In the study, we explored the antimicrobial activities of single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) with different surface groups to bacterial pathogens, including Gram-negative vs Gram-positive species and rod-shaped vs round-shaped species. We report here for the first time that SWNTs' antimicrobial activity is buffer and concentration dependent, and the charge effect of functional groups on the surface of carbon nanotubes (CNTs) is not a critical factor. SWNTs with surface groups of -OH and -COOH exhibited extremely strong antimicrobial activity to both Gram-positive and Gram-negative bacterial cells in DI water and 0.9% NaCl solution regardless of cell shape, but they did not exhibit antimicrobial activity in PBS buffer and brain heart infusion broth. The antimicrobial activities of these two SWNTs increased with their concentration and treatment time. In DI water or 0.9% NaCl solution, SWNTs-OH and SWNTs-COOH started to show their antimicrobial activity at approximately 50 microg/mL; when their concentration increased to 200-250 microg/mL, they could inactivate 10(7) cfu/mL Salmonella cells in 15 min. The approximately 7 log reduction in viable cell count achieved by this CNTs-based method exceeded those of many reported antimicrobial methods. SWNTs-NH2 only exhibited antimicrobial activity at higher concentrations. MWNTs with surface groups of -OH, -COOH, and -NH2 did not show any significant antimicrobial activity to all tested bacterial cells in any of the tested buffers at concentrations up to 500-875 microg/mL. Formation of cell-CNTs aggregates were studied using fluorescence and electron scanning microscopes. The possible mechanism of SWNTs' antimicrobial activities was also discussed.

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In this study, electrical impedance-based measurements were used to distinguish oral cancer cells and non-cancer oral epithelial cells based on their cellular activities on the microelectrodes in a real-time and label-free manner. CAL 27 and Het-1A cell lines were used as the models of oral cancer cells and non-cancer oral epithelial cells, respectively. Various cellular activities, including cell adhesion, spreading, and proliferation were monitored. We found that both the kinetics of cell spreading and the static impedance-based cell index were feasible to distinguish the two cell types. At each given cell number, CAL 27 cell spreading produced a smaller cell index change rate that was 60-70% of those of Het-1A cells. When cells were fully spread, CAL 27 cells generated a cell index more than four times greater than that of Het-1A cells. Since cell spreading and attachment occurs in the first few hours when they were cultured on the microelectrodes, this impedance-based method could be a rapid label-free and non-invasive approach to distinguish oral cancer cells from non-cancer oral epithelial cells. Cell viability analysis was performed along with the impedance-based analysis. Confocal microscopic imaging analysis showed the difference in cell morphology and the thickness of cell monolayers between the two cell types.

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