Biosynthesis and Characterization of Protein-Capped Silver Nanoparticles using Fungus Fusarium oxysporum f. sp ciceri and their Antibacterial Potential

^1*J. Musarrat, ¹A. A. Al-Khedhairy, ¹B.R. Singh, ²S. Diwedi and ³A. Azam

¹DNA Research Chair, Department of Zoology,

College of Science, King Saud University,

Riyadh, ²Department of Microbiology, ³Department of Applied Physics,

Aligarh Muslim University, Aligarh, India

Microorganisms have lately been explored as potential biofactories for synthesis of metallic nanoparticles. In this study, we have exploited a soil borne fungus Fusarium oxysporum f. sp ciceri for biosynthesis of silver nanoparticles. Incubation of fungal biomass as well as the mycelia-free culture filtrate of fungus with 10^-3M AgNO₃ at 28⁰C resulted in the production of stable silver nanoparticles owing to reduction of Ag⁺ ions to Ag⁰. The progressively more intense surface plasmon resonance bands at 420 nm in the UV-visible spectra with increasing time period suggested the formation of nanoparticles. The silver nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The TEM image revealed predominantly spherical particles in size range of 16 – 22 nm. The XRD data showed the diffraction at 38.5⁰, 44⁰, and 64.5^o and 77^o 2è, indexed to the (111), (200), (220) and (311) planes of the face-centered cubic (fcc) silver, respectively. The full width-at-half-maximum (FWHM) value measured for (111) plane of reflection using Debye-Scherrer algorithm provided the average size of nanoparticles to be 22 nm. The sharp peaks reflected the monodispersity and crystalline nature of the nanoparticles. The analysis of 3D images obtained upon tapping mode scanning of nanoparticles by AFM further validated the shape and size of the nanoparticles. Fourier transform infrared spectroscopy (FTIR) spectrum demonstrated the characteristic amide- I and -II bands at 1651 and 1548cm^-1, produced due to carbonyl stretch and ---N---H bending vibrations in the amide linkage of the protein, respectively. The data suggested the role of fungal surface protein-amide groups in the stabilization of silver nanoparticles. The fungal reductase enzymes as well as other secretory metabolites with strong redox potential may serve as the vital factors in biosynthesis of silver nanoparticles. The biosynthesized silver nanoparticles also exhibited broad-spectrum anti-bacterial activity against both the E. coli (Gram –ve) and Bacillus subtilis (Gram +ve) bacteria, which substantiate their role as a potential antibacterial agent for various industrial applications.

Key words: Nanoparticles, Silver, X-ray Diffraction, Fusarium oxysporum, Antibacterial agents

*Corresponding author: Prof. Javed Musarrat, DNA Research Chair, College of Science, KSU, Riyadh, SA. Tel No. 46-77249;

email: musarratj1@yahoo.com