4-Hydroxynaphthyl-1-phosphate as a substrate for alkaline phosphatase and its use in sandwich immunoassay Original Research Article

The synthesis and the use of a new substrate, 4-hydroxy-naphthyl-1-phosphate (HNP), for the amperometric detection of alkaline phosphatase activity is described. The product of the enzymatic hydrolysis of HNP was dihydroxy naphthalene (DHN). DHN was rapidly oxidized in air to give naphthoquinone (NQ), which was measured in amperometric flow injection analysis (AFIA) at 300 mV versus Ag/AgCl. DHN standards could be measured at a 60 nM detection limit. There was a linear response to the enzyme with a 300 fM detection limit, which was equivalent to 6 attomole for each injection. The measurement range for human IgG, in an alkaline phosphatase amplified sandwich immunoassay with amperometric, was 1–1000 ng/ml.