An implantable electrochemical glucose sensor

Rechargeable glucose electrodes for long-term implantation

A unique enzyme electrode was designed using glucose oxidase immobilized on fine graphite powder. The graphite-enzyme is in a fluid state which enables recharging of the system when the enzyme activity decreases, therefore allowing the system to have a long lifetime in a diabetic patient. The sensor was tested using glucose concentration in the range of 20-300 mg d-1. The electrode construction includes a hydrophobic membrane and a platinum electrode for detection of hydrogen peroxide. The signal output is large with minimal noise when tested in buffer. The sensor has been performing at ambient temperature for 4 months when stored overnight at 4 degrees C.

Towards implantable glucose sensors: a review

The clinical treatment procedures to monitor and control diabetes mellitus include the use of mechanical devices. Of these devices, closed-loop devices are preferred to open loop devices. However, the development of such devices depends to a great extent on the availability of reliable, long-lasting glucose sensors. In this paper, the status of implantable glucose sensors is reviewed. Glucose sensors are classified and discussed under the following headings: Enzyme catalysed electrodes; metal catalysed sensors; affinity sensors; and coated wire sensors. The relative merits of each of the sensor types are presented and experimental results for both in vitro and in vivo studies are summarized.

Continuous insulin infusion

A major new approach to the improvements of metabolic control in insulin-dependent diabetic patients is the replacement of insulin by delivery systems which simulate non-diabetic insulin secretory patterns. In the last ten years a number of open-loop, extracorporeal, portable infusion pumps have been used in research trials tasting from a few days to several years. Routine treatment by insulin pumps is now being considered. Most infusers are syringe-drivers, although peristaltic and reciprocating pumps have also been employed. All are based on a slow, basal delivery rate, supplemented by insulin boosts at meal-times. The most popular infusion route is via the subcutaneous tissue. Technological development is concentrating on miniaturisation, alarms (such as low battery state and motor over-run) and more flexible/programmable delivery rates.

Attempts are in progress to ‘close the loop’ using an implanted glucose sensor. Most electrodes are amperometric or potentiometric enzyme sensors employing immobilised glucose oxidase. Encouraging in vivo results are being obtained from a novel amperometric biosensor which uses ferrocene to mediate electron transfer. The most likely implantation site is the subcutaneous tissue.