Ceramic-Based Multisite Microelectrode for Electrochemical Recordings

This proposal is a renewal application of a grant that was funded to develop ceramicbased multisite microelectrodes for electrochemical and electrophysiological recordings. The development of ceramic-based multisite microelectrodes represents a parallel technology to the use of semiconductor-based microelectrodes. During the previous 3-year funding period we have successfully designed a multi-layer thin film microelectrode that has 4 Platinum recording sites that are insulated from the substrate, connecting lines and the bonding pads with polyimide. The resulting microelectrodes are cut out from a 1 cm x 1 cm ceramic wafer using a computer-controlled diamond saw. Yield is 64 per wafer with a success rate of 95%. The resulting microelectrodes have a triangular shape, 1 cm length, 2-5 micron tip and range from 37 to 125 microns in thickness. Two major designs were explored during the previous funding period: serial 4-site arrays and side-by-side microelectrode pairs. However, we have assembled over 9 different designs, to investigate optimization of the recording site properties. The current designs have been configured to record glutamate, choline, acetylcholine and gammaaminobutyric acid (GABA), using a Nafion layer coupled with a layer of oxidase enzyme, which is formed with glutaraldehyde and bovine serum albumin. In vitro and in vivo studies in anaesthetized animals support that the microelectrodes are capable of recording rapid changes in glutamate and choline using a new self-referencing recording paradigm. In addition, soak tests and in vivo electrophysiological recordings support that the microelectrodes can last up to 30 days in vivo. This is the first demonstration of microelectrode arrays formed from ceramic substrates and our papers and progress report support that these microelectrodes may be useful for a variety of neurochemical and electrophysiological applications. The present application concerns the more complete development of reliable ceramicbased microelectrode arrays for electrochemical recordings of neurotransmitters in CNS tissues. There are several issues that need to be resolved in order to use these microelectrodes for rapid, selective and sensitive recordings of glutamate, choline, acetylcholine and GABA in vivo. First, while the microelectrodes are sensitive and useful when incorporating our "self-referencing recording procedures", the microelectrodes can record interferents such as dopamine and norepinephrine. We will use two major strategies, the use of electrodeposited polyphenylenediamine films (with Dr. Robert O'Neill) and the use of an oxidase-enzyme based redox polymer (with Dr. Adrian Michael) to further improve the selectivity of the microelectrodes. Second, with the help of PCB Assembly, a local microelectronics engineering and manufacturing company, we will develop a micro-connector system to improve the performance of the microelectrodes and decrease production cost. Third, we are developing a low cost microcoater system, for more reliable micro-application of the enzyme layers to the microelectrodes. This is needed to allow for the use of the technology in other laboratories. Fourth, we will investigate micro-nanostructure formation (with Dr. Todd Hastings) to further reduce the microelectrode size, but try to attain sensitivities that rival larger microelectrode arrays. This is an exciting area for microelectrode development. By reducing the size of the recording sites, we may further enhance sensitivity, response time and packing density of the arrays. This may contribute to a more detailed understanding of the brain. Finally, we will pursue the development of the recording technologies in awake behaving rats. This is an important step in allowing the linkage between behavior and the neurochemical changes that occur during brain function. All of our proposed experiments should contribute to improved performance of the microelectrode arrays for chemical recordings in vivo. These technology improvements should decrease the cost of these sensors and associated devices, so that they can be used by other scientists. Such technology, may contribute to a better understanding of the dynamics of glutamate, choline, acetylcholine and GABA signaling in the brain and spinal cord.