Sorbent Assay

Coating Antigen is adsorbed onto the wells in ELISA plate in coating buffer Blocking A buffer containing unrelated protein is used to block free sites in the wells Remove buffer and wash plate Readout Substrate is catalyzed by the enzyme to generate colored readout Key Remove buffer and wash plate Analyte/ Antigen Detection Enzyme conjugated detection antibody binds antigen Remove buffer and wash plate Enzyme Directly conjugated primary antibody Conjugated secondary antibody Capture antibody During diagnosis the sample suspected to contain the antigen is immobilized on the surface of an ELISA plate (Fig. . ) . The antibody specific to this antigen is added and allowed to react with the immobilized antigen.

The anti-antibody is linked to an appropriate enzyme like peroxidase. The unreacted anti-antibody is washed away and the substrate of the enzyme (hydrogen peroxide) is added with certain reagents such as -chloronaphthol. The activity of the enzyme yields a coloured product indicating the presence of the antigen. The intensity of the colour is directly proportional to the amount of the antigen.

ELISA is highly sensitive and can detect antigens in the range of a nanogram. There are four kinds of ELISA namely,