Inorganic nanoparticles: multifunctional agents for antimicrobial photodynamic inactivation

Abstract The prevalence of antimicrobial resistance has intensified the need for alternative approaches to overcome the limitations of conventional drugs. Photodynamic inactivation (PDI), in which photosensitizers (PSs) generate reactive oxygen species upon light activation, has emerged as a promising strategy by inducing multi-target microbial damage. Nevertheless, low water solubility, aggregation, and limited performance of many molecular PSs, especially in complex environments such as biofilms, can reduce PDI efficacy. This review examines applications of inorganic nanoparticles (iNPs) in the PDI of bacteria and fungi, integrating fundamental principles, physicochemical properties, and biological interactions with PDI outcomes. Illustrative examples include silver nanoparticles associated with Zn(II) porphyrins, which enabled PDI-mediated eradication of Candida albicans at ~ 4- to 8-fold lower PS concentrations, whereas the PS alone caused a reduction of ~ 2–3 log 10 , and a silica-based platform that decreased Rose Bengal dark toxicity in Escherichia coli , increasing viability from ~ 43 to 83–99%. Conversely, Ag-doped TiO 2 induced ~ 30% C. albicans reduction even without irradiation, indicating light-independent antimicrobial activity. These and other examples are reported in the review, which shows that iNPs can broaden the scope of PDI applications through distinct and complementary mechanisms. Challenges, however, remain, such as variability in experimental parameters and data reporting, which may limit the interpretation of reported outcomes, along with limited fungal model diversity and incomplete mechanistic understanding, important aspects for clinical translation. Overall, this review outlines advances and challenges in the field, providing insights to guide the development of improved iNP-based platforms for antimicrobial photodynamic applications.