Antibody products are traditionally divided into two classes based on whether they directly bind to antigens or not. Primary antibodies directly bind to a particular antigen of interest whereas secondary antibodies are those binding to primary antibodies. Primary antibodies could be conjugated to reporter molecules such as fluorescent dyes, horseradish peroxidase (HRP), alkaline phosphatase (ALP), biotin and so on. Conjugated primary antibodies are highly useful because they can be utilized to create a detectable signal via color-generation, fluorescence, or others. Conjugated primary antibody has no risk of cross-reactivity from secondary antibody but lacks signal amplification and flexibility and may result in high background. However, sometimes the primary antibody is not suitable for conjugation. Under these circumstances, the naked primary antibody and conjugated secondary antibody combination is suitable for you.
