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

ABSTRACT

Background: Amidst the growing challenge of antimicrobial resistance, there is an increasing demand for localized antimicrobial delivery systems with enhanced efficacy and safety profiles. Silver nanoparticles (AgNPs) have garnered attention due to their broad-spectrum antimicrobial potential; however, formulation instability and cytotoxicity remain critical barriers to their clinical translation. This study aimed to develop and characterize a silver nanoparticle-loaded microemulsion and evaluate its antimicrobial activity, physicochemical properties, and cytocompatibility. Methods: A silver microemulsion containing AgNPs at a concentration of 1000 ppm was formulated using polyvinyl alcohol and Tween 80 as stabilizers. The formulation was characterized by particle size distribution, zeta potential, and optical absorbance. Antimicrobial activity was assessed against Staphylococcus aureus, Pseudomonas aeruginosa, Streptococcus mutans and Candida albicans using disk diffusion and broth microdilution assays. Cytotoxicity was evaluated in L929 murine fibroblast cells using the MTT assay to determine biocompatibility and estimate the IC50. Results: The AgNP microemulsion demonstrated a mean particle diameter of 175.97 ± 0.97 nm with a zeta potential of −1.06 ± 0.42 mV, indicating moderate colloidal stability. Antibacterial activity was observed, with mean inhibition zones ranging from 8.9 to 9.1 mm across tested bacterial strains. No antifungal activity was noted against Candida albicans. MIC and MBC values exceeded 0.7 mg/mL, suggesting limited bactericidal potency. The formulation maintained acceptable cell viability (>70%) at concentrations up to 16 µg/mL, while cytotoxicity increased markedly at 32 µg/mL. The IC50 was determined to be approximately 28.6 µg/mL, delineating a narrow therapeutic index. Conclusion: The AgNP-based microemulsion exhibits potential as a topical antimicrobial platform; however, its relatively low potency compared to chlorhexidine and narrow safety margin underscore the necessity for formulation refinement. Strategies to enhance bioavailability—such as controlled-release delivery systems or combinatorial approaches with adjuvants—may improve pharmacological performance and clinical applicability.

KEYWORDS

• Silver nanoparticles
• microemulsion
• antimicrobial resistance
• localized drug delivery
• cytotoxicity
• formulation development

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• DOI10.18549/PharmPract.2025.4.3354Copy

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