Artificial membranes, such as monolayers, multilayer assemblies, and large solvent-free lipid bimolecular membranes, will be used as the medium into which biological receptor macromolecules will be functionally incorporated and/or functionally reconstituted. The proposed studies encompass a range of chemosensor prototypes starting from lipid bimolecular membranes in a simple circuit which measures membrane conductance to a multilayer assembly deposited upon chemically sensitive electronic devices, which in principle allows complex discrimination between different chemical substances to be possible. These studies are designed to provide the necessary basis which will lead to the ultimate development of practical chemosensitive electronic devices which provide both ultratrace sensitivity and selectivity for a defined range of organic molecules.
Current projects include detection of molecules in gas by Olfactory Sensors. This work is directed toward the design and construction of a sensor for the detection and identification of specific molecules, and based on their relative size, chemical specificity, and characteristic electrical charge. In this sensor, the relative sizes are distinguished by differences in their diffusion through specially constructed small channels in monolayer films. After the molecules traverse the membrane pores, they impinge on a charge coupled device where they generate a signal proportional to their charge. Unique "signatures," or patterns, of particular molecules and their mixtures will be stored, analyzed, and so the system will "learn" to selectively recognize these molecules. (S. Pathirana, T. Roppel, W.C. Neely, and V. Vodyanoy).
Another current project includes a sensor for detection of pathogenic bacteria by using mass sensors coated with specific membrane immobilizing bacterial antibodies or DNAs. Changes in the mass, mechanical modulus, or electrical properties of a surface layer due to binding of specific proteins (or DNAs) produces corresponding changes in the measured parameters of the sensor. Two methods are utilized to immobilize antibodies or DNAs on the sensor surfaces: (1) deposition of a composite lipid-protein monolayer onto a sensor surfaces and (2) using Langmuir-Blodgett technique and biotin/streptavidin couple. (S. Pathirana, B. Chin, J. Barbaree, R. Zee, W. Gale, P. Hsieh, D. Conner, W.C. Neely, and V. Vodyanoy).
Basic research associated with the Membrane Biosensor program is focused on the initial chemoreceptive events in the animal olfactory system and to find out how is odorant information translated into electrical events in the olfactory receptor. The work involves the transfer of macromolecules from olfactory receptor cells into artificial bimolecular membranes, monolayer and multilayers, and studying the electrical and chemical properties of the reconstituted systems. Another focal point of this research is the use of functional reconstitution of the olfactory receptor cell to produce an artificial system responsive to small (subnanomolar) concentrations of odorant. The objective of this study is to develop a working prototype of an electrochemical sensor which shares basic molecular mechanisms associated with the initial steps in olfaction. We are also studying glutamate receptors reconstituted in bilayers using a combination of patch clamp and biochemical techniques. The main focus of this work is to determine molecular mechanisms of the specific facilitation of electrical activity of some of these receptors involved in the information storage (memory) in the brain. (S. Pathirana, S. Sinnarajah, D. Srikumar, V. B. Bahr, V. Suppiramaniam, E. Morrison, and V. Vodyanoy).