Technologies: Lateral-flow

Lateral-flow: how it works

Step 1

To perform the test, a sample is placed on the sample pad at one end of the strip. The sample may be used alone as is commonly done with urine or serum compatible tests, or it may be mixed with a buffer specific to the test. This buffer may simply be a diluent/running buffer or it may be much more complex and have specific components or properties required to make the strip perform properly, such as a cell lyses buffer. In the following description we are assuming a gold conjugate is being used. While this is one of the most common detection methods; however it is certainly not the only one available.

Step 2

With the addition of the sample, the detector molecules are solubilized. When solubilized the detector molecules mix with and bind to the analyte in the sample (if analyte is present).

Step 3

Then capillary action draws the fluid mixture up the sample pad and into the membrane. The sample/detector molecule mix continues to move up the membrane until it reaches the analyte capture molecule. In these lines a second (and third) antibody or antigen, immobilized as a thin stripe in the nitrocellulose will then capture the complex if it is positive for the target analyte. The control line should always show as a visible line, otherwise the test is invalid and must be repeated. If the test is positive, a colored (typically pink or purple) line develops along with the control line.

Step 4

Excess buffer along with any reagents not captured at the test of control line will then move into the absorbent wicking pad.