Antimicrobial and antioxidant activities of algal-mediated silver and gold nanoparticles

This study focused on the synthesis and application of nanoparticles using Neodesmus pupukensis (MG257914). Cell free extracts of the microalga was employed to synthesize both silver (AgNPs) and gold nanoparticles (AuNPs). The nanoparticles were characterized using UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), and Scanning electron microscopy (SEM). The nanoparticles were screened for their antimicrobial potential and free radical scavenging activity against stable free radical (2,2-diphenyl-1-picrylhydrazyl). The UV absorption spectra showed absorbance peaks of 430 nm and 530 nm for AgNPs and AuNPs respectively. The FTIR spectra at 3283, 2102.87, 1636.02 for AgNPs and 3264.86, 2104.49, 1636.62, 1232.39, 1028.97 cm⁻¹ for AuNPs confirms the participation of proteins in the capping and stabilization of the nanoparticles. The zone of inhibition indicating the activity of the NP-AgNPs were: Pseudomonas sp (43 mm); Escherichia coli (24.5 mm); Klebsiella pneumoniae (27 mm), Serratia marcescens (39 mm) while AuNPs showed activity to only Pseudomonas sp (27.5 mm) and Serratia marcescens (28.5 mm). The antifungal potency of NP-AgNPs was confirmed with mycelial inhibition of 80.6, 57.1, 79.4, 65.4 and 69.8% against Aspergillus niger, A. fumigatus, A. flavus, Fusarium solani and Candida albicans respectively, while NP-AuNPs had 79.4, 44.3, 75.4, 54.9 and 66.4% against A. niger, A. fumigatus, A. flavus, F. solani and C. albicans respectively. Appreciable free radical scavenging properties was obtained with NP-AuNPs (68.9%) and NP-AgNPs (41.21%). The nanoparticles of Neodesmus pupukensis showed appreciable potential as antimicrobial and antioxidant agents and could be explored for various applications in biotechnology.