In vivo Electrochemical Sensors.

Abstract

Analyzing the brain’s extracellular chemical environment has the potential to provide significant insight into neurotransmission, pharmacology, and behavior providing insight into memory, thought, and disorders such as depression. In order to study these complex chemical interactions, scientists need tools that allow them to silmultaneously monitor many different physiological indicators. The Michigan neural probe platform currently allows researchers to study electrophysiological activity through recording and stimulation. However, little attempt has been made to expand the Michigan probe platform by adding chemical sensing capabilities to the probes. This dissertation fills that gap and describes the development and characterization of chemical sensors suitable for inclusion on the current Michigan neural probes. Several key components were developed as part of this project. A biocompatible IrOx reference electrode is described and several deposition processes are examined and compared. The IrOx reference electrodes are stable over a period of twenty days with an average variation in open circuit potential of 3.2 mV/day. The design and testing of a 65 nm potentiostat suitable for inclusion in an implantable neurchemical sensing system is described. The potentiostat consumes 2.2 mW of power in area of less than 0.02 cm2 and is capable of measuring currents as low as 1 nA. Finally several in vivo experiments are described which clearly demonstrate the ability to detect physiological changes in dopamine concentrations down to 100 nM using Michigan neural probes. The long-term goal of the project is the development of an integrated microsystem that will provide duality of sensing/actuation between the electrical and chemical domains for acute and chronic animal preparations.