The impact of pH on the size of biosynthesized silver nanoparticles: Evaluation of antioxidant and antibacterial activities

This study reports the green synthesis of silver nanoparticles (AgNPs) using the microalga Scenedesmus sp. and their characterization via UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). AgNPs were synthesized at pH values of 4, 7, and 10 and analyzed for size and stability using dynamic light scattering (DLS). Mean particle sizes were 223 nm (pH 4), 122 nm (pH 7), and 60 nm (pH 10), with spherical morphologies observed via SEM. Zeta potential measurements indicated increased colloidal stability at higher pH. AgNPs synthesized at alkaline pH (60 nm) demonstrated enhanced antimicrobial activity against Acinetobacter baumannii ATCC196306, Escherichia coli ATCC35218, Staphylococcus aureus ATCC29213, and Pseudomonas aeruginosa ATCC27853, compared to larger nanoparticles. Similarly, antioxidant assays revealed higher activity for these smaller nanoparticles. These results suggest that pH-controlled green synthesis can produce AgNPs with optimized antimicrobial and antioxidant properties, highlighting their potential applications in biomedical fields.