Profiles of Voltage and of Channel Density in a Planar Membrane Cable on Micromachined Silicon

Abstract

A lipid bilayer of glycerolmonoleate is spanned over a microscopic shallow groove etched into the 110 surface of a silicon wafer and insulated by thermal oxidation. The conductance of the bimolecular membrane is modulated by gramicidin. The voltage profile in the groove is recorded by a set of Ag/AgCl electrodes which are integrated into the bottom of the groove. It is used to determine the distribution of ion channels along the membrane on the basis of Kelvin's cable equation.

Membrane-Transistor Cable

“…If we failed to make a cable, the chip was cleaned again with methanol and pure water and the experiment was repeated immediately. Bilayers made from a mixture of POPC and GMO were more stable than bilayers of pure GMO as used in previous experiments. − We were not able to obtain stable BLMs of pure POPC in our system.…”

“…The polyimide remained hydrophobic. However, the walls of the groove have to be hydrophilic in order to obtain a cable. − We filled the groove with chromic acid for 3 min. This treatment gave rise to a hydrophilic surface of polyimide.…”

“…Black Lipid Membrane (BLM) . We spanned a lipid membrane across the groove using a variant of the BLM method. − ,− We made the membranes from a mixture of palmitoyloleylphospatidic acid (POPC) (Avanti Lipids) and glycerol monooleate (GMO) (Sigma) at the molar ratio 4:1. The lipids were dissolved separately in n -decane (Sigma) at concentrations of 10 mM.…”

“…Gramicidin. The conductance of the membrane was modulated by the incorporation of gramicidin D (Sigma). − ,, The peptide was dissolved in methanol at a concentration of 10 ng/mL. The solution (10−100 μL) was added to the decane layer on the water surface.…”

“…We describe here such a hybrid system, which consists of field-effect transistors covered with a lipid membrane. Two different techniques were combined, as developed recently in this laboratory: (i) the planar cable made from a black lipid membrane (BLM) on a shallow groove in silicon − and (ii) the insulated-gate field-effect transistor used in neuron−silicon junctions. − …”