ELISA on a microchip with a photodiode for detection of amphetamine in plasma and urine

A rapid and sensitive assay was developed for the detection of amphetamine in plasma and urine. The method relies on the principle of competitive ELISA (enzyme-linked immunosorbent assay). A flow microchip with a total volume of 7 µL was used for the development of a chemiluminescent ELISA technique. Solutions, samples, and the chemiluminescence substrate were injected by a flow system, and a photodiode detector was used to measure the light intensity. The incubation time of the competitor (competition phase) was reduced to 10 min. Calibration curves corresponding to analyte concentrations ranging from 40 to 1000 µg/L in urine samples and from 6 to 96 µg/L in plasma samples were obtained. The detection limits were in the region of 20 and 6 µg/L in urine and plasma, respectively. The main focus of the work was on speed, reliability, reproducibility, and operational stability of the assay. This method was proven readily adaptable to automation and provided reproducible results.