOL 2010 operated at 200 kV. 2.4. Sensing of metal ions Sensing of heavy metal ions, alkali and alkaline earth metal ions was performed according to the Annadhasan et al., procedure with slight modifications [28,33]. In a typical experiment, 2 mL of the metal NPs solution was mixed with 1 mL of various aqueous metal ions solutions (10−3 M) such as Hg2+ , Pb2+ , Cr3+ , Cd2+ , Li+ , K+ , Ba2+ , Mg2+ , Ca+ and Na+ . The selectivity and sensitivity of the metal nanoparticles (NPs) towards metal ion were monitored using UV–Vis spectroscopy. 2.5. Sensing of Hg2+ ions in lake water The concentration of Hg2+ ions in the lake water was determined via standard addition calibration method. 1 mL of lake water was spiked with 1 mL of known concentrations (10−1 M to 10−12 M) of Hg2+ . 2 mL of the as-synthesized Ag-NPs was then added into the mixture and allowed to react for 30 s followed by monitoring using UV–Vis spectrophotometer. 3. Results and discussion 3.1. Synthesis of metal nanoparticles In this synthesis, gelatin was used as capping agent to stabilize and prevent nanoparticles from aggregation. The whole process is a redox reaction with metal salts acting as oxidant, maltose as reducing agent and nanoparticles as reduction product. Addition
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Fig. 1. Digital images (a, c, e) and corresponding UV–Vis absorption spectra (b, d, f) of gelatin stabilized Ag-NPs, Au-NPs and Pt-NPs at different reaction times. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 2. Particle size distribution with hydrodynamic diameter of the as-synthesized gelatin capped Ag-NPs at different reaction times.
of maltose to the gelatin–metal mixture produced metal NPs by reducing the metal ions to zero oxidation state. This was accompanied with colour change which became darkened with increased reaction time [34]. Fig. 1a shows the colour of the Ag-NPs solutions which was initially yellow and gradually changed to brown and dark brown as the reaction time increased. The Au-NPs in (Fig. 1c) and Pt-NPs in (Fig. 1e) exhibited pink and faint yellow respectively. The formation of metal nanoparticles was monitored using UV–Vis spectroscopy at different reaction time. The obtained AgNPs (Fig. 1b) and Au-NPs (Fig. 1d) displayed characteristic surface plasmon resonance (SPR) absorption maxima peaks, which are, centred around 430 nm and 537 nm respectively. The broad peaks obtained up to 6 h in the spectra of Ag and Au-NPs indicates broad size distribution. As reaction time increased to 24 h for both AgNPs and Au-NPs, the intensity of the peaks increases with time indicating increase in the concentration of nanoparticles present in the solution. The spectra of Pt-NPs (Fig. 1f) showed a SPR peak initially centred at 261 nm, which was attributed to the absorption band of PtCl26− and gelatin complex. As the reaction time increased, this peak gradually disappeared and new broad shoulder SPR peak characteristic of Pt-NPs appeared around 280 nm, indicating the
formation of platinum nanoparticles [35]. As a model of growth, the formation of Ag-NPs was also monitored by using dynamic light scattering (DLS) analysis to measure the hydrodynamic diameter. As seen from Fig. 2, the hydrodynamic diameter increases with time due to the particle growth and 24 h reaction time is found to be the optimum for the Ag NPs with <10 nm. After 24 h, the particles began to aggregate due their smaller sizes and high surface energy coupled with insufficient passivation by the capping agent. The TEM images and particle size distributions of the metal nanoparticles are shown in Fig. 3. The micrographs showed that Ag-NPs synthesized at 24 h are small, well-dispersed and spherical in shape with average size of 5.86 ± 1.56 nm. This is lower than the corresponding DLS analysis as expected because the latter calculation includes the hydration sphere. The TEM micrograph of Au-NPs consists of spherical and small triangular shape particles with average size of 40.29 ± 5.57 nm while the Pt-NPs consist of agglomerated particle that are spherical and cube-like in shape with average size of 42.99 ± 13.55 nm. The surface chemistry of the as-synthesized metal NPs was investigated using the FTIR spectroscopy and the corresponding spectra was shown in Fig. 4. The spectrum of gelatin shows characteristic bands due to the vibrations of the amide group such
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Fig. 3. TEM micrographs (a, b, c) and particle size distributions (d, e, f) of Ag-NPs, Au-NPs and Pt-NPs.
as N–H stretching at 3300 and 3288 cm−1 (amide A band), C==O stretching at 1630 cm−1 (amide I band), N–H bending vibrations at 1543 cm−1 (amide II band), C–N stretching vibrations coupled with in-plane N–H bending at 1237 cm−1 (amide III band). Some changes in these bands for gelatin stabilized Ag and Pt NPs were observed. The shifting of amide I band of gelatin after conjugation with NPs might be attributed to conformational change of gelatin from β -antiparallel to α -helix [36]. One of the N–H stretching in amide A band disappeared indicating the deprotonation from amide. Moreover, the N–H bending in amide II band and C–N stretching in amide III shifted to higher wavenumber with decrease in intensity. The above results revealed the possible interaction of gelatin with Ag and Pt-NPs via coordination with nitrogen from the amide group. Furthermore, we also noticed that the C–O stretching of gelatin at 1081 cm−1 shifted to lower wavenumber with increased intensity after conjugation with nanoparticles. This might be attributed to the breaking of intramolecular hydrogen bonds involved with carboxylic group of gelatin which makes the C–O bond stretch free at lower frequency. Fig. 4. FTIR spectra of (a) gelatin (b) Ag NPs (c) Au NPs and (d) Pt NPs.
3.2. Metal ion sensing The as-synthesized metal NPs were used as colorimetric sensor for the detection of various metal ions in solution. The addition of various metal ions (1 × 10−3 ) to the Ag-NPs solution weakened its colour intensity indicating the interaction between the nanoparticles and metal ions (Fig. 5a). The response of the metal ions to the NPs is reflected in the absorption spectra as shown in Fig. 5b. The SPR band of the absorption spectra showed that Ag-NPs are sensitive to all the metal ions. A drastic reduction in the intensity of the SPR peak was observed (Fig. 5c) when Hg2+ was added to the Ag-NPs solution with the immediate colour change from yellow to colourless. It was also found that, adding a mixture of all metal ions except Hg2+ ions to the Ag-NPs did not result in significant colour change.
However, when Hg2+ ions were included in the mixture, a colourless solution was obtained instantaneously. This indicated that, the interference of other metal ions in the sensing of Hg2+ ions by Ag NPs is negligible and demonstrates high sensitivity and selectivity of Ag-NPs towards Hg2+ ions at this concentration. It has been reported that Hg2+ ion could be reduced in aqueous silver solution and form a mercury layer around silver nanoparticles [30]. This could lead to increase in the size of the nanoparticles and was confirmed by TEM analysis shown in Fig. 6a. After the addition of Hg2+ , Ag-NPs size increased from 5.86 ± 1.56 nm to 15.60±3.19 nm (Fig. 6b). It was found that Au-NPs and Pt-NPs were not selective to any metal ions though they were able to sense most of the metal ions (Fig. S1). The optical sensitivity of Ag-NPs was
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Fig. 7. (a) Optical sensing of different concentration of Hg2+ ions using Ag NPs and (b) corresponding absorption spectra, Inset: Graph of Hg2+ concentration against absorption intensity. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. (a) Optical sensing of different metal ions by Ag NPs (a) Digital images, (b) corresponding UV–Vis absorption spectra and (c) colorimetric. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
further evaluated for the various concentrations of Hg2+ ions. The Hg2+ ion concentration from 10−12 to 10−5 M did not change the colour of the as-synthesized Ag-NPs solution (Fig. 7a). However, for the concentration range between 10−1 M and 10−3 M, immediate colour change from yellow to colourless was observed. At 10−4 M the solution changed to faint yellow. The absorbance of the SPR peak of Ag-NPs decreased with increase in the concentration of
Hg2+ range from 10−12 to 10−4 M (Fig. 7b). It is then suggested that green synthesized Ag-NPs can be used for colorimetric detection of Hg2+ with the minimum concentration of 10−12 M. The proposed sensing technique was employed for the determination of Hg2+ ions in lake water taken from Zoo lake, Johannesburg (Fig. S2). In such environments, the water was found to contain less amount of mercury. Hence, the water sample was spiked with various concentrations of Hg2+ (10−12 to 10−1 M) and sensed by Ag-NPs (Fig. 8) using standard addition method. The concentration of Hg2+ ion in lake water was found to be 4.73 × 10−6 ppm which is much lower than the maximum acceptable concentration of 1 × 10−3 ppm set by World Health Organization (WHO) [37]. This suggests that, the proposed method has a great potential for sensing Hg2+ ions for environmental evaluation purposes.
Fig. 6. (a) TEM image and (b) particle size distribution of Ag-NPs after the addition of Hg2+ ions.
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References
Fig. 8. (a) Optical sensing of Hg2+ ions in lake water using Ag NPs by standard addition method, (b) UV–Vis spectra of Ag NPs (blank) spiked with lake water and different concentrations of Hg2+ ions, Inset: Graph of Hg2+ concentration against absorption intensity.
4. Conclusions Silver, gold and platinum nanoparticles were successfully synthesized via a completely green method using maltose as reducing agent and gelatin as capping agent. The formation of nanoparticles was confirmed by UV–Vis spectroscopy, FTIR spectroscopy and TEM analysis. The average particle diameters according to TEM analysis were 5.86 ± 1.56 nm, 40.29 ± 5.57 nm and 42.99 ± 13.55 nm for Ag-NPs, Au-NPs and Pt-NPs respectively. The colorimetric sensing ability of the as-synthesized nanoparticles was evaluated using heavy, alkali and alkaline earth metals. Among the metal NPs, Ag-NPs were highly sensitive and selective to Hg2+ ions. The minimum concentration of mercury detected was 10−12 M. Furthermore, the concentration of Hg2+ in real water sample by using the as-synthesized Ag-NPs was determined to be 4.73 × 10−6 ppm. This method is recommended for simple and rapid detection and quantification of Hg2+ in water. Acknowledgements The authors would like to thank the National Research Foundation (NRF), South Africa under the Nanotechnology Flagship Programme (Grant no: 97983) for financial support and National Nanoscience Postgraduate Teaching and Training Platform (NNPTTP) through the Department of Science and Technology (DST) for the financial support given to RM throughout this study. Appendix A. Supplementary data Supplementary material related to this article can be found online at https://doi.org/10.1016/j.nanoso.2017.12.008.
[1] K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, The optical properties of metal nanoparticles: The influence of size, shape, and dielectric environment, J. Phys. Chem. B 107 (2003) 668–677. [2] A. García-Ruiz, J. Crespo, J.M. López-de Luzuriaga, M.E. Olmos, M. Monge, M.P. Rodríguez-Álfaro, P.J. Martín-Álvareza, B. Bartolomea, M.V. Moreno, Novel biocompatible silver nanoparticles for controlling the growth of lactic acid bacteria and acetic acid bacteria in wines, Food Control 50 (2015) 613–619. [3] T.K. Sau, A.L. Rogach, F. Jäckel, T.A. Klar, J. Feldmann, Properties and applications of colloidal non-spherical noble metal nanoparticles, Adv. Mater. 22 (2010) 1805–1825. [4] J. Gopal, N. Hasan, M. Manikandan, H.-F. Wu, Bacterial toxicity/compatibility of platinum nanospheres, nanocuboids and nanoflowers, Sci. Rep. 3 (2013) 1–8. [5] B.M.M. May, O.S. Oluwafemi, Sugar-reduced gelatin-capped silver nanoparticles with high selectivity for colorimetric sensing of Hg 2+ and Fe 2+ ions in the midst of other metal ions in aqueous solutions, Int. J. Electrochem. Sci. 11 (2016) 8096–8108. [6] J.C. Ramos, A. Ledezma, E. Arias, I. Moggio, C.A. Martínez, Optical and morphological characterisation of a silver nanoparticle/fluorescent poly (phenylenethynylene) composite for optical biosensors, Vacuum 84 (2010) 1244–1249. [7] X. Li, G. Li, W. Zang, L. Wang, X. Zhang, Catalytic activity of shaped platinum nanoparticles for hydrogenation: a kinetic study, Catal. Sci. Technol. 4 (2014) 3290–3297. [8] R. Sankar, P.K.S.M. Rahman, K. Varunkumar, C. Anusha, A. Kalaiarasi, K.S. Shivashangari, V. Ravikumar, Facile synthesis of curcuma longa tuber powder engineered metal nanoparticles for bioimaging applications, J. Mol. Struct. 1129 (2017) 8. [9] P.D. Nallathamby, K.J. Lee, X.-H.N. Xu, Design of stable and uniform single nanoparticle photonics for in vivo dynamics imaging of nanoenvironments of zebrafish embryonic fluids, ACS Nano. 7 (2008) 1371–1380. [10] J. Yang, X. Liu, L. Huang, D. Sun, Antibacterial properties of novel bacterial cellulose nanofiber containing silver nanoparticles, Chin. J. Chem. Eng. 21 (2013) 1419–1424. [11] C. Rigo, L. Ferroni, I. Tocco, M. Roman, I. Munivrana, C. Gardin, W.R. Cairns, V. Vindigni, B. Azzena, C. Barbante, B. Zavan, Active silver nanoparticles for wound healing, Int. J. Mol. Sci. 3 (2013) 4817–4840. [12] A.J. Mieszawska, W.J.M. Mulder, Z.A. Fayad, D.P. Cormode, Multifunctional gold nanoparticles for diagnosis and therapy of disease, Mol. Pharm. 3 (2013) 831– 847. [13] E.C. Dreaden, L.A. Austin, M.A. Mackey, M.A. El-Sayed, Size matters: gold nanoparticles in targeted cancer drug delivery, Ther. Deliv. 4 (2013) 457–478. [14] S. Jain, D.G. Hirst, J.M. O’sullivan, Gold nanoparticles as novel agents for cancer therapy, Br. J. Radiol. 1010 (2012) 101–113. [15] R. Narayanan, M.A. El-Sayed, Shape-dependent catalytic activity of platinum nanoparticles in colloidal solution, Nano Lett. 7 (2004) 1343–1348. [16] J. Pal, M.K. Deb, D.K. Deshmukh, D.K. Sen, Microwave-assisted synthesis of platinum nanoparticles and their catalytic degradation of methyl violet in aqueous solution, Appl. Nanosci. 4 (2012) 61–65. [17] A.J. Moreira, S. Lopera, N. Ordonez, R.D. Mansano, Platinum nanoparticle deposition on polymeric membranes for fuel cell applications, J. Phys. Conf. Ser. 370 (2012) 12030–12041. [18] I. Pastoriza-Santos, L.M. Liz-Marzán, Synthesis of silver nanoprisms in DMF, Nano Lett. 8 (2002) 903–905. [19] Z.G. Wu, M. Munoz, O. Montero, The synthesis of nickel nanoparticles by hydrazine reduction, Adv. Powder Technol. 21 (2010) 165–168. [20] K. Aslan, Z. Leonenko, J.R. Lakowicz, C.D. Geddes, Fast and slow deposition of silver nanorods on planar surfaces: Application to metal-enhanced fluorescence, J. Phys. B 8 (2005) 3157–3162. [21] A. Manikandan, R. Sridhar, S. Arul Antony, S. Ramakrishna, A simple aloe vera plant-extracted microwave and conventional combustion synthesis: morphological, optical, magnetic and catalytic properties of CoFe2 O4 nanostructures, J. Mol. Struct. 1076 (2014) 188–200. [22] P. Raveendran, J. Fu, S.L. Wallen, A simple and green method for the synthesis of Au, Ag, and Au–Ag Alloy Nanoparticles, J. Green Chem. 8 (2005) 34–38. [23] P. Raveendran, J. Fu, S.L. Wallen, Completely green synthesis and stabilization of metal nanoparticles, J. Am. Chem. Soc. 46 (2003) 13940–13942. [24] D. Philip, Honey mediated green synthesis of gold nanoparticles, Spectrochim. Acta A 4 (2009) 650–653. [25] S. Panigrahi, S. Kundu, S.K. Ghosh, S. Nath, T. Pal, General method of synthesis for metal nanoparticles, J. Nanopart. Res. 6 (2004) 411–414. [26] R.K. Mahajan, I. Kaur, T.S. Lobana, A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone, Talanta 1 (2003) 101–105. [27] N.L. Rosi, C.A. Mirkin, Nanostructures in biodiagnostics, Chem. Rev. 4 (2005) 1547–1562. [28] M. Annadhasan, T. Muthukumarasamyvel, V.R.S. Babu, N. Rajendiran, Green synthesized silver and gold nanoparticles for colorimetric detection of Hg2+ , Pb2+ , and Mn2+ in aqueous medium, ACS Sustain. Chem. Eng. 4 (2014) 887– 896.
138
R. Muthivhi et al. / Nano-Structures & Nano-Objects 13 (2018) 132–138
[29] K. Farhadi, M. Forough, R. Molaei, S. Hajizadeh, A. Rafipour, Highly selective Hg2+ colorimetric sensor using green synthesized and unmodified silver nanoparticles, Sensors Actuators B 161 (2012) 880–886. [30] P. Vasileva, T. Alexandrova, I. Karadjova, Application of starch-stabilized silver nanoparticles as a colorimetric sensor for mercury(II) in 0005 mol/L nitric acid, J. Chem. (2017) 6897960. [31] P. Ramadoss, K. Thanigai Arul, J. Ramana Ramya, M. Rigana Begam, V. Sarath Chandra, E. Manikandan, Enhanced mechanical strength and sustained drug release of gelatin/keratin scaffolds, Mater. Lett. 186 (2017) 109–112. [32] Y. Liu, X. Liu, X. Wang, Biomimetic synthesis of gelatin polypeptide-assisted noble-metal nanoparticles and their interaction study, Nanoscale Res. Lett. 6 (2011) 22. [33] C. Lee, P. Zhang, Highly stable gelatin layer-protected gold nanoparticles as surface-enhanced Raman scattering substrates, J. Nanosci. Nanotechnol. 14 (2014) 4325–4330.
[34] M. Annadhasan, N. Rajendiran, Highly selective and sensitive colorimetric detection of Hg (II) ions using green synthesized silver nanoparticles, RSC Adv. 5 (2015) 94513–94518. [35] X. Luo, T. Imae, Photochemical synthesis of crown-shaped platinum nanoparticles using aggregates of G4-NH2 PAMAM dendrimer as templates, J. Mater. Chem. 17 (2006) 567–571. [36] S. Suarasan, M. Focsan, D. Maniu, S. Astilean, Gelatin–nanogold bioconjugates as effective plasmonic platforms for SERS detection and tagging, Colloids Surf. B 103 (2013) 475–481. [37] World Heath Organizations (WHO), Guidelines for Drinking-water Quality, 2005, pp. 1–18.
Contents lists available at ScienceDirect
Nano-Structures & Nano-Objects journal homepage: www.elsevier.com/locate/nanoso
Green synthesis of gelatin-noble metal polymer nanocomposites for sensing of Hg2+ ions in aqueous media Rudzani Muthivhi, Sundararajan Parani, Bambesiwe May, Oluwatobi Samuel Oluwafemi * Department of Applied Chemistry, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa Centre for Nanomaterials Science Research, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa
highlights
graphical abstract
• Gelatin stabilized Ag, Au, Pt nanopar-
• •
• •
ticles were synthesized via green method. Maltose was used as a green reducing agent. Metal nanoparticles were investigated for optical sensing of various metal ions. Ag NPs are highly selective to Hg2+ ions. Ag NPs were used for the determination of Hg2+ ion in lake water.
article
info
Article history: Received 19 August 2017 Received in revised form 27 November 2017 Accepted 30 December 2017 Keywords: Gelatin Green synthesis Metal nanoparticles Optical sensing Heavy metal detection
a b s t r a c t We herein report a greener method for the synthesis of silver (Ag), gold (Au) and platinum (Pt) nanoparticles (NPs) using gelatin and maltose as non-toxic, capping and reducing agents respectively. The formation of these noble metal NPs was monitored and confirmed by UV–visible absorption spectroscopy, Fourier transform infrared spectroscopy and transmission electron microscopy. The as-synthesized metal NPs were investigated for optical sensing of various metal ions in aqueous solutions by monitoring their surface plasmon resonance. The results showed that Ag NPs showed selective response to mercury (Hg2+ ) ions, though all the metal NPs are sensitive to all the metal ions investigated. Taking this advantage, Ag NPs were then employed for quantitative detection of Hg2+ ions in a local lake water and this was found to be 4.73 × 10−6 ppm. The proposed method is simple, cost-effective and ecofriendly to prepare Ag NPs sensor in assessing the quality of real water samples. © 2018 Elsevier B.V. All rights reserved.
1. Introduction Noble metal nanoparticles such as silver nanoparticles (AgNPs), gold nanoparticles (Au-NPs) and platinum nanoparticles
*
Corresponding author at: Department of Applied Chemistry, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, Johannesburg, South Africa. E-mail addresses: [email protected], [email protected] (O.S. Oluwafemi). https://doi.org/10.1016/j.nanoso.2017.12.008 2352-507X/© 2018 Elsevier B.V. All rights reserved.
(Pt-NPs) have attracted researcher’s attention greatly in the past years due to their unique properties and possible applications in environmental and biological fields [1–4]. These nanoparticles have led to various aspects of applications which include colorimetric sensing [5,6], catalysis [7], bioimaging [8] and optical devices [9]. The special application roles for Ag-NPs include antibacterial treatment [10] and wounds treatment [11]. Au-NPs is advantageous in disease diagnostics [12], drug delivery [13], cancer
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treatment [14], while Pt-NPs have been used for catalysis [15] degradation of dyes [16] and fuel cells [17]. These nanoparticles are usually synthesized via the ‘‘bottom-up’’ method employing conventional chemicals such as sodium borohydrides, dimethylformamide, trisodium citrates, which are used as reducing agents with the drawbacks of polluting environment and affecting human health [18–20]. This concern has led to the emergence of new synthetic route based on green chemistry principles with maximum safety and minimum impact on the environment [20–22]. According to Raveendran et al., [23], there are three factors that need to be considered for the green synthesis of metal nanoparticles. These include (i) the use of green solvent, (ii) use of environmental friendly reducing agent, and (iii) use of non-toxic capping agent. In line with this, he reported the first completely green synthesis of Ag-NPs by using water, starch and D-glucose as solvent, capping and reducing agent respectively [23]. The use of water and starch replaced the use of organic solvents and toxic chemicals in the synthesis. In another development, Philip et al., synthesized anisotropic Au-NPs using honey as both capping and reducing agent without any accelerator [24] while Panigrahi et al. [25] synthesized Pt-NPs using fructose as both reducing and capping agent. Metal ions such as Hg2+ , Pb2+ , Cd2+ and Cr3+ have been reported as pollutant to environment as many of them are toxic even at trace level concentrations. Therefore, it is essential to monitor these metals in biological and environmental fields. Different analytical techniques such as atomic absorption spectroscopy (AAS), inductive coupled plasma optical emission spectroscopy (ICP-OES), ion-selective electrode (ISE) [26] have been used for qualitative and quantitative detection of these metal ions. Although these techniques have been successful, they are associated with some drawbacks which include, time consuming procedures, presence of skilled personnel for operation and high cost. An alternative to this, is the use of colorimetric sensor which is quick to use, inexpensive and shows good response to a wide range of analytes. With the added advantages of nanotechnology, a typical nanosensor works in the same way, in addition it can be able to detect up to part per billion (ppb) levels. This makes nanomaterials promising potential candidate for the detection of elements in trace levels in both biological and chemical systems [27]. In line with this, Annadhasan et al., [28] reported the detection of Hg2+ , Pb2+ and Mn2+ ions with the naked eye by using L-tyrosine stabilized Ag-NPs and Au-NPs. Farhadi et al. [29] also reported the detection of Hg2+ using unmodified Ag-NPs via green synthesis. Recently, Vasileva et al. [30] reported the starch stabilized Ag-NPs for colorimetric sensing of Hg2+ ions. Natural polymers like alginate, chitosan, dextran and gelatin with good biocompatibility and biodegradability have been widely investigated for biological applications such as drug delivery and tissue applications. Among them, gelatin forms a versatile group of naturally occurring biopolymer that it is widely used in food and pharmaceutical industries as a binder because of its gelling nature [31]. It is a denatured form of collagen which has been used to stabilize nanoparticles of Ag and Au [32]. In this present investigation, we herein report a facile and green synthesis of Au, Ag and Pt-NPs by using gelatin as capping agent and maltose, a disaccharide sugar as the reducing agent. To the best of our knowledge, we report first time maltose reduced Au and Pt NPs. The as-synthesized noble metal nanoparticles were tested for colorimetric sensing application. Among these metal nanoparticles, Ag-NPs offered an excellent colorimetric sensor for the detection of Hg2+ ions in aqueous solution and hence it was applied to detect the Hg2+ ions in lake water.
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2. Experimental 2.1. Materials Silver nitrate (AgNO3 ), gold (III) chloride hydrate (HAuCl4 . xH2 O) and chloroplatinic acid hydrate (H2 PtCl6 . xH2 O) were obtained from Sigma-Aldrich, USA. Gelatin and maltose were obtained from Merck, Germany. All reagents were of analytical-grade and used as received without further purification. Deionized water was used throughout the synthesis and analysis. The reactions were carried out in the dark to avoid any photochemical reactions. 2.2. Green synthesis of metal nanoparticles The metal NPs were synthesized based on the previous reported method [5]. In a typical experiment, 1 g of gelatin was added to 100 ml of water and the resulting solution was heated under continuous stirring at 40 ◦ C for some time. This was followed by addition of either AgNO3 (5 mL, 0.1 M) or HAuCl4 .xH2 O (40 mL, 0.4507 mM) or H2 PtCl6 .H2 O (5 mL, 0.01 M) to the hot gelatin solution to obtain a corresponding metal ions–gelatin mixture. Afterwards, maltose solution was added to these mixtures under continuous stirring. The solutions were maintained at 75 ◦ C, 80 ◦ C and 95 ◦ C for Ag-NPs, Au-NPs and Pt-NPs respectively and allowed to react for several hours. Aliquots were taken at different time intervals to monitor the growth of the nanoparticles. 2.3. Characterization The absorption spectra of the samples were obtained in the wavelength range of 200–900 nm using Perkin Elmer Lambda 25 UV–visible (UV–Vis) spectrophotometer. Fourier transform infrared spectroscopy (FTIR) spectra were recorded with universal ATR sampling accessory using a Perkin Elmer Spectrum Two FTIR spectrophotometer. Transmission electron microscopy (TEM) measurements were carried out using JEOL 2010 operated at 200 kV. 2.4. Sensing of metal ions Sensing of heavy metal ions, alkali and alkaline earth metal ions was performed according to the Annadhasan et al., procedure with slight modifications [28,33]. In a typical experiment, 2 mL of the metal NPs solution was mixed with 1 mL of various aqueous metal ions solutions (10−3 M) such as Hg2+ , Pb2+ , Cr3+ , Cd2+ , Li+ , K+ , Ba2+ , Mg2+ , Ca+ and Na+ . The selectivity and sensitivity of the metal nanoparticles (NPs) towards metal ion were monitored using UV–Vis spectroscopy. 2.5. Sensing of Hg2+ ions in lake water The concentration of Hg2+ ions in the lake water was determined via standard addition calibration method. 1 mL of lake water was spiked with 1 mL of known concentrations (10−1 M to 10−12 M) of Hg2+ . 2 mL of the as-synthesized Ag-NPs was then added into the mixture and allowed to react for 30 s followed by monitoring using UV–Vis spectrophotometer. 3. Results and discussion 3.1. Synthesis of metal nanoparticles In this synthesis, gelatin was used as capping agent to stabilize and prevent nanoparticles from aggregation. The whole process is a redox reaction with metal salts acting as oxidant, maltose as reducing agent and nanoparticles as reduction product. Addition
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Fig. 1. Digital images (a, c, e) and corresponding UV–Vis absorption spectra (b, d, f) of gelatin stabilized Ag-NPs, Au-NPs and Pt-NPs at different reaction times. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 2. Particle size distribution with hydrodynamic diameter of the as-synthesized gelatin capped Ag-NPs at different reaction times.
of maltose to the gelatin–metal mixture produced metal NPs by reducing the metal ions to zero oxidation state. This was accompanied with colour change which became darkened with increased reaction time [34]. Fig. 1a shows the colour of the Ag-NPs solutions which was initially yellow and gradually changed to brown and dark brown as the reaction time increased. The Au-NPs in (Fig. 1c) and Pt-NPs in (Fig. 1e) exhibited pink and faint yellow respectively. The formation of metal nanoparticles was monitored using UV–Vis spectroscopy at different reaction time. The obtained AgNPs (Fig. 1b) and Au-NPs (Fig. 1d) displayed characteristic surface plasmon resonance (SPR) absorption maxima peaks, which are, centred around 430 nm and 537 nm respectively. The broad peaks obtained up to 6 h in the spectra of Ag and Au-NPs indicates broad size distribution. As reaction time increased to 24 h for both AgNPs and Au-NPs, the intensity of the peaks increases with time indicating increase in the concentration of nanoparticles present in the solution. The spectra of Pt-NPs (Fig. 1f) showed a SPR peak initially centred at 261 nm, which was attributed to the absorption band of PtCl26− and gelatin complex. As the reaction time increased, this peak gradually disappeared and new broad shoulder SPR peak characteristic of Pt-NPs appeared around 280 nm, indicating the
formation of platinum nanoparticles [35]. As a model of growth, the formation of Ag-NPs was also monitored by using dynamic light scattering (DLS) analysis to measure the hydrodynamic diameter. As seen from Fig. 2, the hydrodynamic diameter increases with time due to the particle growth and 24 h reaction time is found to be the optimum for the Ag NPs with <10 nm. After 24 h, the particles began to aggregate due their smaller sizes and high surface energy coupled with insufficient passivation by the capping agent. The TEM images and particle size distributions of the metal nanoparticles are shown in Fig. 3. The micrographs showed that Ag-NPs synthesized at 24 h are small, well-dispersed and spherical in shape with average size of 5.86 ± 1.56 nm. This is lower than the corresponding DLS analysis as expected because the latter calculation includes the hydration sphere. The TEM micrograph of Au-NPs consists of spherical and small triangular shape particles with average size of 40.29 ± 5.57 nm while the Pt-NPs consist of agglomerated particle that are spherical and cube-like in shape with average size of 42.99 ± 13.55 nm. The surface chemistry of the as-synthesized metal NPs was investigated using the FTIR spectroscopy and the corresponding spectra was shown in Fig. 4. The spectrum of gelatin shows characteristic bands due to the vibrations of the amide group such
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Fig. 3. TEM micrographs (a, b, c) and particle size distributions (d, e, f) of Ag-NPs, Au-NPs and Pt-NPs.
as N–H stretching at 3300 and 3288 cm−1 (amide A band), C==O stretching at 1630 cm−1 (amide I band), N–H bending vibrations at 1543 cm−1 (amide II band), C–N stretching vibrations coupled with in-plane N–H bending at 1237 cm−1 (amide III band). Some changes in these bands for gelatin stabilized Ag and Pt NPs were observed. The shifting of amide I band of gelatin after conjugation with NPs might be attributed to conformational change of gelatin from β -antiparallel to α -helix [36]. One of the N–H stretching in amide A band disappeared indicating the deprotonation from amide. Moreover, the N–H bending in amide II band and C–N stretching in amide III shifted to higher wavenumber with decrease in intensity. The above results revealed the possible interaction of gelatin with Ag and Pt-NPs via coordination with nitrogen from the amide group. Furthermore, we also noticed that the C–O stretching of gelatin at 1081 cm−1 shifted to lower wavenumber with increased intensity after conjugation with nanoparticles. This might be attributed to the breaking of intramolecular hydrogen bonds involved with carboxylic group of gelatin which makes the C–O bond stretch free at lower frequency. Fig. 4. FTIR spectra of (a) gelatin (b) Ag NPs (c) Au NPs and (d) Pt NPs.
3.2. Metal ion sensing The as-synthesized metal NPs were used as colorimetric sensor for the detection of various metal ions in solution. The addition of various metal ions (1 × 10−3 ) to the Ag-NPs solution weakened its colour intensity indicating the interaction between the nanoparticles and metal ions (Fig. 5a). The response of the metal ions to the NPs is reflected in the absorption spectra as shown in Fig. 5b. The SPR band of the absorption spectra showed that Ag-NPs are sensitive to all the metal ions. A drastic reduction in the intensity of the SPR peak was observed (Fig. 5c) when Hg2+ was added to the Ag-NPs solution with the immediate colour change from yellow to colourless. It was also found that, adding a mixture of all metal ions except Hg2+ ions to the Ag-NPs did not result in significant colour change.
However, when Hg2+ ions were included in the mixture, a colourless solution was obtained instantaneously. This indicated that, the interference of other metal ions in the sensing of Hg2+ ions by Ag NPs is negligible and demonstrates high sensitivity and selectivity of Ag-NPs towards Hg2+ ions at this concentration. It has been reported that Hg2+ ion could be reduced in aqueous silver solution and form a mercury layer around silver nanoparticles [30]. This could lead to increase in the size of the nanoparticles and was confirmed by TEM analysis shown in Fig. 6a. After the addition of Hg2+ , Ag-NPs size increased from 5.86 ± 1.56 nm to 15.60±3.19 nm (Fig. 6b). It was found that Au-NPs and Pt-NPs were not selective to any metal ions though they were able to sense most of the metal ions (Fig. S1). The optical sensitivity of Ag-NPs was
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Fig. 7. (a) Optical sensing of different concentration of Hg2+ ions using Ag NPs and (b) corresponding absorption spectra, Inset: Graph of Hg2+ concentration against absorption intensity. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 5. (a) Optical sensing of different metal ions by Ag NPs (a) Digital images, (b) corresponding UV–Vis absorption spectra and (c) colorimetric. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
further evaluated for the various concentrations of Hg2+ ions. The Hg2+ ion concentration from 10−12 to 10−5 M did not change the colour of the as-synthesized Ag-NPs solution (Fig. 7a). However, for the concentration range between 10−1 M and 10−3 M, immediate colour change from yellow to colourless was observed. At 10−4 M the solution changed to faint yellow. The absorbance of the SPR peak of Ag-NPs decreased with increase in the concentration of
Hg2+ range from 10−12 to 10−4 M (Fig. 7b). It is then suggested that green synthesized Ag-NPs can be used for colorimetric detection of Hg2+ with the minimum concentration of 10−12 M. The proposed sensing technique was employed for the determination of Hg2+ ions in lake water taken from Zoo lake, Johannesburg (Fig. S2). In such environments, the water was found to contain less amount of mercury. Hence, the water sample was spiked with various concentrations of Hg2+ (10−12 to 10−1 M) and sensed by Ag-NPs (Fig. 8) using standard addition method. The concentration of Hg2+ ion in lake water was found to be 4.73 × 10−6 ppm which is much lower than the maximum acceptable concentration of 1 × 10−3 ppm set by World Health Organization (WHO) [37]. This suggests that, the proposed method has a great potential for sensing Hg2+ ions for environmental evaluation purposes.
Fig. 6. (a) TEM image and (b) particle size distribution of Ag-NPs after the addition of Hg2+ ions.
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References
Fig. 8. (a) Optical sensing of Hg2+ ions in lake water using Ag NPs by standard addition method, (b) UV–Vis spectra of Ag NPs (blank) spiked with lake water and different concentrations of Hg2+ ions, Inset: Graph of Hg2+ concentration against absorption intensity.
4. Conclusions Silver, gold and platinum nanoparticles were successfully synthesized via a completely green method using maltose as reducing agent and gelatin as capping agent. The formation of nanoparticles was confirmed by UV–Vis spectroscopy, FTIR spectroscopy and TEM analysis. The average particle diameters according to TEM analysis were 5.86 ± 1.56 nm, 40.29 ± 5.57 nm and 42.99 ± 13.55 nm for Ag-NPs, Au-NPs and Pt-NPs respectively. The colorimetric sensing ability of the as-synthesized nanoparticles was evaluated using heavy, alkali and alkaline earth metals. Among the metal NPs, Ag-NPs were highly sensitive and selective to Hg2+ ions. The minimum concentration of mercury detected was 10−12 M. Furthermore, the concentration of Hg2+ in real water sample by using the as-synthesized Ag-NPs was determined to be 4.73 × 10−6 ppm. This method is recommended for simple and rapid detection and quantification of Hg2+ in water. Acknowledgements The authors would like to thank the National Research Foundation (NRF), South Africa under the Nanotechnology Flagship Programme (Grant no: 97983) for financial support and National Nanoscience Postgraduate Teaching and Training Platform (NNPTTP) through the Department of Science and Technology (DST) for the financial support given to RM throughout this study. Appendix A. Supplementary data Supplementary material related to this article can be found online at https://doi.org/10.1016/j.nanoso.2017.12.008.
[1] K.L. Kelly, E. Coronado, L.L. Zhao, G.C. Schatz, The optical properties of metal nanoparticles: The influence of size, shape, and dielectric environment, J. Phys. Chem. B 107 (2003) 668–677. [2] A. García-Ruiz, J. Crespo, J.M. López-de Luzuriaga, M.E. Olmos, M. Monge, M.P. Rodríguez-Álfaro, P.J. Martín-Álvareza, B. Bartolomea, M.V. Moreno, Novel biocompatible silver nanoparticles for controlling the growth of lactic acid bacteria and acetic acid bacteria in wines, Food Control 50 (2015) 613–619. [3] T.K. Sau, A.L. Rogach, F. Jäckel, T.A. Klar, J. Feldmann, Properties and applications of colloidal non-spherical noble metal nanoparticles, Adv. Mater. 22 (2010) 1805–1825. [4] J. Gopal, N. Hasan, M. Manikandan, H.-F. Wu, Bacterial toxicity/compatibility of platinum nanospheres, nanocuboids and nanoflowers, Sci. Rep. 3 (2013) 1–8. [5] B.M.M. May, O.S. Oluwafemi, Sugar-reduced gelatin-capped silver nanoparticles with high selectivity for colorimetric sensing of Hg 2+ and Fe 2+ ions in the midst of other metal ions in aqueous solutions, Int. J. Electrochem. Sci. 11 (2016) 8096–8108. [6] J.C. Ramos, A. Ledezma, E. Arias, I. Moggio, C.A. Martínez, Optical and morphological characterisation of a silver nanoparticle/fluorescent poly (phenylenethynylene) composite for optical biosensors, Vacuum 84 (2010) 1244–1249. [7] X. Li, G. Li, W. Zang, L. Wang, X. Zhang, Catalytic activity of shaped platinum nanoparticles for hydrogenation: a kinetic study, Catal. Sci. Technol. 4 (2014) 3290–3297. [8] R. Sankar, P.K.S.M. Rahman, K. Varunkumar, C. Anusha, A. Kalaiarasi, K.S. Shivashangari, V. Ravikumar, Facile synthesis of curcuma longa tuber powder engineered metal nanoparticles for bioimaging applications, J. Mol. Struct. 1129 (2017) 8. [9] P.D. Nallathamby, K.J. Lee, X.-H.N. Xu, Design of stable and uniform single nanoparticle photonics for in vivo dynamics imaging of nanoenvironments of zebrafish embryonic fluids, ACS Nano. 7 (2008) 1371–1380. [10] J. Yang, X. Liu, L. Huang, D. Sun, Antibacterial properties of novel bacterial cellulose nanofiber containing silver nanoparticles, Chin. J. Chem. Eng. 21 (2013) 1419–1424. [11] C. Rigo, L. Ferroni, I. Tocco, M. Roman, I. Munivrana, C. Gardin, W.R. Cairns, V. Vindigni, B. Azzena, C. Barbante, B. Zavan, Active silver nanoparticles for wound healing, Int. J. Mol. Sci. 3 (2013) 4817–4840. [12] A.J. Mieszawska, W.J.M. Mulder, Z.A. Fayad, D.P. Cormode, Multifunctional gold nanoparticles for diagnosis and therapy of disease, Mol. Pharm. 3 (2013) 831– 847. [13] E.C. Dreaden, L.A. Austin, M.A. Mackey, M.A. El-Sayed, Size matters: gold nanoparticles in targeted cancer drug delivery, Ther. Deliv. 4 (2013) 457–478. [14] S. Jain, D.G. Hirst, J.M. O’sullivan, Gold nanoparticles as novel agents for cancer therapy, Br. J. Radiol. 1010 (2012) 101–113. [15] R. Narayanan, M.A. El-Sayed, Shape-dependent catalytic activity of platinum nanoparticles in colloidal solution, Nano Lett. 7 (2004) 1343–1348. [16] J. Pal, M.K. Deb, D.K. Deshmukh, D.K. Sen, Microwave-assisted synthesis of platinum nanoparticles and their catalytic degradation of methyl violet in aqueous solution, Appl. Nanosci. 4 (2012) 61–65. [17] A.J. Moreira, S. Lopera, N. Ordonez, R.D. Mansano, Platinum nanoparticle deposition on polymeric membranes for fuel cell applications, J. Phys. Conf. Ser. 370 (2012) 12030–12041. [18] I. Pastoriza-Santos, L.M. Liz-Marzán, Synthesis of silver nanoprisms in DMF, Nano Lett. 8 (2002) 903–905. [19] Z.G. Wu, M. Munoz, O. Montero, The synthesis of nickel nanoparticles by hydrazine reduction, Adv. Powder Technol. 21 (2010) 165–168. [20] K. Aslan, Z. Leonenko, J.R. Lakowicz, C.D. Geddes, Fast and slow deposition of silver nanorods on planar surfaces: Application to metal-enhanced fluorescence, J. Phys. B 8 (2005) 3157–3162. [21] A. Manikandan, R. Sridhar, S. Arul Antony, S. Ramakrishna, A simple aloe vera plant-extracted microwave and conventional combustion synthesis: morphological, optical, magnetic and catalytic properties of CoFe2 O4 nanostructures, J. Mol. Struct. 1076 (2014) 188–200. [22] P. Raveendran, J. Fu, S.L. Wallen, A simple and green method for the synthesis of Au, Ag, and Au–Ag Alloy Nanoparticles, J. Green Chem. 8 (2005) 34–38. [23] P. Raveendran, J. Fu, S.L. Wallen, Completely green synthesis and stabilization of metal nanoparticles, J. Am. Chem. Soc. 46 (2003) 13940–13942. [24] D. Philip, Honey mediated green synthesis of gold nanoparticles, Spectrochim. Acta A 4 (2009) 650–653. [25] S. Panigrahi, S. Kundu, S.K. Ghosh, S. Nath, T. Pal, General method of synthesis for metal nanoparticles, J. Nanopart. Res. 6 (2004) 411–414. [26] R.K. Mahajan, I. Kaur, T.S. Lobana, A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone, Talanta 1 (2003) 101–105. [27] N.L. Rosi, C.A. Mirkin, Nanostructures in biodiagnostics, Chem. Rev. 4 (2005) 1547–1562. [28] M. Annadhasan, T. Muthukumarasamyvel, V.R.S. Babu, N. Rajendiran, Green synthesized silver and gold nanoparticles for colorimetric detection of Hg2+ , Pb2+ , and Mn2+ in aqueous medium, ACS Sustain. Chem. Eng. 4 (2014) 887– 896.
138
R. Muthivhi et al. / Nano-Structures & Nano-Objects 13 (2018) 132–138
[29] K. Farhadi, M. Forough, R. Molaei, S. Hajizadeh, A. Rafipour, Highly selective Hg2+ colorimetric sensor using green synthesized and unmodified silver nanoparticles, Sensors Actuators B 161 (2012) 880–886. [30] P. Vasileva, T. Alexandrova, I. Karadjova, Application of starch-stabilized silver nanoparticles as a colorimetric sensor for mercury(II) in 0005 mol/L nitric acid, J. Chem. (2017) 6897960. [31] P. Ramadoss, K. Thanigai Arul, J. Ramana Ramya, M. Rigana Begam, V. Sarath Chandra, E. Manikandan, Enhanced mechanical strength and sustained drug release of gelatin/keratin scaffolds, Mater. Lett. 186 (2017) 109–112. [32] Y. Liu, X. Liu, X. Wang, Biomimetic synthesis of gelatin polypeptide-assisted noble-metal nanoparticles and their interaction study, Nanoscale Res. Lett. 6 (2011) 22. [33] C. Lee, P. Zhang, Highly stable gelatin layer-protected gold nanoparticles as surface-enhanced Raman scattering substrates, J. Nanosci. Nanotechnol. 14 (2014) 4325–4330.
[34] M. Annadhasan, N. Rajendiran, Highly selective and sensitive colorimetric detection of Hg (II) ions using green synthesized silver nanoparticles, RSC Adv. 5 (2015) 94513–94518. [35] X. Luo, T. Imae, Photochemical synthesis of crown-shaped platinum nanoparticles using aggregates of G4-NH2 PAMAM dendrimer as templates, J. Mater. Chem. 17 (2006) 567–571. [36] S. Suarasan, M. Focsan, D. Maniu, S. Astilean, Gelatin–nanogold bioconjugates as effective plasmonic platforms for SERS detection and tagging, Colloids Surf. B 103 (2013) 475–481. [37] World Heath Organizations (WHO), Guidelines for Drinking-water Quality, 2005, pp. 1–18.