Brain tissue oxygen pressure monitoring using polyphenylenediamine-polyurethane-coated carbon fiber microelectrodes

Brain tissue oxygen pressure (PbtO2) monitoring is important to understand brain metabolism at rest or during neuronal activation. Electrochemistry provides high spatial and temporal resolution to achieve PbtO2 monitoring, especially platinum (so-called Clark electrodes) and carbon fiber microelectrodes (CFMEs). However, a major problem with in vivo PbtO2 recordings is a significant loss of sensitivity due to sensor fouling in the living brain tissue. Here, we tested a polyphenylenediamine-polyurethane (PPD-PU) coating to minimize electrode fouling in vivo and improve the stability of PbtO2 recordings. PPD and PU coatings were deposited on CFMEs (7 μm diameter, 100 μm long, 4400 μm2) and displayed less fouling in vivo than bare CFMEs, or CFMEs coated with PPD only. Oxygen reduction started around -300 mV vs Ag/AgCl and PPD-PU deposition increased microelectrode diameter by 1-2 μm. Carbon fiber microelectrodes coated with PPD-PU were used for 2.5-5 h of PbtO2 monitoring in anesthetized rats and there was no significant change in O2 sensitivity before and after in vivo implantation. These results indicate that PbtO2 monitoring can be achieved reliably using PPD-PU coating on carbon fiber microelectrodes, preventing electrode fouling in vivo, and providing an inexpensive and minimally invasive tool to study brain oxygen metabolism.