Antibacterial properties of two-dimensional (2D) nanomaterials are of great interest in fields such as environmental engineering, biomedical engineering, and medicine. Ti 3 C 2 T x 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.

Thin-film composite (TFC) membranes still suffer from fouling and biofouling. In this work, by incorporating a graphene oxide (GO)−silver-based metal−organic framework (Ag-MOF) into the TFC selective layer, we synthesized a thin-film nanocomposite (TFN) membrane that has notably improved anti-biofouling and antifouling properties. The TFN membrane has a more negative surface charge, higher hydrophilicity, and higher water permeability compared with the TFC membrane. Fluorescence imaging revealed that the GO−Ag-MOF TFN membrane kills Escherichia (E.) coli more than the Ag-MOF TFN, GO TFN, and pristine TFC membranes by 16, 30, and 92%, respectively. Forward osmosis experiments with E. coli and sodium alginate suspensions showed that the GO−Ag-MOF TFN membrane by far has the lowest water flux reduction among the four membranes, proving the exceptional anti-biofouling and antifouling properties of the GO−Ag-MOF TFN membrane.

For well over a century, Hans Christian Gram's famous staining protocol has been the standard go-to diagnostic for characterizing unknown bacteria. Despite continuous and ubiquitous use, we now demonstrate that the current understanding of the molecular mechanism for this differential stain is largely incorrect. Using the fully complementary time-resolved methods: second-harmonic light-scattering and bright-field transmission microscopy, we present a real-time and membrane specific quantitative characterization of the bacterial uptake of crystal-violet (CV), the dye used in Gram's protocol. Our observations contradict the currently accepted mechanism which depicts that, for both Gram-negative and Gram-positive bacteria, CV readily traverses the peptidoglycan mesh (PM) and cytoplasmic membrane (CM) before equilibrating within the cytosol. We find that not only is CV unable to traverse the CM but, on the time-scale of the Gram-stain procedure, CV is kinetically trapped within the PM. Our results indicate that CV, rather than dyes which rapidly traverse the PM, is uniquely suited as the Gram stain.

Two-dimensional (2D) nanomaterials have attracted considerable attention in biomedical and environmental applications due to their antimicrobial activity. In the interest of investigating the primary antimicrobial mode-of-action of 2D nanomaterials, we studied the antimicrobial properties of MnO and MoS, toward Gram-positive and Gram-negative bacteria. Bacillus subtilis and Escherichia coli bacteria were treated individually with 100 μg/mL of randomly oriented and vertically aligned nanomaterials for ∼3 h in the dark. The vertically aligned 2D MnO and MoS were grown on 2D sheets of graphene oxide, reduced graphene oxide, and TiC MXene. Measurements to determine the viability of bacteria in the presence of the 2D nanomaterials performed by using two complementary techniques, flow cytometry, and fluorescence imaging showed that, while MnO and MoS nanosheets show different antibacterial activities, in both cases, Gram-positive bacteria show a higher loss in membrane integrity. Scanning electron microscopy images suggest that the 2D nanomaterials, which have a detrimental effect on bacteria viability, compromise the cell wall, leading to significant morphological changes. We propose that the peptidoglycan mesh (PM) in the bacterial wall is likely the primary target of the 2D nanomaterials. Vertically aligned 2D MnO nanosheets showed the highest antimicrobial activity, suggesting that the edges of the nanosheets were likely compromising the cell walls upon contact.

Silver‐based nanomaterials have attracted considerable attention due to their antimicrobial activities. In this work, a silver (Ag)‐based metal organic framework (Ag‐MOF) is embellished with graphene‐oxide (GO), leading to the fabrication of a novel Ag‐based nanocomposite (GO‐Ag‐MOF) whose biocidal activity is higher than those of Ag‐MOF and GO nanomaterials. The nanocomposite is characterized using X‐ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscope, Fourier transform infrared spectra, ultraviolet−visible absorption spectra, X‐ray powder diffraction, dynamic light scattering, and nitrogen gas adsorption/desorption. The characterization shows that the Ag‐MOF nanoparticles are uniformly dispersed on the GO nanosheets surfaces without any agglomeration. Toxicities of GO‐Ag‐MOF, Ag‐MOF, and GO are assessed against the Gram‐negative bacteria, Escherichia coli and the Gram‐positive bacteria, Bacillus subtilis using the growth curve, fluorescence imaging, and flow cytometry methods. GO‐Ag‐MOF shows an outstanding antibacterial activity (higher than those of the Ag‐MOF and GO alone). The interaction of GO‐Ag‐MOF and Ag‐MOF with the bacteria leads to the extirpation of 95 and 85% of live bacteria cells, respectively. This study indicates that GO‐Ag‐MOF is a promising antibacterial nanocomposite, especially for biomedical applications.