Design of Surface-Coatable NIR-Responsive Fluorescent Nanoparticles with PEI Passivation for Bacterial Detection and Killing.

The ability to quickly detect and kill bacteria is crucial in the realm of antibiotic resistance. In this study, we synthesized a detection probe consisting of polyethylenimine (PEI)-passivated polydopamine-based fluorescent carbon (FDA:PEI) nanoparticles, generating a cationic adhesive material for bacterial detection that is surface-coatable, photothermal, and antibacterial. The cationic FDA:PEI nanoparticles effectively bound to the anionic bacterial cell wall, resulting in a dramatic quenching effect visible in fluorescence spectra and confocal images. In this fluorescence on/off system, FDA:PEI nanoparticles showed similar bacterial detection abilities between aqueous- and solid-phase assays. Scanning electron microscopy clearly showed the attachment of FDA:PEI nanoparticles to the surface of bacteria, both in solution and as a coating on the surface of a polypropylene film. In addition to detection, this versatile material was found to have an antibacterial potential, via near-infrared irradiation to induce a heat release, killing bacteria by thermolysis. Thus, by exploiting the cationic and catechol moieties on the surface of polydopamine carbon dots, we developed a novel bacterial-detection platform that can be used in a broad range of conditions.