Horseradish peroxidase-catalyzed polymerization of L-DOPA for mono-/bi-enzyme immobilization and amperometric biosensing of H2O2 and uric acid.

Horseradish peroxidase (HRP)-catalyzed polymerization of L-DOPA (vs. dopamine) in the presence of H2O2 (and uricase (UOx)) was exploited to immobilize mono-/bi-enzymes for hydroquinone-mediated amperometric biosensing of H2O2 and uric acid (UA). The relevant polymeric biocomposites (PBCs) were prepared in phosphate buffer solution containing HRP and L-DOPA (or plus UOx) after adding H2O2. The mono-/bi-enzyme amperometric biosensors were prepared simply by casting some of the PBCs on Au-plated Au (Au(plate)/Au) electrodes, followed by coating with an outer-layer chitosan (CS) film for each. UV-vis spectrophotometry, scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy were used for film characterization and/or process monitoring. The HRP immobilized by enzyme catalysis well preserved its bioactivity, as confirmed by UV-vis spectrophotometry. Under optimized conditions, the monoenzyme CS/HRP-poly(L-DOPA) (PD)/Au(plate)/Au electrode potentiostated at -0.1V responded linearly to H2O2 concentration from 0.001 to 1.25mM with a sensitivity of 700μA mM(-1)cm(-2) and a limit of detection (LOD) of 0.1μM, and the bienzyme CS/UOx-HRP-PD/Au(plate)/Au electrode at -0.1V responded linearly to UA concentration from 0.001 to 0.4mM with a sensitivity of 349μA mM(-1)cm(-2) and a LOD of 0.1μM. The mono-/bi-enzyme biosensors based on biosynthesized PD performed better than many reported analogues and those based on similarly biosynthesized polydopamine.