Electrochemical Sensing of Dopamine with an Implantable Microelectrode Array Microprobe Including an On-Probe Iridium Oxide Reference Electrode

Inclusion of an on-probe iridium oxide (IrOx) reference electrode on an implantable microelectrode array (MEA) microprobe enabled dopamine (DA) sensing with high sensitivity, an ultralow limit of detection, and high selectivity against common electroactive interferents. The monitoring of DA signaling in vivo is important for the study of brain disorders such as Parkinson’s disease and substance abuse. A postfabrication method for electrochemical deposition of an IrOx film onto a targeted microelectrode enabled integration of an IrOx reference electrode (RE) onto the same MEA as the DA sensing, working electrode (WE). The on-probe IrOx RE is an attractive alternative to commonly used external Ag/AgCl wire REs, which can be unstable and can cause inflammatory responses in vivo. The on-probe IrOx RE was tested for support of DA sensing performance in two-electrode (i.e., WE and RE) and three-electrode (i.e., WE, RE and counter electrode) configurations. The sensitivities of the integrated and externally referenced DA sensing microprobes were comparable at ∼2500 nA/(μM·cm²), however the integrated three-electrode configuration exhibited a 6-fold lower limit of detection of ∼9 nM due to an 82% reduction in baseline noise. In addition, excellent 1000:1 selectivity against common electroactive interferents makes these DA sensing microprobes attractive for implementation in vivo.