Electrochemistry of supported bilayer lipid membranes: background and techniques for biosensor development

Uphill Accumulation of Ionic Species into a Lipid Vesicle by the Concentration Gradient of Counter Ions

The "uphill (against the concentration gradient)" accumulation of a hydrophobic cation (rhodamine 6G, R6G⁺) into the inner phase of a giant unilamellar vesicle (GUV) was realized with the concentration gradient of the counter anion (X^- = ClO₄^-, BF₄^-, or Br^-) in the presence of phosphate buffer (P^-, pH = 7) in the inner and outer phase of the GUV and detected as the increase of the R6G⁺ fluorescence intensity in the inner phase using a confocal laser scanning fluorescence microscope. The addition of X^- in the outer phase of the GUV caused the accumulation of R6G⁺ in the inner phase. The degree and kinetics of the accumulation were dependent on the concentration and type of X^-; e.g., the inner concentration of R6G⁺ reached 2.5 times that in the outer phase of GUV after adding 10 mM ClO₄^-. The accumulation was theoretically simulated by assuming the distribution of ion pairs (R6G⁺ and X^-, R6G⁺, and P^-) between the aqueous phase and the lipid bilayer membrane (ion pair distribution model) and the transmembrane fluxes of R6G⁺, X^- and P^-. The theoretical simulation rationalized the accumulation degree and kinetics of the experimental results. The accumulation of the target cation by the concentration gradient of the counter anion demonstrated in this study can be an effective method for the preparation of liposomal drugs.

Dynamic behavior analysis of ion transport through a bilayer lipid membrane by an electrochemical method combined with fluorometry

The ion transport through a bilayer lipid membrane was analyzed by an electrochemical method combined with fluorometry. The distribution of a cation and an anion predominantly determines membrane conductivity.

Supported lipid bilayer membrane arrays on micro-patterned ITO electrodes

Lipid bilayer arrays were formed on micropatterned ITO electrodes. With this bilayer array platform both the fluorescence microscopy and electrochemical detection can be realized to explore the biophysical properties of cell membrane.

Recent advances in application of biosensors in tissue engineering

Biosensors research is a fast growing field in which tens of thousands of papers have been published over the years, and the industry is now worth billions of dollars. The biosensor products have found their applications in numerous industries including food and beverages, agricultural, environmental, medical diagnostics, and pharmaceutical industries and many more. Even though numerous biosensors have been developed for detection of proteins, peptides, enzymes, and numerous other biomolecules for diverse applications, their applications in tissue engineering have remained limited. In recent years, there has been a growing interest in application of novel biosensors in cell culture and tissue engineering, for example, real-time detection of small molecules such as glucose, lactose, and H2O2 as well as serum proteins of large molecular size, such as albumin and alpha-fetoprotein, and inflammatory cytokines, such as IFN-g and TNF-α. In this review, we provide an overview of the recent advancements in biosensors for tissue engineering applications.

Protein-phospholipid interactions in nonclassical protein secretion: problem and methods of study

Extracellular proteins devoid of signal peptides use nonclassical secretion mechanisms for their export. These mechanisms are independent of the endoplasmic reticulum and Golgi. Some nonclassically released proteins, particularly fibroblast growth factors (FGF) 1 and 2, are exported as a result of their direct translocation through the cell membrane. This process requires specific interactions of released proteins with membrane phospholipids. In this review written by a cell biologist, a structural biologist and two membrane engineers, we discuss the following subjects: (i) Phenomenon of nonclassical protein release and its biological significance; (ii) Composition of the FGF1 multiprotein release complex (MRC); (iii) The relationship between FGF1 export and acidic phospholipid externalization; (iv) Interactions of FGF1 MRC components with acidic phospholipids; (v) Methods to study the transmembrane translocation of proteins; (vi) Membrane models to study nonclassical protein release.

Miniaturised technologies for the development of artificial lipid bilayer systems

Artificially reproducing cellular environments is a key aim of synthetic biology, which has the potential to greatly enhance our understanding of cellular mechanisms. Microfluidic and lab-on-a-chip (LOC) techniques, which enable the controlled handling of sub-microlitre volumes of fluids in an automated and high-throughput manner, can play a major role in achieving this by offering alternative and powerful methodologies in an on-chip format. Such techniques have been successfully employed over the last twenty years to provide innovative solutions for chemical analysis and cell-, molecular- and synthetic- biology. In the context of the latter, the formation of artificial cell membranes (or artificial lipid bilayers) that incorporate membrane proteins within miniaturised LOC architectures offers huge potential for the development of highly sensitive molecular sensors and drug screening applications. The aim of this review is to give a comprehensive and critical overview of the field of microsystems for creating and exploiting artificial lipid bilayers. Advantages and limitations of three of the most popular approaches, namely suspended, supported and droplet-based lipid bilayers, are discussed. Examples are reported that show how artificial cell membrane microsystems, by combining together biological procedures and engineering techniques, can provide novel methodologies for basic biological and biophysical research and for the development of biotechnology tools.

Carbon nanotube transistor controlled by a biological ion pump gate

We report a hybrid bionanoelectronic transistor that has a local ATP-powered protein gate. ATP-dependent activity of a membrane ion pump, Na(+)/K(+)-ATPase, embedded in a lipid membrane covering the carbon nanotube, modulates the transistor output current by up to 40%. The ion pump gates the device by shifting the pH of the water layer between the lipid bilayer and nanotube surface. This transistor is a versatile bionanoelectronic platform that can incorporate other membrane proteins.

Using wavelets to analyze AFM images of thin films: surface micelles and supported lipid bilayers

This paper presents micro- and nanoanalysis of thin films based on images obtained by atomic force microscopy (AFM). The analysis exploits the discrete wavelet transform and the resulting wavelet spectrum to study surface features. It is demonstrated that the wavelet technique can characterize micro- and nanosurface features and distinguish between similar surface structures. The use of a feature extraction method is shown. The method involves the separation of certain frequency content from the original AFM images and analyzing the data independently to gain quantitative information about the images. By using the feature extraction method, soft surfaces in water are analyzed and nanofeatures are measured. The packing of surface micelles of sodium dodecyl sulfate on a self-assembled monolayer is analyzed. The characteristics of pore formation, due to penetration of the antibacterial peptide protegrin, into a solid-supported lipid bilayer are quantified. The sizes of the pores are obtained, and it is observed that the line tension of the pores reduces the fluctuations of the lipid bilayer.

Impedance measurements of self-assembled lipid bilayer membranes on the tip of an electrode

Supported lipid membranes were self-assembled on the tip of a freshly cleaved silver wire, in the presence of an appropriate polarization voltage, to facilitate, during the membrane formation, the organization of the lipids into an ordered structure. Radiowave impedance spectroscopy measurements have been carried out to provide information on the relaxation properties of the system. We have measured the conductometric and dielectric properties of bilayers built up of different lipids [dipalmitoylphosphatidic acid (DPPA), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), linoleic acid (LIN)] in a wide frequency range (from 10(3) to 10(6) Hz) and in electrolyte solutions of different ionic strengths, in the presence of uni-univalent (KCl) and di-univalent (CaCl(2), MgCl(2), ZnCl(2)) electrolytes. This made it possible to measure the influence of different cations and different lipid compositions on the membrane properties. In particular, we have found a different capacitive behaviour of the supported lipid bilayer membrane (s-BLM) structure in the presence of different counterions in the electrolyte solution. This peculiarity offers the opportunity for the preparation of a variety of biosensors with diverse applications in membrane biophysics, biochemistry and biotechnology.

Electrochemical studies of blocking properties of solid supported tethered lipid membranes on gold

The insulating properties of self-assembled thiolipid monolayers and tethered lipid bilayers on polycrystalline gold electrodes were studied by means of cyclic voltammetry (CV). These films were formed by two-step self-assembly processes. Electrochemical measurements of the heterogeneous electron transfer rate constant of different redox couples such as potassium ferrocyanide (K(4)[Fe(CN)(6)]) and dopamine (DP) were used to examine the molecular integrity and structural defects and pinholes within the monolayers. We demonstrate by means of cyclic voltammetry that the bilayer lipid membranes tethered to the gold surface are blocking, stable, yet retaining their dynamic properties and can be used as a model of the cell membrane.

A fiber-optic lactate sensor based on bacterial cytoplasmic membranes

A new type of fiber-optic biosensor based on bacterial cytoplasmic membranes (CPM) as the biological recognition element and an oxygen sensitive dye layer as the transducer is described for the detection of lactate. CPMs from bacteria with an induced lactate oxidase system are adsorbed onto a cellulose disk. The disk is fixed mechanically over an oxygen sensitive siloxane layer on the distal end of an optical fiber. This system detects lactate with no interference from glucose, fructose or glutamic acid.