Abstract Based on the different permeability of DNA-intercalant dyes YO-PRO-1(YP) and propidium iodide (PI) to the membrane of vialble, apoptotic and necrotic cells, cell samples were was stained with 4mmol/L YP and 4mg/ml PI for 10 min, and the fluorescence intensity of both YP and PI were measured by fluorometer at Ex/Em wavelength of 485/538 nm and 530/590nm, respectively. The correlation between YP fluorescence intensity and the apoptotic cell number was confirmed by fluorescence microscope and linear regression (r = 0.999，P<0.01). As a result, the equation that accounted for the dependence of apoptotic cell number on the fluorescence intensity of YP was derived. This method proved highly sensitive, as it was able to detect as few as 180 apoptotic cells in a sample. Furthermore, apoptosis detection could be easily and quickly carried out in 96-well plates, which made it suitable for high-throughput applications.
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