In the diaphorase method for enzymatic glucose measurement, the colorimetric product is which color?

• A. Formazan blue
• B. Formazan red
• C. Indigo carmine
• D. Methylene blue

Answer: (A)

The essential idea is that the diaphorase system transfers electrons from NADH to a tetrazolium dye, producing a colored form of formazan. In this glucose assay, glucose oxidation generates NADH, and diaphorase uses those electrons to reduce a tetrazolium salt such as nitroblue tetrazolium to formazan. That reduced product appears as a blue color, which can be measured spectrophotometrically. Therefore, the colorimetric readout is blue (formazan blue). Indigo carmine and methylene blue are not formed in this reaction, so they don’t appear as the color product in this method.