A solid-phase, competitive immunoassay was adapted to a card format (QUIK-CARD)_the size and thickness are equivalent to an ordinary credit card. Antibody to the delta-9 tetrahydrocannabinol is incorporated in the two open spots of the card. In the test procedure, one drop of sample and one drop of control are added to the corresponding spot. Then one drop of enzyme-labeled drug solution is added to both spots. If the drug is present in the sample, the binding of enzyme label to the antibody will be inhibited while enzyme label in the control spot will bind to the full capacity. The binding of enzyme label is visualized with blue color resulting from the addition of two drops of enzyme substrate. A negative test is judged by the blue color in both spots while a positive test shows blue in the control spot and white in the sample spot. The entire process takes less than 5 minutes. The assay is very sensitive, as low as 5 ng/ ml. No instrumentation or special skill are required. The QUIK-CARD assay is ideal for quick-screening a large number of samples and can be used in the field or in the laboratory.National Institute on Drug Abuse (NIDA)
