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Colloids and Surfaces A: Physicochem. Eng. Aspects 353 (2010) 69–76

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l homepage: www.e lsev ier .com/ locate /co lsur fa

ucrose ester micellar-mediated synthesis of Ag nanoparticles and thentibacterial properties

.M. Huanga,∗, H.N. Limb, S. Radimanc, P.S. Khiewd, W.S. Chiud, R. Hashime, C.H. Chiac

Solid State Physics Research Laboratory, Physics Department, University of Malaya, 50603 Kuala Lumpur, MalaysiaChemistry Department, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, MalaysiaSchool of Applied Physics, Faculty of Science & Technology, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor Darul Ehsan, MalaysiaFaculty of Engineering, University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor Darul Ehsan, MalaysiaChemistry Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia

r t i c l e i n f o

rticle history:eceived 23 July 2009eceived in revised form 21 October 2009ccepted 22 October 2009vailable online 31 October 2009

a b s t r a c t

Ag nanoparticles with diameter in the range of 10–25 nm had been synthesized using a simple sucroseester micellar-mediated method. Ag nanoparticles were formed by adding AgNO3 solution into thesucrose ester micellar solution containing sodium hydroxide at atmospheric condition after 24 h of agingtime. Trace amount of dimethyl formamide (DMF) in the sucrose ester solution served as a reducingagent while NaOH acted as a catalyst. The produced Ag nanoparticles were highly stable in the sucrose

eywords:icellaranoparticlesucrose esterilver

ester micellar system as there was no precipitation after 6 months of storage. The as-synthesized Agnanoparticles were characterized using transmission electron microscope (TEM), X-ray diffractometer(XRD), dynamic light scattering (DLS) and UV–vis spectroscopy (UV–vis). Formation mechanism of Agnanoparticles in the micellar-mediated synthesis is postulated. The antibacterial properties of the Agnanoparticles were tested against Methicillin-resistant Staphylococcus aureus (MRSA) (Gram-positive)and Aeromonas hydrophila (Gram-negative) bacteria. This work provides a simple and “green” method for

ble A

the synthesis of highly sta

. Introduction

There are huge amount of researches reported on the synthe-is of nanosized Ag. Synthesis of Ag nanoparticles involves twoain factors, which are precipitation of Ag nanoparticles from its

recursor Ag+ and controlling the size/shape of the Ag nanopar-icles after their formation. The precipitation of Ag nanoparticlesan be done using various methods, which includes chemicaleduction [1–4], photochemical reduction (�-ray [5–7], electroneam [8,9], microwave [10–12], laser [13] and ultra violet [14,15]),lectrochemical [16], sonochemical [17] and ultrasonic synthesis18,19]. The control of size/shape of the Ag nanoparticles formedill require stabilizing agents or templating agents. Some of theost commonly used stabilizers include cetyl trimethylammonium

romide (CTAB) [20–22], sodium dodecyl sulfate (SDS) [23] biosur-actants [21], block copolymers [24], poly(vinylpyrrolidone) (PVP)

25], polyvinyl alcohol (PVA) [1,4], polyaniline [26], sodium cit-ate [27], polyelectrolytes [2], polyglycol [28], starch [29,30] andhitosan [6,31]. While for templating synthesis there are anodicluminum oxide (AAO) [32], reverse micelles [33], microemulsion

∗ Corresponding author. Tel.: +60 12 2091008; fax: +60 3 58911088.E-mail address: huangnayming@gmail.com (N.M. Huang).

927-7757/$ – see front matter © 2009 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2009.10.023

g nanoparticles in aqueous solution with promising antibacterial property.© 2009 Elsevier B.V. All rights reserved.

[34], hexagonal [35] and lamellar liquid crystal [36]. In some cases,the stabilizers act as both reducing agent and stabilizing agent[8,37,38].

For the last decade, the increased awareness towards the envi-ronment has encouraged nanomaterial scientists to look into“greener” methods. The use of non-toxic chemicals, environmental-friendly solvents and renewable resources are important issuesin “green” synthesis strategies [39]. Nanomaterials significantlyaffect the fields of physics, chemistry, electronics, optics, mate-rials science and biomedical science. Even though nanomaterialsexhibit special properties due to their size-related effects,their synthesis methods reflect negatively on the environ-ment.

There are recent reports using environmentally benign reduc-tants such as sodium citrate [40], PVP [41], polyethylene glycol(PEG) [42] and glucose [43]. Also, there were reports using biologi-cal methods like bacteria [18–20] and fungus [44,45] as the particlesgrowth medium. These methods offer potential green chemistrymethod for the fabrication of nanomaterials. However, most of

the Ag nanoparticles synthesis methods reported were still highlydependent on the use of significantly large quantity of toxic reduc-tants such as sodium borohydride [46], hydrazine [47], dimethylformamide [48]. These chemicals are very reactive, causing envi-ronmental and biological risks.

7 : Physicochem. Eng. Aspects 353 (2010) 69–76

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tration of 10 CFU (colony forming unit). The concentration of Agnanoparticles was determined at 10, 50 and 100 ppm, with 0 ppmas a negative control. The bacteria mixture was left in the incubator-shaker at 37 ◦C and monitored for 8 h. The mixture was withdrawnhourly for analysis at 600 nm [53] using a UV–vis spectroscopy

0 N.M. Huang et al. / Colloids and Surfaces A

Sucrose ester is a food grade surface active agent with sucroses the headgroup (hydrophilic) and carboxylic acids (stearic acid,auric acid and palmitic acid are commercially available) as the tailroup (hydrophobic). The hydrophobic tail group consists of mix-ures of mono, di, tri and polyesters of the respective carboxyliccids. Sucrose ester has been used as surfactant in microemulsionethod for the synthesis of nanomaterials such as PbS [49], NiS

50], CdS [51] and brushite [52]. For the synthesis of nanomateri-ls involving surfactants, it is important that the surfactants usedre mild in nature in order to reduce the toxicity of the producedanomaterials and also to reduce the pollution towards the envi-onment.

In this work, we synthesized Ag nanoparticles using sucrosester micellar-mediated method. NaOH was added to acceleratehe formation of Ag nanoparticles. The reduction of Ag nanopar-icles with different concentration of AgNO3 happened in theucrose ester micellar solution at atmospheric condition. MRSA anderomonas hydrophila were used as model bacteria for the antibac-erial testing.

. Experimental

.1. Chemicals

AgNO3 dihydrate (98%) and sodium hydroxide (98%) were pur-hased from Sigma–Aldrich. Sucrose ester, nonionic surfactant ofood grade sucrose fatty acid ester (S-1670S), was purchased from

itsubishi-Kagaku Foods. Doubly distilled and deionised waterPurelab Prima Elga, with 18.2 M� electrical resistivity) was usedhroughout the sample preparations. All the chemicals were of ana-ytical grade and were used without further purification.

.2. Synthesis of Ag nanoparticles

In a typical procedure for the synthesis of sucrose ester micellar-ediated Ag nanoparticles, sucrose ester S1670S was used as

he surfactant. Sucrose ester (0.1 wt%) was added into 100 ml ofqueous solution containing 0.04 M of NaOH. Later, 100 ml AgNO3olution with concentrations of 0.04 M, 0.02 M, 0.01 M and 0.005 M,espectively, were added into the above sucrose ester solutionhrough titration. The mixing was carried out at a stirring rate of00 rpm at 30 ◦C. The experiments were conducted on a magnetictirring hotplate. The initial colorless solution changed to yellow-sh immediately after the addition of AgNO3 solution, which finallyurned into dark brown. The solution was stirred for 30 min and waseft for 1 day before characterization. After that, Ag nanoparticles

ere extracted by a Kubota centrifuge at 13 000 rpm and washedhree times with distilled water to remove the residues of ions anducrose ester. The nanoparticles were dried at 60 ◦C in an MMMacucell vacuum oven for 1 day before further characterization.

.3. Characterizations of Ag nanoparticles

The resulting nanoparticles after vacuum dried at 60 ◦C wereedispersed in ethanol. A drop of the Ag nanoparticles solutionas deposited onto a carbon-coated copper grid and was allowed

o evaporate at room temperature. The size and morphology ofhe Ag nanoparticles were investigated under a transmission elec-ron microscope (TEM) with an accelerating voltage of 120 kV.he size distribution of the Ag nanoparticles was based on diam-

ter measurement of >200 particles on TEM micrographs usingmage analysis software I-Solution (IMT). Furthermore, dynamicight scattering (DLS) measurement was carried out using a higherformance particle sizer (HPPS) supplied by Malvern Instrumentsor particle size measurement. The nanoparticles crystalline phase

Fig. 1. TEM micrograph of 0.1 wt% sucrose ester solution added with phospho-tungstic acid as a contrast agent, portraying micellar structure with diameter∼10 nm.

was determine by X-ray diffraction (XRD) using a Philip diffrac-tometer employing a scanning rate of 0.02◦ s−1 in a 2� range from

20◦ to 80◦ with CuK� radiation (� = 1.5418 ´̊A). The ultraviolet-visible(UV–vis) absorption spectra of the nanoparticles were recorded ona Perkin Elmer Lambda 35 spectrophotometer in the wavelengthrange of 350 to 800 nm using a 10 mm quartz cuvette. All the mea-surements were carried out at room temperature (∼25 ◦C).

2.4. Antibacterial efficacy test of Ag nanoparticles

Antibacterial test was carried out on Methicillin-resistantStaphylococcus aureus (MRSA) (Gram-positive) and A. hydrophila(Gram-negative) bacteria. All the apparatus used in this test weresterilized in an autoclave at 120 ◦C with pressure at 1 bar for 3 h.The Ag nanoparticles were added into 50 ml liquid Luria Bertani(LB) medium which was added with 200 �l bacteria at a concen-

7

Fig. 2. XRD patterns of (a) Ag standard based on JCPDS 04-0783 and (b) Ag nanopar-ticles synthesized in the sucrose ester micellar solution.

N.M. Huang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 353 (2010) 69–76 71

Fig. 3. TEM micrographs of Ag nanoparticles produced in 0.1 wt% sucrose ester micellar solution with AgNO3 concentrations of (a) 0.04 M, (b) 0.02 M, (c) 0.01 M and (d)0.005 M. Size distribution of the Ag nanoparticles is shown on the right-hand side of the TEM micrographs.

7 : Physicochem. Eng. Aspects 353 (2010) 69–76

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antibacterial activity as unstable Ag particles will not be able to dis-perse homogenously thus, reducing the antibacterial efficacy. Fig. 6shows the UV–vis spectra of the Ag nanoparticles produced using0.04 M AgNO3. The solid line shows the UV–vis spectrum of the

2 N.M. Huang et al. / Colloids and Surfaces A

Thermo Spectronic, USA). UV–vis absorption of 0.1 unit signifies08 CFU bacteria. Minimum inhibition concentration (MIC) is the

owest concentration of Ag nanoparticles to inhibit the growth oficroorganism.

. Results and discussion

The structure of the sucrose ester micellar solution was stud-ed under TEM. Prior to observing sucrose ester solution underEM, the solution was added with phosphotungstic acid solutions a contrast agent. The critical micellar concentration (CMC) ofucrose ester is 0.0006% [54]. Hence, the sucrose ester solution of.1 wt% in this study was sufficient for the formation of micelles,hich was observed in the TEM micrograph (Fig. 1). The micro-

raph exhibits white round spots, indicating micellar structures,hich were formed from the sucrose ester. The white round spots

re formed by the assembly of the tail groups of the sucrose esterhereas the dark areas are the aqueous phase that has been ‘dark-

ned’ by the phosphotungstic acid, which is only soluble in aqueoushase. The diameter of the micelles estimated from the TEM micro-raph is ∼10 nm. The estimated diameter of the micelles is largerhan the actual diameter of the micelles (∼3–5 nm) formed byucrose ester [55] because during the vaporization/drying pro-ess, the water molecules pull the sucrose ester molecules towardshe continuous aqueous phase, causing the micellar structure tonlarge.

XRD pattern of the Ag nanoparticles obtained from the sucrosester solution is shown in Fig. 2. The XRD pattern shows four peakst 38.1◦, 44.3◦, 64.5◦, and 77.3◦, which are assigned to the (1 1 1),2 0 0), (2 2 0) and (3 1 1) planes of face-centered cubic (FCC) AgJCPDS File No. 04-0783). The absence of silver oxide peaks indi-ates that the as-prepared nanoparticles are made of pure silver.he calculated lattice constant, according to the spacing (dg) of the1 1 1) plane and the equation 1/dg

2 = (h2 + k2 + l2)/a2 is 0.4088 nm,hich is in good agreement with the standard value of 0.4086 nm.

Ag nanoparticles synthesized via the chemical reductionethod in the sucrose ester micellar solution with various AgNO3

oncentrations were observed under TEM as shown in Fig. 3. Basedn the TEM micrographs, low concentration of sucrose ester at.1 wt% was sufficient to produce Ag nanoparticles with smallimension. Ag nanoparticles with smaller diameters were pro-uced with higher concentrations of AgNO3 at 0.04 M and 0.02 M,hich are 10.85 ± 4.34 nm and 14.31 ± 8.11 nm, respectively. Con-

ersely, Ag nanoparticles produced with lower concentrations ofgNO3 at 0.01 M and 0.005 M have larger diameters, which are1.93 ± 8.96 nm and 22.41 ± 9.10 nm, respectively. The Ag nanopar-icles produced from the higher AgNO3 concentrations exhibitomparatively narrower size distribution, as shown on the right-and side of every TEM micrograph and also from the standardeviation of average diameter. This is because higher concentrationf Ag ions gives rise to higher production rate of nuclei at the initialrowth of nanoparticles. The faster growth rate and the abundancef nuclei at the initial stage are essential in producing nanoparticlesith narrow size distribution [56]. Besides that, the nanoparticles

re distributed fairly well, which is due to the protection of sucrosester anchoring on the surface of the Ag nanoparticles.

The size of the Ag nanoparticles produced was further con-rmed using dynamic light scattering as shown in Fig. 4. Theesults are in accordance with the TEM observation, with Aganoparticles synthesized using higher AgNO3 concentrations of

.04 M and 0.02 M having smaller diameters of 11.42 ± 1.86 nm ashown in Fig. 4(a) and 16.48 ± 6.48 nm in Fig. 4(b), respectively.

hile at lower concentrations of AgNO3, the diameters measuredere 21.23 ± 7.70 nm as shown in Fig. 4(c) and 25.45 ± 5.95 nm

n Fig. 4(d) for 0.01 M and 0.005 M, respectively. The DLS mea-

Fig. 4. Dynamic light scattering measurements for Ag nanoparticles synthesized insucrose ester micellar solution with AgNO3 concentration of 0.04 M (a), 0.02 M (b),0.01 M(c) and 0.005 M (d). Concentration of NaOH was fixed at 0.04 M.

sured size is slightly bigger as compared to the particle sizemeasured from the TEM micrographs because dynamic light scat-tering method measures the hydrodynamic radius, which takes thesucrose ester coating on the surface of Ag into consideration thus,making the particles bigger [57].

UV–vis spectra of Ag nanoparticles produced have an absorptionpeak at around 415–425 nm, which is the characteristic of surfaceplasmon resonance peak for Ag materials (Fig. 5). The wavelengthof the absorption peak for the Ag nanoparticles stabilized by thesucrose ester is relatively longer due to the larger dielectric con-stant of sucrose ester, which is more than 3.3 [58]. When the AgNO3concentration increased from 0.005 M to 0.04 M, there is a vast dif-ference in the absorption intensity. The intensity increases withthe increase of AgNO3 concentration due to the higher amount ofAg nanoparticles produced with higher concentration of Ag+ ions.Surface plasmon resonance absorption peak of the Ag nanoparticlesunderwent a ‘blue’ shift from 425 nm to 415 nm when the AgNO3concentration increased from 0.005 M to 0.04 M. The shift suggeststhat there is a decrease in terms of size of the Ag nanoparticles asthe AgNO3 concentration increased, which is in agreement with theobservation from the TEM micrographs and DLS measurements.

The Ag nanoparticles synthesized in this work are highly sta-ble as there are no precipitates visually observed. The stabilityof the nanoparticles in solution is very important with respect to

Fig. 5. UV–vis spectra of Ag nanoparticles synthesized with various AgNO3 concen-tration in 0.1 wt% sucrose ester micellar solution. Concentration of NaOH was fixedat 0.04 M.

N.M. Huang et al. / Colloids and Surfaces A: Phys

Fig. 6. Stability test of Ag nanoparticles in the sucrose ester solution. UV–vis spectrafor as-synthesized Ag nanoparticles (solid line) and after 6 months of storage inlaboratory condition (dotted line).

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<40% at Ag concentration of 50 ppm. Nevertheless, the presence of

ig. 7. UV–vis spectra of sample after reaction aging time of (a) 30 min and (b) 1ay in 0.1 wt% sucrose ester. Inset shows the band gap estimation for spectrum (a).

s-synthesized Ag nanoparticles while dotted line represents thepectrum of the Ag nanoparticles after 6 months of storage in labo-atory condition. The absence of significant changes on the spectraf the Ag nanoparticles after storage suggests high stability of theg nanoparticles.

We postulated the formation mechanism of the Ag nanopar-icles in this work. When the AgNO3 solution is added into theucrose ester solution that contains NaOH, Ag2O nanoparticles areormed immediately (stoichiometry (3)). Fig. 7(a) shows the UV–vispectrum of sample after reaction aging time of 30 min after addi-ion of AgNO3 and NaOH solution. From the spectrum, there is nopparent absorption peak around 400–430 nm corresponding tourface plasmon resonance of Ag nanoparticles. The UV–vis absorp-ion spectrum exhibits a typical pattern of semiconductor materialhich indicates the formation of Ag2O as predicted. It has been

eported in the literature that Ag2O is a material exhibiting semi-onductor behavior with band gap energy of 2.2 eV [59]. The opticalbsorption data of the spectrum have been analyzed using the fol-owing equation in order to determine the optical band gap energyf the Ag2O nanocrystals [60].

h� = k(h� − Eg)n/2 (1)

here ˛ is the absorption coefficient, � is frequency, h is Planck’sonstant, Eg is the band gap energy of the nanocrystals and k equals

constant while n carries the value of either 1 or 4. The value of

bsorption coefficient can be calculated by the following equation:

= 1t

− log It/Iolog e

= 1t

A

log e(2)

icochem. Eng. Aspects 353 (2010) 69–76 73

in which t is the thickness of the quartz cell, It and Io are the inten-sities of transmitted and incident lights, respectively and A is theabsorbance of the samples in UV–vis measurements. The curves of(˛hv)2/n against h� is shown in the inset of Fig. 7. The plot is lin-ear when n = 1, indicating direct electron transition. The band gapenergy of Ag2O is estimated from the extrapolation of the curve tothe energy axis for zero absorption coefficients, which is around3.2 eV. The estimated band gap energy is higher than that of thereported value, 2.2 eV as the Ag2O produced has smaller size, thus,the higher band gap energy.

After reaction aging time of 1 day, Ag nanoparticles are formedas can be seen from the UV–vis spectrum in Fig. 7(b) with typicalAg surface plasmon resonance peak at ∼415 nm. However, it isinteresting to note that the Ag2O is reduced to Ag without additionof reductant because sucrose is not a reducing sugar. Even thoughthe synthesis of gold and platinum using sucrose as a reducingagent has been reported, the reaction has to be carried out in anacidic condition [61]. In our case, the environment is alkaline.From the literature, the manufacturing of sucrose ester is basedon the transesterification cation process in solvents i.e. dimethylformamide (DMF) [62]. Even after purification using liquid–liquidextraction and crystallization, there would still be a trace amountof DMF residue present in sucrose ester. Thus, we suggest thatthe DMF has acted as the reducing agent for the reduction ofAg2O to Ag as shown by stoichiometry (4). The presence of traceamount of DMF is sufficient to reduce Ag2O to form Ag nanopar-ticles with NaOH as the catalyst. The formation of pure Ag asthe final compound was confirmed by the XRD measurement(Fig. 2).

2Ag+ + 2OH− → Ag2O + H2O (3)

(CH3)2NCOH + Ag2O → 2Ag + (CH3)2NCOOH (4)

Based on the above results, the formation mechanism of Agnanoparticles obtained from the chemical reduction method in thesucrose ester solution is postulated as shown schematically in Fig. 8.The as-produced Ag2O nanoparticles after addition of NaOH arestabilized by sucrose ester. Due to the steric interaction of the OHgroups of sucrose ester with the Ag2O nanoparticles, sucrose esterwill form a bilayer on the surface of Ag2O nanoparticles and Agnanoparticles when reduced by DMF (Fig. 8). The schematic bilayerstructure arrangement is adopted from Cheng et al. [63], whichused CTAB as the surfactant. The as-synthesized Ag nanoparticlesare very stable because during the formation of the Ag nanoparti-cles in the sucrose ester micellar solution, the nanoparticles wereprotected by the bilayer of sucrose ester. The bilayers hinder theAg nanoparticles from aggregation thus, controlling the size of thenanoparticles.

The stability of Ag nanoparticles in liquid LB media is of highimportance because the aggregation of nanoparticles will affecttheir antibacterial efficacy. Fig. 9 shows the screening of bacte-rial growth in liquid LB by measuring the absorbance at 600 nm.Only a small amount of MRSA growth was inhibited by Ag con-centration of 10 ppm as depicted in Fig. 9(a). For Ag concentrationof 50 ppm, the growth of MRSA was inhibited by >40% after 8 h.Meanwhile, MRSA could not survive in the presence of 100 ppm ofAg nanoparticles. When Ag nanoparticles were introduced in theLB medium containing A. hydrophila (Fig. 9(b)), the resistance ofthe bacteria is higher towards the Ag nanoparticles compared toMRSA. At Ag concentration of 10 ppm, the inhibition of the bacterialgrowth is almost nonexistant whereas the growth was inhibited by

bacteria was not detected in the medium comprising 100 ppm of Agnanoparticles. Based on the antibacterial test, the MIC value of Agnanoparticles is ∼100 ppm. Sucrose ester also exhibits antibacterialproperty but is ineffective if the sucrose ester concentration is <0.2%

74 N.M. Huang et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 353 (2010) 69–76

Fig. 8. Formation mechanism schematic of Ag nanoparticles in the sucrose ester solution. The number of surfactants and micelles does not represent the real system.

N.M. Huang et al. / Colloids and Surfaces A: Phys

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ig. 9. Ag nanoparticles antibacterial efficacy using liquid nutrient media culturedith (a) MRSA and (b) Aeromonas hydrophila.

64]. Thus, sucrose ester does not contribute to the antibacterialroperties in this case.

Antibacteria mechanism or destruction has been extensivelynvestigated. The interaction stage between Ag nanoparticles andacteria (Escherichia coli) has been studied in detail by Shrivas-ava et al. [53] using TEM. At the initial stage of the interaction,g nanoparticles were found to adhere to the wall of the bacteriaue to the charge of the functional group of the bacteria. Subse-uently, the nanoparticles penetrated the bacteria and destroyedhe membrane, which eventually killed the bacteria.

The difference in sensitivity is contributed by the nature of theacteria, in which A. hydrophila is Gram-negative and MRSA isram-positive. Gram-negative bacteria have four layers of protec-

ive membranes consisting of a plasma membrane, a periplasmicrea, a peptidoglican layer and an outermost layer known asxternal membrane made-up of protein and lipopolysaccharide.ram-positive is only enveloped by three layers, which are thelasma membrane, periplasmic area and peptidoglican layer.herefore, the lack of an extra layer of membrane results in Gram-ositive bacteria being more sensitive towards the presence of Aganoparticles. The observation is similar to that of Brayner et al.65] and Fan et al. [66].

. Conclusion

This work provides a simple, convenient and “green” methodor the synthesis of highly stable Ag nanoparticles in sucrosester micellar solution. The bilayer coating of sucrose ester on Aganoparticles provides a good steric hindrance, which prevents the

g nanoparticles from aggregation. The diameter of the nanopar-

icles decreases with increasing AgNO3 concentration, which is inhe range of 10–20 nm depending on the precursor concentration.he optimum AgNO3 concentration in this study, which was 0.04 M,ielded nanoparticles with an average diameter of 10.85 ± 4.34 nm.

[

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icochem. Eng. Aspects 353 (2010) 69–76 75

Ag2O, obtained from the reaction between AgNO3 and NaOH, wasreduced to Ag by the trace amount of DMF present in sucrose ester.This simple and effective method can also be employed for thepreparation of metal nanoparticles, for example silver, gold, palla-dium and platinum. The efficacy of Ag nanoparticles in antibacterialactivity was manifested on MRSA dan A. hydrophila. The promis-ing antibacterial testing underlines the potential of adopting Agnanoparticles as antibacterial agents in various fields.

Acknowledgements

This work is supported by Universiti Kebangsaan Malaysiathrough the UKM-OUP-NBT-27-138/2008 grant. N.M. Huang wouldlike to thank MOSTI for the NSF scholarship.

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