Novel mycosynthesis of cobalt oxide nanoparticles using Aspergillus brasiliensis ATCC 16404-optimization, characterization and antimicrobial activity

Abstract

Aims: Investigate the capability of Aspergillus brasiliensis ATCC 16404 to mycosynthesize Co₃ O₄ -NPs.

Methods and results: Mycelial cell-free filtrate of A. brasiliensis ATCC 16404 was applied for mycosynthesis of Co₃ O₄ -NPs. The preliminary indication for the formation of Co₃ O₄ -NPs was the change in colour from yellow to reddish-brown. One-factor-at a time-optimization technique was applied to determine the optimum physicochemical conditions required for the mycosynthesis of Co₃ O₄ -NPs and they were found to be: 72 h for reaction time, pH 11, 30°C, 100 rev min^-1 for shaking speed in the darkness using 4 mmol l^-1 of CoSO_4. 7H₂ O and 5·5% of A. brasiliensis dry weight mycelium (w/v). The mycosynthesized Co₃ O₄ -NPs were characterized using various techniques: spectroscopy including UV/Vis spectrophotometry, dynamic light scattering (DLS), zeta potential measurement, energy-dispersive X-ray analysis, Fourier transform infrared spectroscopy and X-ray diffraction; and vibrating sample magnetometry and microscopy including field emission scanning electron microscopy and high-resolution transmission electron microscopy. Spectroscopic techniques confirmed the formation of Co₃ O₄ -NPs and the microscopic ones confirmed the shape and size of the mycosynthesized Co₃ O₄ -NPs as quasi-spherical shaped, monodispersed nanoparticles with a nano size range of 20-27 nm. The mycosynthesized Co₃ O₄ -NPs have excellent magnetic properties and exhibited a good antimicrobial activity against some pathogenic micro-organisms.

Conclusion: Ferromagnetic Co₃ O₄ -NPs with considerable antimicrobial activity were for the first time mycosynthesized.

Significance and impact of the study: The use of fungi as potential bionanofactories for mycosynthesis of nanoparticles is relatively a recent field of research with considerable prospects.

Keywords: antimicrobial activity; cobalt oxide nanoparticles; magnetic properties; mycosynthesis; physicochemical factors; spectroscopic and microscopic techniques.