Fig. 4. (a) Fluorescence histograms of the M-270 MBs in the presence of different concentrations of PSA. PSA from left to right: 0 (blank), 0.5 pg mL^–1, 1 pg mL^–1, 5 pg mL^–1, 10 pg mL^–1, 25 pg mL^–1, 50 pg mL^–1, 100 pg mL^–1, 250 pg mL^–1, 500 pg mL^–1, 1 ng mL^–1, 2.5 ng mL^–1, 5 ng mL^–1, 10 ng mL^–1, and 20 ng mL^–1, respectively. (b) The correlation between the MFI values and PSA concentrations. The inset shows the plot between the MFI values and PSA concentrations in the range of 0–50 pg mL^–1. Error bars represent the standard deviation of three replicates. FL1 voltage for FCM measurements: 420 V.