Bioactive electroconductive hydrogels: The effects of electropolymerization charge density on the storage stability of an enzyme-based biosensor

Electrode-supported hydrogels were conferred with the biospecificity of enzymes during the process of electropolymerization to give rise to a class of bioactive, stimuliresponsive co-joined interpenetrating networks of inherently conductive polymers and highly hydrated hydrogels. Glucose responsive biotransducers were prepared by potentiostatic electropolymerization [750 mV vs. Ag/AgCl (3 M KCl)] of pyrrole at Poly(hydoxyethyl methacrylate)-based hydrogel-coated Pt micro-electrodes (Φ=100 μm) from aqueous solutions of pyrrole and glucose oxidase (GOx; 0.4Mpyrrole, 1.0 mg/ml GOx) to 1.0 and 10.0 mC/cm². Polypyrrole was them over-oxidized by cyclic voltammetry (0-1.2 V vs. Ag/AgCl, 40 cycles in PBKCl, pH=7.0). Biotransducers were stored at 4°C in PBKCl for up to 18 days. Amperometric dose-response at 0.4 V vs. Ag/AgCl followed by Lineweaver-Burk analysis produced enzyme kinetic parameters as a function of electropolymerization charge density and storage time. Apparent Michaelis constant (K_Mapp) increased from 18.6-152.0 mM (1.0 mC/cm²) and from 2.7-6.1 mM (10.0 mC/cm²). Biotransducer sensitivity increased to 21.2 nA/mM after 18 days and to 12.8 pA/mM after 10 days for the 1.0 and 10.0 mC/cm² membranes, respectively. Maximum current, I_max, also increased over time to 2.7 nA (1.0 mC/cm ²) and to 170 pA (10.0 mC/cm²). Electropolymerization of polypyrrole is shown to be an effective means for imparting bioactivity to a hydrogel-coated microelectrode. GOx was shown to be stabilized and to increase activity over time within the electroconductive hydrogel.