Impedance analysis and single-channel recordings on nano-black lipid membranes based on porous alumina

Formation of high-resistance supported lipid bilayer on the surface of a silicon substrate with microelectrodes

We have developed two basic technologies for fabrication of supported planar lipid bilayer membrane ion channel biosensors: a defect-free lipid bilayer formation on the substrate surface with electrode pores and a patterning technique for the hydrophobic self-assembled-monolayer to form the guard ring that reduces the lipid bilayer edge-leak current. The importance of the supported-membrane structure to achieve low noise and high-speed performance is suggested on the basis of the observed relation between the single-ion-channel current noise and the pore size.

Porous membranes for reconstitution of ion channels

Functional biological synthetic composite (BSC) membranes were made using phospholipids, biological membrane proteins and permeable synthetic supports or membranes. Lipid bilayers were formed on porous polycarbonate (PC), polyethylene terephthalate (PETE) and poly (l-lactic acid) (PLLA) membranes and in 10-100 microm laser-drilled pores in a 96-well plastic plate as measured by increased resistance or decreased currents. Bilayers in 50 microm and smaller pores were stable for up to 4 h as measured by resistance changes or a current after gramicidin D reconstitution. Biological membrane transport reconstitution was then carried out. Using vesicles containing Kv1.5 K(+) channels, K(+) currents and decreased resistance were measured across bilayers in 50 microm pores in the plastic plate and PLLA membranes, respectively, which were inhibited by compound B, a Kv1.5 K(+) channel inhibitor. Functional reconstitution of Kv1.5 K(+) channels was successful. Incorporation of membrane proteins in functional form in stable permeable membrane-supported lipid bilayers is a simple technology to create BSC membranes that mimic biological function which is readily adaptable for high throughput screening.

Photocurrents generated by bacteriorhodopsin adsorbed on nano-black lipid membranes

Purple membranes were adsorbed on freestanding lipid bilayers, termed nano-black lipid membranes (nano-BLMs), suspending the pores of porous alumina substrates with average pore diameters of 280 nm. Nano-BLMs were obtained by first coating the upper surface of the highly ordered porous alumina substrates with a thin gold layer followed by chemisorption of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol and subsequent addition of a droplet of 1,2-diphytanoyl-sn-glycero-3-phosphocholine and octadecylamine dissolved in n-decane onto the hydrophobic submonolayer. By means of impedance spectroscopy, the quality of the nano-BLMs was verified. The electrical parameters confirm the formation of single lipid bilayers with high membrane resistances covering the porous matrix. Adsorption of purple membranes on the nano-BLMs was followed by recording the photocurrents generated by bacteriorhodopsin upon continuous light illumination. The membrane system exhibits a very high long-term stability with the advantage that not only transient but also stationary currents are recordable. By adding the proton ionophore carbonyl cyanide-m-chlorophenylhydrazone the conductivity of the nano-BLMs increases, resulting in a higher stationary current, which proves that proton conductance occurs across the nano-BLMs.

Neutron reflectivity study of lipid membranes assembled on ordered nanocomposite and nanoporous silica thin films

Single bilayer membranes of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were formed on ordered nanocomposite and nanoporous silica thin films by fusion of small unilamellar vesicles. The structure of these membranes was investigated using neutron reflectivity. The underlying thin films were formed by evaporation induced self-assembly to obtain periodic arrangements of silica and surfactant molecules in the nanocomposite thin films, followed by photocalcination to oxidatively remove the organics and render the films nanoporous. We show that this platform affords homogeneous and continuous bilayer membranes that have promising applications as model membranes and sensors.

Channel Activity of a Viral Transmembrane Peptide in Micro-BLMs: Vpu1-32from HIV-1

We report for the first time on pore-suspending lipid bilayers, which we call micro-black lipid membranes (micro-BLMs), based on a highly ordered macroporous silicon array. Micro-BLMs were established by first functionalizing the backside porous silicon surface with gold and then chemisorbing 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol followed by spreading 1,2-diphytanoyl-sn-glycero-3-phosphocholine dissolved in n-decane. Impedance spectroscopy revealed the formation of single lipid bilayers confirmed by a mean specific capacitance of 0.6 +/- 0.2 microF/cm2. Membrane resistances were in the G omega-regime and beyond. The potential of the system for single channel recordings was demonstrated by inserting the transmembrane domain of the HIV-1 accessory peptide Vpu(1-32), which forms helix bundles with characteristic opening states. We elucidated different amilorides as potential drugs to inhibit channel activity of Vpu.