Antimicrobial Mode-of-Action of Colloidal Ti3C2Tx MXene Nanosheets

Antibacterial properties of two-dimensional (2D) nanomaterials are of great interest in fields such as environmental engineering, biomedical engineering, and medicine. Ti3C2Tx MXene, a novel 2D nanomaterial, has been reported to have excellent antibacterial activity against both Gram-negative and Gram-positive bacteria. This paper presents the first study aimed at determining the primary antibacterial mode-of-action of the MXene. We studied the antibacterial properties of MXene nanosheets with lateral sizes of 0.09, 0.35, 0.57, and 4.40 μm against Escherichia coli and Bacillus subtilis bacteria for 3 and 8 h in the dark. Quantitative analyses of bacteria species performed with complementary techniques, fluorescence imaging, and flow cytometry confirmed that the antibacterial activity of the MXene nanosheets is both size- and exposure-time-dependent. Smaller nanosheets showed higher antibacterial activities against both bacteria. For the first time, we applied broth microdilution assay to determine whether direct physical interactions between the MXene nanosheets and bacteria cells play a part in antibacterial properties of the nanosheets. Growth kinetics measurements evidently indicate that direct physical interactions between the sharp edges of the nanosheets and bacteria membrane surfaces play a crucial part in antibacterial properties of the nanosheets. The MXene nanosheets were found to damage the bacterial cells significantly in less than 3 h, leading to the release of bacteria DNA from the cytosol followed by bacteria cell dispersion. These results point to the great potential of MXene-based antibacterial products for water treatment, medical, and biomedical applications.