A visual membrane immunoassay for the detection of methamphetamine using an enzyme-labeled tracer derived from methamphetamine and amphetamine.

A visual membrane enzyme immunoassay is described for the measurement of methamphetamine in urine. To increase assay sensitivity, tracers with chemically similar structures were cross-checked with the antibodies to determine their influence on the antibody binding. Tracers of horseradish peroxidase-labeled methamphetamine (MA-HRP) and amphetamine (A-HRP) derivatives were prepared for this purpose. Significant differences in antibody specificity were found between the two tracers. Based on the results of this study, a pair of an antibody and a tracer was selected and a membrane enzyme immunoassay (EIA) was developed utilizing the competitive binding between methamphetamine and the drug-HRP tracer. UltraBind membrane (0.45 micron) was used as the solid matrix to which the antibody was attached. Using diaminobenzidine substrate with Co2+ ion, a stable grey color appeared on the surface of membrane for MA-negative urine samples. No color appeared for MA-positive urine with a cut-off level of 0.8 ppm.