Amperometric Biosensors for On-Line Monitoring of Extracellular Glucose and Glutamate in the Brain

Two designs of thin film amperometric enzyme biosensor flow cell are described for the on-line measurement of glucose and glutamate concentrations in the extracellular fluid of the brain in conjunction with a microdialysis probe. The biosensors have high sensitivity and speed of response, enabling them to be used in the investigation of short term phenomena. The effects of oxidisable chemical compounds and other interferences on the amperometric current are discussed and strategies for eliminating these effects are described. Whereas the interferences can be adequately overcome with ease for glucose measurements in the millimolar range using platinised carbon paper-based enzyme electrodes, they are much more serious in the case of glutamate, which is present in brain extracellular fluid at much lower concentrations. Results are presented to demonstrate the applicability of two types of biosensor module for in vivo measurements.