Colorimetric method Luminescent method   CV % Recovery % CV % Recovery % Unspiked DS -   20.9   25 ng/ml spiked DS 9.8 109 5.5 98.75 5 ng/ml spiked DS 14.4 121.04 6.3 94.52 1 ng/ml spiked DS - 39.39 30.5 77.35

Table 5: The CV and recovery of spiked DS as back-calculated from the log-log fit calibration curve of luminescent or colorimetric ELISA.