Reading the conformational state of membrane proteins is central to understanding their role ir cell signaling, to using them as sensor elements and for screening candidate drug compounds that are targeted toward this important class of biomolecules. While the patch clamp technique for doing this is ubiquitous, it does have significant limitations: two electrodes are required to measure current flow, the gigaohm input impedance combines with unavoidable stray capacitance to limit the amplifier's bandwidth (typically to -10 kHz), and the gigaohmseal required at the cell membrane precludes scanning to image both distribution and dynamics of membrane proteins. To address these limitations, we will develop near-field probes, readouts, positioners and software to make a prototype system that confines high-frequency excitation to sub-wavelength proportions, enabling interaction with single membrane proteins. Since there are inherent dielectric contrast mechanisms available in protem-lipid systems, these can be used at high frequencies to provide a new method of protein readout. We have succeeded in demonstrating simultaneous recordings from alpha-hemolysin blocked by beta-cyclodextrin using both a conventional patch-clamp amplifier and a microwave source and detector. The microwave probe has the advantage of approximately 1 MHz bandwidth, so it is able to resolve more temporal detail than the patch clamp. Furthermore, the microwave probe is sensitive to changes both in conductance and capacitance, i.e. the movement of charge groups in the channel. This opens the door to probing for the first time changes in conformation that do rot otherwise change channel conductance. Finally, the microwave probe by its nature does not require a gigaohm seal (in fact, its impedance is 50 ohms), enabling us to realize a scanning electrode that can map both distribution and dynamics of channel activity. We will develop this prototype in conjunction with a collaborator in neuroscience so that the feedback gained from a field test will be used in making the system commercially viable.
