Synthesis of a PEDOT-TiO heterostructure as a dual biosensing platform operating via photoelectrochemical and electrochemical transduction mode.

A new organic-inorganic heterostructure was prepared by the hydrothermal deposition of poly (3,4-dioxoethylthiophene) (PEDOT) on TiO nanowire arrays (TiONWs) to construct a biosensor that can simultaneously function as photoelectrochemical (PEC) and electrochemical (EC) sensor to detect lactate. In both cases, the PEDOT-TiONWs heterostructure not only acted as an immobilization platform for lactate dehydrogenase (LDH) and coenzyme NAD, but also generated current signals, which were further amplified by the cyclic catalytic mechanism. Specifically, LDH catalytically converted lactate to pyruvate, meanwhile NAD was transformed to NADH. For PEC sensing, the photo-generated holes from PEDOT-TiONWs could oxidize NADH back to NAD, fulfilling a catalytic cycle. Herein, PEDOT significantly promoted the separation of electron-hole pairs and enhanced PEC signals due to its well-matched energy levels with TiONWs, high conductivity and strong visible light absorption. A dynamic range of 0.5-300 μM was observed between the PEC signals and lactate concentration, based on which a sensitivity of 0.1386 ± 0.0053 μA μM and a detection limit of 0.08 ± 0.0032 μM were estimated. For EC sensing, PEDOT-TiONWs could directly oxidize NADH to NAD at ~0.54 V to realize the cyclic amplification due to the high conductivity and strong electrocatalytic capability of the heterostructure. The EC biosensor displayed a similar performance upon PEC mode of operation, except the relatively poor selectivity due to the possible oxidation of the interferences at the potentials > 0.54 V.