Ion channel behavior of supported bilayer lipid membranes on a glassy carbon electrode

A new kind of solid substrate, a glassy carbon (GC) electrode, was selected to support lipid layer membranes. On the surface of the GC electrode, we made layers of didodecyldimethylammonium bromide (a synthetic lipid). From electrochemical impedance experiments, we demonstrated that the lipid layers on the GC electrode were bilayer lipid membranes. We studied the ion channel behavior of the supported bilayer lipid membrane. In the presence of perchlorate anions as the stimulus and ruthenium(II) complex cations as the marker ions, the lipid membrane channel was open and exhibited distinct channel current. The channel was in a closed state in the absence of perchlorate anions.     

Optical anisotropy of supported lipid structures probed by waveguide spectroscopy and its application to study of supported lipid bilayer formation kinetics

Supramolecular conformation and molecular orientation was monitored during supported lipid bilayer (SLB) formation using dual polarization interferometry (DPI). DPI was shown to enable real time sensitive determination of birefringence of the lipid bilayer together with thickness or refractive index (with the other a fixed value). This approach removes differences in mass loading due to anisotropy, so the mass becomes solely a function of the lipid d n/d c value. DPI measurements show highly reproducible qualitative and quantitative results for adsorption of liposomes of different lipid compositions and in buffers with or without CaCl 2. The packing of solvent-free self-assembled SLBs is shown to differ from other preparation methods. Birefringence analysis accompanied by mass and thickness measurements shows characteristic features of vesicle adsorption and SLB formation kinetics previously not demonstrated by evanescent optical techniques, including indications of percolation-type rupture of clusters of liposomes on the surface and correlated adsorption kinetics induced by liposome charge repulsion. Our study demonstrates that understanding of mechanistic details for an adsorption process for which conformational changes and ordering occur can be elucidated using DPI and greatly enhanced by modeling of optical birefringence. The data is in some respects more detailed than what can be obtained with conventional biosensing techniques like surface plasmon resonance and complementary to methods such as the quartz crystal microbalance.     

Pinpoint and bulk electrochemical reduction of insulating silicon dioxide to silicon

Silicon dioxide (SiO(2)) is conventionally reduced to silicon by carbothermal reduction, in which the oxygen is removed by a heterogeneous-homogeneous reaction sequence at approximately 1,700 degrees C. Here we report pinpoint and bulk electrochemical methods for removing oxygen from solid SiO(2) in a molten CaCl(2) electrolyte at 850 degrees C. This approach involves a 'contacting electrode', in which a metal wire supplies electrons to a selected region of the insulating SiO(2). Bulk reduction of SiO(2) is possible by increasing the number of contacting points. The same method was also demonstrated with molten LiCl-KCl-CaCl(2) at 500 degrees C. The novelty and relative simplicity of this method might lead to new processes in silicon semiconductor technology, as well as in high-purity silicon production. The methodology may be applicable to electrochemical processing of a wide variety of insulating materials, provided that the electrolyte dissolves the appropriate constituent ion(s) of the material.     

Scanning electrochemical microscopy. 38. Application of SECM to the study of charge transfer through bilayer lipid membranes

The use of the scanning electrochemical microscope (SECM) to probe the kinetics of charge-transfer processes at bilayer lipid membranes (BLM) is presented. Analysis of the SECM tip response demonstrates that an unmodified BLM behaves as an insulator, whereas a BLM doped with iodine shows some positive feedback. The SECM technique thus allows one to probe processes at a BLM and determine the kinetics of the charge-transfer process. The SECM can also be used to determine the shape of the BLM.     

Impact of monoolein on aquaporin1-based supported lipid bilayer membranes

Abstract

Aquaporin (AQP) based biomimetic membranes have attracted considerable attention for their potential water purification applications. In this paper, AQP1 incorporated biomimetic membranes were prepared and characterized. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), infrared absorption spectroscopy, fluorescence microscopy, and contact angle measurements. The nanofiltration performance of the AQP1 incorporated membranes was investigated at 4 bar by using 2 g l^?1 NaCl as feed solution. Lipid mobility plays an important role in the performance of the AQP1 incorporated supported lipid bilayer (SLB) membranes. We demonstrated that the lipid mobility is successfully tuned by the addition of monoolein (MO). Through in situ AFM and fluorescence recovery after photo-bleaching (FRAP) measurements, the membrane morphology and the molecular mobility were studied. The lipid mobility increased in the sequence DPPC < DPPC/MO (R_MO = 5/5) < DOPC/MO (R_MO = 5/5) < DOPC, which is consistent with the flux increment and salt rejection. This study may provide some useful insights for improving the water purification performance of biomimetic membranes.     

Impact of monoolein on aquaporin1-based supported lipid bilayer membranes

Aquaporin (AQP) based biomimetic membranes have attracted considerable attention for their potential water purification applications. In this paper, AQP1 incorporated biomimetic membranes were prepared and characterized. The morphology and structure of the biomimetic membranes were characterized by in situ atomic force microscopy (AFM), infrared absorption spectroscopy, fluorescence microscopy, and contact angle measurements. The nanofiltration performance of the AQP1 incorporated membranes was investigated at 4 bar by using 2 g l⁻¹ NaCl as feed solution. Lipid mobility plays an important role in the performance of the AQP1 incorporated supported lipid bilayer (SLB) membranes. We demonstrated that the lipid mobility is successfully tuned by the addition of monoolein (MO). Through in situ AFM and fluorescence recovery after photo-bleaching (FRAP) measurements, the membrane morphology and the molecular mobility were studied. The lipid mobility increased in the sequence DPPC < DPPC/MO (R_MO = 5/5) < DOPC/MO (R_MO = 5/5) < DOPC, which is consistent with the flux increment and salt rejection. This study may provide some useful insights for improving the water purification performance of biomimetic membranes.     

Scanning electrochemical microscopy. 40. Voltammetric ion-selective micropipet electrodes for probing ion transfer at bilayer lipid membranes

Voltammetric ion-selective micropipet electrodes for use in scanning electrochemical microscopy (SECM) for detection of potassium ion were fabricated. These used pulled borosilicate capillaries with tip orifice radii of 0.7-20 microm with silanized inner walls filled with a solution of 10 mM valinomycin and 10 mM ETH 500 in dichloroethane. The electrodes were characterized by determining the steady-state tip current for K+ concentrations of 0.05-0.3 mM. The tips were used in the SECM feedback and generation-collection modes to study K+ transfer through gramicidin channels in a horizontal bilayer lipid membrane (glycerol monooleate).     

用电化学阻抗谱法研究支撑液膜的不稳定性

采用电化学阻抗法研究支撑液膜膜液的流失行为,并采用等效电路法分析得到的交流阻抗图谱.结果表明,等效电路Rs(RmCm)Q能够较好表征支撑液膜体系的交流电特性,得到的支撑液膜层的电阻和电容值能反映膜液层的特性,电阻值和电容值的变化能直观地反应膜液流失的行为.因而.该方法能很好地用于支撑液膜不稳定性的研究.     

Investigation of silicon etching and silicon dioxide bubble formation during silicon oxidation in HCl-oxygen atmospheres

Experiments performed to characterize the silicon etching occurring at the silicon-silicon dioxide interface during thermal oxidation of silicon in dry oxygen-HCl atmospheres at 1100 °C are described. The etching was accompanied by bubble formation or bowing of the silicon dioxide film and ultimately by complete loss of adhesion of the thermally grown film. Pre-oxidation experiments with dry oxygen suggest that silicon etching is primarily dependent upon the chlorine concentration at the silicon-silicon dioxide interface, with oxide growth prior to HCl addition having a small effect.     

Real-time impedance measurements during electrochemical experiments and their application to aniline oxidation

Development of an in situ technique for measuring electrochemical impedance spectra in real time during an electrochemical experiment is described. The technique is based on staircase voltammetry with relatively large step heights, in which a series of increasing potential steps are applied to an electrochemical system, and the resulting currents are sampled. The first derivatives of the currents thus obtained are then converted to ac current signals in frequency domain, and impedances are computed from them. To demonstrate the technique as a tool for studying the electrode/electrolyte interface during the electrochemical reaction, we chose an electrochemical oxidation reaction of aniline, whose reaction products have been known to continuously change the electrode surface due to the polymer film growth on its surface, and report a number of observations that would not have been obtained without such in situ experiments. A suggestion is also made on the use of staircase voltammetry for mechanistic studies on complex electrochemical reactions by simply varying the sampling time.     

Synthesis and electrochemical properties of bioderived silicon particles for lithium ion battery anodes

Journal of Materials Science: Materials in Electronics - Silicon is a promising high-capacity anode material for lithium ion batteries, but still suffers from the major issue of poor cyclability...     

Characterization of ammonium ion — Sensitive membranes in solution with electrochemical impedance spectroscopy

The electrochemical impedance spectroscopy is used to study the behaviour of a CWE electrode modified with a thin layer of polymeric membrane, in order to detect ammonium ions in solution. This membrane involves the incorporation of a zeolite type ionophore (clinoptilolite) into a polymer (polyvinyl chloride), and a plasticizing agent (dioctylphtalate). The ionic exchanges are characterized using electrochemical impedance spectroscopy. The CWE shows a good sensitivity and a low detection limit of about 10^− 8 M.     

Positive charge traps in silicon dioxide films: A comparison of population by X-rays and band-gap light

Four types of thermally grown amorphous silicon dioxide films were irradiated with kilovolt X-rays and broad-band vacuum UV light (hv = 3?14 eV) under applied electric fields in the range 10⁷–10⁸ V m^-1. The functional forms for the growth of X-ray- and VUV-induced space charge as a function of photon fluence and applied field, together with the annealing of charge by heat treatment or photo-injection, were the same for each form of radiation.     

Supported lipid bilayer formation and lipid-membrane-mediated biorecognition reactions studied with a new nanoplasmonic sensor template

This paper presents the use of the localized surface plasmon resonance (LSPR) sensor concept to probe the formation of macroscopic and laterally mobile supported lipid bilayers (SLBs) on SiOx-encapsulated nanohole-containing Au and Ag films. A comparison between Au- and Ag-based sensor templates demonstrates a higher sensitivity for Au-based templates with respect to both bulk and interfacial refractive index (RI) changes in aqueous solution. The lateral mobility of SLBs formed on the SiOx-encapsulated nanohole templates was analyzed using fluorescence recovery after photobleaching (FRAP), demonstrating essentially complete (>96%) recovery, but a reduction in diffusivity of about 35% compared with SLBs formed on flat SiOx substrates. Furthermore, upon SLB formation, the temporal variation in extinction peak position of the LSPR active templates display a characteristic shape, illustrating what, to the best of our knowledge, is the first example where the nanoplasmonic concept is shown capable of probing biomacromolecular structural changes without the introduction of labels. With a signal-to-noise ratio better than 5 x 10(2) upon protein binding to the cell-membrane mimics, the sensor concept is also proven competitive with state-of-the-art label-free sensors.     

The formation of supported lipid bilayers on silica nanoparticles revealed by cryoelectron microscopy

The controlled fabrication of biocompatible devices made of lipid bilayers deposited onto flat solid supports presents interest as models of cell membranes as well as for their biotechnological applications. We report here on the formation of supported lipid bilayers on silica nanoparticles (nanoSLBs). The successive steps of the adsorption of lipid vesicles on nanoparticles and the formation of nanoSLBs are revealed in detail by cryotransmission electron microscopy (cryo-EM). The formation of nanoSLBs was achieved for liposomes with positive, neutral, and low net negative charge, while liposomes with a high net negative charge adsorbed to silica nanoparticles but did not rupture. The nanoSLBs were found to follow faithfully the surface contours of the particles, information yet unavailable for SLB formation on planar solid substrates.     

Specific features of relief formation on silicon etched by a focused ion beam

The effect of a focused ion beam on the state of a silicon crystal surface has been studied. Periodic ring-shaped ribs have been observed on the walls of an etched cylindrical hole. The formation of periodic structures depends on the conditions of ion beam etching. The observed phenomenon is explained based on the notion of the radiation-induced plasticity.     

Nanocrystalline Si formation in the a-Si/Al system on polyimide and silicon dioxide substrates

Polysilicon (poly-Si) films fabricated on flexible substrates are of considerable interest because of their potential application in flexible displays. In this study, an 800 nm layer of amorphous silicon (a-Si), followed by a 20 nm layer of aluminum (Al), were deposited on polyimide/silicon and silicon dioxide/silicon (SiO₂/Si) substrates. Samples on polyimide were rapid thermal annealed at 900 °C for 20 s, while those on SiO₂/Si were vacuum annealed at temperatures between 200 and 600 °C for 1 h. Film properties were analyzed using Rutherford backscattering spectrometry, cross-section transmission electron microscopy, and X-ray diffraction. Silicon films containing nanocrystallites and pores were obtained, with a pore formation activation energy (E_A) of 0.59 eV. A short-range self-diffusion model is proposed for the formation of Si crystallites in cases where the solid-solubility limit for Si dissolution into Al has not been reached.     

Long-range gettering of microdefects in silicon single crystals during the formation of porous silicon layers on their surface and ion irradiation

Experimental data on the dissolution of microdefects in the near-surface regions of silicon single crystals during the electrochemical formation of porous silicon layers followed by argonion irradiation are presented. A decrease in the microdefect concentration is detected near the interface with porous silicon and near the opposite surface of the samples. Pis’ma Zh. Tekh. Fiz. 25, 50–54 (April 26, 1999)     

Defect-induced amorphization of crystalline silicon as a mechanism of disordered-region formation during ion implantation

An atomic-scale simulation study is presented which demonstrates that siliconamorphization during ion implantation can be caused by defect-induced collapseof the crystalline lattice. The amorphization threshold is calculated in termsof critical defect concentrations required to induce the amorphizationtransition at room temperature. These concentrations are found to be about28%, 20%, and 25% of self-interstitials, vacancies, or Frenkel pairs,respectively. These high defect densities are consistent with experimentalmeasurements in silicon self-implanted with high-energy ions. The structureof the defect-induced amorphous phases is similar to that of the bulkamorphous phase produced by rapid quenching of liquid silicon.