A nano-enzymatic photoelectrochemical L-cysteine biosensor based on Bi₂MoO₆ modified honeycomb TiO₂ nanotube arrays composite

Improving light harvesting behavior and recognition sites of sensor is an effective way to achieve highly sensitive and selective detection of nano-enzymatic photoelectrochemical (PEC) L-cysteine (Cyst). In this work, the Bi₂MoO₆-TiO₂ composite (BMO-HTNTs) with honeycomb TiO₂ nanotube arrays (HTNTs) as light harvesting unit and Bi₂MoO₆ nanoparticles (BMO) as recognition unit was prepared. The typical honeycomb-nanoparticle heterostructure between HTNTs and BMO improves the separation efficiency of the electron-hole pairs. Moreover, BMO nanoparticles fully dispersed on HTNTs with large specific surface area provide more sites for Cyst recognition. The composite exhibited the enhanced light absorption and higher photocurrent density at 0.2 V (vs. Ag/AgCl), which was 4 times than that of HTNTs under simulated light. Ingeniously, Cyst can not only be specifically recognized through the Bi-S bonds but also act as electron donor to scavenge the photogenerated holes of BMO-HTNTs, resulting in the increase of PEC responses. The PEC sensor showed superior analytical performance for Cyst detection with two linear regression equations in the range of 500 nM to 500 μM and a detection limit of 150 nM. The results of the enzyme-free sensor on practical urine and serum samples demonstrated its promising application in biological monitoring.