Electrophoretically Sheathed Carbon Fiber Microelectrodes with Metal/Nitrogen/Carbon Electrocatalyst for Electrochemical Monitoring of Oxygen in Vivo

Metal/nitrogen/carbon (M/N/C, M = Co or Fe) nanomaterials have been demonstrated to catalyze oxygen reduction reaction (ORR) with implication in fuel cell studies; however, their potential application as sensing materials for in vivo monitoring of oxygen (O₂) in the central nervous system has never been reported. This study reports a first demonstration that M/N/C nanomaterials can be used as sensing materials to form an electrochemical assay for in vivo O₂ monitoring. To demonstrate this application, the M/N/C nanocomposites prepared by pyrolysis of zeolitic imidazolate framework (ZIF-67) are used as an example and is electrophoretically deposited onto carbon fiber microelectrodes (CFEs) to catalyze a four-electron reduction of O₂ without producing cell-toxic hydrogen peroxide intermediate. The M/N/C-sheathed CFEs have high catalytic performance toward ORR in a neutral solution, selectivity toward O₂ sensing in the presence of ascorbic acid (AA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), uric acid (UA), and 5-hydroxytryptamine (5-HT) at their physiological levels in rat brain, and capability to real-time monitor O₂ fluctuation during respiring gases. This study offers a new electrochemical approach to in vivo O₂ monitoring with nonplatinum catalyst for ORR.