Combination of enzyme catalysis and electrocatalysis for biosensor fabrication: Application to assay the activity of indoleamine 2,3-dioxygensae

A new strategy to fabricate electrochemical biosensor is reported in this paper based on the selective combination of enzyme catalysis and electorcatalysis, thus an electrochemical method to assay the activity of indoleamine 2,3-dioxygensae (IDO) is proposed. Tryptophan, the substrate of IDO, is firstly covalently immobilized on a gold electrode surface. Oxidation of the tryptophan residue catalyzed by IDO and the subsequent hydrolyzation of the product by acetic acid may yield kynurenine, which may induce the immobilization of dithiobis [succinimidylpropionate] (DSP)-modified platinum nanoparticles (Pt NPs) onto the surface of the gold electrode. Since Pt NPs can electrochemically catalyze the reduction of H2O2 to produce electrochemical signals and the electrochemical wave can be correlated with the enzyme activity, electrochemical method to detect IDO activity is thus achieved. Under optimized conditions, IDO activity can be assayed in the range of 20–400 U/mL with a detection limit of 6.84 U/mL. The proposed biosensor shows high sensitivity, acceptable reliability, and can be used for the investigation of the enzymatic inhibition by inhibitors as well as the screen of the enzymatic activity in complex matrix such as serum samples.