Reporter enzyme binding probes have been widely used in many different experimental applications because of their ability to bind to many different kinds of macromolecules and the availability and variability of substrates. Enzymes are most commonly used for the detection of proteins, through direct and indirect antibody detection strategies or as nucleic acid hybridization probes for sensitive analysis of the required detection methods. Although significant progress has been made in the detection of fluorescence and luminescent labelling enzymes remain the most sensitive reporting group. For most applications, direct enzyme labeling provides the best overall performance, with the highest sensitivity, the least background and rapid detection. Enzymes such as horseradish peroxidase (HRP) or alkaline phosphatase (ALP) can bind to peptides and act as signaling molecules in a variety of applications.