Preparation and Antibacterial Activity of Silver Nanoparticles

doi:10.4236/jbnb.2011.24057

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Journal of Biomaterials and Nanobiotechnology, 2011, 2, 472-475

doi:10.4236/jbnb.2011.24057 Published Online October 2011 (http://www.SciRP.org/journal/jbnb)

Preparation and Antibacterial Activity of Silver

Nanoparticles

Ratan Das1, Sneha Gang2, Siddhartha Sankar Nath3*

1Department of Physics, Assam University , Silchar, India; 2Department of Biotechnology, Assam University, Silchar, India; 3Central

Instrumentation Center, Assam University, Silchar, India.

Email: *[email protected]

Received January 1st, 2011; revised June 27th, 2011; accepted July 28th, 2011.

ABSTRACT

Uniform silver nanoparticles have been prepared through the chemical reduction of silver ions by ethanol in presence of

sodium linoleate. TEM micrograph shows a uniform distribution of the particles with an average size of 12 nm. Further, the

antimicrobial activity of silver nanoparticles shows that these nanoparticles can be used as effective growth inhibitors

against Staphylococcus Basillus, Staphylloccoccus Aureus, and Pseudimonas Aureginosa.

Keywords: Linoleic Acid, Absorption Band, Colloid, Antimicrobial, Microorganisms

1. Introduction

Noble metal nanoparticles show unique electronic, opti-

cal, magnetic and chemical properties, which differ con-

siderably from those of the corresponding bulk materials

[1-3] and hence preparations of noble metal nanoparti-

cles are of technological importance. Recently inorganic

nanoparticles protected by organic ligands have attracted

much interest due to their diverse technological applica-

tions [4-6]. In the present investigation, silver nanoparti-

cles have been synthesized through the chemical reduc-

tion of silver ions by ethanol using linoleic acid as a cap-

ping agent, which is then dispersed in chloroform to

form homogeneous colloidal solution [7] to study the

antimicrobial activity of fatty acid (linoleic acid) capped

silver nanoparticles. The important advantage is that the

silver nanoparticles prepared by this simple reduction

process remain stable for one month without any ag-

glomeration. The prepared silver nanoparticles have been

examined using Transmission Electron Microscope

(TEM) and Fourier Transform Infrared Spectroscopy

(FTIR). These studies reveal that average size of freshly

prepared silv er nanoparticles is 12 nm with a narrow size

distribution.

2. Materials and Methods

Uniform silver nanoparticles can be obtained through the

reduction of silver ions by ethanol at a temperature of

90˚C under atmospheric conditions in presence of li-

noleic acid and sodium linoleate [7]. In this reduction

method, 20 ml of aqueous solution containing silver ni-

trate (0.6 g of AgNO 3), 2 g sodium linoleate (C18 H32ONa),

12 ml ethanol (C2H5OH) and 2.5 ml linoleic acid (C18

H32 O2) are added in a capped tube under continuous agi-

tation. The system is kept at the temperatures 90˚C for 2

hours. In the aqueous solution of silver nitrate, sodium

linoleate and the mixture of linoleic acid and ethanol are

added in order. Ethanol in the solution phases reduced

silver ions into silver nanoparticles. The linoleic acid

caps the silver nanoparticles along with the reduction

process thereby stabilizes the nanoparticles. In this sim-

ple reduction process, the role of linoleic acid is to pro-

tect the silver nanoparticles from aggolomeration, by

making a layer over them with its alkyl chains on the

outside giving a hydrophilic surroundings to the nanopar-

ticles and hence the produced nanoparticles gain hydro-

phobic surfaces [7]. In this way, capping these particle

linoleic acid stabilise them for one month. The product,

collected at the bottom of vessel after cooling to room

temperature, is dispersed in chloroform to form a homo-

genous colloidal solution of silver nanoparticles, which

is reddish brown in colour as shown in Figure 1(a) with

the structure of linoleic acid as shown in Figure 1(b).

3. Results

3.1. TEM Image Analysis

Size and shape of the silver nanoparticles have been ob-

tained from TEM micrograph, which was performed on a

JEM 1000C X II model instrument. TEM micrograph of

the prepared colloidal solution of silver nanoparticles is

shown in the Figure 2(a), which indicates that the size

Preparation and Antibacterial Activity of Silver Nanoparticles473

Figure 1. (a) Silver nanoparticles dispersed in chloroform

showing reddish brown colour; (b) chemical structure of

linoleic acid.

(b)

Figure 2. (a) TEM image of silver nanoparticles; (b) parti-

cle size distribution.

distribution of silver nanoparticles is narrow as shown in

Figure 2 (b), having an average diameter (size) of 12 nm

with the size range 7 - 15 nm. This TEM image suggests

that no clustering of nanoparticles takes place as they are

well separated from each other.

3.2. FTIR Spectroscopy Analysis

Capping of linoleic acid on silver nanoparticle has been

examined by FTIR spectroscopy. The FT-IR absorption

spectra of the samples are shown in Figure 3 with reso-

lution of 4 cm−1, which was performed in Spectrum BX

series. The peak at 3441 cm−1 of the FTIR spectra con-

tains OH stretching modes [8]. The peak around 3018

cm−1 is due to C=C stretching mode. The lack of broad

peak due to OH stretching of the free ligand in the range

3000 cm−1 to 3100 cm−1 is due to the chemisorptions of

linoleic acid on the silver nanoparticles, which is an in-

dicator for the conformational ordering of the metal-

linked alkyl chains of linoleic acid.

3.3. Antimicrobial Activity of Silver

Nanoparticles

The antimicrobial effects of silver salts have been no-

ticed since ancient times [9]. But with the advent of na-

notechnology, the use of silver in nanoparticle form has

opened new treatment avenues. Here antimicrobial activ-

ity of this linoleic acid capped silver nanoparticles have

been investigated against Staphylococcus Basillus,

Staphylloccoccus Aureus, and Pseudimonas Aureginosa

by the Kirby-Bauer diffusion method [10,11]. The bacte-

rial suspension was applied uniformly on the surface of a

Muller Hinton agar (MHA) plate at a concentration of

105 to 106 CFU/mL before placing antibiotic impreg-

nated disks (Kanamycin and Arithromycin) and silver

nanoparticles laden disk (5 mm diameter). For antibacte-

Figure 3. FT-IR spectra of linoleic acid protected silver

nanoparticles dispersed in chloroform.

Preparation and Antibacterial Activity of Silver Nanoparticles

474

rial study silver nanoparticles laden disk have been pre-

pared by keeping 10 disks in 5 ml colloidal solution of

silver nanoparticles for two days. These disks absorb the

silver nanoparticles and become dry and hence there is

no presence of chloroform. So there is no impact of sol-

vent to the bacteria. The plates with the discs were incu-

bated at 35˚C for 24 h, after which the average diameter

of the inhibitio n zon e surround ing th e disk was measured

with a ruler. Figure 4 shows plates to which Staphylo-

coccus Basillus and Staphylloccoccus Aureus bacterial

suspension were applied with nanoparticles laden disk

and antibiotic impregnated disks. The diameter of inhibi-

tion zones around the disk containing silver nanoparticles

in S. Basillus, S. Aureus, and Pseudimonas Aureginosa

bacterial suspension are 9 mm, 11 mm, 10 mm respec-

tively. This test shows that silver nanoparticles are nearly

70%, 85% and 60% effective compare to Kanamycin and

Arithromycin respectively. It is observed that the pres-

ence of silver nanoparticles inhibited bacterial growth by

more than 97%.

The mechanism of the bactericidal effect of silver na-

noparticles is not very well-known. It is believed that

cellular proteins become inactive after treatment with

silver nanoparticles [12]. It is also believed that silver

nanoparticles after penetration into the bacteria have in-

activated their enzymes, generating hydrogen peroxide

and caused bacterial cell death [11]. Heavy metals are

toxic and react with proteins, therefore they bind protein

molecules; as a result cellular metabolism is inhibited

causing death of microorganism [12]. It is known that

silver sources such as silver nitrate and silver sulfadiaz-

ine release Ag+ only [12] but high activity of silver

nanoparticles is attributed to the release of Ag0 and Ag+

clusters when they dissolve [12]. Our experimental result

shows that linoleic acid capped silver nanoparticles can

be used as effective growth inhibitors in various micro-

Figure 4. Shows silver nanoparticles laden disk (a) and an-

tibiotic impregnated disk (b, c) placed on the surface of the

Staphylococcus Basillus(1) and Staphylloccoccus Aureus(2)

bacterial suspension on Muller Hinton agar (MHA) plate

after incubation at 35˚C for 24 h.

organisms, making them applicable to diverse medical

medicines and antimicrobial control systems.

4. Discussion

Uniform linoleic acid capped silver nanoparticles have

been prepared through the reduction of silver ions by

ethanol. TEM micrograph reveals that the prepared nano-

particles are spherical in shape with average size of 12

nm having nearly uniform distribution and FTIR spectra

confirms the capping of linoleic acid on nanoparticles

surfaces. These linoleic acid capped silver nanoparticles

are tested for its antimicrobial activity and the result

shows that silver nanoparticles can be used as effective

growth inhibitors in various microorganisms thereby

applicable to diverse medical devices.

5. Acknowledgements

Authors thanks to Dr B. Dkhar (S.O.), NEHU, Shillong,

India, Dr. A. K. Paul, NEHU, Shillong, India, and Prof.

Arun Chottapadhay, IIT, Guwahati, Assam, India for

their suggestions and assistance during the work.

REFERENCES

[1] D. L. Feldheim and C. A. Foss, “Metal nanoparticles:

Synthesis, Characterization and Applications,” Marcel

Dekker Inc., New York, 2002.

[2] G. Cao, “Nanostructures and Nanomaterials,” Edited by

Imperial College Press, London, 2004.

[3] C. P. Poole and F. J. Owens, “Introduction to Nanotech-

nology,” Edited by Wiley Interscience Publication, New

Jersey, 2005.

[4] M. Brust, M. Walker, D. Bethell, D. J. Schiffrin and R. J.

Whyman, “Synthesis of Thiol Derivatised Gold Nano-

particles in a Two Phase Liquid/Liquid System,” Journal

of the Chemical Society, Chemical Communications, Vol.

7, No. 7, 1994, pp. 801-802. doi:10.1039/c39940000801

[5] A. S. Nair and T. Y. Pradeep, “Halocarbon Mineraliza-

tion and Catalytic Destruction by Metal Nanoparticles,”

Current Science, Vol. 84, No. 12, 2003, pp. 1560-1564.

[6] Y. Fang, “Optical Absorption of Nanoscale Colloidal Sil-

ver: Aggregate Band and Adsorbate-Silver Surface Ban d,”

Journal of Physical Chemistry, Vol. 108, No. 10, 1998, pp.

4315-4318. doi:10.1063/1.475831

[7] X. Wang, J. Zhuang, Q. Peng and Y. Li, “A General Stra-

tegy for Nanocrystal Synthesis,” Nature, Vol. 437, No.

7055, 2005, pp. 121-124. doi:10.1038/nature03968

[8] M. D. Porter, T. B. Bright, D. L. Allara, and C. E. D. Chi-

dsey, “Chemical Functionality in Self-Assembled Mono-

layers and Electrochemistry,” Journal of the American

Chemical Society, Vol. 109, No. 12, 1987, pp. 3559- 3568.

doi:10.1021/ja00246a011

[9] M. Bahadory, “Synthesis of Noble Metal Nanoparticles,”

Dissertation, Drexel University, Philadelphia, 2008.

[10] S. Pal, Y. Kyung and J. M. Song, “Does the Antibacterial

Preparation and Antibacterial Activity of Silver Nanoparticles

475

Activity of Silver Nanoparticles Depend on the Shape of

the Nanoparticle? A Study of the Gram-Negative Bacte-

rium Escherichia coli,” Applied and Environmental Mi-

crobiology, Vol. 73, No. 6, 2007, pp. 1712-1720.

doi:10.1128/AEM.02218-06

[11] M. Raffi, F. Hussain, T. M. Bhatti, J. I. Akhter, A. Hameed

and M. M. Hasan, “Antibacterial Characterization of Silver

Nanoparticles against E. coli ATCC-15224,” Journal of

Materials Science and Technology, Vol. 24, No. 2, 2008,

pp. 192-196.

[12] M. Kokkoris, C. C. Trapalis, S. Kossionides, R. Vlastou,

B. Nsouli, R. Grotzschel, S. Spartalis, G. Kordas and T.

Paradellis, “RBS and HIRBS studies of nanostructured

AgSiO2 Sol-Gel Thin Coatings,” Nuclear Instruments

and Methods B, Vol. 188, No. 1-4, 2002, pp. 67-72.

doi:10.1016/S0168-583X(01)01020-5