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Synthesis of Stable, Polyshaped Silver, and GoldNanoparticles Using Leaf Extract of Lonicera japonicaL.Vineet Kumar a & Sudesh Kumar Yadav aa Biotechnology Division , CSIR-Institute of Himalayan Bioresource Technology , Palampur,IndiaPublished online: 16 Dec 2011.

To cite this article: Vineet Kumar & Sudesh Kumar Yadav (2011) Synthesis of Stable, Polyshaped Silver, and GoldNanoparticles Using Leaf Extract of Lonicera japonica L., International Journal of Green Nanotechnology, 3:4, 281-291, DOI:10.1080/19430892.2011.633474

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International Journal of Green Nanotechnology, 3:281–291, 2011Copyright c© Taylor & Francis Group, LLCISSN: 1943-0892 print / 1943-0906 onlineDOI: 10.1080/19430892.2011.633474

PHYSICS AND CHEMISTRY

Synthesis of Stable, Polyshaped Silver, and GoldNanoparticles Using Leaf Extract of Lonicera japonica L.

Vineet KumarSudesh Kumar Yadav

ABSTRACT. Silver nanoparticles and gold nanoparticles of various shapes and sizes have applicationsin medicine, biosensing, and catalysis. Plant-mediated synthesis is preferred due to ecofriendly natureand enhanced quality of the synthesized nanoparticles. As Lonicera japonica plant has several medicinalproperties, we explored it here for the first time in the synthesis of silver nanoparticles and goldnanoparticles. Capping of synthesized nanoparticles was found with medicinally important moleculespresent in the leaf extract of this plant and these molecules could enhance their value for variousapplications. UV-visible, scanning electron microscope, transmission electron microscope, atomic forcemicroscope, zeta particle size analyzer, and Fourier transform infra-red spectroscopy has been used forthe characterization of both nanoparticles. The leaf extract of L. japonica was found to direct differentsized and shaped silver nanoparticles and gold nanoparticles. Silver nanoparticles were 36–72 nm insize and their shape varied from spherical to a few plate-like polyshaped. While gold nanoparticlessynthesized were polyshaped nanoplates of 40–92 nm in size. Fourier transform infra-red spectroscopyanalysis revealed that carbohydrate, polyphenols, and protein molecules were involved in the synthesisand capping of silver nanoparticles and gold nanoparticles.

Received 27 September 2011; accepted 4 October 2011.The Director of the CSIR-IHBT is duly acknowledged for his continuous guidance and encouragement.

The authors are thankful to the Council of Scientific and Industrial Research (CSIR), the Government ofIndia for financial support. V. Kumar would like to thank CSIR for providing fellowship as Senior ResearchFellow.

V. Kumar and S. K. Yadav are affiliated with the Biotechnology Division, CSIR-Institute of HimalayanBioresource Technology, Palampur, India.

Address correspondence to Sudesh Kumar Yadav, Biotechnology Division, CSIR-Institute of Hi-malayan Bioresource Technology, Palampur-176061 (HP), India. E-mail: skyt@rediffmail.com or sudeshku-mar@ihbt.res.in

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282 V. Kumar and S. K. Yadav

KEYWORDS. Lonicera japonica, silver nanoparticles, gold nanoparticles, polyshaped

INTRODUCTION

There has been immense development in nan-otechnology in the past few years. Each applica-tion requires nanoparticles (NPs) of desired size,shape, stability, and polydispersity. Biological orgreen synthesis based protocols have been con-sidered as a better option for non-toxic metal-lic NPs synthesis.[1–3] Due to the wide rangeof applications, syntheses of silver nanoparti-cles (SNP) and gold nanoparticles (GNP) ofdifferent morphology have been of great in-terest. SNP have applications in antimicrobialointments/creams,[4] catalysis,[5] label-free col-orimetric assay,[6] biological imaging,[7] medi-cal diagnostics, and therapeutics[7–9] to name afew. GNP have applications in bio-sensing,[10,11]

catalysis,[12,2] diagnostic, therapeutic, and drugdelivery.[13–17]

Polyshaped nanoparticles, due to shape vari-ability, can infiltrate cells easily. As a result,these NPs can be used as more effective deliv-ery agents in comparison to uniformly shapedNPs. A variety of differently shaped nanoplatesare useful for optical and electronic applications.Nanoparticles synthesized by chemical methodsare generally spherical.[18–20] Synthesis of dif-ferently shaped nanoplates by a chemical pro-cess is complex; whereas biological methods foranisotropic growth of different crystal planesare simple. Plants are useful tools to vary thesize and shape of NPs. The exact mechanismfor shape-control of SNP and GNP by biolog-ical means is not clear at this time; the optionof achieving NPs of different shapes by usingdifferent plant leaf extracts (LE) is a better al-ternate. The size and shape of NPs have beenreported to vary with plant type.[2,21–23] Here,for the first time we have explored L. japon-ica LE for synthesis of various size and shapedSNPs and GNPs. This plant has good medicinalvalue;[24,25] therefore, we believe that the cap-ping of NPs synthesized with such content willincrease their quality and broaden their applica-tions.

EXPERIMENTAL

Materials

The AgNO3 and HAuCl4 were purchasedfrom Sigma-Aldrich, USA. All other chemi-cals used in the study were of analytical grade.Lonicera japonica leaves were collected fromthe campus of CSIR-IHBT, Palampur (HP), In-dia.

Synthesis of SNP and GNP

L. japonica LE was prepared as described inour previous study with minor modifications.[26]

Briefly fresh L. japonica leaves were thoroughlywashed, dried, and ground to make a fine powder.Four grams of dry leaf powder were suspendedin deionized Milli-Q water, vigorously vortexed,and incubated at room temperature. This suspen-sion was centrifuged and used for further study.The 1.0 mM aqueous AgNO3 and HAuCl4 solu-tions were incubated with 10% (v/v) of LE sep-arately at room temperature for SNP and GNPsynthesis, respectively. The absorption spectrafor each reaction mixture were recorded between300 to 700 nm on an ND 1000 Nanodrop. Twomicroliters of solution were evaluated for NPsynthesis at various time intervals. The NPs’reaction suspension was centrifuged at 10,000rpm for 5 min to purify the NPs. These NPswere washed thrice with water and stored aslyophilized powder.

Characterization of SNP and GNP

Purified NPs were characterized for theirmorphology using a Hitachi S-3400N Scanningelectron microscope (SEM), a FEI Techni G2 200KV Transmission electron microscope (TEM),and a Veeco diNanoscope 3D Atomic force mi-croscope (AFM). For SEM analysis, NP solutionwas placed on carbon tape for SEM imaging.The samples were dried at room temperatureand images were captured on SEM mode atdesired magnification. For AFM analysis, NP

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SNP and GNP Synthesis by L. japonica 283

FIGURE 1. Synthesis and characterization of SNP and GNP. (a) UV-visible absorption spectraof SNP at different time intervals; (b) AFM and (c) TEM image of SNP; (d) UV-visible absorptionspectra of GNP at different time intervals; (e) AFM and (f) TEM image of GNP. (Color figure availableonline.)

suspension was spread on a glass coveredslip mounted on an AFM stub. Samples weredried at room temperature and images wereobtained in tapping mode using a silicon probecantilever. Three images for each sample wereobtained with AFM. For transmission electronmicroscope (TEM) analysis, NP suspensionwas mounted on carbon-coated copper TEMgrids. One drop of NP suspension was pipettedonto a grid and extra suspension was removedusing a clean blotting paper. The grids weredried completely prior to measurement. Thesize and zeta potential of NPs were measured bythe electrophoretic mobility of SNP and GNP at25◦C, using a Zeta particle size analyzer (NanoZS, Malvern).

Effect of Physiochemical Factors on SNPand GNP Synthesis

To see the effect of physiochemical factors onSNP and GNP synthesis, 1–9 mM AgNO3 and

HAuCl4 were incubated with 10% L. japonicaLE at room temperature. Effect of incubationtemperature on NPs synthesis was checked byincubating 1 mM metal ion with 10% LE at 40,60, and 80◦C. Effect of LE ratio was carriedout by incubating 1 mM respective metal ionwith 5, 10, 20, and 40% LE. NP synthesis wasconfirmed by UV-visible spectroscopy. Detailedmorphology characterization was carried out byusing SEM and AFM as detailed in the previoussection.

FTIR Analysis of NPs

Well washed and powdered NP samples weresubjected to Fourier transform infrared (FTIR)on a Thermo Nicolet 6700 FTIR spectroscope(Thermo, USA). To obtain good signal to noiseratio, 256 scans of NPs were taken in the range400–4000 cm−1 and the resolution was keptas 4.0 cm−1. FTIR spectra of NPs samples

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284 V. Kumar and S. K. Yadav

FIGURE 2. Chemical composition analysis of synthesized NPs. (a) Energy dispersive X-ray spec-trometer (EDAX) spectrum of SNP; (b) EDAX spectrum of GNP. (Color figure available online.)

embedded in KBr pellets were recorded to iden-tify NP associated molecules.

RESULTS AND DISCUSSION

Plants are known to direct the synthesis ofvarious metallic nanoparticles (NPs) includingGNPs and SNPs. Size and shape of NPs de-pend on type of metal ions used and moleculespresent in the plant tissue extract. L. japon-ica has shown good potential for SNP as wellas GNP synthesis. 1 mM metal ion has been

used mostly in plant extract mediated synthesisof metallic NPs.[2,23,26–29] In this, we also havefound 1 mM metal ion suitable for SNP and GNPsynthesis.

Characterization of SNP and GNPSynthesized by L. japonica LE

With an increase in reaction time, there wasan increase in peak intensity near 450 nm,indicating quantitative increase in NP synthesis.Most of SNP synthesis was completed in 24 h(Figure 1a). Analysis by SEM, TEM, and AFM

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SNP and GNP Synthesis by L. japonica 285

FIGURE 3. Effect of metal ion concentration on NPs synthesis. (a) UV-visible absorption spectraof SNP; (b) bar diagram showing size of SNP; (c) UV-visible absorption spectra of GNP; (d) bardiagram showing size of GNP. (Color figure available online.)

revealed synthesis of 36 nm SNP (Figure 1b, c).GNP synthesis was completed in less time (4h) as compared to SNP synthesis (Figure 1d).Most of GNP synthesis was completed in 1 h.This may be due to a difference in reductionpotential of metal ions (AgNO3 and HAuCl4)used for NP synthesis in this study. Furtherreaction time had an effect on the size of GNP.Size of GNP increased from 40 nm at 1 h ofreaction (data not shown) to 62 nm after 4 h ofreaction (Figure 1e, f).

Strong signals of Ag (Figure 2a) and Au(Figure 2b) in the energy dispersive X-rayspectrometer (EDAX) spectra revealed thatthe NPs were of silver and gold, respectively.Some weak signals in spectra were due to atomsof molecules attached to the NPs’ surface.Common Cu peaks were due to grids used for

TEM analysis.[30] Zeta particle size analysisrevealed that synthesized SNP and GNP were 54and 85 nm in size, respectively (data not shown).Such a difference in the size of NPs characterizedwith AFM and zeta particle size analyzer hasalso been observed earlier.[31] The zeta potentialof SNP and GNPs were -41 and -35, respectively(data not shown). These values indicated goodstability of both the synthesized NPs.[32]

Effect of Physiochemical Factors on SNPand GNP Synthesis

Effect of Metal Ion Concentration

As we increased metal ion concentration,there was a quantitative increase in SNP syn-thesis with incubation time (Figure 3a). All

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FIGURE 4. Effect of incubation temperature on NPs synthesis. (a) UV-visible absorption spectraof SNP; (b) bar diagram showing size of SNP; (c) UV-visible absorption spectra of GNP; (d) bardiagram showing size of GNP. (Color figure available online.)

concentrations from 1–9 mM led to synthesisof stable NPs. Most of synthesis was over in 24h. AFM analysis revealed an increase in the sizeof NPs with metal ion in a concentration de-pendent manner. SNPs’ size was increased from36 nm (1 mM AgNO3) to 71 nm (9 mM AgNO3)(Figure 3b). This may be due to the fact thatwith increasing metal ion concentration, thereis a quantitative increase in NPs with time (Fig-ure 3a). As incubation time increased, preformedNPs may be interacting with newly formed NPs.Availability of more metal ions in the reactionseems to provide newly formed NPs which con-tinuously lead to increases in their size (Figure3b).

GNP synthesized by 1mM concentration ofmetal ions was stable and 62 nm in size (Fig-ure 2c, d). Increase in metal ion up to 3 mM

led to NP synthesis. Higher 5–9 mM metal iondid not form GNP at 10% LE ratio (Figure 3c),whereas, GNPs synthesized with 3 mM metalion were 92 nm in size with induction of aggre-gation (Figure 3c, d). This could be due to animbalance in the ratio of metal ion and LE. Forstable NP synthesis, a mixing of the reducingagents, stabilizer, and metal ions in an appropri-ate ratio is necessary.[2,23,28]

Effect of Incubation Temperature

Incubation temperature has been reportedearlier to influence both SNP and GNP syn-thesis.[26,27] As incubation temperature was in-creased, quantitative increase in SNP was ob-served (Figure 4a). Size of SNP increased withincrease in incubation temperature from 41 nm

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SNP and GNP Synthesis by L. japonica 287

FIGURE 5. Effect of LE ratio on NP synthesis. (a) UV-visible absorption spectra of SNP; (b) bardiagram showing size of SNP; (c) UV-visible absorption spectra of GNP; (d) bar diagram showingsize of GNP. (Color figure available online.)

(40◦C) to 72 nm (80◦C) as shown in Figure 4b.Similarly, with an increase in incubation temper-ature, there was a quantitative increase in GNPsynthesis (Figure 4c). A slight increase was ob-served in the size of the GNP with an increase inthe incubation temperature. The GNPs size wasincreased from 62 to 64 nm with an increase intemperature from 40 to 80◦C (Figure 4d). This isin agreement with our earlier study.[26] However,some studies have shown a decrease in size withincubation temperature.[20,27]

Effect of LE Ratio

LE contains all the necessary molecules forsynthesis and stabilization of SNP as well asGNP. As L. japonica LE ratio was varied from10% either decreased or increased, there was an

increase in SNP size (Figure 5a, b). Aggregationwas induced at 5% and 40% LE ratio (Figure 5a,b). Some aggregation was visible at the bottomof reaction tubes. These particles were removedby centrifugation at 5000 rpm for 1 min beforecharacterization. SNP size decreased from 71nm at 5% LE to 36 nm at 10% LF. Increasesin LE ratio up to 40% lead to increases in sizeup to 66 nm. Increased interaction of cappingagent bound on the surface of NPs could be re-sponsible for the increase in their size.[26,27] Astudy involving tannic acid as a complete reduc-ing and capping agent has shown that an excessof active molecules (reducing/capping agents) inreaction medium decreases the rate of reactionafter a certain limit. At conditions when metalions are limited, and LE active molecules aremore, these molecules bind to newly nucleated

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288 V. Kumar and S. K. Yadav

FIGURE 6. FTIR spectrum of L. japonica LE synthesized NPs: (a) SNP and (b) GNP. (Color figureavailable online.)

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products leading to a slowdown in the rate ofreaction. The rate of reaction is decided by in-cidence of collision/proximity of such products.The delay in reaction rate is mainly responsiblefor an increase in NPs’ size.[33]

In the case of GNP, there was a quantitativeincrease in synthesis up to 20% LE ratio. Fur-ther increase in LE ratio to 40% led to GNPaggregation and, thereafter, stopped GNP syn-thesis. Lower (5%) LE ratio led to quantitativelyless GNP synthesis. Size was decreased with in-crease in LE% ratio from 75 nm at 5% to 54 nmto 20% (Figure 5c, d). This is in agreement with

an earlier study on GNP and could be due to anexcess of capping agents during synthesis, whichupon interaction causes aggregation.[20] This re-veals that the proportion of LE is a crucial factorand needs to be provided in an appropriate ratiofor stable NP synthesis.

Identification of Molecules Involved inSynthesis of SNP and GNP

FTIR has been used for identification ofmolecules involved in the synthesis and cap-ping of metallic NPs.[26,28,29] Type of molecules

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SNP and GNP Synthesis by L. japonica 289

surrounding NPs determine their toxicity behav-ior, and this information can help in further func-tionalization with other molecules for variousapplications.[34] Powdered NPs were mixed inKBr to make pellets. FTIR spectra of SNP andGNP synthesized by incubating 1 mM of respec-tive metal ions with 10% LE were recorded andshown in Figure 6a, b, respectively.

Peaks at 3415; 2903; 1644; 1430; 1376;1319–1337; 1164; 1060; 898; and 464–777cm−1 in IR spectra of SNP correspond tothe O-H group in polyphenols or proteins orpolysaccharide components;[35,36,20] characteris-tic stretching vibrations of methyl groups oraldehydic C-H stretching;[35] amide I groupof proteins;[3] symmetric stretching vibrationsof -COO- groups of amino acid residuesin the protein;[3] geminal methyl group;[28]

OH deformation vibrations in the aromaticring/phenol;[37,38] C-O/C-OH single bond in al-cohals;[36,39] antisymmetric stretching band ofC-O-C groups of polysaccharides and/or chloro-phyll or CN stretching aliphatic amine or al-cohol/phenols;[35,40] carbohydrate or polyphe-nols;[41,20] and α-glucopyranose ring deforma-tion of carbohydrates,[42] respectively.

While peaks observed in FTIR spectrumfor GNP at 3385–3446; 2957; 2921; 1741;1634; 1542; 1432; 1376; 1257; 1110–1162;1055; 1025; 803–899; 669; and 470–622 cm−1

corresponds to O-H group in polyphenolsor proteins/enzymes or polysaccharide;[35,36,20]

stretching vibrations of methyl groups;[35] sec-ondary amines;[20] carbonyl groups;[20] amideI;[20] stretching vibration of N–H groups inamide II bands, in the proteins;[35] stretchingvibrations of -COO- (carboxylate ion) groupsin the protein;[3] OH deformation vibrationsin the aromatic ring/phenol;[37,38] amide III;[20]

C-O/C-OH single bond in alcohols/phenolicgroups;[36,39] antisymmetric stretching band ofC-O-C groups of polysaccharides and/or chloro-phyll;[35] C-N stretching vibration of aliphaticamines or to alcohols/phenols;[20] carbohydrateor polyphenols;[20,41] plane bending vibrationof N-H groups in the proteins;[35] and α-glucopyranose ring deformation of carbohy-drates,[42] respectively.

These interpretations revealed that NPs syn-thesized using the L. japonica leaf extract were

capped by proteins, carbohydrates, and polyphe-nols in particular. These molecules were in-volved in stabilization and synthesis of SNP andGNP. Surface covering is one of the critical fac-tors in toxicity determination of NPs and theirfuture applications.[34]

CONCLUSIONS

We concluded that medicinally important LEof L. japonica act as reducing, capping, andvalue adding agent for SNP and GNP synthe-sis. This method is environmentally friendly andoffers medicinal value to NPs. Size of NPs isan important factor along with surface coveringin determining toxicity of NPs synthesized. Var-ious sized SNP (36–72 nm) and GNP (40–92nm) were obtained by simply varying physio-chemical factors. These polyshaped NPs can beespecially useful for targeted delivery as wellas in optical and electronic applications, as pro-teins, carbohydrates, and polyphenols are majormedicinally important components in this plant.Capping of SNP and GNP by these componentswill definitely enhance their quality. Therefore,these NPs can be very useful for applicationsin products that come in direct human con-tact such as cosmetics, foods/nutraceuticals, andmedicine.

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