In-situ engineered MXene-TiO

Interfacial charge-carrier recombination is a bottle-neck issue restricting photoelectrochemical biosensors advancement in the wearable clinical electronics. In this study, we propose a simple approach to construct a highly efficient photoactive heterojunction capable of functioning as an active substrate in PEC biosensing of CD44 proteins. Taking the advantage of high photocatalytic activity of BiVO4, and biocompatible yet conductive 2D-Ti3C2Tx nanosheets, a workable heterojunction was constructed between in-situ formed TiO2 from the partially oxidized Ti3C2Tx and lysine functionalized BiVO4 (TiO2/MX-BiVO4). The interfacial arrangement was ideal for promoting fast charge transfer from photo-excited BiVO4 and TiO2 to Ti3C2Tx, constructing an energy level-cascade that permits minimal charge-carrier recombination besides robust photocatalytic redox activity. The PEC biosensor relies on the ligand-protein interaction, where hyaluronic acid was directly immobilized over TiO2/MX-BiVO4 based on the interactions between carboxyl of lysine and amino moieties of hyaluronic acid. The PEC biosensor response depends on the inhibition in the measured photo-oxidation current of mediator species, i.e., ascorbic acid after the addition of CD44 proteins. The superior photo-activity, and robust heterojunction arrangement, produced a sensitive signal capable of recognizing CD44 in the wide concentration window of 2.2 × 10-4 ng mL-1 to 3.2 ng mL-1 with a low-detection limit of 1.4 × 10-2 pg mL-1. The strong interaction between lysine functionalized BiVO4 and hyaluronic acid enabled biosensor to exhibit robust antifouling characteristics towards similar proteins such as PSA and NSE. The quantification of CD44 protein from real-blood serum samples further confirmed the biosensor's reliability for clinical application.