Ion Channel Sensor on a Silicon Support

We are building a biosensor based on ion channels inserted into lipid bilayers that are suspended across an aperture in silicon. The process flow only involves conventional optical lithography and deep Si reactive ion etching to create micromachined apertures in a silicon wafer. In order to provide surface properties for lipid bilayer attachment that are similar to those of the fluorocarbon films that are currently used, we coated the silicon surface with a fluoropolymer using plasma-assisted chemical vapor deposition. When compared with the surface treatment methods using self-assembled monolayers of fluorocarbon chemicals, this novel approach towards modifying the wettability of a silicon dioxide surface provides an easy and fast method for subsequent lipid bilayer formation. Current-Voltage measurements on OmpF ion channels incorporated into these membranes show the voltage dependent gating action expected from a working porin ion channel. INTRODUCTION Biosensor design has become one of the major research topics during recent years. Combining biochemical detection mechanisms with conventional silicon-based electronic signal processing is particularly challenging. Gated ion channels inserted in lipid bilayer membranes are very promising candidates as biochemical transducers, because of their high sensitivity while still being selective. This setup has been used successfully for the detection of a variety of biochemical reagents [1]. The lipid bilayer membranes, which form the host for the ion channel proteins, are typically formed across apertures in hydrophobic substrates, such as polytetrafluoroethylene (PTFE, Teflon). Apertures in these substrates are prepared either mechanically or by electrical discharge [2,3], which both are low-volume production methods with limited reproducibility of hole size and shape. On the other hand silicon micromachining is already in a very mature state. Silicon, however, by itself does not have the properties required for a stable lipid bilayer formation. While silicon itself is hydrophobic, a natural oxide layer increases the surface energy, thus creates a hydrophilic surface on which lipid bilayer attachment is difficult. Surface modification layers that provide a low energy surface can facilitate the lipid bilayer formation and thus enable the combination between biochemical detection and conventional silicon device architecture [4-7]. In this paper we will demonstrate that a plasmadeposited PTFE layer can provide the necessary surface modification to enable lipid bilayer attachment and subsequent ion channel insertion. EXPERIMENTAL DETAILS The first samples were prepared using single-side polished Si wafers with (001) surface orientation and a total thickness of 520 μm. In order to rule out the influence of the initial surface O7.2.1 Mat. Res. Soc. Symp. Proc. Vol. 820 © 2004 Materials Research Society