Carbon Dots: Visible Light Activated Antimicrobial Functions and Their Property-Function Correlations

Carbon dots (CDots), generally defined as small carbon nanoparticles (CNPs) with various surface passivation schemes, represent the nanoscale carbon allotrope at zero-dimension. Attributed to the π-plasmon-associated electronic transitions, CDots have remarkable broad optical absorptions in the entire visible spectrum, extending into both near-UV and near-IR, making them excellent visible light-excitable agents.<br/>In recent years, a large number of studies have provided strong evidence to support the establishment of CDots as a new class of effective and efficient visible/natural light-activated antimicrobial agents. Experimentally, our teams have demonstrated the highly effective photoactive antimicrobial activities of CDots against various bacteria and viruses, ranging from laboratory model bacteria (<i>E. coli, Bacillus subtilis</i>), pathogenic foodborne pathogens (<i>Listeria, Salmonella</i>), to multi-drug resistant (MDR) nosocomial pathogens (<i>Enterococcus</i>), and biofilms, as well as various viruses (model MS2 virus, vesicular stomatitis virus (VSV), marine norovirus (MNV), and norovirus virus-like-particles (VLPs).<br/>Mechanistically, upon photoexcitation on CDots, there are rapid charge transfers and separation to form electrons and holes redox pairs, followed by the radiative recombinations of the separated redox pairs resulting in emissive excited states, which are responsible for the bright fluorescence as well as the photodynamic production of classical reactive oxygen species (ROS). It is the combined action of the initially separated redox pairs and the generated classical ROS that are responsible for the observed uniquely effective photoactivated antimicrobial function of CDots. Associated oxidative damages in CDots-treated bacterial cells have been confirmed, including elevated levels of lipid peroxidation, increased membrane permeability, and cytoplasmic structural disruptions. Degradation in viral proteins and genomic RNAs have also been confirmed.<br/>The presentation will also include the insights on property-function correlations in CDots for their photoactivated antimicrobial activities . Extensive experimental results have revealed that the optical properties, the surface functional groups and charges, the passivation layers of CDots, as well as the synthesis processes, are highly correlated with their photoinduced antimicrobial functions. Such correlations make CDots to be excellent tunable and expandable material platforms for further improvement in their desirable functions. Along with their non-toxic nature, CDots open up new opportunities for the development of highly potent carbon-based non-traditional photodynamic antimicrobial agents.<br/><b>Acknowledgement:</b> The research was supported by NSF grants #2102021 , #2102056, & #1855905,, and USDA grants #2019-67018-29689 & #2023-67018-40681.