In LFIA, the sample flows through the device and uses the antibodies to display whether the targeted antigen exists in the sample or not. There are several parts to the LFIA device: the sample pad, conjugate release pad, test line, control line, and the absorbent pad. The sample pad is where the test taker inserts their sample. The sample is mixed with buffer salts and surfactants on the pad to optimize it to work best in the device. The mixed liquid flows down to the conjugate release pad, where the label, usually colloidal gold nanoparticles or fluorescence, and conjugate antibodies that are designed to target a specific antigen are located at. If the sample has the targeted antigen, it attaches to the labeled conjugate antibody. Colloidal gold nanoparticles are more commonly used than fluorescence because they change the colors when they aggregate due to the shift to longer wavelength within the surface plasmon band, making it easier to identify the existence of certain antigens without the use of another machine to detect fluorescence . The sample mixed with labels and conjugate antibodies moves to the test line, where there is a fixed antibody that attaches to the targeted antigen. If the targeted antigen exists, the antibody attaches to the antigen, its conjugate antibody, and the label from the conjugate pad in a way that the label faces the exterior. When enough labels are close to each other, they aggregate and change in color. If the targeted antigen does not exist, the antigen does not attach to the fixed antibody and move on. Whether the solution attaches to the test line or not, the remaining moves onto the control line. In the control line, the conjugate antibody from earlier should attach to the fixed antibody regardless of the existence of the targeted antigen, while again having the label face outwards. This should automatically change the color in the control line. If the color does not change, this indicates an error in the device, and the test taker must retake the test. Finally, the remaining solution empties in the absorbent pad.