Lipid membrane biosensors

Progress was recently made in the construction of an AC admittance modulation system for surface-stabilized lipid membrane biosensors that operated on the basis of the control of the ion permeation by artificial ion channels [40]. A portable admittance modulation measurement device was designed to measure both the in-phase and out-of-phase signal components for determination of the effective ion current and membrane capacitance, respectively [40]. The sensitivity and detection limit of this AC system were tested by studying the interaction of valinomycin with planar BLMs. The electrochemical phenomena were monitored through the in-phase component and measured as conductance changes of the membrane, providing a detection limit of 1 nM for valinomycin. 

J.L. Tang, B.Q. Wang, Z.Y. Wu, X.J. Han, S.J. Dong, and E.K. Wang, Lipid membrane immobilized horseradish peroxidase biosensor for amperometric determination of hydrogen peroxide. Biosens. Bioelectron. 18, 867-872 (2003). 

Use of bilayer lipid membranes as a generic electrochemical transducer is an exciting future for food biosensors. A taste sensor with multichanneled lipid membrane electrode was recently developed (93). The electric patterns generated from the sensor are similar to human response. The sensor can distinguish different brands of beer. More details on the taste sensor can be found in Chapter 16 of this book. 

Acetylcholineesterase Biosensors were fabricated from filter-supported solventless bilayer lipid membrane (BLM) and used for the analysis of the substrates of hydrolytic enzymes in a flowthrough system. The codeposition of lipid (dipalmitoyl-phosphatidic acid) and protein solutions to form a BLM on a microporous glass fiber or polycarbonate ultra-filtration membrane disc was described. Enzyme was immobilized on the membrane by incorporation of protein solution into the lipid matrix at the air-electrolyte interface before BLM formation. 

Due to their simplicity of construction, ease of modification, electrical methods of detection, fast response time and the fact that they are the principal structural component of all biomembranes, conventional bilayer lipid membrane (BLM) arises as an ideal system for biosensor technology [88] and they have been studied regarding the possibility of developing DNA biosensors consisting of a glassy carbon electrode-modified by a BLM with incorporated ssDNA [89]. 

Favero G, Campanella L, Cavallo S, D Annibale A, Perrella M, Mattei E, Ferri T (2005) Glutamate receptor incorporated in a mixed hybrid bilayer lipid membrane array, as a sensing element of a biosensor working under flowing conditions. J Am Chem Soc 127 8103-8111... 

Membranes, Fluidity of Membrane Proteins, Properties of Membrane Fusion, Mechanisms of Lipid BUayers, Properties of Lipid Rafts Biosensors... 

Entrapment methods of immobilization of bioreceptors utilized the lattice structure of particular base material. They include such methods as entrapment behind the membrane, covering the active surface of biosensors, entrapment within a self-assembled monolayers on the biosensor surface, as well as on freestanding or supported bilayer lipid membranes, and also entrapment within a polymeric matrix membranes, or within bulk material of sensor. All these mentioned methods are widely employed in design of biosensors. The essential condition of success of these methods of immobilization is preservation of sufficient mobility of substrate or products of biochemical reaction, involved in sensing mechanism, as matrix may act as a barrier to mass transfer with significant implications for... 

One of the primary applications of entrapment immobilization has been to prepare enzyme-electrode-based biosensors [27], and one of the first functional enzyme electrodes utilized urease entrapped in an acrylamide film to detect urea using an ammonium ion selective electrode [28]. Highly hydrophobic bilayer lipid membranes and liposomes have also been used to entrap highly labile biomolecules (see chapter 9). Such films and layers are, however, inherently unstable themselves and are useful primarily as research tools. 

BLMs, especially self-assembled bilayer lipid membranes on solid supports (s-BLMs), first reported in 1989, have been used in the last several years as lipid bilayer-based biosensors. 

The implementation of natural ion channel systems for biosensor construction will suffer from the complexity of the structural and regeneration requirements imposed by the biological matrix. In a practical context, a more promising immediate solution seems to be the development of biosensors having an ion channel activity without implementation of ion channel proteins from natural sources, i.e. artificial ion channels. This involves modulation of ion conductivity through lipid membranes by means of alteration of phase structure by a wide variety of different selective binding interactions with, e.g. enzymes, antibodies, lectins, and others. 

Artificial BLMs offer opportunities for development of chemically selective biosensors [6,7], The essential idea is that a receptor (such as a protein molecule) which can selectively bind to a specific organic or biochemical species (stimulant or analyte) can be incorporated into an ordered lipid membrane assembly such that selective binding events between receptor and stimulant will lead to alterations of the phase structure or electrostatic fields of the membrane (transduction). These perturbations can be monitored electrochemically as changes of transmembrane ion conductivity or as alterations in membrane capacitance. 

Biosensors based on metal-supported bilayer lipid membranes. BLMs, especially s-BLMs, have been used in the last three years as lipid bilayer-based biosensors [10,11,74-76,82], Hianik etal [75] have carried out a detailed physical study on the elasticity modulus of s-BLMs. They found that the dynamic viscosity of s-BLMs is one order of magnitude less than that of conventional BLMs [75]. It should be mentioned that in the s-BLM system, albeit attractive for certain purposes such as biosensors and molecular devices, the metallic substrate precludes ion translocation across the lipid bilayer. Therefore, the pursuit of a simple method for obtaining long-lived, planar BLMs separating two aqueous media has been an elusive one until now [81]. As reported, this much improved... 

Biosensors based on conductometric or impedimetric measurements are comparably rarely described in literature. They have two main fields of application sensors utilizing enzyme reactions in which ionic substances are formed and sensors employing receptors (or bilayer lipid membranes containing receptors) or intact cells of higher organisms. 

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