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

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Journal of Photochemistry & Photobiology, B: Biology

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Green synthesis of Ag nanoparticles using Tamarind fruit extract for theantibacterial 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, Indiab Department of Chemistry, SRM Valliammai Engineering College, Chennai 603 203, India.c 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 Africad 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 Africae Materials Division, School of Advanced Sciences, VIT University, Chennai Campus, Chennai 600 048, Indiaf Chemistry Department, College of Science, King Saud University, Riyadh 11451, Saudi Arabiag Department of Botany and Microbiology, College of Science, King Saud University, Riyadh 11451, Saudi Arabia.

⁎ Corresponding author.E-mail addresses: judithvijjaya@loyolacollege.edu, jjvi

http://dx.doi.org/10.1016/j.jphotobiol.2017.03.0131011-1344/© 2017 Published by Elsevier B.V.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 2 February 2017Received in revised form 14 March 2017Accepted 14 March 2017Available online 20 March 2017

In the present study, first timewe report themicrowave-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 forthe synthesis of AgNPs. The formation of spherical shape AgNPs is confirmed by XRD, HR-SEM, and HR-TEM. Thepresence of face-centered cubic (FCC) silver is confirmed by XRD studies and the average crystallite size of AgNPsis calculated to be around 6–8 nm. The average particle diameter is found to be around 10 nm, which is identifiedfrom 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 complicatedkinetic features. To investigate the function-al groups of the extract and their involvement in the reduction of AgNO3 to form AgNPs, FT-IR studies are carriedout. The redox peaks are observed in cyclic voltammetry in the potential range of −1.2 to +1.2 V, due to theredox active components of the T. indica fruit extract. In photoluminescence spectroscopy, the excited and emis-sion peaks were obtained at 432 nm and 487 nm, respectively. The as-prepared AgNPs showed good results to-wards antibacterial activities. Hence, the present approach is a facile, cost- effective, reproducible, eco-friendly,and green method.

© 2017 Published by Elsevier B.V.

Keywords:Silver nanoparticlesGreen synthesisUV–Visible spectroscopyElectron microscopyAntibacterial activity

1. Introduction

Recently, nanomaterials have attracted researchers among the sci-entific world, because of their most important and peculiar propertieswhich are different when compared with their bulk materials. Amongthem, noble metal nanoparticles, such as Ag, Au, Pt, and Pd nanoparti-cles are used in physical, chemical and biological applications [1,2].AgNPs represents a good candidate to carry out the nanostructuredpart of antibacterial and anticancer applications [3–7]. The propertiesof the nanomaterials are controlled by their shape, size and nature.AgNPs are highly in demand, because of its various applications inmed-icine, water treatment and catalysis. In general, colloidal dispersionslead to the formation of AgNPs and their morphology differ, based onthe methods adopted for the synthesis [8–10]. The size and shape of

jaya78@gmail.com (J.J. Vijaya).

AgNPs can be controlled by different synthesis methods, for example,are discharge, lazer CVD, physical adsorption and emulsion polymeriza-tion are used as commonmethods to prepare AgNPs. But, because of theusage of the toxic chemicals or solvents or non-biodegradable agents,these methods should be avoided. Without using the above said toxicchemicals as reducing or stabilizing agents, AgNPs cannot be prepared.Since, these methods are potential threats to the environment and bio-logical systems; there is a need for a green synthesis to prepare eco-friendly AgNPs. The use of capping agents is also important. Since, asper thermodynamics, oxidation of AgNPs is not a favorable one, becauseof its higher positive reduction potential, whichwill lead to a stable con-dition in both aqueous and alcoholic medium.

Recently, green synthesis has gained importance over other physicaland chemical methods, since, it offers environmental friendly, cheap,biocompatible, shape, and size controlled nanoparticles. The key aspectof nanotechnology is primarily aimed at the development of suitableand reliable synthesis routes, which in turn governs the size and

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

Fig. 3. UV–Visible absorption spectra of the solutions containing synthesized AgNPs atdifferent time intervals of 30, 60, 90, 120, 150, 180, and 210 s.

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shape, chemical composition and large scale production with bettermonodispersion for the synthesis of nanomaterials. Various synthesismethods are available in literature including green routes based onusing plants, bacteria, and fungi, and they are given importance becauseof their non-toxic, economical and eco-friendly method of preparationand bio-compatible nature. Also, AgNPs prepared by using the abovementioned methods donot/less use of toxic chemicals, which makesthem to be used in medical and pharmaceutical applications [11–13].Also, AgNPs based antimicrobial packaging is a promising form of activefood packaging, which plays an important role in extending shelf-life offoods and reduce the risk of pathogens. Also, the use of AgNPs as antimi-crobial agents in food packaging is amature technology,which concernson the risks associated with the potential ingestion of the Ag ions mi-grated into food and drinks. This leads to a prudent attitude of food safe-ty authorities [14]. There are reports available on the formation ofAgNPs using plant extracts like Murraya koenigii leaf [15], Mangosteenleaf [16], Mangifera indica leaf [17], Jatropha curcas [18], Cinnamomumzeylanicum leaf [19], Camellia sinensis [20], Aloe vera [21], mushroom[22], and honey [23]. There are few reports on the preparation ofAgNPs using fruit extract, such as papaya [24], tansy [25], pear [26],lemon [27] and goose berry [28]. The advantage of using plant andfruit extract includes the formation of stable nanoparticles without mo-lecular aggregation even if they are stored for a longer time.

In our study, we have synthesized AgNPs using T. indica fruit, whichis commonly known as Tamarind fruit. In general, Tamarind is sweetand sour in taste and has tartaric acid, sugar and vitamins. In traditionalmedicine and food, it is used as the main ingredient in general. Hencewe have explained the synthesis of AgNPs using T. indica fruit extract

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

without the addition of any external surfactant, capping agent or tem-plate. Thus, we have attempted a simple, non-toxic, eco-friendly andeconomically viable green synthesis of AgNPs, which stands stable formore 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, TamilNadu, 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 in50 mL of hot de-ionized water for 5 min. Then this Tamarind wassqueezed well. The extract of T. indica fruit was then filtered usingWhatman 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. 4. Plot of absorbance versus microwave irradiation time.

Fig. 5. Plot of ln[a/(1-a)] against microwave irradiation time.Fig. 7. FT-IR spectrumof a) pure Tamarindus indica fruit extract, and b) AgNPs stabilized bythe Tamarindus indica fruit extract.

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and 10 mL of T. indica fruit extract was added into the above silver ni-trate solution. The above mixed solution was kept in the microwaveoven (model: MS-2049 UW) (input power 230 V, 50 Hz) for 180 s.The solution finally shows yellowish brown color, which in turn affirmsthe formation of AgNPs. Fig. 1 shows the digital photo of the AgNPs col-loidal 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 spectro-photometer. Emission spectrum of the AgNPs was recorded by usingVARIAN CARY ECLIPSE fluorospectrometer. The X-ray diffraction pat-tern 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 resolutionand 2o m/s scanning speed. The morphology and size of AgNPs werefound using a TECHNAI, FEI G2model T-30, S-twin, 300 kV, High-resolu-tion transmission electronmicroscope (HR-TEM) and a FE-I Quanta FEG200 High-resolution scanning electronmicroscope (HR-SEM). The puri-ty of the samples was analyzed by energy dispersive X-ray analysis(EDX). Electrochemical measurements were carried out with a CHI600A electrochemical workstation attached with a personal computer.

Fig. 6. Emission spectrum of AgNPs.

0.1MKNO3was used as an electrolytic solution. A platinumwire, glassycarbon electrode (GCE) and a saturated calomel electrode (SCE) wereused as the counter, working, and reference electrode respectively.

2.5. Antibacterial Assay

The AgNPs were tested in the sterilized de-ionized water for theirantibacterial activity by the agar diffusion method. Nine bacterialstrains, Bacillus cereus, Staphylococcus aureus, Micrococcus Luteus, Bacil-lus Subtilis and Enerococcus sp. as Gram-positive bacteria and pseudomo-nas aeruginosa, Salmonella typhi, Escherichia coli and Klebsiellapneumonia as Gram-negative bacteria were used for the antibacterialactivity analysis. The bacterial strains used in thepresent studywere ob-tained from the Department of Medical Microbiology, Taramani Cam-pus, University of Madras, India. These bacteria were grown on liquidnutrient agar media for 24 h prior to the experiment, and were seededin agar plates by the pour plate technique. Different trails were carriedout by preparing different plates for each and every bacterial strain. Ineach petri plate, three cavities were made using a cork borer at anequal distance. In each cavity, 50 μL of AgNPs, T. indica fruit extract,and AgNO3 solutions were filled. The plates were incubated for 24 h at35 °C. The reproducibility of the results was analyzed by repeating theantibacterial experiments for 3 times.

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

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3. Results and Discussion

3.1. UV–Visible Spectral Studies of AgNPs

The solution of AgNO3, T. indica fruit extract and synthesized AgNPswere taken and their respective UV–Visible absorption spectra werestudied (Fig. 2). The presence of an intense peak at 432 nm confirmsthe formation of AgNPs [29–31]. The UV–Visible spectrum of AgNPs col-loidal solution is similarwith that of Ag nanoparticles prepared by usingTriton X 100 [32]. As per the Mie's theory [33], spherical AgNPs willshow a single symmetric absorption peak, whereas anisotropic AgNPswill give two or more bands. Also, the UV–Visible spectrum of the as-synthesized AgNPs is symmetrical with sphere-like morphology.

The UV–Visible absorption spectra of AgNPs solutions were studiedat different time intervals as shown in Fig. 3. The sufficient peaks areformed 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. Itshows that the curve is sigmoid in nature, which suggests that the reac-tion 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 stepis the formation of Ag nucleation centre, which will reduce other Ag+

ions in the solutions and thus lead to autocatalytic reaction towardsthe formation of AgNPs [34].

3.2. Photoluminescence (PL) Spectroscopy of AgNPs

The AgNPs were excited at 432 nm, and the emission peak was ob-tained at 487 nmas shown in Fig. 6. The stabilization of AgNPs by [poly(-styrene)]-dibenzo-18-crown-6-[poly(styrene)] with the emission bandat 486 nm is reported [35]. The emission band at 491 nm upon excita-tion at 416 nm for PVP capped AgNPs is also reported [36]. Due to thepromotion of d-band electrons of the AgNPs by absorbing the incidentradiation to higher electronic states in the sp-band the origin of fluores-cence occurs.

3.3. Fourier Transform Infrared Spectral Studies of AgNPs

To investigate the functional groups of the extract and their involve-ment in the reduction of AgNO3 to form AgNPs, FT-IR studies are carriedout (Fig. 7a–b). FT-IR spectrum of colloidal AgNPs and T. indica fruit ex-tract is similar with a slight shift in the band positions. T. indica fruit ex-tract 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 corre-sponds to the stretching vibration of_C_O (carbonyl group) [28]. Thepeaks at 1632 cm−1 and 1415 cm−1 are assigned to the stretching vi-brations of\\C_C (aliphatic) and stretching vibration of\\C_C (aro-matic ring) respectively. The peak at 1075 cm−1 is because of thestretching vibrations of\\C_O (ester). These peaks confirm the pres-ence of active components of T. indica fruit extract, such as, heterocycliccompounds (alkanoids, flavonoids, and alkaloids), which act as the

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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 numberthan in the FT-IR spectra of pure T. indica fruit extract. The weak bandsappearing at 1074 and 1042 cm−1 in the spectra of leaf extract andAgNPs, respectively, was due to\\C\\C\\stretching and it correspondsto the interface between silver/Tamarindus fruit extract [37].

The above mentioned shift confirmed that the intensity of\\OH vi-bration is decreased because of the formation of AgNPs. At the sametime, the intensity of bands due to C_O group is increased. These twobands are primarily reproducible for the formation of AgNPs.

The various functional groups in the final AgNPs are because of theheterocyclic compounds present in the T. indica fruit. They are responsi-ble for the reduction and stabilization of AgNPs and they are soluble inwater [38]. Hence, these water soluble compounds (alkanoids, flavo-noids, and alkaloids) play the role of a capping and stabilizing agent inthe synthesis of AgNPs.

3.4. XRD Analysis of AgNPs

The X-ray diffraction pattern of AgNPs produced by using the extractof 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.

Fig. 10. a) EDX spectrum of the synthesized AgNPs

96-900-8460. Inter planar spacing (dcalculated) values for the abovemen-tioned planes are 2.3169 Å, 2.0127 Å, 1.4325 Å, 1.2251 Å and 1.1722 Årespectively. It also agrees to the standard values [39]. The size of thecrystallites of AgNPs is calculated to be around 6–8 nm from the full-width at half maximum (FWHM) of the high intense diffraction peakusing well-known Scherrer's formula [40].

3.5. Morphological Analysis of AgNPs

The morphology of the AgNPs was examined by using HR-SEM andHR-TEM. The HR- SEM image of AgNPs is shown in Fig. 9(a–h) showsthe typical HR-TEM images of the as-synthesized AgNPs. It confirmsthat the particles are relatively uniform in diameter and almost spheri-cal in shape. The presence of biomolecules that act as a capping agent isshown in Fig. 9(b, d, f, h). The advantage of the present green synthe-sized 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 suit-able to synthesize stable AgNPs. The graphical representation of the for-mation 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 purityof the as-synthesized AgNPs. It shows the peaks for the presence ofAg, O and C. The Ag peak could be originated from AgNPs, and other

b) Histogram of the particle size distribution.

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

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peaks of O and C from the heterocyclic compounds of the T. indica fruitextract. Due to the surface plasmon resonance, metallic silvernanocrystals show an optical absorption peak approximately at 3 keV

Fig. 12. Results of inhibition zones of antibacterial activity (1. AgNO3, 2. AgNPs and 3. pure Tamaeruginosa, (d) Salmonella typhi, (e)Micrococcus luteus, (f) Escherichia coli, (g) Klebsiella pneum

[41]. Fig. 10b shows the histogram of the particle size distribution andthe average particle diameter is found to be 10 nm. It confirms thatthe size range of AgNPs is 5–12 nm.

3.7. Cyclic Voltammetry Studies

Cyclic voltammograms (CV) of pure T. indica fruit extract and AgNPsat the scan rate of 0.05Vs−1 shows that the CV of AgNPs is similar to thatof the pure T. indica fruit extract. Because of the presence of redox activecomponents of the T. indica fruit extract, AgNPs show the redox peaks inthe potential range of−1.2 to +1.2 V (Fig. 11). Since, T. indica fruit ex-tract gains the electron, it shows the oxidation peak and the reductionpeak arises because of the oxidation when the electric field is applied.The oxidation of Ag(0) into Ag+ is confirmed by the presence of asharp peak at 0.13 V [42]. Hence, the present study confirms that theas-synthesized 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 Bacilluscereus, Staphylococcus aureus,Micrococcus luteus, Bacillus subtilis, Entero-coccus species (Gram-positive bacteria) and Pseudomonas aeruginosa,Salmonella typhi, Escherichia coli, and Klebsiella pneumonia (Gram-nega-tive bacteria). Agar diffusion method is used which usually shows theinhibition zone around the holes with the increase in bacteria growth.

arindus indica fruit extract). (a) Bacillus cereus, (b) Staphylococcus aureus, (c) Pseudomonasoniae, (h) Bacillus subtilis, and (i) Enterococcus sp.

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

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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 Entero-coccus sp. are 15, 16, 14, 18, and 16 mm respectively and Pseudomonasaeruginosa, Salmonella typhi, Escherichia coli, and Klebsiella pneumoniaare 22, 15, 15, and 10 mm respectively. The diameter of the inhibitingzones of AgNO3 against Bacillus cereus, Staphylococcus aureus,Micrococ-cus luteus, Bacillus subtilis, and Enterococcus sp. are 14, 15, 13, 16, and15 mm respectively and Pseudomonas aeruginosa, Salmonella typhi,Escherichia coli, and Klebsiella pneumonia are 20, 13, 13, and 10 mm re-spectively. The inhibition zone is absent in the cavities having T. indicafruit extract. The above mentioned values are taken as the mean valuesafter conducting the experiments for three times. From the results, it isfound that the inhibition zone of AgNPs was slightly better than AgNO3

against the bacterial strains and the respective inhibition zone is repre-sented in Fig. 13.

Antibacterial activity is a well-known property of AgNPs. Themech-anism of antibacterial activity is shown in Scheme 2. (i) AgNPs get at-tached and penetrate into the cell membrane of bacteria to disrupt thepermeability and respiration functions of the cell, and thus kill thecells [44–46]. (ii) Reactive oxygen species (ROS) or oxygen radical

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

species, which could be generated by the gaining of electrons fromAgNPs has caused the damage of DNA by the help of oxidative stress[47]. (iii) Ag+ produced from AgNPs might also cause the disruptionof ATP production and DNA replication [48,49]. (iv) Phosphate andthiols in nucleic acids and amino acids containing nitrogen, oxygenand sulphur (electron donor groups) forms a complex with Ag+.

It is a well-known fact that silver salts have a good antibacterial ac-tivity. If taken in higher concentration, it is toxic to microbes and con-sumers. Therefore, AgNPs of smaller concentration in nano-regime isin demand for a better antimicrobial activity and the present green syn-thesis of AgNPs pave a way for the same.

4. Conclusions

Green synthesis of highly stable AgNPs by a simple microwavemethod is proposed. The use of T. indica fruit extract avoids the use ofextra reducing and capping agent. The as-synthesized AgNPs are char-acterized by UV–Visible, FT-IR, XRD, CV, HR-SEM and HR-TEM and theobtained results confirm the formation of cubic Ag-phase with spheri-cally-shaped particles at the nanoscale. Another advantage of thismeth-od is that the AgNPs formed are stable without any oxide formation formore than six months. Hence, this green method shows reproducibleresults, eco-friendly, less reaction time, cost effective and straight for-ward method that leads to the formation of highly stable nanoparticleswith better antibacterial activity. Also, the as-synthesized AgNPs in thepresent study could be used in the field of medicine, food industriesand sensors.

Acknowledgements

The authors duly acknowledge the Loyola College Management forthe funding through LOY-TOI project [Project Code: 2LCTOI14CHM003,dated 25.11.2014] and the authors extend their appreciation to theDeanship of Scientific Research at King Saud University for funding thiswork through research group no RGP-148. The first author thanks SRMUniversity, and SRMValliammai Engineering College, Chennai, India fortheir 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 Dioscoreabulbifera tuber extract and evaluation of its synergistic potential in combinationwith antimicrobial agents, Int. J. Nanomedicine 7 (2012) 483–496.

[3] K. Kaviyarasu, D. Premanand, J. Kennedy, E. Manikandan, Synthesis of Mg dopedTiO2 nanocrystals prepared bywet-chemical method: optical andmicroscopic stud-ies, 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 confinementand 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 nanorodsforenhancing 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 oforganic 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 assistedby 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 asolvothermal route, Mater. Lett. 183 (2016) 351–354.

185N. 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 ac-tivity of binary metal oxide nanocomposites of CeO2/CdO nanospheres: investiga-tion 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 thefood 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-assiatedgreen 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 andevaluation 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 dimension-al 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 silvernanoparticles 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 usingCinnamomum 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 nanoparticlesusing Camellia sinensis extract, Mater. Lett. 62 (2008) 3103–3105.

[21] S.P. Chandran, M. Chaudhary, R. Pasricha, A. Ahmad, M. Sastry, Synthesis of goldnanotriangles 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 ex-tract, Spectrochim. Acta A 73 (2009) 374–381.

[23] D. Philip, Honey mediated green synthesis of gold nanoparticles, Spectrochim. ActaA 73 (2009) 650–653.

[24] D. Jain, H.K. Daima, S. Kachhwaha, S.L. Kothari, Synthesis of plant-mediated silvernanoparticles using papaya fruit extract and evaluation of their antimicrobial activ-ities, Dig. J. Nanomater. Biostruct. 4 (2009) 723–727.

[25] S.P. Dubey, M. Lahtinen, M. Sillanpaa, Tansy fruit mediated greener synthesis of sil-ver 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 room-temperature biosynthesis of gold nanoplates, Colloids Surf. B. Biointerfaces 75(2010) 584–589.

[27] T.C. Prathna, N. Chandrasekaran, A.M. Raichur, A. Mukherjee, Biomimetic synthesisof silver nanoparticles by Citrus limon (lemon) aqueous extract and theoretical pre-diction 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 nano-particles using emblica officialis fruit extract, their phase transfer andtransmetallation 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 ofsilver nanoparticles, Colloids Surf. A Physicochem. Eng. Asp. 441 (2014) 539–543.

[30] V.K. Vidhu, D. Philip, Spectroscopic, microscopic and catalytic properties of silvernanoparticles 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, Antibacte-rial activity of silver nanoparticles synthesized from serine, Mater. Sci. Eng. C 49(2015) 316–322.

[32] N. Jayaprakash, J.J. Vijaya, L.J. Kennedy, Microwave-assisted synthesis and character-ization of Triton X 100 capped silver nanospheres, J. Dispers. Sci. Technol. 34 (2013)1597.

[33] G. Mie, Contributions to the optics of turbidmedia, particularly of colloidal metal so-lutions, Ann. Phys. 25 (1908) 377–445.

[34] Z. Zoya, Rafiuddin, Silver nanoparticles formation using tyrosine in presencecetyltrimethylammonium 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 andphotoluminescence of silver nanoparticles stabilized by a two-armed polymerwith a crown ether core, Langmuir 20 (2004) 9775–9779.

[36] P. Angshuman, S. Sunil, D. Surekha, Microwave-assisted synthesis of silver nanopar-ticles 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 nano-particles 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 competitivediffusion of carboxylic acid derivatized colloidal gold particles in thermally evapo-rated fatty amine films, Langmuir 15 (1999) 8197–8206.

[39] B. Ankamwar, M. Chaudhary, M. Sastri, Gold Nanotriangles biologically synthesizedusing 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 stepphytosynthesis of highly stabilized silver nanoparticles using Piper nigrum extractand their antibacterial activity, Mater. Lett. 137 (2014) 358.

[41] N. Jayaprakash, J. Judith Vijaya, L. John Kennedy, Microwave-assisted rapid facilesynthesis, characterization, and their antibacterial activity of PVP capped silverNanospheres, 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, Designand Construction of Solid State Ag/AgCl Reference Electrodes Through Electrochem-ical Deposition of Ag and AgCl Onto a Graphite/Epoxy Resin-Based Composite. Parte1: 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 nano-spheres 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, Bio-materials 32 (2011) 9810.

[47] Q.L. Feng, J. Wu, G.Q. Chen, F.Z. Cui, T.N. Kim, J.O. Kim, Amechanistic study of the an-tibacterial 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 envi-ronmentally relevant conditions, J. Chromatogr. A 1216 (2009) 9099.

[49] S. Kittler, C. Greulich, J. Diendorf, M. Koller, M. Epple, Toxicity of silver nanoparticlesincreases during storage because of slow dissolution under release of silver ions,Chem. Mater. 22 (2010) 4548.