Immunohistochemistry (IHC) is the most common method of immunostaining. It uses antibodies to selectively identify antigens in biological tissues. In order to visualize antibody-antigen binding, the antibody is typically labeled with reporter molecules. In the most common instance, the antibody is conjugated to an enzyme, such as horseradish peroxidase (HRP) that can catalyze a color-producing reaction with its respective substrate. The signal output is generally colorimetric. Another alternative is to label your antibody with a fluorophore, such as fluorescein, and image using a fluorescence microscope.