Some Electrochemical Features of Supported Bilayer Lipid Membranes

Influence of nanotopography on phospholipid bilayer formation on silicon dioxide

We have investigated the effect of well-defined nanoscale topography on the 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) lipid vesicle adsorption and supported phospholipid bilayer (SPB) formation on SiO2 surfaces using a quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). Unilamellar lipid vesicles with two different sizes, 30 and 100 nm, were adsorbed on pitted surfaces with two different pit diameters, 110 and 190 nm, as produced by colloidal lithography, and the behavior was compared to results obtained on flat surfaces. In all cases, complete bilayer formation was observed after a critical coverage of adsorbed vesicles had been reached. However, the kinetics of the vesicle-to-bilayer transformation, including the critical coverage, was significantly altered by surface topography for both vesicle sizes. Surface topography hampered the overall bilayer formation kinetics for the smaller vesicles, but promoted SPB formation for the larger vesicles. Depending on vesicle size, we propose two modifications of the precursor-mediated vesicle-to-bilayer transformation mechanism used to describe supported lipid bilayer formation on the corresponding flat surface. Our results may have important implications for various lipid-membrane-based applications using rough or topographically structured surfaces.

Interaction of K7Fe3+P2W17O62H2 with supported bilayer lipid membranes on platinum electrode

The influence of K(7)Fe(3+)P(2)W(17)O(62)H(2) on l-alpha-phosphatidylcholine/cholesterol bilayer lipid membrane on Pt electrode was studied by voltammetry and AC impedance spectroscopy. The interaction of the polyoxometalates with the BLM can promote the access of Ru(NH(3))(6)(3+) and [Fe(CN)(6)](3-/4-) to the electrode surface. It was found that some kind of pores had been formed on the BLM by AFM. The phenomenon is attributed to the interaction of K(7)Fe(3+)P(2)W(17)O(62)H(2) with phosphatidylcholine phosphate groups located in its outer leaflet. Experimental results are helpful to understand the biological activity of the polyoxometalates in vivo.

Nanostructured platinum-lipid bilayer composite as biosensor

The present work describes the preparation of supported bilayer lipid membrane (s-BLM) doped with metal nanoparticles for the design of biosensors. Platinum (Pt) nanoparticles were deposited through s-BLM to build a hybrid device of nanoscale electrode array by potential cycling in 1 mM K(2)PtCl(6) solution containing 0.1 M KCl. The properties of Pt nanoparticle-doped s-BLM composite were then characterized by cyclic voltammetry, electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). Our results showed that Pt nanoparticles grew in voids of the s-BLMs, through which the underlying glassy carbon (GC) electrode was connected, with maximum length extended out of the lipid membrane around 40 nm. Doping of Pt nanoparticles through s-BLM increased the membrane capacitance and decreased the membrane resistance of s-BLM. Pt nanoparticles array in s-BLM electrocatalyzed the reduction of oxygen (O(2)) in phosphate buffer solution (PBS). Practical application of Pt nanoparticle-doped s-BLM for the construction of glucose biosensor was also demonstrated in terms of its dose-response curve, stability and reproducibility. Thus, lipid membrane doped with Pt nanoparticles is a novel electrode system at nanoscale that can penetrate through the insulating membrane to probe molecular recognition and catalytic events at the lipid membrane-solution interface.

Ion sensing and inhibition studies using the transmembrane ion channel peptide gramicidin A entrapped in sol-gel-derived silica

The development of new, targeted drugs relies heavily on innovative technologies that allow for high-throughput screening of drug libraries against biologically relevant targets, particularly membrane-associated receptors. Therefore, immobilization of natural receptors is of the utmost importance to allow for screening of small molecule libraries. Herein, we describe the immobilization of liposomes containing the transmembrane peptide ion-channel gramicidin A into sol-gel-derived silicate materials. Steady-state fluorescence measurements of the intrinsic tryptophan residues of reconstituted gramicidin A in phospholipid vesicles consisting of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) were obtained in solution and following entrapment in diglyceryl silane (DGS)-derived silicate to examine the effects of entrapment on the conformation of the ion channel. Only minor deviations were observed in the fluorescence properties of gramicidin following entrapment in DGS-derived silicate. DOPC vesicles containing a 50 microM internal solution of the potential sensitive fluorescent dye safranine O were used to study ion flux through the membrane ion channel. The dependence of ion flux on both ion concentration and amount of gramicidin embedded in the membrane were examined before and after entrapment in sol-gel-derived silicate. It was found that ion channel activity upon entrapment in DGS-derived silicate mirrored very closely that observed in solution. Moreover, the ability to inhibit ion flux through gramicidin A due to blockage by calcium ions was retained after the immobilization procedure. The implications for development of drug-screening and -sensing platforms are discussed.