Elsevier

Materials Letters

Volume 62, Issue 29, 30 November 2008, Pages 4411-4413
Materials Letters

Extracellular biosynthesis of silver nanoparticles by the culture supernatant of Bacillus licheniformis

https://doi.org/10.1016/j.matlet.2008.06.051Get rights and content

Abstract

Development of reliable and eco-friendly processes for synthesis of metallic nanoparticles is an important step in the field of application of nanotechnology. One of the options to achieve this objective is to use ‘natural factories’ such as biological systems. In this study, we report the synthesis of nanoparticles of silver by reduction of aqueous Ag+ ions with the culture supernatant of Bacillus licheniformis. The morphology of the nanoparticles was characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The Debye–Scherrer equation was used to calculate particle sizes and the silver nanoparticles of approximate size 40 nm were observed. The process of reduction is extracellular, which makes it an easier method for the synthesis of silver nanoparticles.

Introduction

The biosynthesis of nanoparticles as an emerging highlight of the intersection of nanotechnology and biotechnology has received increasing attention due to a growing need to develop environmentally-benign technologies in material synthesis. The significance of such a synthetic protocol has been well demonstrated [1]. Biologically synthesized silver nanoparticles could have many applications: they might be used as spectrally-selective coatings for solar energy absorption and intercalation material for electrical batteries; they also find use as optical receptors and as catalysts in chemical reactions [2]. There are several reports in the literature on the cell-associated biosynthesis of silver nanoparticles using several microorganisms, particularly Fusarium oxysporum [3]. The cell mass of F. oxysporum, and the leached components from the fungal cells have been reported for the reduction of silver ions to silver nanoparticles [4]. Also, for the past few years, various rapid chemical methods have been developed for the synthesis of silver nanoparticles [5]. Different natural products such as monosaccharides or plant extracts have been used as reducing agents in these studies. In a previous study the culture supernatant of Klebsiella pneumoniae was used, but as the organism is a pathogen it is risky to handle, which happens to be the main disadvantage of that method [6]. In this study we report the use of the culture supernatant of the non-pathogenic Bacillus licheniformis for the synthesis of silver nanoparticles from the standpoint of ease of mass production and safety in handling the organism.

Section snippets

Synthesis of nanoparticles of silver

B. licheniformis was inoculated into flasks containing sterile Nutrient Broth and the flasks were incubated at 37 °C for 24 h in 220 rpm. After the incubation period the culture was centrifuged at 8000 ×g and the supernatant used for the synthesis of silver nanoparticles. Three Erlenmeyer flasks, one containing supernatant with silver nitrate (Merck, Germany, 99.9% pure) at a concentration of 0.1 g/L and the second containing only the supernatant and the third containing only silver nitrate

Results and discussion

A study on extracellular biosynthesis of silver nanoparticles by the culture supernatant of B. licheniformis was carried out in this work. During the visual observation, culture supernatant incubated with silver nitrate showed a color change from yellow to brown whereas no color change could be observed in culture supernatant without silver nitrate and only silver nitrate solution (figure not shown). The appearance of a yellowish-brown colour in silver nitrate treated flask suggested the

Conclusion

Silver nanoparticles in the range of 50 nm are synthesized by the supernatant of B. licheniformis when silver nitrate is added to it. The silver nanoparticles synthesized are highly stable and this method has advantages over other methods as the organism used here is a non-pathogenic bacterium. This study would therefore lead to an easy procedure for producing silver nanoparticles with the added advantage of biosafety.

Acknowledgements

The authors gratefully acknowledge the Tamil Nadu State Council for Science and Technology (TNSCST) and Kalasalingam University, India, for financial assistance, Dr. Gurulinga (IISc, Bangalore) for help in SEM, Mr. Vasanthakumar (CECRI, Karaikudi) for help in the XRD and Dr. Kottaisamy (Asso. Prof., Department of Chemistry & Centre for Nanotechnology, KLU) for critical reading of the paper.

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