Probing Nanoscale Interactions of Antimicrobial Zinc Oxide Quantum Dots on Bacterial and Fungal Cell Surfaces

The need for novel antimicrobial agents in response to a growing antibiotic and antimicrobial resistance crisis is now at a breaking point. In this work, the use of 5 nm zinc oxide quantum dots (ZnO QDs), demonstrating rapid and high antimicrobial activity against Gram-positive methicillin-resistant Staphylococcus aureus and highly pathogenic yeast Candida auris cells under both non-photocatalytic and photocatalytic conditions, is showcased. Results show ZnO QDs adhere and cluster around the microbial cell surfaces, and exhibit antimicrobial response toward attached cells, resulting in the cell membrane damage. With the introduction of ultraviolet-A light, autogenous reactive oxygen species (ROS) are produced and caused further increase in cell membrane/wall disruption, in particular Gram-negative Escherichia coli. Nanoscale Fourier transform infrared is used to further confirm the intrinsic biochemical changes that occur with the Gram-negative cell membrane within 30 min and spectra demonstrate that biochemical alterations are achieved for the protein and carbohydrate component of the membrane, which is a common mechanism of ROS damage. Investigation of the cell membrane-material interaction and mechanism is crucial in developing and optimizing effective antimicrobial materials in combating the rise of antimicrobial resistance.