Simultaneous electrochemical measurements of oxygen and dopamine in vivo

Fast-scan cyclic voltammetry, a demonstrated analytical method for the in vivo detection of catecholamine neurotransmitters, is extended to the simultaneous determination of molecular oxygen (O2). Cyclic voltammograms were recorded at a scan rate of 400 V/s at carbon-fiber disk electrodes coated with a perfluorinated ion-exchange material. The peak current for O2 occurs near -1.2 V under these conditions. In flow-injection experiments, these electrodes respond to step changes in dopamine and O2 with a half-rise time of less than 200 ms. The voltammetric peak current is independent of flow rate, indicating a diffusion-limited response unaffected by convection. Several compounds present in the in vivo matrix (adenosine, glutathione, and NAD and glutamic, lactic, and uric acids) were tested and shown not to interfere with the voltammetric signal for O2. These electrodes maintain a stable response in vivo for at least 6 h. They have been used to measure transient increases in both dopamine and O2 in the extracellular fluid of the caudate nucleus of an anesthetized rat in response to an electrical stimulus.