Intramolecular Electron Transfer through Poly-Ferrocenyl Glucose Oxidase Conjugates to Carbon Electrodes: 1. Sensor Sensitivity, Selectivity and Longevity

Enzyme-based amperometric biosensors measure target analyte concentrations through the transduction of enzymatically generated electrons into a detectable current at an electrode surface. To achieve efficient electron transfer, many such systems rely on the use of diffusive electron mediators or intricate, nanostructured electrode materials, which can limit applicability. Herein, we report on the development and characterization of enzyme-based glucose biosensors operating using a combination of intramolecular electron transfer and electron self-exchange through ferrocene-containing redox mediators covalently coupled directly to glucose oxidase (GOX). To accomplish this, we applied polymer-based protein engineering to grow poly(N-(3-dimethyl(ferrocenyl)methylammonium bromide)propyl acrylamide (pFcAc) via atom-transfer radical polymerization from initiator molecules attached to the GOX surface. The use of these GOX-pFcAc conjugates allowed the fabrication of simple, paper-based glucose biosensors through crosslinking with the carrier protein human serum albumin (HSA) within a viscous chitosan solution and drop casting onto carbon paper strips. Chit-GOX-pFcAc-HSA-carbon paper biosensors yielded a glucose sensitivity of 0.33 ± 0.01 μA mM−1 cm−2 and exhibited selectivity when challenged with other sugars. The ease of sensor fabrication further afforded a tailorable response through variation of GOX-pFcAc concentration upon crosslinking and drop casting. The reported approach shows the glucose sensing capabilities of a system that merges the characteristics of bioelectronics fabricated using redox-containing polymer networks with those based on the surface modification of enzymes with electron relays.