An amperometric enzyme electrode for bile acids

An amperometric enzyme electrode for the detection of bile acids using 3-α-hydroxysteroid dehydrogenase coupled to an N-methyl phenazinium tetracyanoquinodimethanide electrode (NMPTCNQ) is described. Kinetic analysis shows that the rate limiting step is the transport of substrate through the membrane. The response time of the electrode is less than 5 min and it has a detection limit of 1 μM. The electrode has the advantage over conventional methods of being able to detect the amount of free bile acid in solution. It has been tested in clinically derived samples of gastric aspirate. Excellent agreement has been found between the enzyme electrode and the more cumbersome conventional assay which involves incubation and the spectrophotometric determination of enzymatically produced NADH. The enzyme electrode has also been used to measure bile acid concentrations in plasma.