Green Bio-Manufacturing of Silver Nanoparticles Using the Green Microalga Cosmarium sp. (Desmidiaceae) and Assessment of Their Microbial Efficacy

This study aimed to prepare silver nanoparticles (AgNPs) using the green microalga Cosmarium sp. by mixing its crude methanolic and hexane extracts with silver nitrate solution (1:1, v/v), as well as assessing their antimicrobial characterization. Alga-mediated AgNPs were characterized by color change. UV-Vis spectroscopy, field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and energy dispersive X-ray diffraction (EDX) analysis were used in this study. This green bio-manufacturing approach led to the formation of AgNPs based on the color-changing evidence after 10-15 min of the mixing process. The UV absorption peaks at 408 nm and 414 nm, for the hexane and methanolic extracts, respectively, confirmed AgNPs formation. FE-SEM and EDX approaches showed that AgNPs particles were rod-shaped and ranged between 50-77 nm in size. For their antibacterial activity, the methanolic nano-extract of Cosmarium sp. was more effective against Klebsiella pneumonia, where the average diameter of the inhibition zone was 20 mm, while the hexane nano-extract exhibited the most antibacterial effect against Salmonella typhi with a diameter range of 22 mm. In addition, the synthesized AgNPs exhibited a prominent antifungal activity, particularly against Mucor racemosus, where the inhibition zones were 23 mm and 30 mm for the algal nano-methanolic and nano-hexane extracts, respectively.