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

Aims Investigate the capability of Aspergillus brasiliensis ATCC 16404 to mycosynthesize Co 3 O 4 ‐NPs. Methods and Results Mycelial cell‐free filtrate of A. brasiliensis ATCC 16404 was applied for mycosynthesis of Co 3 O 4 ‐NPs. The preliminary indication for the formation of Co 3 O 4 ‐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 Co 3 O 4 ‐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. 7H 2 O and 5·5% of A. brasiliensis dry weight mycelium (w/v). The mycosynthesized Co 3 O 4 ‐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 Co 3 O 4 ‐NPs and the microscopic ones confirmed the shape and size of the mycosynthesized Co 3 O 4 ‐NPs as quasi‐spherical shaped, monodispersed nanoparticles with a nano size range of 20–27 nm. The mycosynthesized Co 3 O 4 ‐NPs have excellent magnetic properties and exhibited a good antimicrobial activity against some pathogenic micro‐organisms. Conclusion Ferromagnetic Co 3 O 4 ‐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.