Biocompatible l-Cysteine-Capped MoS₂ Nanoflowers for Antibacterial Applications: Mechanistic Insights

The development of multidrug-resistant bacterial infections seriously threatens public health. Hence, efforts are needed to develop a class of safe and effective antibacterial agents. Here, we report the synthesis of surface-modified molybdenum disulfide nanoflowers using a biogenic capping agent l-cysteine (MoS2-cys NFs). The morphological characterizations confirm the flower-like morphology with a 537 ± 12 nm size. Further, structural and surface investigations confirm the formation of the hexagonal phase of NFs and modification by l-cysteine. Also, the surface alteration of NFs by l-cysteine contributes to enhanced colloidal stability in aqueous media. The as-prepared MoS2-cys NFs exhibit excellent bactericidal activity against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria. The scanning electron microscopy images of the bacteria confirm the membrane-directed antibacterial mechanisms, where the nanosheets in the NFs act as nanoblades and cause cell membrane damage. The antibacterial mechanisms of MoS2-cys NFs are primarily attributed to membrane damage and the generation of oxidative stresses, which destroy both bacterial strains. The generation of oxidative stress can occur through reactive oxygen species-dependent and -independent pathways validated using flow cytometry and fluorescence imaging with DCFH-DA staining and Ellman's assay, respectively. The excessive generation of ROS leads to inactivation of the bacterial antioxidant defense mechanism. The toxicity studies of the MoS2-cys NFs toward human foreskin fibroblast cell lines suggested good biocompatibility with a cell viability of nearly 90%. We report an excellent intrinsic antibacterial efficiency of MoS2-cys NFs without any external stimulus (light, H2O2, etc.), additional functionalization or complexation, doping, drug loading, etc. Our study indicates that the appropriate surface modification of the flower-like morphology of MoS2 can enhance their colloidal stability and intrinsic antibacterial potency for further applications such as antibacterial coatings, water disinfection, and wound healing.