ONLINE MEASUREMENT OF BRAIN GLUTAMATE WITH AN ENZYME POLYMER-COATED TUBULAR ELECTRODE/

An on-line tubular electrode system is described which provides real t ime measurements of glutamate in brain microdialysate. It is based on the enzyme glutamate oxidase (EC 1.4.3.11) and the detection of H2O2 o n a platinum electrode at 600 mV vs Ag/AgCI. The enzyme is immobilized in a layer of o-phenylenediamine electropolymerized at 750 mV in a ph osphate buffer, pH 7.0. The layer is 10-15 nm thick and enables good e nzyme loading and fast response time. The ability of the polymer to bl ock out electroactive interferents like ascorbate and uric acid combin ed with a preoxidation system run at 600 mV resulted in a virtually in terference free glutamate assay with a lower detection limit of 0.3 mu M in the presence of physiological levels of interferents, a sensitiv ity of 4 nA/mu M, and a linear region up to 30 mu M. The system is opt imized for use with a microdialysis probe implanted in the brain and p erfused at 2 mu L/min. It provides a time resolution of <1 min and has been tested in vivo.