A real-time cell-electronic sensing method for comparative analysis of toxicity of water contaminants

Abstract

We report a real-time cell-electronic sensing (RT-CES) technique using the T24 bladder cancer cell line as a probe to analyze the comparative cytotoxicity of water contaminants. The RT-CES system consists of a 96-well E-plate embedded with microelectrodes in each micro-well. As T24 cells grow on the surface of the microelectrodes, the impedance between the cell-microelectrodes continuously increases with increasing cell number. When the cells are exposed to a chemical, the toxic effects on the cells resulting in cell death, detachment, and morphological changes reduce impedance. These dynamic changes are continuously monitored to provide real-time detection of cell responses. This method was successfully applied to analyze the cytotoxic characteristics of four halobenzoquinones (HBQs), emerging disinfection byproducts in drinking water, 2,6-dichloro-1,4-benzoquinone (DCBQ), 2,6-dichloro-3-methyl-1,4-benzoquinone (DCMBQ), 2,3,6-trichloro-1,4-benzoquinone (TCBQ), and 2,6-dibromobenzoquinone (DBBQ). T24 cells were seeded in each of the 96 microwells on the 96-E-plate, and treated with varying concentrations of the four HBQs. The RT-CES technique provides continuous profiles of HBQ induced cytotoxic responses and temporal IC₅₀ histograms in T24 cells, demonstrating concentration-, time- and compound-dependent cytotoxic effects. These results enable ranking of cytotoxicity of the four HBQs: DCBQ > DBBQ > DCMBQ > TCBQ. We further examined and compared the cytotoxicity of HBQs using the conventional neutral red uptake (NRU) and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assays, to complement the RT-CES data. The 24 h IC₅₀ values of HBQs obtained from RT-CES correlated with those from the NRU assay (R² = 0.9480, P < 0.05), while MTS results presented moderate and less consistent correlation with the results of the RT-CES and NRU (R² = 0.5281 and 0.3144, respectively). All three assays show that DCBQ causes greater toxic effects on T24 than the other three HBQs, although the IC₅₀ values are dependent on the assays. The RT-CES technique can provide sensitive and high-throughput testing of cytotoxicity of environmental contaminants.