Green synthesis of Ag nanoparticles using Tamarind ...

Journal of Photochemistry & Photobiology, B: Biology 169 (2017) 178–185

Contents lists available at ScienceDirect

Journal of Photochemistry & Photobiology, B: Biology journal homepage: www.elsevier.com/locate/jphotobiol

Green synthesis of Ag nanoparticles using Tamarind fruit extract for the antibacterial studies N. Jayaprakash a,b, J. Judith Vijaya a,⁎, K. Kaviyarasu c,d, K. Kombaiah a, L. John Kennedy e, R. Jothi Ramalingam f, Murugan A. Munusamy g, Hamad A. Al-Lohedan f a

Catalysis and Nanomaterials Research Laboratory, Department of Chemistry, Loyola College, Chennai 600 034, India Department of Chemistry, SRM Valliammai Engineering College, Chennai 603 203, India. UNESCO-UNISA Africa Chair in Nanosciences/Nanotechnology Laboratories, College of Graduate Studies, University of South Africa (UNISA), Muckleneuk Ridge, P O Box 392, Pretoria, South Africa d Nanosciences African network (NANOAFNET), Materials Research Group (MRG), iThemba LABS-National Research Foundation (NRF), 1 Old Faure Road, 7129, P O Box 722, Somerset West, Western Cape Province, South Africa e Materials Division, School of Advanced Sciences, VIT University, Chennai Campus, Chennai 600 048, India f Chemistry Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabia g Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia. b c

a r t i c l e

i n f o

Article history: Received 2 February 2017 Received in revised form 14 March 2017 Accepted 14 March 2017 Available online 20 March 2017 Keywords: Silver nanoparticles Green synthesis UV–Visible spectroscopy Electron microscopy Antibacterial activity

a b s t r a c t In the present study, first time we report the microwave-assisted green synthesis 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-centered cubic (FCC) silver is confirmed by XRD studies and the average crystallite size of AgNPs is calculated to be around 6–8 nm. The average particle diameter is found to be around 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 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 in cyclic voltammetry in the potential range of −1.2 to +1.2 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, respectively. The as-prepared AgNPs showed good results towards antibacterial activities. Hence, the present approach is a facile, cost- effective, reproducible, eco-friendly, and green method. © 2017 Published by Elsevier B.V.

1. Introduction 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 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 ⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (J.J. Vijaya).

http://dx.doi.org/10.1016/j.jphotobiol.2017.03.013 1011-1344/© 2017 Published by Elsevier B.V.

AgNPs can be controlled by different synthesis methods, for example, are discharge, 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; there is a need for a green synthesis to prepare ecofriendly AgNPs. The use of capping agents is also important. Since, as per thermodynamics, oxidation of AgNPs is not a favorable one, because of its higher positive reduction potential, which will lead to a stable condition in both aqueous and alcoholic medium. 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 development of suitable and reliable synthesis routes, which in turn governs the size and

N. Jayaprakash et al. / Journal of Photochemistry & Photobiology, B: Biology 169 (2017) 178–185

179

Fig. 1. Digital photo of the synthesized AgNPs colloidal solutions at different time intervals of 30, 60, 90, 120, 150, 180, and 210 s. (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.)

shape, chemical composition and large scale production with better monodispersion for the synthesis of nanomaterials. Various synthesis methods are available in literature including green 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, 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 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 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 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, sugar and vitamins. In traditional medicine and food, it is used as the main ingredient in general. Hence we have explained the synthesis of AgNPs using T. indica fruit extract

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.

without the addition of any external surfactant, capping agent or template. Thus, we have attempted a simple, non-toxic, eco-friendly and economically viable green synthesis of AgNPs, which stands stable for more than six months in the liquid form. 2. Experimental 2.1. Materials & Methods 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 Tamarind tree in Kanchipuram, Tamil Nadu, India. De-ionized water was used in the whole process. 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-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. 2.3. Green Synthesis of AgNPs A microwave irradiation was used for the synthesis of AgNPs. 5 mM/100 mL silver nitrate solution was taken in 250 mL conical flask

Fig. 2. UV–Visible absorption spectra of the solutions containing synthesized AgNPs, Tamarind fruit extract, and AgNO3.

Fig. 4. Plot of absorbance versus microwave irradiation time.

180


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

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.

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

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 reference electrode respectively.

2.5. Antibacterial Assay

The UV–Visible spectra were recorded by a Shimadzu 1800 spectrophotometer. Emission 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 resolution and 2o m/s scanning speed. The morphology and size of AgNPs were found using a TECHNAI, FEI G2 model T-30, S-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 was analyzed by energy dispersive X-ray analysis (EDX). Electrochemical measurements were carried out with a CHI 600A electrochemical workstation attached with a personal computer.

The AgNPs were tested in the sterilized de-ionized water for their antibacterial activity by the agar diffusion method. Nine bacterial strains, Bacillus cereus, Staphylococcus aureus, Micrococcus Luteus, Bacillus Subtilis and Enerococcus sp. as Gram-positive bacteria and pseudomonas aeruginosa, Salmonella typhi, Escherichia coli and Klebsiella pneumonia as Gram-negative bacteria were used for the antibacterial activity analysis. The bacterial strains used in the present study were obtained from the 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 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 °C. The reproducibility of the results was analyzed by repeating the antibacterial experiments for 3 times.

Fig. 6. Emission spectrum of AgNPs.

Fig. 8. XRD pattern of AgNPs produced by the Tamarindus indica fruit extract.

2.4. Characterization Techniques


181

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. (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.)

3. Results and Discussion 3.1. UV–Visible Spectral Studies of AgNPs The solution of AgNO3, T. indica fruit extract and synthesized 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 of AgNPs colloidal solution is similar with that of Ag nanoparticles prepared by using Triton X 100 [32]. As per the Mie's theory [33], spherical AgNPs will show a single symmetric absorption peak, whereas anisotropic AgNPs will give two or more bands. Also, the UV–Visible spectrum of the assynthesized AgNPs is symmetrical with sphere-like morphology. 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 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]. The plot of ln[a/(1-a)] against time is shown in Fig. 5, where a = At/A∞, and At and A∞ are the absorbance at time (t) and infinite (∞) time respectively. This figure is helpful in confirming the autocatalytic

Scheme 1. Graphical representation for the formation mechanism of AgNPs.

reaction paths involved during the formation of AgNPs. The first 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]. 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 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 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 active components of T. indica fruit extract, such as, heterocyclic compounds (alkanoids, flavonoids, and alkaloids), which act as the

182


capping agent during the synthesis of AgNPs. The 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 1074 and 1042 cm− 1 in the spectra of leaf extract and AgNPs, respectively, was due to\\C\\C\\stretching and it corresponds to the interface between silver/Tamarindus fruit extract [37]. 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 increased. These two bands are primarily reproducible for the formation of AgNPs. 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 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 AgNPs. 3.4. XRD Analysis of AgNPs The X-ray diffraction pattern of AgNPs produced by using the extract of T. indica fruit is 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 fullwidth at half maximum (FWHM) of the high intense diffraction peak using well-known Scherrer's formula [40]. 3.5. Morphological Analysis of AgNPs The morphology of the AgNPs was examined by using HR-SEM and HR-TEM. The HR- SEM image of AgNPs is shown in Fig. 9(a–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 is shown in Fig. 9(b, d, f, h). The advantage of the present green synthesized AgNPs is that they are highly stay stable for more than 6 months. Thus, it is confirmed that the T. indica fruit extract is effective and suitable to synthesize stable AgNPs. The graphical representation of the formation of AgNPs is shown in Scheme 1. 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 from AgNPs, and other

Fig. 10. a) EDX spectrum of the synthesized AgNPs b) Histogram of the particle size distribution.


183

[41]. Fig. 10b shows the histogram of the particle size distribution and the average particle diameter is found to be 10 nm. It confirms that the size range of AgNPs is 5–12 nm. 3.7. Cyclic Voltammetry Studies Cyclic voltammograms (CV) of pure T. indica fruit extract and AgNPs at the scan rate of 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 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 as-synthesized AgNPs could be used as electrochemical sensors [43]. 3.8. Antibacterial Activity Studies of AgNPs Fig. 11. Cyclic voltammogram of (a) pure Tamarindus indica fruit extract and (b) AgNPs stabilized by the Tamarindus indica fruit extract.

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 absorption peak approximately at 3 keV

In order to study the antibacterial effect of AgNPs towards Bacillus cereus, Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, Enterococcus species (Gram-positive bacteria) and Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, and 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. Results of inhibition zones of antibacterial activity (1. AgNO3, 2. AgNPs and 3. pure Tamarindus indica fruit extract). (a) Bacillus cereus, (b) Staphylococcus aureus, (c) Pseudomonas aeruginosa, (d) Salmonella typhi, (e) Micrococcus luteus, (f) Escherichia coli, (g) Klebsiella pneumoniae, (h) Bacillus subtilis, and (i) Enterococcus sp.

184


species, which could be generated by the gaining of electrons from AgNPs has caused the damage of DNA by the help 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 acids containing nitrogen, oxygen and sulphur (electron donor groups) forms a complex with Ag+. 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. 4. Conclusions

Fig. 13. Bar diagram of inhibition zones of antibacterial activity of AgNPs.

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 Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli, and Klebsiella pneumonia are 22, 15, 15, and 10 mm respectively. The diameter of the inhibiting zones of AgNO3 against Bacillus cereus, Staphylococcus aureus, Micrococcus luteus, Bacillus subtilis, and Enterococcus sp. are 14, 15, 13, 16, and 15 mm respectively and Pseudomonas aeruginosa, Salmonella typhi, 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 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. Antibacterial activity is a well-known property of AgNPs. The mechanism of 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 kill the cells [44–46]. (ii) Reactive oxygen species (ROS) or oxygen radical

Scheme 2. A schematic showing the various possibilities of antibacterial activities by AgNPs.

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 as-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 that leads to the formation of highly stable nanoparticles with better antibacterial activity. Also, the as-synthesized AgNPs in the present study could be used in the field of medicine, food industries and sensors. Acknowledgements The authors duly acknowledge the Loyola College Management for the funding through LOY-TOI project [Project Code: 2LCTOI14CHM003, dated 25.11.2014] and the authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group no RGP-148. The first author thanks SRM University, and SRM Valliammai Engineering College, Chennai, India for their support. References [1] S. Prabhu, E.K. Poulose, Silver nanoparticles: mechanism of antimicrobial action, synthesis, medical applications and toxicity effects, Int. Nano Lett. 2 (2012) 32–42. [2] S. Ghosh, S. Patil, M. Ahire, R. Kitture, S. Kale, K. Pardesi, S.S. Cameotra, J. Bellare, D.D. Dhavale, A. Jabgunde, B.A. Chopade, Synthesis of silver nanoparticles using Dioscorea bulbifera tuber extract and evaluation of its synergistic potential in combination with antimicrobial agents, Int. J. Nanomedicine 7 (2012) 483–496. [3] K. Kaviyarasu, D. Premanand, J. Kennedy, E. Manikandan, Synthesis of Mg doped TiO2 nanocrystals prepared by wet-chemical method: optical and microscopic studies, Int. J. Nanosci. 12 (2013), 1350033. . [4] K. Kaviyarasu, E. Manikandan, J. Kennedy, M. Maaza, RSC Adv. 5 (2015) 82421–82428. [5] K. Kaviyarasu, E. Manikandan, J. Kennedy, M. Jayachandran, Quantum confinement and photoluminescence of well-aligned CdO nanofibers by a solvothermal route, Mater. Lett. 120 (2014) 243–245. [6] K. Kaviyarasu, E. Manikandan, J. Kennedy, M. Jayachandran, R. Ladchumananandasivam, U.U.D. Gomes, M. Maaza, Synthesis and characterization studies of NiO nanorods forenhancing solar cell efficiency using photon upconversion materials, Ceram. Int. 42 (2016) 8385–8394. [7] K. Kasinathan, J. Kennedy, E. Manikandan, M. Henini, M. Malik, Photodegradation of organic pollutants RhB dye using UV simulated sunlight on ceria based TiO2 nanomaterials for antibacterial applications, Sci. Rep. 6 (2016), 38064. . [8] S. Chang, K. Chen, Q. Hua, Y. Ma, W. Huang, S. Chang, K. Chen, Q. Hua, Y. Ma, W. Huang, Evidence for the growth mechanisms of silver nanocubes and nanowires, J. Phys. Chem. C 115 (2011) 7979–7986. [9] L. Huang, Y. Zhai, S. Dong, J. Wang, Efficient preparation of silver nanoplates assisted by non-polar solvents, J. Colloid Interface Sci. 331 (2009) 384–388. [10] A. Sarkar, S. Kapoor, T. Mukherjee, Synthesis of silver nanoprisms in formamide, J. Colloid Interface Sci. 287 (2005) 496–500. [11] K. Kaviyarasu, A. Ayeshamariam, E. Manikandan, J. Kennedy, R.L. Nandasivam, U.U. Gomes, M. Jayachandran, M. Maaza, Mater. Sci. Eng. B 210 (2016) 1–9. [12] K. Kaviyarasu, Xolile Fuku, Genene T. Mola, E. Manikandan, J. Kennedy, M. Maaza, Photoluminescence of well-aligned ZnO doped CeO2nanoplatelets by a solvothermal route, Mater. Lett. 183 (2016) 351–354.

N. Jayaprakash et al. / Journal of Photochemistry & Photobiology, B: Biology 169 (2017) 178–185 [13] C.M. Magdalane, K. Kaviyarasu, J.J. Vijaya, B. Siddhardha, B. Jeyaraj, Photocatalytic activity of binary metal oxide nanocomposites of CeO2/CdO nanospheres: investigation of optical and antimicrobial activity, J. Photochem. Photobiol. B 163 (2016) 77–86. [14] M. Cushen, J. Kerry, M. Morris, M.C. Romero, E. Cummins, Nanotechnologies in the food industry – recent developments, risks and regulation, Trends Food Sci. Technol. 24 (2012) 30–46. [15] D. Philip, C. Unni, S. Aswathy Aromal, V.K. Vidhu, Murraya koenigii leaf-assiated green synthesis of silver and gold nanoparticles, Spectrochim. Acta A 78 (2011) 899–904. [16] R. Veerasamy, T.Z. Xin, S. Gunasagaran, T.F.W. Xiang, E.F.C. Yang, N. Jeyakumar, S.A. Dhanaraj, Biosynthesis of silver nanoparticles using mangosteen leaf extract and evaluation of their antimicrobial activities, J. Saudi Chem. Soc. 15 (2011) 113–120. [17] K. Kaviyarasu, E. Manikandan, P. Paulraj, S.B. Mohamed, J. Kennedy, One dimensional well-aligned CdO nanocrystal by solvothermal method, J. Alloys Compd. 593 (2014) 67–70. [18] H. Bar, D.K. Bhui, G.P. Sahoo, P. Sarkar, S.P. De, A. Misra, Green synthesis of silver nanoparticles using latex of Jatropha curcas, Colloids Surf. A Physicochem. Eng. Asp. 339 (2009) 134–139. [19] S.L. Smitha, D. Philip, K.G. Gopchandran, Green synthesis of gold nanoparticles using Cinnamomum zeylanicum leaf broth, Spectrochim. Acta A 74 (2009) 735–739. [20] A.R.V. Nestor, V.S. Mendieta, M.A.C. Lopez, R.M.G. Espinosa, M.A.C. Lopez, J.A. Alatorre, Solvent less synthesis and optical properties of Au and Ag nanoparticles using Camellia sinensis extract, Mater. Lett. 62 (2008) 3103–3105. [21] S.P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad, M. Sastry, Synthesis of gold nanotriangles and silver nanoparticles using aloevera plant extract, Biotechnol. Prog. 22 (2006) 577–583. [22] D. Philip, Biosyntheie of Au, Ag and Au-Ag nanoparticles using edible mushroom extract, Spectrochim. Acta A 73 (2009) 374–381. [23] D. Philip, Honey mediated green synthesis of gold nanoparticles, Spectrochim. Acta A 73 (2009) 650–653. [24] D. Jain, H.K. Daima, S. Kachhwaha, S.L. Kothari, Synthesis of plant-mediated silver nanoparticles using papaya fruit extract and evaluation of their antimicrobial activities, Dig. J. Nanomater. Biostruct. 4 (2009) 723–727. [25] S.P. Dubey, M. Lahtinen, M. Sillanpaa, Tansy fruit mediated greener synthesis of silver and gold nanoparticles, Process Biochem. 45 (2010) 1065–1071. [26] G.S. Ghodake, N.G. Deshpande, Y.P. Lee, E.S. Jin, Pear fruit extract-assisted roomtemperature biosynthesis of gold nanoplates, Colloids Surf. B. Biointerfaces 75 (2010) 584–589. [27] 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, Colloids Surf. B. Biointerfaces 82 (2011) 152–159. [28] B. Ankamwar, C. Damle, A. Ahmad, M. Sastry, Biosynthesis of gold and silver nanoparticles using emblica officialis fruit extract, their phase transfer and transmetallation in an organic solution, J. Nanosci. Nanotechnol. 5 (2005) 1665–1671. [29] R.A. de Matos, L.C. Courrol, Saliva and light as templates for the green synthesis of silver nanoparticles, Colloids Surf. A Physicochem. Eng. Asp. 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 activity of silver nanoparticles synthesized from serine, Mater. Sci. Eng. C 49 (2015) 316–322.

185

[32] N. Jayaprakash, J.J. Vijaya, L.J. Kennedy, Microwave-assisted synthesis and characterization of Triton X 100 capped silver nanospheres, J. Dispers. Sci. Technol. 34 (2013) 1597. [33] G. Mie, Contributions to the optics of turbid media, particularly of colloidal metal solutions, Ann. Phys. 25 (1908) 377–445. [34] Z. Zoya, Rafiuddin, Silver nanoparticles formation using tyrosine in presence cetyltrimethylammonium bromide, Colloids Surf. B Biointerfaces 89 (2012) 211–215. [35] J. Gao, F. Jun, L. Cuikun, L. Jun, H. Yanchun, Y. Xiang, P. Caiyuan, Formation and photoluminescence of silver nanoparticles stabilized by a two-armed polymer with a crown ether core, Langmuir 20 (2004) 9775–9779. [36] P. Angshuman, S. Sunil, D. Surekha, Microwave-assisted synthesis of silver nanoparticles using ethanol as a reducing agent, Mater. Chem. Phys. 114 (2009) 530–532. [37] N. Ahmad, S. Bhatnagar, S.S. Ali, R. Dutta, Phytofabrication of bioinduced silver nanoparticles for biomedical applications, Int. J. Nanomedicine 10 (2015) 7019–7030. [38] V. Patil, R.B. Malvankar, M. Sastry, Role of particle size in individual and competitive diffusion of carboxylic acid derivatized colloidal gold particles in thermally evaporated fatty amine films, Langmuir 15 (1999) 8197–8206. [39] B. Ankamwar, M. Chaudhary, M. Sastri, Gold Nanotriangles biologically synthesized using tamarind leaf extract and potential application in vapor sensing, Synth. React. Inorg., Met.-Org., Nano-Met. Chem. 35 (2005) 19. [40] N. Jayaprakash, J. Judith Vijaya, L. John Kennedy, K. Priadharsini, P. Palani, One step phytosynthesis of highly stabilized silver nanoparticles using Piper nigrum extract and their antibacterial activity, Mater. Lett. 137 (2014) 358. [41] N. Jayaprakash, J. Judith Vijaya, L. John Kennedy, Microwave-assisted rapid facile synthesis, characterization, and their antibacterial activity of PVP capped silver Nanospheres, Synth. React. Inorg., Met.-Org., Nano-Met. Chem. 45 (2015) 1533. [42] G. Valdes-Ramirez, M.T. Ramirez-Silva, M. Palomar-Pardave, M. Romero-Romo, G.A. Alvarez-Romero, P.R. Hernandez-Rodriguez, J.L.J. Marty, M. Juarez-Garcia, Design and Construction of Solid State Ag/AgCl Reference Electrodes Through Electrochemical Deposition of Ag and AgCl Onto a Graphite/Epoxy Resin-Based Composite. Parte 1: Electrochemical Deposition of Ag Onto a Graphite/Epoxy Resin-Based Composite, Int. J. Electrochem. Sci. 6 (2011) 971. [43] J. Sophia, G. Muralidharan, Preparation of vinyl polymer stabilized silver nanospheres for electro-analytical determination of H2O2, Sensors Actuators B Chem. 193 (2014) 149. [44] J.R. Morones, L.J. Elechiguerra, A. Camacho, K. Holt, J.B. Kouri, J.T. Ramírez, M.J. Yacaman, The bactericidal effect of silver nanoparticles, Nanotechnology 16 (2005) 2346. [45] I. Sondi, B.S. Salopek, Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria, J. Colloid Interface Sci. 275 (2004) 177. [46] M.V.D.Z. Park, A.M. Neigh, J.P. Vermeulen, L.J.J. de la Fonteyne, H.W. Verharen, J.J. Briede, H. van Loveren, W.H. de Jong, The effect of particle size on the cytotoxicity, inflammation, developmental toxicity and genotoxicity of silver nanoparticles, Biomaterials 32 (2011) 9810. [47] Q.L. Feng, J. Wu, G.Q. Chen, F.Z. Cui, T.N. Kim, J.O. Kim, A mechanistic study of the antibacterial effect of silver ions on Escherichia coli and Staphylococcus aureus, J. Biomed. Mater. Res. 52 (2000) 662. [48] S.A. Cumberland, J.R. Lead, Particle size distributions of silver nanoparticles at environmentally relevant conditions, J. Chromatogr. A 1216 (2009) 9099. [49] S. Kittler, C. Greulich, J. Diendorf, M. Koller, M. Epple, Toxicity of silver nanoparticles increases during storage because of slow dissolution under release of silver ions, Chem. Mater. 22 (2010) 4548.