Practice question

ELISA relies on enzyme conjugated antibodies converting chromogenic substrates into colored products measurable spectrophotometrically. Horseradish peroxidase commonly uses TMB, ABTS and O phenylenediamine OPD producing orange brown soluble product read at 492 nm after acid stop. Alkaline phosphatase uses pNPP. OPD offers good sensitivity and stability for peroxidase detection. RIA uses radiolabeled isotopes measured by gamma counter, Southern and Western blotting may use chemiluminescence or colorimetric substrates but OPD is classic ELISA chromogen, not used in nucleic acid hybridization or radioactivity detection protocols.