kromogen

Kromogen, more commonly spelled chromogen, refers to a chemical species that can be transformed into a colored compound through oxidation, reduction, or enzymatic reaction. In chemistry and biology, chromogens serve as substrates that yield a visible color change, enabling detection of chemical activity, enzyme presence, or biomolecular localization. The spelling with a K appears in older or non-English texts; modern usage generally favors chromogen.

In practical use, chromogenic reactions are foundational to many diagnostic and research techniques. In immunohistochemistry, chromogens act as substrates for enzymes such as peroxidase or alkaline phosphatase, producing a colored precipitate at sites where the target antigen is present. In clinical chemistry and laboratory diagnostics, chromogenic substrates are used in assays and rapid tests; the intensity of the produced color correlates with the amount of the target analyte or enzyme activity.

Common examples of chromogens include diaminobenzidine (DAB), which yields a brown pigment when oxidized by peroxidase in the presence of hydrogen peroxide; aminoethyl carbazole (AEC), which produces a red product; and substrates like TMB (3,3',5,5'-tetramethylbenzidine), which generate a blue color that can shift to yellow with stopping solutions. Other enzyme–substrate systems, such as nitro-blue tetrazolium with BCIP for alkaline phosphatase, produce purple or blue precipitates.

Safety and handling considerations are important, as some chromogenic substrates can be hazardous or carcinogenic. Proper ventilation, protective equipment, and disposal procedures are routinely recommended.