Atomic Force Microscopy Imaging and Electrical Recording of Lipid Bilayers Supported over Microfabricated Silicon Chip Nanopores: Lab-on-a-Chip System for Lipid Membranes and Ion Channels

Abstract

We describe a silicon chip-based supported bilayer system to detect the presence of ion channels and their electrical conductance in lipid bilayers. Nanopores were produced in microfabricated silicon membranes by electron beam lithography as well as by using a finely focused ion beam. Thermal oxide was used to shrink pore sizes, if necessary, and to create an insulating surface. The chips with well-defined pores were easily mounted on a double-chamber plastic cell recording system, allowing for controlling the buffer conditions both above and below the window. The double-chamber system allowed using an atomic force microscopy (AFM) tip as one electrode and inserting a platinum wire as the second electrode under the membrane window, to measure electrical current across lipid bilayers that are suspended over the pores. Atomic force imaging, stiffness measurement, and electrical capacitance measurement show the feasibility of supporting lipid bilayers over defined nanopores:  a key requirement to use any such technique for structure−function study of ion channels. Online addition of gramicidin, an ion-channel-forming peptide, resulted in electrical current flow across the bilayer, and the I−V curve that was measured using the conducting AFM tip indicates the presence of many conducting gramicidin ion channels.

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