ZnO Nanoporous Spheres with Broad-Spectrum Antimicrobial Activity by Physicochemical Interactions

The extensive range of applications where synthetic nanomaterials are nowadays used is causing a huge commercial market. An incipient use of these nanomaterials arises from the need to generate alternative antimicrobial agents, anticipating the development of resistant micro-organisms. Here, we show a nanostructured ZnO with antimicrobial properties and low cytotoxicity based on a nanoparticle's arrangement by controlling the formation of sintering neck into nanoporous spheres. The antimicrobial effectiveness of ZnO spheres is tested in a broad spectrum of microorganisms such as fungi as well as Gram-negative and Gram-positive bacteria. The hierarchical structures show highly effective antimicrobial activity at low concentrations and in relatively short action times (24-72 h). We demonstrate that the enhanced antimicrobial properties against microorganisms are ascribed to a combining of both physical and chemical interactions between microorganism and ZnO. The approximation mechanism between microorganism and ZnO is provided through electrostatic forces (physical interaction) which, thanks to the ZnO-microorganism proximity, promote a rapid release of zinc cations and the reactive oxygen species penetration into microorganisms (chemical interaction). We believe that this work provides insights into the mechanisms underlying the interactions ZnO-microorganism and possesses a combined action mechanism for which nanostructured ZnO is so effective to combat microorganisms.