Mn Doping Enhances the Antibacterial, Antibiofilm and Anti-Virulence Activity of ZnO Nanoparticles

The modulation of ZnO physicochemical properties through Mn doping represents a promising strategy for the development of multifunctional nanomaterials with enhanced biological performance. In this study, we investigate how the nominal Mn concentration influences both the physicochemical properties and antibacterial, antibiofilm, and anti-virulence activities of ZnO nanoparticles (NPs). Mn-doped ZnO nanoparticles containing nominal Mn from 2.5 to 10 mol% were synthesized through a simple wet-chemical approach and characterized by UV–Vis, Raman, TEM, EDX, and EELS analyses. The resulting ZnO-based NPs showed average dimensions of 3.7–4.8 nm, while increasing Mn incorporation produced measurable changes in optical response and morphology of nanoparticles. Antibacterial activity was evaluated against Gram-positive and Gram-negative bacterial models by assessing planktonic growth inhibition, biofilm formation, and pyocyanin production. The sample with the highest Mn amount (Mn10-ZnO) markedly enhanced antibacterial performance by reducing MIC90 from 150 to 37.5 μg/mL against Staphylococcus aureus and from 300 to 75 μg/mL for Pseudomonas aeruginosa. Mn doping also enhanced biofilm inhibition and produced a progressive reduction in pyocyanin synthesis. These results establish a concentration-dependent relationship between Mn concentration, nanoparticle properties, and antibacterial performance, highlighting the potential of Mn-doped ZnO nanoparticles for the development of anti-infective biomaterials, including antimicrobial coatings for implantable medical devices.