Characterisation of carbon paste electrodes for real-time amperometric monitoring of brain tissue oxygen

Tissue O2 can be monitored using a variety of electrochemical techniques and electrodes. In vitro and in vivo characterisation studies for O2 reduction at carbon paste electrodes (CPEs) using constant potential amperometry (CPA) are presented. Cyclic voltammetry indicated that an applied potential of −650 mV is required for O2 reduction at CPEs. High sensitivity (−1.49 ± 0.01 nA/μM), low detection limit (ca. 0.1 μM) and good linear response characteristics (R2 > 0.99) were observed in calibration experiments performed at this potential. There was also no effect of pH, temperature, and ion changes, and no dependence upon flow/fluid convection (stirring). Several compounds (e.g. dopamine and its metabolites) present in brain extracellular fluid were tested at physiological concentrations and shown not to interfere with the CPA O2 signal. In vivo experiments confirmed a sub-second response time observed in vitro and demonstrated long-term stability extending over twelve weeks, with minimal O2 consumption (ca. 1 nmol/h). These results indicate that CPEs operating amperometrically at a constant potential of −650 mV (vs. SCE) can be used reliably to continuously monitor brain extracellular tissue O2.

Research highlights▶ High sensitivity, low detection limit and good linear response characteristics. ▶ No effect of pH, temperature, ion changes, and no dependence upon fluid convection. ▶ No interference from endogenous species with the CPA O2 signal. ▶ Minimal O2 consumption and a sub-second response time both in vitro and in vivo. ▶ Long-term in vivo stability extending over twelve weeks.