Lactate biosensor based on human erythrocytes

An amperometric lactate biosensor based on human erythrocytes is described. The erythrocyte suspension is retained near the platinum electrode by means of a semipermeable membrane. The response is based on lactate dehydrogenase activity in the erythrocytes and uses the oxidation of NADH by hexacyanoferrate(III) and amperometric detection of the resulting hexacyanoferrate(II). The limit of detection is 2.8 × 10^?5 mol l^?1, and the response is linear up to 1 mmol l^?1 lactate in the analyzed solution (11 mmol l^?1 in a blood sample). The response time is 7 min, and the useful lifetime is 2 weeks. The response is influenced only by reducing substances (uric acid) and malic acid. The effect of uric acid is readily compensated, and there is insufficient malic acid in blood to affect the results.