Well-Defined Morphology Enables Tuning of the Antimicrobial Activity of ZnO Nanoparticles

Abstract

The antimicrobial activity of zinc oxide nanoparticles (ZnO-NPs) is intimately linked to their physicochemical properties, yet the specific contribution of morphology remains insufficiently understood due to current Zn2+ leaching and reactive oxygen species (ROS) generation. This work investigates the key role of ZnO-NPs morphology in governing the biological performance. Spherical (ZnO-S, 60–70 nm diameter) and needle-like (ZnO-N, ∼800 nm length) nanostructures were synthesized via a Metal–Organic Framework template-approach and hydrothermal synthesis, respectively, achieving precise morphological control. SEM characterization confirmed the distinct architectures produced, while XRD and Raman spectroscopy verified a wurtzite crystalline phase with minimal oxygen vacancies, preventing Zn2+ leaching. Antibacterial assays revealed that needle-like morphology displayed superior inhibition against Escherichia coli and Staphylococcus aureus, showing an inhibition of 90% and 80%, respectively, at a ZnO concentration of 1.2 mg mL–1. In contrast, spheric particles showed a concentration-dependent effects with a maximum inhibition of 50% under the same particle concentration. Antifungal activity of the ZnO-NPs was evaluated through the radial growth of Aspergillus niger and Penicillium citrinum using the Gompertz model. A needle-like loading of 0.055 mg cm–2 was sufficient to rapidly reduce the specific growth rate of A. niger from 0.049 h–1 to 0.013 h–1, while P. citrinum showed higher resistance irrespective of the morphology. Although both particles inhibited fungal growth, distinct morphology-driven mechanisms were observed: ZnO-S interfered with conidiation in A. niger, whereas ZnO-N rapidly suppressed colony expansion. Against P. citrinum, ZnO-N minimally altered the radial growth but strongly reduced spore production. Finally, ROS quantification revealed higher ROS generation in ZnO-S (74.8 ± 4.9 μg H2O2 eq/mg NP) compared to ZnO-N (60.4 ± 4.4 μg H2O2 eq/mg NP), highlighting morphology as a key determinant of antimicrobial activity. By directly linking nanoscale morphology with an antimicrobial mode of action, this study establishes morphology as a design principle for ZnO-based nanomaterials targeting specific pathogens.