This study investigated the effect of SWCNTs' length on their antimicrobial activity to bacterial cells in suspensions. Three different lengths of SWCNTs (<1 μm, 1-5 μm, and ∼5 μm) were tested. At same weight concentration, longer SWCNTs exhibited stronger antimicrobial activity. The fluorescence and SEM images revealed that the longer SWCNTs aggregated with bacterial cells more effectively, whereas short length SWCNTs tended to aggregate themselves without involving many bacterial cells. Moreover, longer SWCNTs exhibited more pronounced concentration-dependence and treatment time-dependence on their antimicrobial activity.
In this study, electric/electrochemical impedance spectroscopy and cyclic voltammetry were used to study the cellular activities of oral cancer cell line CAL 27, including the kinetics of cell adhesion, spreading, and cell proliferation on interdigitated microelectrodes (IMEs). Impedance spectra of CAL 27 cells on IMEs electrodes were obtained in cell growth medium and in 0.1 M PBS with 50 mM [Fe(CN)₆]³⁻/⁴⁻ as redox probe. Equivalent circuits were used to model both cases. In cell growth medium, impedance spectra allowed us to analyze the changes in capacitance and resistance due to cell attachment on the IMEs over the entire experiment period. It was found that cell spreading caused the most significant decrease in capacitance component and slight increase in resistance component. Impedance change at given frequencies (between 10 kHz to 100 kHz) was found to be linearly increased with increasing cell number of CAL 27 on the IMEs. In comparison with non-cancer oral epithelial cells (Het-1A), at equal cell number, cancer cells always generated impedance several folds higher than that of non-cancer cells. In the presence of [Fe(CN)₆]³⁻/⁴⁻, impedance spectra allowed us to analyze the change in electron transfer resistance of IMEs due to cell attachment, in which an increase trend was observed at 24 h with increasing cell number from 2500 cells to 10,000 cells on IMEs. Double layer capacitance was also affected by cell attachment, and a decrease in double layer capacitance was observed with increasing cell number on the electrodes. Cyclic voltammetric measurements correlated well with the impedance results. The results of this study demonstrated the use of electrochemical approaches to obtain and understand cellular behaviors/activities of oral cancer cells, potentially providing useful tools for cancer cell research.
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.
In this study, single-walled carbon nanotubes (SWCNTs) coupled with near infrared (NIR) laser treatment to enhance SWCNT's antimicrobial activity were studied. Salmonella, agram-negative pathogenic bacteria, was used as a model bacteria in this study. We found that NIR treatment (800 nm, 475 mW, for 20 min) to bacterial suspension with 50 microg/ml SWCNTs reduced the cell growth by approximately 55.5% compared with the cell sample with 50 microg/ml SWCNTs alone. Determined by the plating method, the viable cell number in the SWCNTs-NIR treated samples reduced by 2.2 log, while SWCNTs alone only had 0.7 log reduction. Imaging analysis of bacterial cells with and without NIR treatment correlated well with the growth and viable cell reduction measurement. We also found that the enhancement of SWCNTs' antimicrobial activity by NIR treatment was related to the NIR power, the NIR treatment time, and SWCNTs' concentration. The localized heating of SWCNTs under NIR treatment was the likely mechanism to enhance the antimicrobial efficiency of SWCNTs beyond its intrinsic antimicrobial activity. The results of this study suggested that SWCNTs-NIR treatment has the potential to be an effective antimicrobial method.
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