Enzyme electrode response in solution containing enzyme substrate and species that associates with the substrate

An enzyme electrode response to the substrate (S) reduced by the addition of a species (S′) that form a complex with S: an S–S′ complex formed was enzymatically inactive and the complexation, of course, brought about the decrease in the free S-concentration. This could be applied to the measurements of S in a high concentration range. For example, the addition of a phenylboronic acid, which was known to form a complex with diols, to a conventional glucose oxidase (GOx)-based electrode system enabled to determine glucose up to 50 mM. Furthermore, the concentration of S′ was determined from the current decrease of the enzyme electrode: the concentration of DNA could be measured by using a peroxidase (HRP)-modified electrode and leuco-methylene blue (MBred), which intercalated into DNA. In a solution containing methylene blue (MB) and hydrogen peroxide, a catalytic current was obtained on the HRP-modified electrode owing to the MB/MBred-recycling sequences. From the decrease of the catalytic current, the concentration of DNA (from salmon testes) was determined with the detection limit of 5 ng ml−1.