Schematic representation of synthesis of organic-inorganic heterostructure and sensing mechanism of the proposed platform
Collaborative research efforts between an Indian research group, Dr Subbiah Alwarappan, CSIR-CECRI (Central Electro Chemical Research Institute), Karaikudi, and Chinese researcher, Prof. Xiaoqiang Liu, Henan University resulted in a biosensing platform that can operate in dual transducing mode viz., Electrochemical (EC) and Photoelectrochemical mode (PEC) for the detection of lactate. The construct was made by the hydrothermal deposition of poly (3,4-dioxo-ethyl thiophene) (PEDOT) on TiO2 Nanowire Arrays (TiONWs) which resulted in an organic-inorganic heterostructure.
In both the transducing mode, PEDOT-TiONWs heterostructure acted as an immobilization platform for Lactate Dehydrogenase (LDH), co-enzyme NAD+ and also generated current signals which were subsequently amplified by a cyclic catalytic mechanism. During PEC sensing, the photo-generated holes from PEDOT-TiONWs oxidize NADH back to NAD+ thereby completing a catalytic cycle. Herein, PEDOT extensively promoted the separation of electron-hole pairs and enhanced PEC signals due to its excellent energy level overlap (or matching) with TiONWs, high conductivity and strong visible light absorption.
A dynamic range of 0.5 - 300 ?M was achieved between the PEC signals and lactate concentration, based on which a sensitivity of 0.1386 ± 0.0053 ?A ?M?1 and a detection limit of 0.08 ± 0.0032 ?M were estimated. On the other hand, during electrochemical detection mode, LDH catalytically converted lactate to pyruvate and NAD+ was transformed to NADH.
Moreover, PEDOT-TiONWs directly oxidized NADH to NAD+ at 0.54 V to achieve the cyclic amplification due to the high conductivity and strong electrocatalytic capability of the heterostructure. EC biosensor exhibited 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.
H. Zheng, S. Zhang, X. Liu, Y. Zhou, S. Alwarappan, Biosensors and Bioelectronics, 162 (2020) 112234