3-INDOXYL PHOSPHATE - AN ALKALINE-PHOSPHATASE SUBSTRATE FOR ENZYME IMMUNOASSAYS WITH VOLTAMMETRIC DETECTION

The voltammetric detection of the indigo blue generated when 3-indoxyl phosphate is used as the substrate for the alkaline phosphatase enzym e has been studied. This molecule undergoes a reversible process on a carbon paste electrode at 0.0 V in 0.1 M HClO4 and at around -0.4 V in 0.1 M Tris buffer. Moreover, it is strongly adsorbed on the electrode surface. For these reasons, a comparative study of the electrochemica l behavior of both, substrate and product, was carried out by cyclic v oltammetry and alternating current voltammetry. At the same time, the adsorption of an alkaline phosphatase labeled immunoglobulin G on a ca rbon paste electrode has been explored by these two techniques, using 3-indoxyl phosphate as the enzymatic substrate.