Silver nanoparticle microemulsion as a novel localized antimicrobial therapy: Formulation, efficacy, and safety evaluation

Background: The increasing prevalence of antimicrobial resistance necessitates the development of alternative therapeutic strategies. Silver nanoparticles (AgNPs) have demonstrated broad-spectrum antimicrobial activity, yet formulation challenges limit their clinical translation. This study aims to develop and evaluate an AgNP microemulsion as a novel localized antimicrobial therapy, focusing on its formulation stability, antimicrobial efficacy, and biocompatibility. Methods: A silver nanoparticle microemulsion was formulated using a bottom-up synthesis approach, stabilized with polyvinyl alcohol (PVA) and Tween 80, and characterized for particle size, zeta potential, and UV-visible spectroscopy. Antimicrobial efficacy was assessed against Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus mutans using disk diffusion and broth dilution assays. Cytotoxicity was evaluated in L929 fibroblast cells using the MTT assay to establish a therapeutic window. Results: The AgNP microemulsion exhibited a mean particle size of 175.97 ± 0.97 nm, with a zeta potential of -1.06 ± 0.42 mV, indicating moderate colloidal stability. UV-visible spectroscopy confirmed nanoparticle formation, with a plasmon resonance peak at 250 ± 0.42 nm. Antimicrobial testing revealed limited efficacy, with inhibition zones of 9.11 mm (S. aureus), 8.93 mm (P. aeruginosa), and 9.04 mm (S. mutans), significantly lower than 0.2% chlorhexidine. MIC and MBC values exceeded 0.7 mg/mL, suggesting suboptimal bactericidal potency. Cytotoxicity studies demonstrated >70% cell viability at concentrations ≤16 µg/mL, but significant toxicity at 32 µg/mL, indicating a narrow therapeutic window.Conclusion: This study highlights the potential of AgNP microemulsions as a localized antimicrobial alternative but emphasizes the need for formulation optimization to enhance bactericidal efficacy while minimizing cytotoxicity. Future studies should explore surface modifications, synergistic agents, and controlled-release strategies to improve clinical applicability.