Comparative Evaluation of Nano-based Ointments: AgNP, CuNP and ZnNP Formulations

This study presents a comparative assessment of silver (AgNP), copper (CuNP), and zinc (ZnNP) nanoparticle-based ointments with respect to their physicochemical, spectroscopic, antimicrobial properties, and long-term stability. All formulated ointments initially exhibited suitable characteristics for topical application, including acceptable pH values (5.2–5.7), high viscosities (~ 25,000 cP), and appropriate moisture content, hardness, spreadability, and ash values, confirming their suitability for dermal use. Spectroscopic analyses verified the successful incorporation and stability of the nanoparticles within the ointment bases. UV–Vis spectra showed distinct absorption peaks at 433 nm (AgNPs), 583 nm (CuNPs), and 310 nm (ZnNPs), indicating that the nanoparticles retained their nanoscale identity and optical activity without aggregation. FTIR spectra displayed characteristic O–H, C = O, C = C, C–O, and metal–ligand vibration bands, confirming the presence of nanoparticles and their chemical interactions with the excipients. Antimicrobial evaluation demonstrated that AgNP ointment exhibited the strongest and broadest activity, producing inhibition zones up to 21 mm at 500 mg/L and showing the lowest MIC and MBC/MFC values (50 and 100 mg/L). The CuNP ointment showed moderate antimicrobial effects, while the ZnNP ointment exhibited comparatively stronger activity against Gram-positive bacteria and fungal species. After 12 months of storage, the AgNP ointment retained excellent physicochemical and microbial stability. In contrast, the CuNP and ZnNP ointments developed phase separation, reduced viscosity, and increased microbial loads. Overall, the AgNP ointment demonstrated superior antimicrobial performance and long-term stability, whereas the CuNP and ZnNP formulations, though promising, require improved stabilization strategies to enhance shelf life and consistency.