Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 349–355

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Spectrochimica Acta Part A: Molecular andBiomolecular Spectroscopy

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Spectroscopy investigation on chemo-catalytic, free radical scavengingand bactericidal properties of biogenic silver nanoparticles synthesizedusing Salicornia brachiata aqueous extract

1386-1425/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.saa.2013.08.114

⇑ Corresponding authors. Tel.: +91 4362 264101 657; fax: +91 4362 264120.E-mail addresses: arvi@biotech.sastra.edu (A. Sivasubramanian), anbazhagan@

scbt.sastra.edu (A. Veerappan).

Janani Seralathan a, Priscilla Stevenson a, Shankar Subramaniam a, Rachana Raghavan a,Brindha Pemaiah b, Aravind Sivasubramanian a,⇑, Anbazhagan Veerappan a,⇑a Department of Chemistry, School of Chemical and Biotechnology, SASTRA University, Thanjavur, Tamil Nadu, Indiab CARISM, School of Chemical and Biotechnology, SASTRA University, Thanjavur, Tamil Nadu, India

h i g h l i g h t s

� Aqueous extract of the aerial parts ofSalicornia brachiata are efficient inproducing silver nanoparticles.� SbAgNPs shows remarkable catalytic

activity in the reduction of 4-nitrophenol to 4-amino phenol.� SbAgNPs, minimum inhibitory

concentration is lower than thecontrol antibiotic, ciprofloxacin.� SbAgNPs exhibit excellent free radical

scavenging activity.

g r a p h i c a l a b s t r a c t

AgNO3 AgNPs NH2

OH

S brachiata aq. extract S brachiata AgNPs 4-aminophenol

S brachiata

Catalysis

a r t i c l e i n f o

Article history:Received 3 July 2013Accepted 23 August 2013Available online 5 September 2013

Keywords:Green synthesisCatalysisAntioxidantAntibacterialSilver nanoparticlesSalicornia brachiata

a b s t r a c t

Nanosized silver have been widely used in many applications, such as catalysis, photonics, sensors, med-icine etc. Thus, there is an increasing need to develop high-yield, low cost, non-toxic and eco-friendly pro-cedures for the synthesis of nanoparticles. Herein, we report an efficient, green synthesis of silvernanoparticles utilizing the aqueous extract of Salicornia brachiata, a tropical plant of the Chenopodiaceaefamily. Silver nanoparticles have been characterized by ultraviolet–visible spectroscopy, scanning elec-tron microscopy and transmission electron microscopy. The morphology of the particles formed consistsof highly diversified shapes like spherical, rod-like, prism, triangular, pentagonal and hexagonal pattern.However, addition of sodium hydroxide to the extract produces mostly spherical particles. The stablenanoparticles obtained using this green method show remarkable catalytic activity in the reduction of4-nitro phenol to 4-amino phenol. The reduction catalyzed by silver nanoparticles followed the first-order kinetics, with a rate constant of, 0.6 � 10�2 s�1. The bactericidal activity of the synthesized silvernanoparticles against the pathogenic bacteria, Staphylococcus aureus, Staphylococcus aureus E, Bacillus sub-tilis and Escherichia coli, was also explored using REMA. The obtained results showed that the minimuminhibitory concentration required to induce bactericidal effect is lower than the control antibiotic, cipro-floxacin. In addition to these, the biogenic synthesized nanoparticles also exhibited excellent free radicalscavenging activity.

� 2013 Elsevier B.V. All rights reserved.

350 J. Seralathan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 349–355

Introduction

Nanoparticles (NPs) exhibit new and improved physicochemicalproperties, based on size, morphology, distribution and by theirconjugation with other organic/biological substance, when com-pared to their macro scale counterparts. The state of research onthe synthesis and application of nanoparticles is rapidly increasing[1]. Although conventional chemical and physical methods areavailable for synthesizing NPs, they remain expensive and requirethe use of chemical compounds/organic solvents as reducingagents [2]. Thus, there is an increasing need to develop high-yield,low cost, non-toxic and eco-friendly procedures for the synthesisof NPs. As a result, novel biological methods to the synthesis NPshave been proposed by exploiting bacteria, fungus, bio-derivedchemicals and plant extracts [3]. Studies have indicated that bio-molecules like proteins, polyphenols, and flavonoids not only playa role in reducing the ions to the nanosize, but also play an impor-tant role in the capping of NPs. NPs integrated with biological mol-ecules has lead to the development of diagnostic devices, contrastagents, and important tools in cancer therapy [4].

Silver has long been recognized as antimicrobial agent and silvernitrate was directly used for wound healing during World War II[5]. Before the introduction of silver NPs, silver has been used as amain component in the preparation of various creams for treatingwounds [6,7]. However, silver ions have a disadvantage of formingcomplexes with interfering molecules and the effect of the ions re-mained only for a short time. This limitation has been overcome bythe use of the AgNPs, which are in inert form and are highly reac-tive, due to their large surface area and, they also exhibit antimicro-bial function [8]. The AgNPs have also been reported to be nontoxicto humans and are most effective against various bacteria, viruses,and other eukaryotic micro-organisms at very low concentration.More recent advancement in researches on metal nanoparticles,AgNPs has lot of scope in the field of health care products such asburn dressings, scaffolds, water purification systems, antimicrobialapplications and medical devices [8]. Plant extract (leaf, flower,seed, tuber and bark) mediated NPs syntheses are gaining moreinterest in recent years due its eco-friendliness [9]. There have beenrecent reports on the biogenic synthesis of silver nanoparticles byemploying Vinca rosea leaf extract [10], Prosopis juliflora leaf extract[11], Ireasine herbstii leaf aqueous extract [12] as reducing agents.Moreover, use of plant extracts as reducing and capping agentsfor the synthesis of NPs can be advantageous over other environ-mentally benign biological process, because it eliminates the elab-orate process of maintenance which is present in other bio-inspiredprocess. It can also be suitably scaled up for large-scale production.

Life style modification and environmental pollution creates animbalance between pro-oxidants and anti-oxidants inside the cells,leading to the excess production of free radicals in the body. Excessfree radicals have been implicated in the oxidative deterioration offood products and also recognized as a key player in the develop-ment of over 200 different patho-physiologies, ranging from ath-erosclerosis to cancer and inflammatory diseases, diabetes, andaging [13]. A potent scavenger of these fatal free radicals may serveas a possible intervention to treat free radical mediated diseases[14,15]. A number of plant products, such as polyphenolic sub-stance (e.g., flavonoids and tannins) derived from various plantsand herbal extracts are known to exert antioxidant action [16–18]. Recent studies showed that inorganic NPs exert free radicalscavenging activity in in vitro and in vivo systems [19,20]. Herbalextracts have long been used in Indian traditional medicine fortreating diverse pathologic processes including cardiovascular,pulmonary, and neurodegenerative diseases [21,22]. Thus, NPs pre-pared by using such an herbal extract may serve both as bacterici-dal and antioxidant.

In this work, we have investigated the biosynthesis of AgNPsusing the aerial part aqueous extract of Salicornia brachiata. S.brachiata, known as Umari keerai in Tamil language, is a tropicalplant of the Chenopodiaceae family that originated from India. S.brachiata has been used in traditional medicine for the treatmentof itches [23–25]. There are studies showing the presence of phen-olics and flavonoids in S. brachiata. However, there are no reportstill date that documents its potential in nanobiotechnology to syn-thesize nanoparticles and thereby evaluating its chemocatalytic,antioxidant and bactericidal applications. Herein, we report thebiogenic synthesis of AgNPs utilizing the aqueous extract of S.brachiata for the reduction of Ag+ ions. We also explored the bacte-ricidal activity of synthesized silver nanoparticles (SbAgNPS)against the pathogenic bacteria, Staphylococcus aureus, Staphylococ-cus aureus E, Bacillus subtilis and Escherichia coli. Further, we dem-onstrated its chemo-catalytic potential in reduction of 4-nitrophenol (4-NP) to 4- amino phenol (4-AP).

Materials and methods

Collection and processing of plant samples

The aerial parts of S. brachiata were collected from the coast ofBay of Bengal, near Pichavaram, Tamil Nadu, India. A voucher spec-imen was matched with the authentic specimen (herbarium no5555, regional plant resource center, Puri, India) and was depositedin the herbarium.

Preparation of S. brachiata extract

The aerial parts (�1 kg) were shade dried and powdered. 100 gof the powder was percolated with Millipore water and after 24 h,the extract were filtered through a Whatman No. 41 filter paper.The extraction was repeated thrice and the combined extractswere concentrated in vacuo and further lyophilized to obtain a res-idue (35 g).

Synthesis of silver nanoparticles from the aqueous extract of S.brachiata

50 mg of lyophilized aqueous extract of S. brachiata was mixedwith 50 ml of deionized water and filtered through Whatman filterpaper No. 41. 12 ml of the filtrate was added to 42 ml of 0.75 mMAgNO3 solution and the reaction was left to take place at ambientconditions. The observed change in color from colorless to yellowindicated the formation of AgNPs. Under similar conditionsSbAgNPs containing NaOH was prepared by using 50 mg of S.brachiata extract dissolved in 0.5 mM NaOH.

S. brachiata silver nanoparticles (SbAgNPs) characterization

Optical absorbance of synthesized AgNPs was monitored byUV–vis spectrophotometer (Thermo Scientific Evolution 201) be-tween the wavelength 350–800 nm at a resolution of 1 nm.SbAgNPs morphology was characterized by scanning electronmicroscope (SEM) (JEOL-JSM 6701-F, Japan). The samples wereplaced over a carbon tape and dried. Prior to imaging the samplewere coated with a thin layer of platinum in an auto fine coater.The transmission electron micrographs (TEM) were performed onthe SbAgNPs using JEM 1011, JEOL, Japan. A drop of the AgNPswas placed on a carbon coated copper grid and dried prior to themeasurement.

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a

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Fig. 1. Absorption spectra of AgNPs (a) S. brachiata extract, (b) SbAgNPs, and (c)SbAgNPs prepared with 0.5 mM NaOH. Inset corresponds to the photograph of (a) S.brachiata extract, (b) SbAgNPs, and (c) SbAgNPs prepared with 0.5 mM NaOH.

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Chemical analysis of S. brachiata aqueous extract

The aqueous extract of S. brachiata was analyzed by LC/ESI/MSusing Bruker UHPLC 3000 chromatograph coupled to a quadru-pole-ToF mass selective detector (microToF QII, Bruker, Germany).Liquid chromatographic separation of the aqueous extract wasdone using RP C18 column (100 mm � 3.9 mm with internal diam-eter of 5 mm, Acclaim�, Sunnyvale, CA, USA). Gradient elution wasperformed by using a mobile phase A represented by acetonitrileand mobile phase B represented by MilliQ water acidified with ace-tic acid (2%) with the following gradient profile: initially 95% B to80% B over 5 min; to 70% B over 5 min; to 65% B over 5 min; to40% B over 5 min; to 0% B over 5 min; to 95% B over 2.5 min andcontinuing at 95% B until completion of the run. Flow rate wasset to 200 mL/min and UV absorbance was detected at 335 nm.Mass spectra in negative ion mode were generated.

DPPH free radical scavenging assay

The scavenging activity of DPPH free radical by S. brachiataplant extract and SbAgNPs was done according to the method

Fig. 2. TEM images of the silver nanoparticles prepared from Salicornia brachiata aqueous

previously reported [26]. 10 lL of 0.1 mM DPPH (dissolved in eth-anol) was added to different concentration of S. brachiata extractand SbAgNPs. The reaction mixture was shaken and incubated inthe dark for 30 min. The reduction of the DPPH free radical wasmeasured by reading the absorbance at 517 nm. Ascorbic acidwas used as the positive control. The lower absorbance of thereaction mixture indicated a higher percentage of scavengingactivity. The inhibition ratio was calculated from the followingequation:

%inhibition ¼ ½ðcontrol absorbance

� sample absorbanceÞ=control absorbance� � 100

SbAgNPs antibacterial activity

Antibacterial activity of SbAgNPs was tested by standard resa-zurin microtiter (REMA) plate method [27] against the pathogenicbacteria, S. aureus MTCC 96, S. aureus E (MTCC 3160), B. subtilis(MTCC 441) and E. coli (MTCC 723). Briefly, the bacterial specieswere grown in 25 ml LB medium for overnight. Exactly 10 lL ofthe diluted cultures (105 CFU/well) of test organisms were addedto 96-well microtiter plates and the final volume in each wellwas made to 100 lL. SbAgNPs (10 lg/ml) was serially dilutedand added to the 96-well microtiter plates and incubated at30 �C for 24 h. To test for cell viability, 15 lL of a 0.01% (wt/vol)resazurin solution was added to each well. After the incubationperiod of 2 h, the presence of viable microganisms in each well isestimated by microfluorimeter plate reader (FLX-800 fluorimeter,BioTek, Winooski, VT), setting the excitation and emission to530 nm and 590 nm, respectively. Ciprofloxacin was used as con-trol antibacterial drug. All the experiments were done in duplicatesand averages of the MIC are reported.

SbAgNPs catalytic activity

The catalytic activity of SbAgNPs were evaluated using thereduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP).Briefly, 4-NP (3.0 mL of a 0.1 mM solution in water) was mixedwith NaBH4 (14 mM) in the quartz cell, this lead to color changefrom light yellow to yellow-green. After that 200 lL of 0.425 mMSbAgNPs suspension was added to the solution and the absorptionwas spectra were recorded immediately by Thermo scientific Evo-lution 201 UV–vis spectrophotometer. The change in absorption at404 nm was used for kinetic analysis.

extract (A) and salicornia brachiata aqueous extract containing 0.5 mM of NaOH (B).

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Fig. 3. LC–MS profile: (A) liquid chromatography profile of the Salicornia brachiata aqueous extract and (B–D) representative mass spectra pattern obtained at different timeinterval of LC.

352 J. Seralathan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 349–355

Fig. 4. Percent scavenging of DPPH free radicals by (a) ascorbic acid, (b) S. brachiataextract, (c) S. brachiata with NaOH, (d) SbAgNPs, and (e) SbAgNPs prepared withNaOH.

Fig. 5. Representative REMA assay. Antibacterial activity of SbAgNPs againstpathogenic bacteria, Staphylococcus aureus, Row A to H corresponds to decreasingconcentration of S. brachiata extract (Lane 1, 2, 3), SbAgNPs (Lane 4,5,6), Ciproflox-acin (Lane 7,8,9). Lane A11,12 – control, uninoculated medium; Lane B11,12 – negativecontrol, inoculated medium without SbAgNPs; Lane C11,12 – positive control, silvernitrate.

J. Seralathan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 349–355 353

Result and discussion

The color of the freshly prepared aqueous extract obtained fromthe aerial parts of S. brachiata changed, when incubated withAgNO3 solution for 1 day. The appearance of a yellow color indi-cated the reduction of silver ion (Ag+) to metallic silver (Ag0) nano-particles (AgNPs). The extract without AgNO3 did not show anychange in color. The absorption spectrum of AgNPs suspension pre-pared by this method showed a characteristic plasmon resonancepeak at 404 nm with a shoulder at 500 nm. It is well known thatthe position and shape of the AgNPs surface plasmon peak dependson particle size, shape and dielectric constant of the surroundingmedium [28]. Thus, the observed absorbance spectra in this study,indicates the existence of polydisperse AgNPs in the suspension.The AgNO3 solution incubated with sodium hydroxide containingextract produced a dark yellow color suspension, within an hour,indicating the formation of AgNPs. The absorption spectrum ofSbAgNPs suspension prepared by this method also showed a broadsingle peak with center at 402 nm, indicating the presence of wellcapped stable AgNPs (Fig. 1). The complete elimination of the peakat 500 nm presumably indicates the change in the polydispersity ofthe nanoparticles. It was found that the color and UV–VIS

absorption peak of the biosynthesized SbAgNPs does not changeeven after a month, indicating well dispersed stable nanoparticlesin the solution.

SEM analyses were carried to understand the topology and sizeof the nanoparticles, and the size for the synthesized polydispersenanoparticles was found in the 30–40 nm range (Fig. S1). Nanopar-ticles prepared in the presence of NaOH also showed polydispersenanoparticles with a size distribution range in 28–33 nm, aug-menting the observed UV–vis spectral characteristics of the AgNPs.It is visible from the TEM images that the SbAgNPs synthesized bythis green method contains highly diversified shapes like spherical,rod-like, prism, triangular, pentagonal and hexagonal pattern(Fig. 2A, Fig. S1). Presence of these features may be attributed tothe stabilization of AgNPs by diverse range of chemical constitu-ents present in the S. brachiata extract. Interestingly, AgNPs pre-pared with extract containing 0.5 mM of NaOH shows mostlyspherical morphology with particle size range from 25 to 35 nm(Fig. 2B, Fig. S2). The obtained spherical shape SbAgNPs may beresponsible to the observed single broad peak in the UV–Vis spec-tra (Fig. 1). At the same time, UV spectral characteristics of AgNPsprepared directly from the aqueous extract was not affected byadding NaOH to the preformed SbAgNPs (data not shown). Thisindicates that initial nucleation is the prerequisite factor for form-ing diversified shapes.

Phytochemical screening of S. brachiata aqueous extract showsstrong evidence for the presence of phenols, flavonoids, carbohy-drates, proteins and salts [23]. To analyze for its chemical constit-uents, the S. brachiata aqueous extract was subjected to a LC–MSanalysis. As expected for a plant extract, many peaks were presentin the liquid chromatogram and the corresponding mass profiles,indicated a set pattern (Fig. 3). Mass spectra showed a complexmass pattern with higher molecular weight components. In mostcompounds, a base peak of 241 was found. This can be inferredfor the presence of a possible glycoside phosphate residue [29].The genus Salicornia is known to contain quinic acid and phenylpropanoid containing secondary metabolites [30]. The presenceof polyphenols in S. brachiata extract was confirmed by Folin–Cio-calteau method. Thus the higher molecular weight componentsmay be derivatives of quinic acids and polyphenols. Since phenolicacids with one or more phenolic hydroxyl groups are able to do-nate electrons [31], it can be postulated that the polyphenols andglycoside phosphates present in the S. brachiata aqueous extractmay play an important role in reducing Ag+ to AgNPs and alsoact as a capping agent.

In order to test the antioxidant potential of the SbAgNPs, freeradical scavenging activity of S. brachiata aqueous extract andSbAgNPs was assessed by DPPH assay. As shown in Fig. 4, both S.brachiata aqueous extract and SbAgNPs demonstrated a significantinhibitory activity against the DPPH radical, indicating a source forantioxidants. Free radical scavenging activity of SbAgNPs wasfound to increase in a dose-dependent manner. When comparedto standard ascorbic acid, SbAgNPs shows stronger antioxidantactivity. More importantly, SbAgNPs exhibit higher antioxidantactivity with more than 60% scavenging activity of DPPH. It is alsonoteworthy that SbAgNPs shows higher effectiveness than S.brachiata aqueous extract at all the tested concentrations. It is anobvious indication that the resulting activity of the SbAgNPs isnot only due to the capping agents (chemical constituents presentin the extract), but it is enhanced due to the elemental silver.

AgNPs are very well known for its antibacterial activity againstmany gram positive and gram negative bacteria. However theselectivity for different bacterial strains differs due to the presenceof capping agents and stabilizers used in the preparation of AgNPs.In this study, the antibacterial activity of SbAgNPs and ciprofloxa-cin was tested by resazurin microtiter assay against pathogenicbacteria, S. aureus, S. aureus E, B. subtilis and E. coli. Resazurin assay

Fig. 6. (A) Time-dependent UV–vis absorption spectra over the full time of reduction of 4-NP with NaBH4 catalyzed by SbAgNPs. The time between the consecutive curves is3 min. Nitrophenolate ion peak at 404 nm decreases as reaction time proceeds, whereas a second peak at 293 nm, referring to the product 4-aminophenol, slowly increases(see arrows). (B) Plot of ln(Ct/C0) versus reaction time. The reaction starts after an induction period t0, the line corresponds to the linear section, from which k was determined.(s) 4-NP with NaBH4 and catalytic amount of SbAgNPs, and (d) 4-NP with NaBH4, control.

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is a simple method used to detect viable cells in the medium. Thebacterial species were grown on a microtitre plate for 24 h in pres-ence of increasing concentration of SbAgNPs. Addition of resazurinto the control well shows fluorescent pink color indicating thepresence of viable cells in the medium. However with increasingconcentration of SbAgNPs, pink color turns to non-fluorescent bluecolor, indicating the decrease in the amount of viable cells in themedium (Fig. 5). Minimum inhibitor concentrations (MIC) werecalculated from the change in fluorescence with respect to concen-tration of SbAgNPs. The obtained result showed that MIC concen-tration of the pathogenic bacteria, S. aureus, S. aureus E, B. subtilisand E. coli are 1.0, 7.5, 0.45 and 0.6 lg/ml, respectively. Ciproflox-acin, which was used as a positive control, showed antibacterialactivity against S. aureus, S. aureus E, B. subtilis and E. coli. TheMIC for ciprofloxacin estimated as 2.5, 15.6, 2.5 and 1.6 lg/ml,respectively- is higher than the values for SbAgNPs. AlthoughSbAgNPs itself can serve as a better antimicrobial agent against hu-man pathogens, the combination of AgNPs with available antibiot-ics may facilitate speedy recovery from the bacterial infections.

Further, we have evaluated the catalytic activity of SbAgNPsusing a standard model reaction: the reduction of 4-nitrophenol(4-NP) by NaBH4[32]. Addition of NaBH4 to 4-NP shifts the absorp-tion peak, from 317 nm to 400 nm, due to the formation of 4-nitro-phenolate ion. Also, the color of the 4-NP changed from lightyellow to yellow-green. The addition of 50 lL of an aqueous sus-pension of SbAgNPs to 4-nitrophenolate ion gradually diminishedthe yellow color of the reaction mixture in a time dependent man-ner. As shown in Fig. 6A, the 4-NP absorption peak at 404 nm de-creases and a new absorption peak due to the formation of 4-aminophenol (4-AP) appears at 293 nm. Two isosbestic points arevisible at 312 nm and 280 nm, inferring that only one product isformed during this reaction. In absence of SbAgNPs or in the pres-ence of Sb extract, the peak at 404 nm remains undisturbed. Thus,it is clear that a catalytic amount of SbAgNPs is a prerequisite factorin the reduction of 4-NP by NaBH4.

In order to follow the kinetics of the reduction reaction, timedependent change in the intensity of absorption at 400 nm wasmonitored using UV–vis spectrophotometer. Before the catalyticreduction of 4-NP, an induction time up to 140 s was observed(Fig. 6B). This induction period is typical for a heterogeneouscatalytic process and commonly related to an activation or

restructuring of the metal surface by 4-NP before the reactioncould start [32]. After an induction time t0 in which no reductiontakes, the reaction starts and completed within 5 min, as evidencedby a fading of the yellow green color of the reaction solution. Sincethe concentration of NaBH4 was much higher than that of 4-NP, thereduction kinetics can be described by first-order rate law withregard to 4-NP alone. Therefore, the reaction kinetics can be de-scribed as ln(Ct/C0) = �kt, where k is the apparent first-order rateconstant, t is the reaction time. Ct and C0 are the concentrationsof 4-NP at time t and 0, respectively. As shown in Fig. 6B, the linearrelation between ln(Ct/C0) versus reaction time (t) was observedafter the induction period (t0) and the reduction catalyzed bySbAgNPs follows the first-order kinetics. The rate constant, k(0.6 � 10�2 s�1) was obtained directly from the slope of the linearpart of the kinetic trace. The obtained rate constant is comparableto that of substrate-supported metallic nanoparticles in the litera-ture [32].

Conclusion

Nanosize metals have brought a new revolution to the modernera of science; particularly silver and gold nanoparticles have beenexploited in various fields of chemistry, physics, biology andmedicine. In this work, we conclude that the aqueous extract ofthe aerial parts of S. brachiata are capable of producing silver nano-particles. The biosynthesized SbAgNPs showed excellent stabilityfor 3 months from the date of synthesis. This clearly suggests thatour eco-friendly procedure is an alternative to chemical synthesisprotocols, with scope for low cost scale up for the production ofAgNPs. The free radical scavenging and antibacterial activity ofthe newly synthesized SbAgNPs opens the door for a new rangeof antibacterial and antioxidant agents. The green chemistry ap-proach of reducing 4-NP to 4-AP using SbAgNPs might be usefulfor the development of novel nanocatalyst.

Acknowledgement

The authors are very grateful to the Management, SASTRAUniversity, Tamil Nadu, India for providing the necessary facilities.VA acknowledges the financial support through the Prof. T.R.

J. Seralathan et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 349–355 355

Rajagopalan research fund and the Department of Science andTechnology, Government of India (SB/FT/LS-217/2012). SA ear-nestly acknowledges the funding source from Department of Sci-ence and Technology, Government of India (SR/FT/CS-10/2011).

Appendix A. Supplementary material

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.saa.2013.08.114.

References

[1] P.K. Jain, X. Huang, I.H. El-Sayed, M.A. El-Sayed, Acc. Chem. Res. 411 (2008)1578–1586.

[2] M. Chen, Y.G. Feng, X. Wang, T.C. Li, J.Y. Zhang, D.J. Qian, Langmuir 23 (2007)5296–5304.

[3] L. Sintubin, W. Verstraete, N. Boon, Biotechnol. Bioeng. 109 (2012) 2422–2436.[4] E. Boisselier, D. Astruc, Chem. Soc. Rev. 38 (2009) 1759–1782.[5] E.A. Deitch, A. Marin, V. Malakanov, J.A. Albright, J. Trauma 27 (1987) 301–304.[6] L.J. Wilkinson, R.J. White, J.K. Chipman, J. Wound Care 20 (2011) 543–549.[7] Z. Aziz, S.F. Abu, N.J. Chong, Burns 38 (2012) 307–318.[8] C. You, C. Han, X. Wang, Y. Zheng, Q. Li, X. Hu, H. Sun, Mol. Biol. Rep. 39 (2012)

9193–9201.[9] O.V. Kharissova, H.V. Dias, B.I. Kharisov, B.O. Pérez, V.M. Pérez, Trends

Biotechnol. 31 (2013) 240–248.[10] V.S. Kotakadi, Y.S. Rao, S.A. Gaddam, T.N. Prasad, A.V. Reddy, D.V. Gopal,

Colloids Surf. B 105 (2013) 194–198.[11] K. Raja, A. Sarnakumar, R. Vijayakumar, Spectrochim. Acta A 97 (2012) 490–

494.[12] C. Dipankar, S. Murugan, Colloids Surf. B 98 (2012) 112–119.[13] J.T. Coyle, P. Puttfarcken, Science 262 (1993) 689–695.

[14] M. Valko, D. Leibfritz, J. Moncol, M.T. Cronin, M. Mazur, J. Telser, Int. J. Biochem.Cell Biol. 39 (2007) 44–84.

[15] O. Firuzi, R. Miri, M. Tavakkoli, L. Saso, Curr. Med. Chem. 18 (2011) 3871–3888.[16] G. Agati, E. Azzarello, S. Pollastri, M. Tattini, Plant Sci. 196 (2012) 67–76.[17] F. Dajas, J. Ethnopharmacol. 143 (2012) 383–396.[18] S.M. Nabavi, S.F. Nabavi, W.N. Setzer, H. Alinezhad, M. Zare, A. Naqinezhad, J.

Diet Suppl. 9 (2012) 285–292.[19] C.H. Ramamurthy, M. Padma, I.D. Samadanam, R. Mareeswaran, A. Suyavaran,

M.S. Kumar, K. Premkumar, C. Thirunavukkarasu, Colloids Surf. B 102 (2013)808–815.

[20] L. Du, S. Suo, G. Wang, H. Jia, K.J. Liu, B. Zhao, Y. Liu, Chemistry 19 (2013) 1281–1287.

[21] H.R. Vasanthi, S. Mukherjee, I. Lekli, D. Ray, G. Veeraraghavan, D.K. Das, J.Cardiovasc. Pharmacol. 53 (2009) 499–506.

[22] S. Mutheeswaran, P. Pandikumar, M. Chellappandian, S. Ignacimuthu, J.Ethnopharmacol. 137 (2011) 523–533.

[23] K.C. Ravindran, K. Venkatesan, V. Balakrishnan, K.P. Chellappan,Balasubramanian, Indian J. Traditional Knowledge 4 (2005) 409–411.

[24] M. Chandrasekaran, K. Kannathasan, V. Venkatesalu, Z. Naturforsch C 63(2008) 331–336.

[25] T. Manikandan, T. Neelakandan, U.G. Rani, J. Phytol. 1 (2009) 441–443.[26] M.A. Gyamfi, M. Yonamine, Y. Aniya, Gen. Pharmacol. 32 (1999) 661–667.[27] J.C. Palomino, A. Martin, M. Camacho, H. Guerra, J. Swings, F. Portaels,

Antimicrob. Agents Chemother. 46 (2002) 2720–2722.[28] E. Kelly, L. Coronado, L. Zhao, G.C. Schatz, J. Phys. Chem. B 107 (2003) 668–677.[29] C. Antonio, T. Larson, A. Gilday, I. Graham, E. Bergström, J. Thomas-Oates, J.

Chromatogr. A 1172 (2007) 170–178.[30] Y.C. Chung, H.K. Chun, J.Y. Yang, J.Y. Kim, E.H. Han, Y.H. Kho, H.G. Jeong, Arch.

Pharm. Res. 28 (2005) 1122–1126.[31] J.A. Jacob, H.S. Mahal, N. Biswas, T. Mukherjee, S. Kapoor, Langmuir 24 (2008)

528–533.[32] P. Hervés, M. Pérez-Lorenzo, L.M. Liz-Marzán, J. Dzubiella, Y. Lu, M. Ballauff,

Chem. Soc. Rev. 41 (2012) 5577–5587.