Used as a chromogenic substrate for horseradish peroxidase (HRP) in immunoassays such as ELISA, where it produces a blue color upon oxidation that can be measured spectrophotometrically. Commonly applied in diagnostic tests for detecting proteins, antibodies, or antigens due to its high sensitivity and low background signal. Also used in forensic science for latent blood detection, as it reacts with heme in blood to produce a visible color change. Stable in storage and provides consistent results in various assay formats.