Secondary antibodies are used to detect an unconjugated primary antibody that has bound to a target antigen. The term "secondary antibody" usually denotes an anti-immunoglobulin from a species different from the one producing the primary antibody.
The secondary antibody is usually modified so as to produce a visible signal by conjugation with an enzyme, fluorophore, radioisotope or a suitable particulate material. The characteristics of these secondary antibodies will influence both sensitivity and specificity of the assays in which they are used. Thorough knowledge of these characteristics is thus needed for critical evaluation of results.
Secondary antibodies are used in a second step to detect and amplify primary antibody signal by colour or light emission as fluorescence or chemiluminescence. Secondary antibodies can be either enzyme labeled (peroxidase, alkaline phosphatase), fluorescence labeled (FITC, Alexa-Fluor, Qdot) or biotin conjugated in order to amplify the detection signal which leads to sensitivity than that achieved with an enzyme or fluorescence conjugated secondary antibody alone.
SignalChem offers a number of secondary antibody products that can be used to detect the primary antibody from different species.