Microdialysis fiber enzyme electrode involving amplification by substrate recycling

A microdialysis fiber electrode involving amplification for the NAD + /NADH couple is described. The electrode contains glucose‐6‐phosphate dehydrogenase, lactate dehydrogenase and lactate oxidase held stationary within its cavity, with a platinum fiber coated with poly(1,2‐diaminobenzene) film as a working electrode and a silver/silver chloride fiber as a reference electrode. Both NAD + and NADH are recycled enzymatically in the presence of an excess of glucose‐6‐phosphate and pyruvate in the measuring buffer solution. As a result, a large amount of L‐lactate produced in the electrode cavity is converted to pyruvate to produce hydrogen peroxide, which can be detected ampero metrically at the platinum fiber with a size‐exclusion film. Both NAD + and NADH were detected with a 25‐fold increase in sensitivity compared with the unamplified responses. The detection limit was 1 × 10 −7 M.