Linearity of the measured fluorescence intensity. (A) Corrected total fluorescence from fluorescent beads of different (100%, 33%, 10% and 3%) nominal fluorescence intensity was measured in different PMT settings (450, 500, 550 and 600 volts) and analyzed using ImageJ. Linear regression and R-square are shown for each PMT setting. (B) Box plot presenting the mean values (minimum to maximum) of keratin expression in different breast cancer cell lines. Fluorescence was measured in 550 volts and a total of 100 cells were evaluated for each cell line.