Infectious diseases caused by bacterial pathogens have been a serious threat to public health for decades and remain one of the major concerns of our society. Control and prevention of pathogen contamination are effective ways to reduce the risk of infectious disease. The advancement of nanotechnology has brought various nanomaterials with remarkable properties for a wide range of applications, including the antimicrobial fields. Carbon-based nanomaterials represent a class of relatively safe and cost-effective materials yet with desirable antimicrobial properties which are applicable to the antimicrobial fields. This research explored the antimicrobial activity of two types of carbon-based nanomaterials and their composites: carbon nanotubes (CNTs) and carbon “quantum” dots.

We investigated the applications of single-walled CNTs (SWNTs), multi-walled CNTs (MWNTs), CNTs-Ag, CNTs-chemicals/natural peptides, CNTs-NIR, CNTs-coated surfaces, for inactivation of bacterial pathogens, bacterial spores, and viruses, inhibition of biofilms, as well as for capturing and concentrating bacterial pathogens (Fig. 1). The results indicated that SWNTs effectively inactivated Salmonella, E. coli cells, Bacillus anthracis cells in suspensions, but did not effective in inactivating bacterial spores. The microbial activity of SWNTs was concentration-, treatment time-, buffer-, CNTs’ length- and surface group- dependent. SWNTs coupled with H₂O₂ or NaOCl had the synergistic effect contributed by the two individual antimicrobial mechanisms of SWNTs and the oxidizing antimicrobial chemicals, and resulted in much stronger sporicidal effect compared to treatment with H₂O₂ or NaOCl alone at the same concentrations, doubling the log reduction of viable spore number (~3.3 log vs. ~1.6 log). MWNTs were not effective in inactivating bacterial cells in suspension, but MWNTs modified surfaces, including MWNT forest on silicon wafer and MWNT sheet on poly(methyl methacrylate) (PMMA) film, significantly increased surface hydrophobicity and enhanced the attachment of spores on their surfaces compared to the uncoated substrates, respectively, showing their potential as adsorbents for removal of Bacillus spores from fluids.

Carbon dots (CDots), defined as small carbon nanoparticles with various surface passivation schemes, with their optical properties and photocatalytic functions, were evaluated for their photoinduced bactericidal functions, with the results suggesting that the dots were highly effective in bacteria-killing with visible light illumination (Fig.1). Correlations between CDots property, including CDots quantum yield and surface functionalization, and antimicrobial activity were studied. Concentration- and time- dependency of CDots’ antimicrobial activity was examined. Mechanistic implications of the results will be discussed. Challenges and opportunities in the development of carbon dots into a new class of effective visible/natural light-responsible bactericidal agents for a variety of bacteria control applications will be discussed

Acknowledgement: The research was supported by NSF grants: DMR# 1701399 and NIH grant R15GM114752.