Glucose enzyme electrode with percutaneous interface which operates independently of dissolved oxygen.

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An enzyme glucose electrode that operates even when no oxygen is dissolved in the glucose solution has been developed and its in vitro performance evaluated. The electrode has been designed to be used with a percutaneous interface for future in vivo use. Oxygen is supplied to the electrode from the atmosphere. The electrode is based on the conventional H2O2 detecting enzyme electrode, in which an Ag cylinder 4.5 mm in diameter and 16 mm in length is used as a cathode. A Pt wire 0.5 mm in diameter is fixed in the centre for an anode, and 0.5 micrograms of albumin-linked glucose oxidase is immobilised at the tip of the anode. A recess of 3.6 mm diameter and 5 mm depth is made at the top of the electrode, and a breathing orifice 0.8 mm in diameter is drilled along the axis of the electrode to link the recess to the atmosphere. A thin oxygen permeable silicone layer fills the recess, allowing oxygen in the atmosphere to be supplied to the enzyme through the silicone layer. The electrode has a linear response to glucose concentration at an electrode output current ranging from 0 to 20 nA even when the oxygen concentration of the glucose solution is zero. The use of polyurethane as a diffusion barrier to glucose limits the electrode output current at a glucose concentration of 500 mg dl-1 (27.8 mmol 1-1] to 20 nA. Therefore, the electrode can measure glucose concentrations up to 500 mg dl-1 (27.8 mmol 1(-1] with no oxygen dissolved in the glucose solution. The electrode with the percutaneous interface seems suitable for implantation in sites of low oxygen concentration such as subcutaneous tissues.