Rapid communication Membrane transistor with giant lipid vesicle touching a silicon chip

Lipid bilayers on silicon may become the matrix of future bioelectronic devices if the junction is sufficiently insulating. We touched the open gate of a field-effect transistor with a preformed giant lipid vesicle and bound the membrane by means of polyelectrolyte interaction. The sheet resistance along the junction was 100 GΩ and the membrane resistance was above 100 GΩ at a contact area of 1000 μm2. The bilayer was fluid and smoothly followed the surface profile of the chip. The compound lipid–silicon structure is suitable to couple semiconductor and electroactive proteins. PACS: 73.40.Mr; 87.16.Dg; 85.30.Tv Semiconductor devices may be coupled to wet biological systems without electrochemical perturbations: an electrical field created by a biomolecule can affect the electrons in the semiconductor; a voltage applied to the solid can affect ionic charges in an attached biomolecule. Such biophysical hybrids will be tools for probing and controlling biomolecular processes for scientific and technological applications. Prerequisite is sufficient electrical insulation between the coupling region and the surrounding electrolyte with the biological component kept in a proper environment. An attached lipid bilayer with integral protein — natural or designed — may be the material of choice. The geometry of a membrane on an open field-effect transistor in silicon is illustrated in Fig. 1a. The contact area of membrane and solid is a planar electrical core-coat conductor as illustrated in Fig. 1b. The insulation of the junction is determined both by the resistance of the membrane and by the resistance of the cleft between membrane and substrate. So far membrane–semiconductor contacts have been made by either (a) depositing monomolecular films or spreading lipid vesicles [1–5] or (b) spanning a bilayer over a shallow groove [6, 7]. The first approach is prone to defect formation with a low resistance of the membrane; the second method implies a large distance between membrane and support with a low resistance of the cleft. In the present study we avoided assembly of the bilayer on the chip. Instead we adapted an approach used to couple individual nerve cells to Fig. 1a,b. Membrane–silicon junction. a A lipid bilayer follows the surface profile of a metal-free field-effect transistor with thin gate oxide and thick field oxide. Membrane and oxide are separated by a cleft of electrolyte. The insert is scaled with a membrane thickness of about 4 nm. The white box symbolizes a membrane protein. b ac circuit of planar core-coat conductor formed by the sandwich electrolyte–membrane–cleft–oxide–silicon in the attached region of a vesicle. It is probed by ac voltages VE( f ) of frequency f applied to the bulk electrolyte. The voltage profile VJ(x, y, f ) in the junction is recorded with an array of transistors