On the Development of Biomimetic Sensors: Immobilizaton of Lipid Bilayers in Layered Ceramics
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ON THE DEVELOPMENT OF BIOMIMETIC SENSORS: IMMOBILIZATON OF LIPID BILAYERS IN LAYERED CERAMICS MICHAEL W. RUSSELL, VIVEK MEHROTRA, AND EMMANUEL P. GIANNELUS DepartmentofMaterials Science and Engineering,Cornell University, Ithaca,NY 14853
ABSTRACT Artificial membranes possessing physicochemical properties simila to biological membranes have been synthesized by immobilization of synthetic amphiphiles in layered ceramics. The intercalated bilayer-forming amphiphiles exhibit a gallery height of about 39 A. Retention of bilayer-forming characteristics is further confirmed by the presence of a crystal to liquid-crystal phase transition. A dramatic increase in the membrane capacitance at the tansition temperature is attributed to an increase in membrane fluidity. INTRODUCTION Biotechnology, medicine, as well as the food and pharmaceutical industries require sensing devices that can be employed to continuously detect specific molecules [I]. Chemical sensors can provide real-time, on-site information about the presence and concentration of foreign species in the environment thus mitigating the cumbersome steps of sample collection, preparation and analysis. Naturally occurring biological membranes serve as ideal prototypes in designing artificial sensing devices. Their capabilities of molecular recognition, signal transduction and amplification with high selectivity and sensitivity are well known and would seem to provide a sound foundation for the development of new classes of chemical sensors [2]. Paramount to the sensing ability of the biomembrane is the protein-containing lipid bilayer which separates the cell into compartments, functioning as an active filter and participant in transport processes. The role of the proteincontaining membranes in living organisms is to convert chemical stimuli into an electrical signal that is subsequently propagated into the synaptic region of the brain [3,4]. Artificial-bilayer membranes can be formed from a variety of synthetic amphiphiles. Immobilization of bilayer membranes, which facilitates their use as thin films capable of mimicing the properties of biomembranes, can be achieved by simple casting methods. Immobilization techniques which have been described previously include poly-(vinyl alcohol) blends (PVA), casting on glass, cellulose acetate sandwiched films, andLangmuir-Blodgeu films [5]. Artificial membranes possess characteristics which are similar to those of biological membranes, such as molecular alignment and phase transition.
Bilayer formation can be
considered as a general physicochemical phenomenon observed for a large variety of amphiphiles [6]. Factors which effect this spontaneous organization include the relative hydrophobicityhydrophilicity of the lipid as well as its geometry. Similar to other organic compounds with stiff, linear morphologies, bilayer forming lipids form an intermediate (mesophase) while undergoing a thermal transition from crystalline to isotropic states. The intermediate phase incorporates the crystalline order of the solid phase as well
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