Synthesis of a PEDOT-TiO2 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 TiO2 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 mu M was observed between the PEC signals and lactate concentration, based on which a sensitivity of 0.1386 +/- 0.0053 mu A mu M-1 and a detection limit of 0.08 +/- 0.0032 mu M were estimated. For EC sensing, PEDOT-TiONWs could directly oxidize NADH to NAD(+) at similar to 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.