The Melatonin rapid test strip is an immuno-chromatographic test, using colloidal gold immunoassay method. It relies on the competition between Melatonin residues in the sample and the Melatonin on T line, to the limited amount of dye-antibody. As a sufficient amount of drug in the sample is presenting, the drug will saturate the antibody. Consequently, it will show an extremely light or even invisible T line, indicating a positive result. On the other hand, if there is a negative sample (or the amount of the drug is lower than the minimum detectable concentration), it will generate two obvious lines in both the T and C line section.