Individual probes and arrays of probes which take advantage of thermoelectric principles to measure and modulate temperature on the cellular level will be microfabricated with the LIGA process. The LIGA process is a German-developed process which combines x-ray lithograpy,electrodeposition, and plastic molding. Within the arrays, probes for temperature measurement and temperature modulation will be interspersed according to the requirements for a specific process, and all probes will be individually addressable. The devices will give the biologist or bioengineer highly localized control of the temperature over large areas, or monitor temperatures at many locations in the same volume. In addition to being independent instruments for thermal and energetic studies of biological systems, the probes and probe arrays can become basic components in instruments requiring fine thermal control to assist in other investigations. Thermoelectric probes for temperature measurement are based on the Seebeck effect, and in the form of thermocouples are common sensor. The new development in this proposal will be the microfabrication of arrays of thermocouples at the cellular level or over a broad range of dimensions above that. Probes and probe arrays for temperature modulation based on the Peltier effect will also be a new develcpment. Prior applications of thermoelectric heating and cooling in microsystems have been limited by material issues. Materials with a suitable figure of merit for use in Peltier effect elements include bismuth and its alloys, which can be electrodeposited as one step in the LIGA process, overcoming those constraints. By taking advantage of the high aspect ratio microfabrication capabilities of the LIGA process, probes combining Peltier and Seebeck capabilities can be produced. The principal investigators and their collaborators are members of the LSU Microsystems Engineering Team (IlSET), which is one of the leading groups in LIGA process microfabrication in the United States. The team has the use of the synchrotron x-ray source at the Center for Advanced Microstructures and Devices (CAMD) at LSU, which is currently the premiere x-ray lithography facility in the world. In related work, IlSET investigators have produced arrays of scanning probe microscope (SPM) tips with initial diameters as small as 2 micrometers and heights up to 15 micrometers. With the LIGA microfabrication process probes with extremely high aspect ratios may be fabricated with single layers as deep as one millimeter. The spacing and arrangement of the thermocouples on a substrate will be a design variable open to change with each application. The proposed instruments will give biologists and bioengineers powerful new tools for studying and manipulating cellular systems. Three representative areas of application are: (1 ) Cryobiology, (2) Neuroscience, (3) Metabolic studies of cellular systems. The Pls have contacted and discussed applications and possible collaboration in the first two areas with investigators in those fields. Additional relationships will be developed as the design and fabrication of the probes progresses.
