ILLUSTRAIONS  

A typical lateral flow rapid test strip consists of the following components:

Sample pad - an adsorbent pad onto which the test sample is applied.

the sample is treated to make it compatible with the rest of the test

Conjugate or reagent pad -  a particulate conjugate has been  immobilized, typically a  colloidal gold  or a  colored, fluorescent, or paramagnetic monodisperse latex particle or  cellulose nanobead.This particle has been conjugated to one of the specific biological components of the assay, either antigen or antibody depending on the assay format. The sample  remobilises  the dried conjugate, and the analyte in the sample interacts with the conjugate as they both migrate into the next section of the strip

Reaction membrane - typically a nitrocellulose or cellulose acetate membrane onto which anti-target analyte antibodies are  immobilized  in a line that crosses the membrane to act as a capture zone or test line (a control zone will also be present, containing antibodies specific for the conjugate antibodies).

Negative : The antibodies and the sample reach the T-line. The  immobilized  target substance is  recognized  and bound by gold-conjugated antibodies. The gold particles accumulate causing a visible line.

Positive : The drugs present in the sample are bound by the gold-conjugated antibodies in the conjugate pad. With drug concentrations in the patients sample higher than the cut-off, all binding sites are occupied and cannot bind in the t-line region. No T-tine will appear.

Control line   - a further absorbent pad designed to draw the sample across the reaction membrane by capillary action and collecting it on the final control line. The appearance of this line illustrates that the test has been  finalized.