An in vitro characterisation comparing carbon paste and Pt microelectrodes for real-time detection of brain tissue oxygen

Abstract

In vitro characterisation results for O₂reduction at Pt-based microelectrodes are presented and compared with those for carbon-paste electrodes (CPEs). Cyclic voltammetry indicates a potential of −650 mV vs. SCE is required for cathodic reduction at both electrode types, and calibration experiments at this potential revealed a significantly higher sensitivity for Pt (−0.091 ± 0.006 μAmm⁻²μM⁻¹vs. −0.048 ± 0.002 μAmm⁻²μM⁻¹ for CPEs). Since Pt electrodes are readily poisoned through contact with biological samples selected surface coated polymers (polyphenylenediamine (PPD), polymethyl methacrylate (PMMA) and Rhoplex^®) were examined in biocompatibility studies performed in protein, lipid and brain tissue solutions. While small and comparable decreases in sensitivity were observed for bare Pt, Pt-Rhoplex and PMMA there was minimal change at the Pt-PPD modified electrode for each 24h treatment, including an extended 3 day exposure to brain tissue. The polymers themselves had no effect on the O₂ response characteristics. Further characterisation studies at the Pt-based microelectrodes confirmed interference free signals, no effect of pH and ion changes, and a comparable detection limit (0.08 ± 0.01 μM) and response time (<1 s) to CPEs. Although a significant temperature effect (ca. 3% change in signal for each 1 °C) was observed it is predicted that this will not be important for in vivo brain tissue O₂ measurements due to brain temperature homeostasis. These results suggest that amperometric Pt electrodes have the potential to be used reliably as an alternative to CPEs to monitor brain tissue O₂ over extended periods in freely-moving animals.