A novel ISFET-based NAD(+)-dependent enzyme sensor for lactate

An integrated NAD(+)-dependent enzyme field-effect transistor (ENFET) devic e for the biosensing of lactate is described. The aminosiloxane-functionali zed gate interface is modified with pyrroloquinoline quinone (PQQ) that act s as a catalyst for the oxidation of NADH. A synthetic amino-derivative of NAD(+) is covalently linked to the PQQ monolayer. Faradaic impedance spectr oscopy and chronopotentiometry are used as electrochemical methods for prob ing in situ bioaffinity interaction between NAD+-dependent enzyme, lactate dehydrogenase (LDH) (E.C. 1.1.1.27), and the NAD(+)-functionalized Au-elect rode surface. The association constant of 1.5 x 10(5) M-1 was found by both techniques. The affinity complex formed between the NAD(+)/PQQ-assembly an d the LDH is cross-linked and yields an integrated biosensor ENFET-device f or the analysis of lactate. The device reveals the lower detection limit of 1 x 10(-4) M for lactate and the sensitivity of 24 +/- 2 mV dec(-1). The r esponse time of the device is as low as 15 s. (C) 2001 Elsevier Science B.V . All rights reserved.