In Vitro and In Vivo Charge Capacity of AIROF Microelectrodes

Activated Iridium Oxide Film (AIROF) microelectrodes are thought to be well-suited for neural stimulation of the cortex because they can sustain high charge capacity (about ten times higher than Pt microelectrodes) when characterized in phosphate-buffered saline (PBS) or other high ionic strength electrolytes. However, it is known that their capacity diminishes after they are implanted in vivo. It has been suggested that tissue encapsulation is an underlying cause. In this paper, we report electrochemical measurements of AIROF microelectrodes that were performed acutely in the brain of the zebra finch. The experiment showed that the interstitial fluid environment in the bird's brain did not maintain the high charge delivery capacity of the AIROF microelectrodes. A simple compensation for access resistance may create hazards to sustained electrode integrity.