Amperometric Biosensors Based on Oxidoreductases Immobilized in Photopolymerized Poly(ethylene glycol) Redox Polymer Hydrogels

Abstract

The photoinitiated free-radical polymerization of redox polymer hydrogels permitted the efficient entrapment of oxidoreductases and the transfer of electrons from the enzymatic oxidation/reduction through the gel to the electrode surface. These hydrogels, based on networks of poly(ethylene glycol) diacrylate and vinylferrocene, were formed by illuminating at 365 nm, 20 W/cm2 a solution of the comonomers and an ultraviolet photoinitiator, 2,2‘-dimethoxy-2-phenylacetophenone. The kinetics of photopolymerization were characterized using ATR/FT-IR, which indicated rapid gelation of the comonomers. Electrochemistry of the redox polymer hydrogel indicated reversible oxidation/reduction with a formal potential of 184 mV (Ag/AgCl). The diffusion coefficient of charge transfer through the fully hydrated gel was measured at 2.0 × 10-12 cm2/s at 25 °C. Glucose enzyme electrodes were formed by dissolving lyophilized glucose oxidase or a concentrated aqueous solution of glucose oxidase into the comonomer/photoinitiator mixture followed by photopolymerization. Glucose enzyme electrodes based on these hydrogels had an extended linear range of 2−20 mM with a sensitivity of 0.5 μA mM-1 cm-2. A preliminary demonstration of photolithographic patterning of the hydrogels was also performed, using a shadow mask to form mesoscale patterns of ∼1 mm on a SiO2 surface.