Preparation and validation of implantable electrodes for the measurement of oxygen and glucose.

In realizing the continuous measurement of pO2 and glucose concentration in the subcutaneous tissue, miniaturized electrochemical oxygen- and enzyme glucose sensors, based on modified Clark-type electrodes for transient implantation, were developed and investigated. The electrodes were prepared by means of sequential dipping procedures in glucose oxidase and in different polymer solutions at well-defined environmental conditions in an incubator. By means of combining a hydrophobic membrane with a glucose permeable area and a hydrophilic membrane in the case of the glucose sensor, linearity of the glucose dependent electrode signal up to greater than 20 mmol/l could be achieved. After subcutaneous implantation in the neck of dogs, the enzyme sensor is able to follow glucose profiles in the normo- and in the hyperglycaemic range, e.g. as caused by oral glucose loads. Looking for the difference in sensitivity of the enzyme sensor measured in vitro and calculated from in vivo data, the influence of potential nonspecific, interfering substances in vivo such as urea, amino acids, electrolytes, and albumin was estimated.