Colloids and Surfaces B: Biointerfaces 102 (2013) 578– 584
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Colloids and Surfaces B: Biointerfaces
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tarch-directed green synthesis, characterization and morphology of silveranoparticles
aheer Khana,∗, Taruna Singha, Javed Ijaz Hussaina, Abdullah Yousif Obaidb,haeel Ahmed AL-Thabaitib, E.H. El-Mossalamyb
Nanoscience Research Laboratory, Department of Chemistry, Jamia Millia Islamia (Central University), New Delhi 110025, IndiaDepartment of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah 21413, Saudi Arabia
r t i c l e i n f o
rticle history:eceived 26 June 2012eceived in revised form 30 August 2012ccepted 31 August 2012vailable online 6 September 2012
a b s t r a c t
Silver nanoparticles were prepared by a simple chemical reduction method using ascorbic acid and starchas reducing and stabilizing agents, respectively. The effect of starch, silver ions and ascorbic acid wasstudied on the morphology of the silver nano-particles using UV–visible spectrophotometry. The initialreaction time min and amount of starch were important parameters for the growth of Ag-nanoparticles.
The morphology was evaluated from transmission electron microscopy (TEM). The truncated trianglenano-plates (from 17 to 30 nm), polyhedron, spherical with some irregular shaped Ag-nanoparticles wereformed in presence of starch. Particles are aggregated in an irregular manner, leads to the formation ofbutterfly-like structures of silver. Starch acts as a stabilizing, shape-directing and capping agent duringthe growth processes. Silver nanoparticles adsorbed electrostatically on the outer OH groups of amyloseleft-handed helical conformation in solution.
Noble metal nanoparticles such as silver and gold have pre-iously been modified with numerous stabilizing and cappinggents for various applications [1]. Generally, a large numberf stabilizers, namely, surfactants, proteins, peptides, polymers,ligonucleotides, carbohydrates, plants extract and organic sol-ents have been used to obtain the desired shape nano-materialsf silver and gold [2]. Out of these, some stabilizers control and/orirect the growth of nanoparticles. Raveendran and his coworkerssed starch (polysaccharide and natural polymer) as a cappinggent to the preparation of starch-stabilized silver nanoparticlesor the first time [3a] and suggested that the extensive network ofydrogen bonds in the templates provides surface passivation orrotection against nanoparticle aggregation [3b]. The presence oftarch in the reaction mixture avoids use of relatively toxic organicolvents [4]. Huang and Yang developed a simple green method forhe synthesis of gold and silver nanoparticles by using polysaccha-
ides (chitosan and heparin) as reducing/stabilizing agents [5]. Theositively and negatively charged gold and silver nanoparticlesere characterized with UV–vis spectroscopy and transmission
electron microscopy. Morphology strongly depends on the heparinconcentration which acts as a nucleation controller and stabi-lizer. Huang et al. [6] also used chitosan to stabilize the silvernanoparticles.
Esumi and his co-workers [7] used sugar-per substitutedpoly(amidoamine) dendrimers as a protective colloid as well asa reducing agent for the synthesis of silver and gold nanopar-ticles in aqueous solution. It was also suggested that the redoxreaction occurred on the surface of sugar ball. Stable silver nanopar-ticles (size range ca. 10–34 nm) have been synthesized by usingsoluble starch as both the reducing and stabilizing agents. Thepreparation was carried out in an autoclave at constant pressure(=15 psi) and high temperature (=121 ◦C) for 5 min [8]. Shervaniand Yamamoto [9] reported the carbohydrate-directed synthesisof spherical nanoparticles and nanowires of silver and gold. Theyused monosaccharide (�-d-glucose) and polysaccharide (solublestarch) as structure directing and subsequently stabilizing agents.The binding interaction between starch and Ag-nanoparticles wasweak and could be reversible at higher temperatures, allowingseparation of the synthesized particles. Our recent studies on theshape-directing role of cetyltrimethylammonium bromide [10] in
the growth of silver nanoparticels using tyrosine-Ag+ redox sys-tem, prompted us to explore the role of starch in the growth ofsilver nanoparticles. We have chosen ascorbic acid to see the for-mation of Ag-nanoparticles, because it has high affinities toward
Table 1Relative viscosities (�r) of reaction mixtures at different [ascorbic acid].
104 [Ascorbic acid] (mol dm−3) �r
0.0 1.010.2 1.100.6 1.120.8 1.121.0 1.10
Z. Khan et al. / Colloids and Surface
g+ ions. Incidentally, this study appears to be the first report onhe formation, aggregation, and cross-linking of Ag-nanoparticlesn presence of starch.
. Experimental
.1. Materials
Doubly distilled (first time from alkaline KMnO4) and deion-zed water (specific conductance (1–2) × 10−6 �−1 cm−1) from anll glass apparatus was used as solvent to the preparation of alleagents. Silver nitrate (99.9%, BDH), ascorbic acid (99.5%, Fluka,uriss) and starch (98%, Fluka) were used without further purifi-ation. Ascorbic acid solution was prepared daily (to arrest theerial oxidation) in boiled and cooled water. The required amount oftarch was added in the deionized water and the aqueous solutionas boiled for 10 min in a 500 cm3 Erlenmeyer flask with constant
apid stirring to avoid the aggregation of starch. Starch becomesoluble in water when heated due to the presence of amylose,0%, which forms a colloidal dispersion in hot water whereas amy-
opectin, 80%, was completely insoluble. The mixture was coolednd filtered with Whatman paper No. 1. Filtrate was collected,tored at room temperature and used as the stabilizer for the prepa-ation of Ag-nanoparticles.
.2. Preparation of Ag-nanoparticles
In a typical experiment, ascorbic acid (5 cm5 of 0.01 mol dm−3)as added to starch (5 cm3 of 2%) and diluted with distilledater (total volume = 50 cm3). After complete mixing, silver nitrate
5 cm5 of 0.01 mol dm−3) solution was added into the reactionixture containing ascorbic acid + starch and stirred well. As the
eaction proceeded, the appearance of yellow to brownish coloras observed indicating the formation of Ag-nanoparticles [11].
.3. Characterization of Ag-nanoparticles
In order to characterize the resulting Ag-nanoparticles, a UV/Vispectrophotometer (UV-260 Shimadzu, with 1 cm quartz cuvettes),ransmission electron microscope (JEOL, JEM-1011; Japan) andisher Scientific digital pH meter 910 fitted with a combinationlectrode were used. For TEM measurements, samples were pre-ared by placing a drop of working solution on a carbon-coatedtandard copper grid (300 mesh) operating at 200 kV and dried theample grid in open air. The electron diffraction pattern was alsoecorded for the selected area. A 0.4% starch solution was used ashe blank for the spectrophotometric measurements.
.4. Kinetic procedure
The required solution of all the reactants (except Ag+ ions solu-ion) was taken in a two-necked reaction vessel equipped with aouble-surface condenser to arrest evaporation. The reaction was
nitiated with the addition of required volume of thermally equili-rated Ag+ ions solution. The progress of the reaction was followedpectrophotometrically at 425 nm (neither ascorbic acid nor Ag+
ons have any absorbance at this wavelength) on a UV–vis spec-rophotometer. Other details of kinetic procedure were the sames described elsewhere [10].
.5. Viscosity measurements
Viscosity measurements were made by using an Ubbelohde vis-ometer thermostated at room temperature ±0.1 ◦C. The relativeiscosities (�r) of solutions were obtained to get an idea about the
structural changes in the aqueous starch solution at the end of reac-tion, formation of prefect transparent yellow colored silver sol. The�r of reaction mixtures were determined against the water by usingthe relation:
� = �0
�1= d1t1
d0t0
where �1 and d1 represent the viscosity and the density of the reac-tion mixture, �0 and d0 are the viscosity and the density of water atthe experimental temperature and t1 and t0 are the time of flow forthe mixed volume for the reaction mixture and water, respectively.Density corrections were not made, as these were negligible [12].Therefore, �o was calculated by the relation of t1 and t0 (Table 1).
3. Results and discussion
3.1. Effect of [starch] on the morphology of Ag-nanoparticles
In order to see the actual role of starch as reductant and/or sta-bilizing agent, initially experiments were carried out in absence ofascorbic acid. Appearance of perfectly transparent yellow any color(characteristic of Ag-nanoparticles) was not observed in the solu-tion containing [Ag+] (10.0 × 10−4 mol dm−3) and [starch] (0.4%)for a short reaction time, i.e., 3 h. On the other hand, aqueoussolution of Ag+ ions becomes turbid in presence of ascorbic acid.Interestingly, the absorbance of reaction mixture containing [Ag+](10.0 × 10−4 mol dm−3) and [starch] (0.4%) changed very rapidlyin presence of ascorbic acid (10.0 × 10−4 mol dm−3). The reactionwas very sensitive to small concentrations of starch, a concen-tration of ≥0.2% being enough to produce a perfect transparentbrownish color silver sol. This indicates that the starch acts as sta-bilizing and/or capping agent under our experimental conditions.To confirm the nature of yellow color, the spectrum of reactionmixture was recorded at different [starch] as a function of time(Fig. 1). The most characteristic part of silver sol is a narrow sur-face resonance plasmon (SRP) absorption band observable in the350–600 nm region. Our spectrum consist a single absorption SRPband at 450 nm (Fig. 1(A); (�)). Interestingly, band position (�max)shifts to shorter wavelength, blue shift (ca. 425 nm) with increas-ing reaction time (Fig. 1; (�), (�), (�)). In addition to blue shift,the width of the SRP band as also increased, which might be dueto the excitation of different multiple modes present in facetedand anisotropic growth of particles [13]. The position of �max andshape of the spectra of Ag-nanoparticles depend on the experimen-tal conditions, i.e., nature of reducing agent, method of preparation,acidity of the reaction mixture and absence/or presence of stabi-lizers [14]. The initial reduction rate was high, but yellow colorformation decreased after a certain reaction time. The positionand shape of the SRP absorption depends on the particles size,shape,/and dielectric constant of the surrounding medium andsurface-adsorbed species. The boarding, red- and/or blue-shifting
of the absorption band with [starch] (Fig. 1(A)–(E); Table 1) indicatethat initially reduced Ag-nanoparticles grow to form larger parti-cles and finally starch acts as a shape-directing agent. Thus, we maysafely conclude that the morphology (size, shape and distribution)
580 Z. Khan et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 578– 584
Fig. 1. Spectra of starch stabilized Ag-nanoparticles at different time intervals. Reaction conditions: [Ag+] = 10.0 × 10−4 mol dm−3, [ascorbic acid] = 0.6 × 10−4 mol dm−3,temperature = 30 ◦C, [starch] = 0.2% (A), 0.4% (B), 0.6% (C), 0.8% (D) and 1.0% (E).
Z. Khan et al. / Colloids and Surfaces B: B
0 20 40 60 80 10 0 12 00.0
0.1
0.2
0.3
0.4
Ab
so
rban
ce a
t 425 n
m
Time(min)
Ftt
oa
t
ably, on the interparticle distance [15]. These results are in good
F[c
ig. 2. Effects of [starch] on the SRP of Ag-nanoparticles silver nanoparticles. Reac-ion conditions: [ascorbic acid] = 0.6 × 10−4 mol dm−3, [Ag+] = 10.0 × 10−4 mol dm−3,emperature = 30 ◦C.
f Ag-nanoparticles strongly depends on the initial reaction-time
s well as small [starch].
The effect of varying [starch] range: (0.4–1.0%) on the reac-ion rate was studied at fixed [Ag+] (=10.0 × 10−4 mol dm−3),
ig. 3. TEM images of starch stabilized Ag-nanoparticles at different magnificatioAg+] = 10.0 × 10−4 mol dm−3, [ascorbic acid] = 0.6 × 10−4 mol dm−3, [starch] = 0.4%, tempeasting on it a drop of the solution and allowing the solvent to evaporate.
iointerfaces 102 (2013) 578– 584 581
temperature (=30 ◦C) and [ascorbic acid] (=10.0 × 10−4 mol dm−3).The observed results are depicted graphically in Fig. 2 as thetime dependence absorbance at different [starch], suggesting thenucleation and growth paths concerned in the formation of Ag-nanoparticles. As can be seen in Figs. 1 and 2 (typical example), thenew Ag-nanoparticles were not formed after the first 20 min of thereaction (SRP absorbance remained the nearly constant for each[starch] after a certain reaction time, indicating that the nuclea-tion might be finished). Fig. 1 also shows the changes in the shapeand position of SRP band of Ag-nanoparticles in solution for a shortreaction-time, following the increasing of the [starch] in the solu-tion. After a certain reaction-time, i.e., ca. 20 min, the concentrationof starch does not produce any significant effect (no shift) on theposition and shape of the SRP band (Fig. 1(A)–(E)) in the UV–visspectrum.
The morphology of Ag-nanoparticles particles were determinedby recording TEM images. Interestingly, only few truncated tri-angular nano plates are observed along with some spherical andoctahedral particles, and a large abundance of tetrahedral particles,either isolated or in multiple twinned arrangements (Fig. 3A–C).Finally, particle aggregates in irregular shape, likely arising fromcoalescence of a particle aggregate, depending on the shape of theaggregate, much like in the case of solid particles, and remark-
agreement to the observations of Callegari et al. for the prepara-tion of silver nanoparticles having mixed geometries [16]. Fig. 3A(0.5 �m scale) clearly shows that the faceted and anisotropic
n scales (A = 0.5 �m, B = 50 nm and C = 20 nm) and SAED ring patterns (D).rature = 30 ◦C. The particles have been deposited on a carbon-coated TEM grid by
582 Z. Khan et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 578– 584
0 20 40 60 80 10 0 12 00.0
0.2
0.4
0.6
0.8
1.0
Ab
so
rban
ce a
t 425
Time (min)
Fig. 4. Effects of [Ag+] on the SRP of starch stabilized Ag-nanoparticles sil-ver nanoparticles. Reaction conditions: [ascorbic acid] = 0.6 × 10−4 mol dm−3,[ ◦ + −4 −3
1(
AistcowbaAFmansitAalatrb
3A
sA0abo(faso
0 20 40 60 80 10 0 12 0
0.0
0.2
0.4
0.6
0.8
1.0
Ab
so
rban
ce a
t 425 n
m
Time(min)
Fig. 5. Effects of [ascorbic acid] on the SRP of starch stabilized Ag-nanoparticles sil-ver nanoparticles. Reaction conditions: [Ag+] = 10.0 × 10−4 mol dm−3, [starch] = 0.2%,
g-nanoparticles are aggregated and/or interconnected in arregular manor, leads to the formation of butter-fly like structure ofilver. As shown in the large magnified picture (Fig. 3B), truncatedriangles are formed as the main product of Ag-nanocrystals, indi-ating the role of starch in the starch-induced anisotropic growthf nanocrystals [8,9]. The edge of truncated triangular nanoplatesas about 17–30 nm. The tetrahedron with width of ca. 40 nm could
e formed by the dissolution of the corner atoms of truncated tri-ngular nanoplates (Fig. 3C) along with some irregularly shapedg-nanoparticles which are aggregated in a irregular manors. Fromig. 3A we can see that this self-assembled butter-fly structure isade up of some big and small truncated triangular nanoplates
nd/or tetrahedron of Ag-nanoparticles clusters. Single-crystallineature of truncated triangular particles was also confirmed byelected area electron diffraction ring patterns image (Fig. 3D) andndicated that the nanoplates were oriented with {1 1 1} planes ashe basal plane [17]. Fig. 3D also ruled out the encapsulation ofg-nanoparticles inside the soluble starch matrix [7]. A TEM imagelso shows that the Ag-nanoparticles are surrounded by a faint thinayer of other material, which we suppose is due to the cappingction of amylose from soluble starch. The small size truncatedriangular nano-plates and nano-rods are in consistent with theesults of Lee et al. to the preparation of silver nano-plates fromiological to bio-mimetic synthesis [18].
.2. Effects of reactants concentrations on the growth ofg-nanoparicles
In order to see the role of ascorbic acid, a solution oftarch (0.2%) was added to a series of solutions containinggNO3 (5.0 cm3, 0.01 mol dm−3) and ascorbic acid (=0.10–5.0 cm3,.01 mol dm−3, total vol. 50 cm3) at 30 ◦C. At higher [ascorbiccid] (≥2.0 × 10−4 mol dm−3), the reaction mixtures becomes tur-id and a yellowish precipitate appears where as, the formationf perfect transparent stable yellow color is observed in [CTAB]<1.0 × 10−4 mol dm−3). Therefore, all the experiments were per-
+
ormed at lower ascorbic acid concentrations. The effects of [Ag ]nd [ascorbic acid] on the rate of Ag-nanoparticles formation weretudied at constant [starch] (=0.2%) and temperature (=30 ◦C). Thebserved results are summarized graphically in Figs. 4 and 5 to
the variation of [Ag+] and [ascorbic acid], respectively. Inspec-tion of these Figs. indicates that the nucleation process stoppedafter 20 min. We did not observe any significant change in theabsorbance for the long reaction time (absorbance remainedsame with time). The most important and interesting findingsof the present observations are the decrease (Figs. 4 and 5) inthe absorbance of Ag-nanoparticles formation with [Ag+] and/or[ascorbic acid] at 425 nm. Reaction–time curves reveal that [Ag+]has a marked influence on the SRP absorbance of silver sol.Absorbance of silver sol is lower to the solution containing higher[Ag+] and/or [ascorbic acid] (Figs. 4 and 5; (�)), which may be due tothe adsorption or complexation of Ag+ ions and ascorbic acid ontothe surface of Ag-nanoparticles. These results are in good agree-ment with the observation of Henglein [19].
Chang [20] reported a simple procedure (gold seeds method)to the preparation of different shaped Au–Ag nano-composites (I-,dumbbell-, and/or sphere-shaped) by adjusting the pH of the work-ing solution and suggested that the pH, the nature of the aminoacid, and its concentration all have significant impact mainly on thereducing ability of ascorbate. It is well known that dehydroascorbicacid is the main two-electrons oxidation product of ascorbic acid[21]. The complexities of ascorbate as a reducing agent have dis-cussed by Creutz [22]. In aqueous solution, various species ascorbicacid acids exist in equilibrium due to the presence of pH sensitive
OH groups. Therefore, a series of experiments were performedin order to see any change in the macroscopic pH of the work-ing solution in presence of starch. The pH values was found tobe nearly constant (pH = 4.0, 4.1, 4.0, 4.2, 4.1 and 4.1 for [ascor-bic acid] = 8.0, 9.0, 10.0, 12.0, 14.0 and 16.0 × 10−4 mol dm−3) withincreasing [ascorbic acid] (weak acid; pK1 = 4.6 and pK2 = 11.6). Itis not surprising because ascorbic acid was a good buffer agentfor pH control and an excellent antioxidant [23]. Henglein et al.reported the formation of long-lived clusters of silver by the chem-ical method using silver(I)- sodium borohydride for the first time[24,25] and also proposed the reduction of Ag+ ions (Ag+ + e-aq → Ag0; Ag0 + Ag+ → Ag2
+; Ag 2+ + Ag2
+ → Ag42+) into olgomeric
silver clusters. All these considerations, along with the abovekinetic results, lead to the proposal of the following mechanism
for the reduction of Ag+ ions by ascorbic acid.
In Scheme 1, Eq. (1) represents the oxidation of ascorbic acidby Ag+ ions (one-electron transfer from ascorbic acid to Ag+;
Z. Khan et al. / Colloids and Surfaces B: Biointerfaces 102 (2013) 578– 584 583
on of
rab(pptfatAy
Scheme 1. Mechanism to the formati
ate-determining step) which leads to the formation of radicalnd metallic silver (Ag0). The presence of radical were detectedy adding acrylonitrile as a scavenger in the reaction mixtureAg+ + ascorbic acid + CTAB), the formation of a polymer (whiterecipitate [26]) appeared slowly as the reaction proceeded. Theositive response indicated in situ generation of free radicals. Con-rol experiments with ascorbic acid or Ag+ ions only did not showormation of a precipitate. In the next step, radical reacts with
nother Ag+ and yields Ag0 and dehydroascorbic acid [21]. Afterhe slow step, the complexation of the formed Ag0 atoms withg+ ions yields Ag2+ ions and then the Ag2+ ions dimerize to yieldellow-color silver sol; Ag4
2+ (Eqs. (3)–(5)) [27,28]. As a result,
Scheme 2. Adsorption of Ag-nanoparticl
amylose-stabilized Ag-nanoparticles.
yellow colored amylose-stabilized Ag-nanoparticles were formedas a prefect transparent silver sol [19].
3.3. Probable role of starch
Water soluble, amylose and water insoluble, amylopectin arethe main constituents of the starch. Under our experimental con-ditions, amylase is present in the aqueous solution of soluble
starch. Upon heating the starch solution, granules swell and burst,the semi-crystalline structure is lost and the smaller amylosemolecules start leaching out of the granule, forming a network thatholds water and increasing the mixture’s viscosity. The structure
es on the outer surface of amylose.
584 Z. Khan et al. / Colloids and Surfaces B: B
Table 2Effects of [starch] on the position and shape of SRP band of silver nanoparticles at30 ◦C.
f amylose consists of long polymer chains of glucose units con-ected by the �-(1–4) linkages between d-glucose units and adopts
left-handed helical conformation in aqueous solution. Neutral sta-ilizing polymers and neutral nucleophiles have strong effect onhe SRP of silver and/or metal nanometer particles and donate thelectron density to the particles via lone pairs of electrons [19].nterestingly, we did not observed any appreciable change of �r
ith increasing [ascorbic acid] at fixed amounts of starch (10.0%)nd Ag+ ions (Table 2), which ruled out the possibility of structuralhange in the amylose molecule. Thus, we may safely conclude thathe amylose acted as a stabilizing agent. In order to explain thectual role of amylose, the presence of positive charge on the metalarticles (Ag4
2+) must be considered. It is certainly possible thathe positive charge on Ag-nanoparticles forms an ion pair with theone pairs of OH groups present in the amylose polymer chain.n the other hand, adsorption of Ag-nanoparticles onto the amy-
ose OH groups through electrostatic interactions can not be ruledut completely. Thus, the shape-directing role may be explained inerms of amylose adsorption (although highly schematic) onto theurface of Ag-nanoparticles (Scheme 2).
When the electron diffraction is carried out a limited numberf crystals one observes only some spots of diffraction distributedn concentric circles. A typical selected-area diffraction patterns also shown in Fig. 3D and it clearly exhibited diffraction rings
ith interplanar spacing that could be indexed ({1 1 0}, {2 0 0}),2 1 1}, {2 2 0}, {2 2 2}, {3 1 1} and {4 2 2}) according to the pureace-centered cubic (fcc) silver structure and are consistent withhe literature (JCPDS, File No. 4-0787) [29,30]. Presence of diffrac-ion rings also suggests that Ag-nanoparticles adsorbed on the outeride of the helical structure of amylose and ruled out their deepresence inside the soluble starch matrix [8].
. Conclusions
A simple, bio-reductive, green and room temperature methodas reported to the preparation of Ag-nanoparticles using ascor-
ic acid and soluble starch. The effects of various parameters suchs [reductant], [oxidant], [stabilizer], pH and reaction-time weretudied and discussed. TEM analysis showed the presence of amy-ose on the surface of nanoparticles which acted as a probable
[[[[
iointerfaces 102 (2013) 578– 584
stabilizer and/or capping agent. The hydrophilic poly OH groupswere mainly responsible for the adsorption of amylose onto thesurface of nanoparticles through electrostatic interactions. The sizedispersity of quasi-spherical, triangular nano-plates and nano-rodsof pure crystalline metallic silver could be synthesized in presenceof starch.
Acknowledgments
The authors are thankful to Deanship of Scientific Research, KingAbdul Aziz University, Jeddah for providing financial assistance inthe form of research project (320/130/1431). The authors also wishto thank Microscopic lab, King Abdul Aziz University, for their helpin TEM studies and useful suggestions.
References
[1] (a) Y. Sun, Y. Xia, Science 298 (2002) 2176;(b) M.-C. Daniel, D. Astruc, Chem. Rev. 104 (2004) 293;(c) C. Burda, X. Chen, R. Narayanan, M.A. El-Sayed, Chem. Rev. 105 (2005) 1025;(d) J.A. Dahl, B.L.S. Maddux, J.E. Hutchison, Chem. Rev. 107 (2007) 2228;(e) V.K. Sharma, R.A. Yngard, Y. Lin, Adv. Colloid Interface Sci. 145 (2009) 83.
[2] (a) R.C. Jin, Y.W. Cho, C.A. Markin, K.L. Kelly, G.C. Schatz, J.G. Zheng, Science 294(2001) 1901;(b) T.K. Sau, C.J. Murphy, J. Am. Chem. Soc. 126 (2004) 8648;(c) M.S. Bakshi, Langmuir 25 (2009) 12697;(d) S.S. Shankar, A. Rai, A. Ahmad, M. Sastry, J. Colloid Interface Sci. 275 (2004)496;(e) J. Xie, J.Y. Lee, D.I.C. Wang, Y.P. Ting, ACS Nano 1 (2007) 429;(f) Y. Liu, X. Liu, X. Wang, Nanoscale Res. Lett. 6 (2011) 22.
[3] (a) P. Raveendran, J. Fu, S.L. Wallen, J. Am. Chem. Soc. 125 (2003) 13940;(b) P. Raveendran, J. Fu, S.L. Wallen, Green Chem. 8 (2005) 34.
[4] M. Amanullah, L. Yu, J. Petrol Sci. Eng. 48 (2005) 199.[5] H. Huang, X. Yang, Carbohydr. Res. 339 (2004) 2627.[6] H. Huang, Q. Yuan, X. Yang, Colloids Surf., B 39 (2004) 31.[7] K. Esumi, T. Hosoyo, A. Yamahira, K. Torigoe, J. Colloid Interface Sci. 226 (2000)
346.[8] N. Vigneshwaran, R.P. Nachane, R.H. Balasubramanya, P.V. Varadarajan, Carbo-
hydr. Res. 341 (2006) 2012.[9] Z. Shervani, Y. Yamamoto, Carbohydr. Res. 346 (2011) 651.10] (b) Z. Khan, S.A. Al-Thabaiti, A.Y. Obaid, Z.A. Khan, A.O. Al-Youbi, J. Colloid Inter-
face Sci. 367 (2012) 101;(b) Z. Khan, J.I. Hussain, A.A. Hashmi, Colloids Surf., B 98 (2012) 85.
11] R. Jin, Y.C. Cao, E. Hao, G.S. Metraux, G.C. Schatz, C.A. Mirkin, Nature 425 (2003)487.
12] D.W. Kim, S.I. Shin, S.G. Oh, Adsorption and aggregation of surfactants in solu-tion, in: K.L. Mittal, D.O. Shah (Eds.), Surfactant Sciences Series, 109, MarcelDekker, NY, 2003, pp. 255–268.
13] M. Maillard, S. Giorgio, M.P. Pileni, Adv. Mater. 14 (2002) 1084.14] S.A. Al-Thabaiti, F.M. Al-Nowaiser, A.Y. Obaid, A.O. Al-Youbi, Z. Khan, Colloids
Surf., B 67 (2008) 230.15] T. Jensen, L. Kelly, A. Lazarides, G.C. Schatz, J. Cluster Sci. 10 (1999) 295.16] A. Callegari, D. Tonti, M. Chergui, Nano Lett. 3 (2003) 1565.17] B. Wiley, T. Herricks, Y. Sun, Y. Xia, Nano Lett. 4 (2004) 1733.18] J. Xie, J.Y. Lee, D.I.C. Wang, Y.P. Ting, ACS Nano 1 (2007) 429.19] A. Henglein, J. Phys. Chem. 97 (1993) 5457.20] Y.-F. Huang, Y.-W. Lin, H.-T. Chang, Nanotechnology 17 (2006) 4885.21] M.B. Davies, Polyhedron 11 (1992) 285.22] C. Creutz, Inorg. Chem. 20 (1981) 4449.23] S. Liu, C.E. Ellars, D.S. Edwards, Bioconjug. Chem. 14 (2003) 1052.24] T. Linnert, P. Mulvaney, A. Henglein, J. Am. Chem. Soc. 112 (1990) 4657.25] E. Janata, A. Henglein, B.G. Ershov, J. Phys. Chem. 98 (1994) 10888.26] S. Signorella, M. Rizzotto, V. Daier, M.I. Frascaroli, C. Palopoli, D. Martino, A.
Bousseksou, L.F. Sala, J. Chem. Soc., Dalton Trans. 1607 (1996).
27] M. Harada, K. Saijo, N. Sakamoto, K. Ito, J. Colloid Interface Sci. 343 (2010) 423.28] B.G. Ershov, A. Henglein, J. Phys. Chem. B 102 (1998) 10667.29] H. Huang, Y. Yang, Compos. Sci. Technol. 68 (2008) 2948.30] A. Serra, E. Filippo, M. Re, M. Palmisano, M. Vittori-Antisari, A. Buccolieri, D.
