Subjects specimen is collected and introduced to the sample pad or device.
The sample moves onto a conjugate pad. This pad is typically coated with the desired conjugated antibody, such as colloidal gold or other fluorescent particles. If the target is present, the immobilized conjugated antibodies and labels will bind to the target forming complexes and continue to migrate along the test.
As the sample and antibody complex moves onto the antigen-coated nitrocellulose test line, interaction occurs. If the target antigen is present, a colored line will form and the density of the line depends on the quantity of that antigen present. To quantify and determine target concentration results, a rapid test can be combined with a digital reader. When there are no antibodies specific to the antigen, this results in no colored line to develop indicating a “negative” test.
Most tests will contain a second line, called the control line, which is coated with antibodies to pick up the excess gold conjugates particles. This results in a second colored line indicating the flow test operated correctly.
The sample will then reach an absorbent pad. This primary function of the absorbent pad is to allow an increase in the total sample volume to enter the test strip. This increased volume can be used to wash unbound detector complexes away from the test and control line, therefore lowering potential background and enhancing test sensitivity.