Selecting an appropriate secondary antibody depends on several factors. The species in which the primary antibody was raised is critical; the secondary antibody must be directed against the host species of the primary antibody. For example, if the primary antibody is a mouse monoclonal, an anti-mouse secondary antibody is required. Additionally, the detection method (e.g., fluorescence or enzymatic) will determine whether the secondary antibody should be conjugated with a fluorophore or an enzyme like horseradish peroxidase (HRP).
