One step synthesis of positively charged gold nanoclusters as effective antimicrobial nanoagents against multidrug-resistant bacteria and biofilms.

Positively charged gold nanoclusters (AuNCs) hold great promises as novel nanoagents in many biomedical applications, but their controllable synthesis in a simple and efficient manner remains a challenge. In the present work, by using a commercial cationic ligand, (11-mercaptoundecyl) - N,N,N-trimethylammonium bromide (MUTAB), we demonstrated that water-soluble, positively charged AuNCs can be facilely synthesized in a one-step reaction. These MUTAB-AuNCs possess near-infrared luminescence, ultra-small size, good stability and biocompatibility as well as abundant positive charges in a wide pH range. Importantly, these positively charged MUTAB-AuNCs exhibit efficient antibacterial activity against both Gram-negative bacteria and Gram-positive bacteria without inducing drug-resistance, including multidrug-resistant (MDR) bacteria and clinical bacteria. The unique antibacterial mechanism of these positively charged AuNCs was also systematically investigated by different techniques, including surface plasmon resonance, scanning electron microscopy, fluorescence imaging, DNA leakage and reactive oxygen species (ROS) assays.