Original Article
Experimental
Antimicrobial effects of silver nanoparticles

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Abstract

The antimicrobial effects of silver (Ag) ion or salts are well known, but the effects of Ag nanoparticles on microorganisms and antimicrobial mechanism have not been revealed clearly. Stable Ag nanoparticles were prepared and their shape and size distribution characterized by particle characterizer and transmission electron microscopic study. The antimicrobial activity of Ag nanoparticles was investigated against yeast, Escherichia coli, and Staphylococcus aureus. In these tests, Muller Hinton agar plates were used and Ag nanoparticles of various concentrations were supplemented in liquid systems. As results, yeast and E. coli were inhibited at the low concentration of Ag nanoparticles, whereas the growth-inhibitory effects on S. aureus were mild. The free-radical generation effect of Ag nanoparticles on microbial growth inhibition was investigated by electron spin resonance spectroscopy. These results suggest that Ag nanoparticles can be used as effective growth inhibitors in various microorganisms, making them applicable to diverse medical devices and antimicrobial control systems.

Section snippets

Preparation of Ag nanoparticles

Ag nanoparticles were made according to the recipe described in the literature [8], [9]. Briefly, a 100-mL aqueous solution of 1.0 × 10–3 M silver nitrate was mixed with a 300-mL aqueous solution of 2.0 × 10-3 M sodium borohydride. Triply distilled water was used for solutions, and both solutions were chilled to ice temperature before mixing. By mixing both solutions, Ag ions were reduced and clustered together to form monodispersed nanoparticles as a transparent sol in aqueous medium. The Ag

Characterization of the synthesized Ag nanoparticles

The prepared aqueous solution of Ag nanoparticles showed an absorption band at 391 nm as shown in Figure 1, which is a typical absorption band of spherical Ag nanoparticles due to their surface plasmon [8]. The stability of the concentrated solution was checked by observing its absorption spectrum after rediluting 10 times. The absorption spectrum of the rediluted solution depicts almost identical spectral features to the spectrum of the original solution of Ag nanoparticles (Figure 1, A). This

Discussion

It is well known that Ag ions and Ag-based compounds have strong antimicrobial effects [12], and many investigators are interested in using other inorganic nanoparticles as antibacterial agents [4], [12], [13], [14]. These inorganic nanoparticles have a distinct advantage over conventional chemical antimicrobial agents. The most important problem caused by the chemical antimicrobial agents is multidrug resistance. Generally, the antimicrobial mechanism of chemical agents depends on the specific

Acknowledgments

This work was supported by the NSI-NCRC program of KOSEF. D.H.J. was supported by BK21 program. H.J.L. was supported by the the Korean Research Foundation Grant funded by the Korea Government (MOEHRD) (R05-2004-10627-0).

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No conflict of interest was reported by the authors of this paper.

J.S. Kim and E. Kuk contributed equally to this work.

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