CHO-K1 cell number response was measured with Cell Viability Assay Kit (Fluorometric - Blue Ex 405 nm) (ab176748). CHO-K1 cells were seeded overnight at 0 - 5,000 cells/well/100 µL in a black wall/clear bottom 96-well plate. The cells were incubated with 100 µL/well of CytoCalcein Violet 450 dye-loading solution for 1 hour at room temperature. The fluorescence intensity was measured at Ex/Em = 405/460 nm. The fluorescence intensity was linear (R2 = 1) to the cell number as indicated.The detection limit was 70 cells/well (n=6).