Making lipid membranes even tougher
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Biosensors based on lipid membranes promise an inexpensive and versatile platform for application in many fields of molecular sensing. An extensive review of the applications for tethered membranes was reported in the July 2006 MRS Bulletin [A.N. Parikh and J.T. Groves, Materials science of supported lipid membranes. MRS Bull. 31(8), 507 (2006)]. The commercial use to which tethered lipid membranes have been applied has been limited by their stability under long-term storage. This report describes a novel membrane construct that is stable at room temperature for months, eliminates the mobile lipid phase present in lipid bilayers, and is robust against detergents under conditions that would destroy a lipid bilayer. I. INTRODUCTION
A recent review1 described the opportunities and applications for the interdisciplinary field of tethered lipid membranes. Biosensors based on tethered lipid membranes are of particular interest and are under development by many groups.2–13 These biosensors use a variety of approaches to modulate the admittance of ion channels incorporated into the membrane and promise an inexpensive versatile platform for applications across the field of point-of-care, time-critical diagnostics. Advantages of this approach include avoiding the optical interference effects arising from biological samples, which affect nephelometry, fluorescence, or similar optical measurement techniques. Membrane-based biosensors may be miniaturized and addressed to permit multiple measures from a single test sample and provide an objective, direct electrical output. A problem limiting the commercial applications of membrane-based biosensors has been the short storage lifetime of these devices, which, even under refrigeration, has been only 3–6 months.1,13 The market requirement for a widely applicable technology platform is stability of six to twelve months at room temperature. This report describes a novel, tethered monolayer membrane incorporating a gated ion channel that has been successfully stored at room temperature for up to three months and is free of any untethered mobile lipid. II. MATERIALS AND METHODS A. Membrane structure
In earlier reports, we demonstrated a functioning biosensor based on a modified form of the ion channel, a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0288 J. Mater. Res., Vol. 22, No. 8, Aug 2007
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gramicidin A.14–18 Modulation of the two-dimensional monomer–dimer reaction kinetics of the gramicidin channels was used as a means to measure the binding kinetics of analyte–protein interactions at the membrane surface. The change in conduction as a result of this interaction can be directly related to the concentration of the target analyte. Figure 1 shows the structure of both the bilayer membrane and the novel monolayer membrane presented here. B. Membrane composition
As seen in Fig. 1, the bilayer consists of seven synthetic organic compounds and the monolayer of three comp
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