We introduce instrumentation and methodology for twochannel chemical cytometry of sister cellsstwo cells born from division of the same mother cell. The method is based on capillary electrophoresis with laser-induced fluorescence detection and allows simultaneously probing multiple intracellular components in sister cells. To test the new technology, we compared the expression patterns of green fluorescent protein (GFP) between the sisters in cultured cancer cells stably transfected with a GFPexpressing construct. We found that all sister cells had detectable asymmetry in the GFP expression patterns with a confidence level of higher than 95%. To our best knowledge, this is the first reported observation of asymmetric patterns of protein expression in sister cells in a cancer cell line. The proposed technology can reliably detect minor differences in chemical contents between sister cells, which makes it a potentially indispensable tool in studying the molecular mechanisms of developmental processes. It will be especially valuable in quantitative studies of cells with complex proliferation kinetics (e.g., stem cells).

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