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