Eco-friendly synthesis of silver nanoparticles (AgNPs) using biological systems offers a sustainable alternative to conventional physicochemical methods. In this study, we employed cell-free extracts from three thermotolerant bacterial strains, Bacillus haynesii CamB6, Pseudomonas alcaligenes Med1, and Staphylococcus sp. BSP3 for the biosynthesis of AgNPs, aiming to explore their antioxidant and antibacterial properties.

The biosynthesized AgNPs were characterized through UV-Vis spectroscopy, FTIR, TEM, and DLS analyses, which revealed distinct physicochemical profiles among the nanoparticles. Notably, AgNP2 and AgNP3 exhibited smaller particle sizes, enhanced colloidal stability, and superior biological activities compared to AgNP1. Antioxidant evaluation demonstrated significant free radical scavenging potential, with AgNP2 showing the highest DPPH activity (65.18% at 5 mg mL-1). Antibacterial activity, assessed via agar well diffusion and cell viability assays against Bacillus cereus and Pseudomonas putida, revealed that AgNP2 achieved the lowest bacterial viability (0.74%) for P. putida at 1 mg mL-1 concentration.

The study highlights the potential of biosynthesized AgNPs, particularly AgNP2, as sustainable for biomedical applications. Their antioxidant and antibacterial activities suggest valuable applications in managing oxidative stress and combating antimicrobial resistance.