RESEARCH ARTICLE Copyright © 2008 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Biobased Materials and Bioenergy Vol. 2, 1–5, 2008 Exploitation of Aspergillus Niger for Synthesis of Silver Nanoparticles A. K. Gade 1 , P. Bonde 1 , A. P. Ingle 1 , P. D. Marcato 2 , N. Durán 2 3 , and M. K. Rai 1 ∗ 1 Department of Biotechnology, SGB Amravati University, Amravati 444602, MS State, India 2 Instituto de Química, Universidade Estadual de Campinas-UNICAMP, C.P. 6154, Campinas, CEP 13083-970, S.P., Brazil 3 NCA- Universidade de Mogi das Cruzes, Mogi das Cruzes, S.P., Brazil Extracellular biosynthesis of silver nanoparticles by Aspergillus niger isolated from soil is being reported in the present paper. The production of silver nanoparticles was evidenced by UV-vis spectrum, showing the absorbance at 420 nm (Perkin Elmer Lambda-25). The nanoparticles charac- terized by Transmission Electron Microscopy exhibited spherical silver nanoparticles with diameter of around 20 nm. Elemental Spectroscopy imaging showed the presence of fungal protein around the silver nanoparticles thereby increasing their stability in the suspension. The silver nanoparticles (10 g/ml) showed remarkable antibacterial activity against gram-positive (Staphylococcus. aureus) and gram-negative (Escherichia coli) bacteria. The reduction of the silver ions might have occurred by a nitrate-dependent reductase enzyme and a shuttle quinone extracellular process. Reduction of silver ions was an extracellular and rapid process; this knowledge may lead to the development of an easy process for biosynthesis of the silver nanoparticles. Potential of fungal-mediated biosyn- thesis of silver nanoparticles is important for development of effective antibacterial agents showing resistance to drugs available in the market. Keywords: Silver Nanoparticles, Extracellular, Aspergillus Niger, Synthesis, Exploitation. 1. INTRODUCTION It is known that metal nanoparticles have novel magnetic, electronic and optical properties, which vary on the basis of their size, shape and composition. It has been known for long time that silver ions are highly toxic to a wide range of bacteria, and silver-based compounds have been used extensively as antibacterial agents. 1 Silver has an advan- tage of having broad antimicrobial activity against Gram- negative and Gram-positive bacteria. This quality of silver has developed interest in researchers. 2–3 Silver nanoparti- cles are more effective, partly because of the high surface/ volume fraction so that a large proportion of silver atoms are in direct contact with their environment. 4 Various methods such as chemical, physical and biologi- cal have been employed for the synthesis of metal nanopar- ticles. Among these, chemical methods are important because of their advantage in producing large quantities of nanoparticles in relatively short duration but these meth- ods are often energy intensive, employ toxic chemicals and need an stabilization path. 5–6 Synthesis of nanoparticles by ∗ Author to whom correspondence should be addressed. Email: mkrai123@rediffmail.com or pmkrai@hotmail.com microbial means is extensively used, because microorgan- isms typically live under comfortable conditions of temper- ature, pressure, and acidity. 7–8 Microbes are the candidates for development of manufacturing techniques that are more environment-friendly than today’s often hot, high- pressure, and chemical processes. Recognizing the impor- tance of developing eco-friendly nanoparticle synthesis methods, many researchers have turned to biological syn- thesis by microorganisms. 9–13 Microorganisms while inter- acting with metal ions reduce into metallic nanoparticles. Microorganisms 14–21 and plant extracts 22–26 have shown ability to reduce metal ions to form metallic nanoparticles. The metallic nanomaterials is playing a pivotal role in many technologies and would be a great asset to agriculture and medicine in near future. One key aspect of nanotechnology concerns the development of reliable experimental protocols for the synthesis of nanomateri- als over a range of chemical compositions, sizes and high monodispersity. In the context of the current drive to develop green technologies in materials synthesis, this aspect of nanotechnology assumes considerable impor- tance. An attractive possibility is to use microorganisms in the synthesis of nanoparticles. J. Biobased Materials and Bioenergy 2008, Vol. 2, No. 3 1556-6560/2008/2/001/005 doi:10.1166/jbmb.2008.401 1