NOVEL HEXACYANOFERRATE (III)-MODIFIED CARBON ELECTRODES - APPLICATIONIN MINIATURIZED BIOSENSORS WITH POTENTIAL FOR IN-VIVO GLUCOSE SENSING

We adapted a new technology for the modification of carbon base electr odes for use as probe-type, potentially-implantable glucose sensors. C arbon rods (diameter 0.3 mm) were modified by repeated potential cycli ng in 0.1 M potassium hexacyanoferrate (III). The modified-carbon elec trodes were sealed in plastic pipette tips with an exposed reaction ar ea where glucose oxidase was immobilized using glutaraldehyde. An oute r membrane of Nafion, followed by 15% (w/v) polyurethane, was applied over the enzyme layer. The miniature modified-carbon glucose sensors d isplayed a sensitivity to glucose in phosphate-buffered saline of 91.4 +/-19 nA/mM (mean+/-SEM) and a linear range up to 5.3+/-1 mM glucose w hen operated at 750 mV versus a silver/silver chloride reference. Corr esponding, unmodified-carbon based glucose sensors displayed a lower s ensitivity of 20.7+/-3 nA/mM with a linear range up to 3.8+/-0.5 mM. T he modified-carbon glucose sensors responded to glucose when operated in plasma but with a reduced sensitivity compared with that in buffere d saline. Glucose sensors displayed good stability for up to 6.5 days during continuous operation in 5 mM buffered glucose solution. Interfe rence from ascorbate and 4-acetamidophenol at both physiological and p harmacological ranges was significantly lower at the modified-carbon b ase electrodes than that at the unmodified-carbon base electrodes. Als o, the relatively large effect of ascorbate and 4-acetamidophenol at t he unmodified-carbon base electrode was reduced considerably when the base electrode was coated with glucose oxidase, Nafion and polyurethan e membranes. (C) 1996 Elsevier Science Limited