Antimicrobial Activity and Cytotoxicity of Submicron Silver Phosphate: Synthesis, Characterization, and Mechanistic Insights

Silver phosphate submicron particles (SPSMs) were synthesized using a hydrothermal method and characterized using X-ray diffraction (XRD) to confirm their crystalline structure, scanning electron microscopy (SEM) for morphological analysis, diffuse reflectance spectroscopy (DRS) for optical properties, and Fourier transform infrared (FTIR) spectroscopy to analyze the molecular vibrations of phosphate groups. FTIR spectra revealed two distinct bands at 920 cm⁻¹ and 523 cm⁻¹, corresponding to the symmetric and asymmetric stretching modes of the P-O bonds and the bending mode of the P-O–P bonds, respectively. The antimicrobial activity of SPSMs was evaluated against bacterial and fungal pathogens using agar-well diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) tests. SPSMs exhibited significant antimicrobial activity, with inhibition zones ranging from 10 mm to 33 mm, depending on the pathogen and concentration. MIC values ranged from 0.24 to 1.95 µg/mL, indicating potent inhibition, while MBC values ranged from 0.48 to 3.9 µg/mL, demonstrating effective killing. The antimicrobial action is attributed to the release of silver ions, disruption of microbial membranes, and generation of reactive oxygen species (ROS), which contribute to microbial cell damage. Cytotoxicity tests on human skin fibroblast (HSF) cells showed a dose-dependent reduction in cell viability, with 81.83% viability at 500 µg/mL and 12.7% at 0.97 µg/mL. These findings highlight the dual nature of SPSMs: while they exhibit strong antimicrobial properties, their cytotoxicity at higher concentrations must be carefully considered in their potential applications. Overall, SPSMs show promise as antimicrobial agents for medical, environmental, and industrial applications, but further research is needed to optimize their synthesis, reduce toxicity, and enhance their selectivity for microbial targets.