Photoelectrochemical TiO₂ nanotube arrays biosensor for asulam determination based on in-situ generation of quantum...

Inspired by the photoelectrochemical (PEC) properties of TiO₂ nanotubes arrays (TNA) and their application as a super vessel for immobilizing biomolecules, we constructed an inhibition-effect PEC biosensor for determination of asulam based on the in-situ generation of CdS quantum dots (QDs) on TNA using an enzymatic reaction. Horseradish peroxidase (HRP) enzyme was covalently assembled on the inner-wall of TNAs, which exhibited good electrochemical and catalytic properties. In the mixture solution containing H₂O₂, CdY and S₂O₃^2-, HRP enzyme in TNAs catalyzed H₂O₂ reduce S₂O₃^2- to S^2-. The generated S^2- reacted with CdY to form CdS QDs in situ on the TNAs, improving the PEC performance of TNA under visible light irradiation. The photocurrent would decrease after addition of asulam due to its inhibitory effect towards HRP enzyme activity. Under the optimal experimental conditions, the constructed PEC TNA/HRP biosensor exhibited a satisfying linear range (0.02-2.0 ng mL^-1), low limit of detection (4.1 pg mL^-1) and good selectivity towards asulam determination, and has been successfully applied for the analysis of real environmental water samples with good accuracy of the recoveries ranged from 90% to 114%.