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Unformatted text preview: Appl. Phys. A 69, 571–576 (1999) / Digital Object Identifier (DOI) 10.1007/s003399900153 Applied Physics A Materials Science & Processing Springer-Verlag 1999 Rapid communication Membrane transistor with giant lipid vesicle touching a silicon chip P. Fromherz, V. Kiessling, K. Kottig, G. Zeck Department of Membrane and Neurophysics, Max-Planck-Institute for Biochemistry, D-82152 Martinsried / München, Germany (Fax: +49-89 / 8578-2822, E-mail: [email protected]) Received: 12 August 1999 / Accepted: 16 August 1999 / Published online: 6 October 1999 Abstract. Lipid bilayers on silicon may become the matrix of future bioelectronic devices if the junction is sufficiently in- sulating. 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 G Ω and the membrane resistance was above 100 G Ω at a contact area of 1000 μ m 2 . The bi- layer 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 sys- tems without electrochemical perturbations: an electrical field created by a biomolecule can affect the electrons in the semi- conductor; 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 pro- cesses for scientific and technological applications. Prereq- uisite 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 mem- brane 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 spread- ing lipid vesicles [1–5] or (b) spanning a bilayer over a shal- low groove [6, 7]. The first approach is prone to defect for- mation with a low resistance of the membrane; the second method implies a large distance between membrane and sup- port 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.field oxide....
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