Inhibition of 2,4-Dichlorophenoxyacetic Acid to Catalase Immobilized on Hierarchical Porous Calcium Phosphate: Kinetic Aspect and Electrochemical Biosensor Construction

The inhibition mechanism of 2,4-dichlorophenoxyacetic acid (2,4-D) to catalase was studied by a catalase biosensor in a flow-injection analysis (FIA) system. This system provides an ideal sensing platform to electrochemically evaluate the chemical mechanism of enzyme inhibition. Hierarchical porous calcium phosphate (hp-CaP), as a biocompatible nanomaterial, was used to immobilize catalase for repeat use. 2,4-D together with H2O2 was injected into the bioreactor of the immobilized catalase-FIA system during the experimental procedure. The activity of the immobilized catalase was inhibited, which caused a decrease of the catalase-catalyzed H2O2 reduction current. LineweaverBurk, Dixon, and CornishBowden plots confirmed that the inhibition of catalase by 2,4-D followed an competitive mechanism with a inhibition constant of 4.78 x 10(-7) M. Based on this inhibition characters, a biosensor for 2,4-D detection was constructed. This biosensor showed a linear range from 0.03 to 3.00 mu M with a detection limit of 0.015 mu M. It demonstrated good stability, acceptable reproducibility and low cost for 2,4-D screening. It has been successfully applied for the determination of 2,4-D in commercial bean sprouts samples. It is anticipated that a rapid evaluation of the chemical mechanism of catalase inhibition by the FIA system could pave the way to rationally designing biosensors.