What is the difference between capture antibody and marker-antigen?

A capture antibody is an antibody that is first immobilized on the surface of the plate when conducting a sandwich ELISA, instead of affixing the antigen onto the plate, as is done in non-sandwich ELISAs. In this case, the antigen is added afterwards to bind to the capture antibody, followed by a detector antibody.

“Marker antigen” is a term that can be used to refer to biomarkers, which are molecules that are used as indicators of a disease, condition, or process. The marker antigen can be tested for by using an antibody that is specific for that marker antigen.