Biological-to-electronic interface with pores of ATP synthase subunit C in silicon nitride barrier.
An oscillator pore is identified that generates intermittent, large amplitude, ionic current in the plasma membrane. The pore is thought to be composed of 10-12 units of subunit c of ATP synthase. Pore opening and closing is a co-operative process, dependent on the release, or binding, of as many as six calcium ions. This mechanism suggests a more general method of co-operative threshold detection of chemical agents via protein modification, the output being directly amplified in a circuit. Here the authors describe steps in the development of a sensor of chemical agents. The subunit c pore in a lipid bilayer spans a nanometer-scale hole in a silicon nitride barrier. Either side of the barrier are electrolyte solutions and current through the pore is amplified by circuitry. The techniques of laser ablation, electron beam lithography and ion beam milling are used to make successively smaller holes to carry the lipid patch. Holes of diameter as small as 20 nm are engineered in a silicon nitride barrier and protein activity in lipid membranes spanning holes as small as 30 nm in diameter is measured. The signal-to-noise ratio of the ionic current is improved by various measures that reduce the effective capacitance of the barrier. Some limits to scale reduction are discussed.