A method for the intracranial delivery of reagents to voltammetric recording sites

Carbon fiber microelectrodes are widely used for electrochemical monitoring in the intact brain. The local delivery of reagents to the recording site is often desirable. The approach of co-implanting a micropipette near the microelectrode presents some limitations that are overcome by the use of double-barreled devices. One barrel supports the carbon fiber and the other barrel serves as a pipet for local reagent delivery. Some studies have used iontophoretic delivery but here we consider the alternative approach of pressure ejection. However, placing the pipet so close to the electrode raises the risk that reagent can leak into the recording site. This problem is easily solved. We filled the tip of the pipet with vehicle solution, the barrel with a reagent solution, and separated the two solutions with an air gap to prevent their mixing. With this approach, reagent is delivered only after 'priming' pressure pulses: we show in two examples that unintended reagent delivery (leakage) prior to the priming pulses is non-detectable.