Electrochemical transduction of an immunological reaction via s-BLMs

The application of cyclic voltammetry to biosensor devices based on solid supported bilayer lipid membranes (s-BLMs) is investigated. s-BLMs have been used for receptor-ligand contact interactions. This paper reports the electrochemical transduction of an antigen-antibody (AgAb) reaction by an s-BLM. The antigen (HBsAg) is incorporated into an s-BLM, which then can interact with its corresponding antibody (HBsAb) in the bathing solution. This AgAb interaction results in some remarkable changes in the electrical parameters (conductance, potential and capacitance) of s-BLMs. The magnitude of these changes are directly related to the concentration of the antibody in the bathing solution. The use of such an AgAb interaction via s-BLM as a transducing device for the detection of ligand-receptor contact reaction is proposed.     

Biosensors for the Rapid Repetitive Detection of Adrenaline Using Stabilized Bilayer Lipid Membranes (BLMs) with Incorporated Calix[4]resorcinarene Receptor

This work uses lipid film based biosensors with incorporated calix[4]resorcinarene receptor (lipophilic macrocyclic host molecule) for the rapid electrochemical detection of adrenaline. Freely‐suspended and metal supported BLMs (composed of egg phosphatidylcholine (PC) and 35% (w/w) dipalmitoyl phosphatidic acid) modified with the resorcin[4]arene receptor were used as one shot sensors to rapidly detect this catecholamine. The interactions of this compound with freely‐suspended BLMs were found to be electrochemically transduced in the form of a transient current signal with duration of seconds, which reproducibly appeared about 14 s after exposure of the membranes to adrenaline. The response time for these BLMs without incorporated receptor for adrenaline was about 1.5 min. The magnitude of the transient current signal was related to the concentration of adrenaline in bulk solution in the micromolar range. Differential scanning calorimetric (DSC) experiments were performed to explore the mechanism of interactions of BLMs with incorporated receptor with adrenaline. The interactions of adrenaline with surface‐stabilized bilayer lipid membranes (sBLMs) with incorporated receptor produced electrochemical ion current increases, which reproducibly appeared within a few seconds after exposure of the membranes to the stimulant. The use of the receptor in sBLMs increased the sensitivity of the method 6‐fold. The current signal increases were related to the concentration of adrenaline in bulk solution in the micromolar range. Stabilized lipid membranes formed by polymerization on glass fiber microfilters were used as practical chemical biosensors for the rapid detection of adrenaline. The interactions of polymerized lipid films with adrenaline were also found to provide transient current signals similar to those of freely‐suspended BLMs. The magnitude of the transient current signal was also related to the concentration of the stimulating agent in bulk solution in the micromolar range and these stabilized lipid films can be used again after storage in air. No interferences from ascorbic acid were noticed because of the negatively charged lipids in membranes. The effect of other compounds such as proteins and other compounds closely related to adrenaline was also investigated. Results of recovery experiments using human urine have shown recoveries ranged between 94 to 105%, which shows no interferences from matrix effects due to the presence of urine constituents. The present sensor based on stabilized lipid films can be used for the rapid repetitive detection of this pharmaceutical substance and keep prospects for the selective determination of catecholamines in biofluids.     

Nitric oxide enhances the capacitance of self-assembled,supported bilayer lipid membranes

The effect of nitric oxide (NO) at biologically relevant concentrations on the electrochemical features of the membrane was investigated by cyclic voltammetry (CV) at self-assembled, stainless steel supported lipid bilayer membranes (s-BLMs) using a three-electrode system. The results showed that the membrane capacitance (C_m) of s-BLMs was dramatically enhanced by the presence of increasing NO concentration from 0 to 70 μM. For comparison, fullerene C₆₀ doped s-BLMs (C₆₀@s-BLMs) was also studied. The C_m of C₆₀@s-BLMs increased with NO concentration from 0 to 16 μM and gradually reached a plateau value when NO concentration was over 16 μM. We concluded that (i) NO accumulated inside lipid bilayer increases the C_m of s-BLMs, and (ii) C₆₀ inside s-BLMs changes the dielectric constant of lipid bilayer, thus reducing the effect of NO on the C_m of C₆₀@s-BLMs. This novel self-assembled lipid modified probe provides a simple yet interesting model to study the effect of NO on the electrical conductance of the membrane.     

An electrochemical approach tunes the electric property of benzoylferrocene-modified supported lipid membrane

A benzoylferrocene (BFc) supported 3-sn-phosphatidylcholine (PC) film electrode was prepared by casting the solution of BFc and PC in chloroform onto the surface of platinum (Pt). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results showed that BFc, retained in the biological membrane, acted as a shuttle for electron transfer across the supported bilayer lipid membranes (s-BLMs). Doping of BFc increased membrane conductivity, while electrochemical oxidation of BFc greatly changed the membrane conductivity, the membrane impedance characterized by charge transfer resistance (R_ct) dramatically increased about 400 times (from 10.32 to 3919.67 kΩ). Interestingly, the electrochemical oxidized BFc buried in the membranes could be reduced by applying a low potential, and this led to recurrent of a conductive membrane. The conductivity of the s-BLMs could be controlled by the redox status of embedded BFc molecules. The approach provided a facile and novel way to electrochemically control the membrane conductance of s-BLMs by embedding BFc as a switchable redox mediator.     

Fabrication and photoelectric properties of self-assembled bilayer lipid membranes on conducting glass

Supported bilayer lipid membranes (s-BLMs with and without the doping of fullerene C60) self-assembled on indium-tin oxide (ITO) glass were fabricated and characterized by cyclic voltammetry and electrochemical impedance spectroscopy using a three-electrode system. The photoelectric properties of the ITO supported planar lipid bilayers were studied. Light intensity of irradiation, bias voltage, and concentration of donors have been found to be limiting factors of the transmembrane photocurrent. The facilitation effect of C60 doping in s-BLMs on the photoinduced electron transfer across s-BLM is discussed. This novel self-assembled ITO/s-BLM system may provide a simple and mechanically stable model for the study of the photoelectric and photodynamic properties of biomembranes.     

冠醚修饰的固体支撑双层类脂膜的形成及性能研究

用饱和了胆固醇和饰用冠醚的角鲨烷／氯仿溶液作成膜液，制备了冠醚修饰的固体支撑双层类脂分子膜。重点考察了成膜物种及技术对膜稳定性及电特生影响。其膜电势随接触水相中的变化呈现Ｎｅｒｎｓｔ响应，线性范围１０＾－４－１０＾－１ｍｏｌ／Ｌ。     

Effects of direct current bias voltages on supported bilayer lipid membranes on a glassy carbon electrode

The effects of dc bias voltages on supported bilayer lipid membranes (s-BLMs) on a glassy carbon (GC) electrode have been investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The experiments suggested that an appropriate positive bias voltage facilitated the formation of electrically dense membranes, but if the voltage is enough high, the lacunas on s-BLMs increased, and eventually caused the complete oxidation of the lipid membrane. While negative bias voltages could induce the damage of supported membranes to different extent. The changes of the form and quantity of graphite oxide on the surface of the electrode caused by dc bias voltages and the electroporation and damage of the membrane at high potentials may be responsible for the effects.     

直流偏压对于在玻碳电极上双层类脂膜成膜过程的影响

应用循环伏安法和电化学阻抗谱研究了直流偏压对卵磷脂在玻碳电极表面自组装成膜过程及其结构的影响.实验发现:无论在正偏压还是负偏压条件下,卵磷脂在玻碳电极上均可组装成膜.施加正偏压时,由于玻碳电极表面所带的正电荷与卵磷脂端基之间的静电作用,使得卵磷脂在电极表面倾向于形成双层的类脂膜,并在0.4V偏压下电极阻抗达到最大值.继续增大电极正向偏压,s-BLM缺陷增加,以至趋于被击穿.提出了适宜的等效电路,并据此非线性拟合电极过程,求得部分阻抗的模型参数.研究发现:膜电容和电荷传递电阻呈现良好的互补效应.     

Self-assembled BLMs: biomembrane models and biosensor applications

In the last few years, there have been a number of research papers on self-assemblies of molecules as ‘advanced’ or ‘smart’ materials. The inspiration for this exciting research, without question, comes from the biological world, where, for example, the lipid bilayer of the cell membrane is the most important self-assembling system. Although the first report on self-assembled bilayer lipid membranes (BLMs) in vitro was published in 1962, interface science, including surface and colloid science, has been dealing with these interfacial self-assemblies of amphiphilic molecules since Robert Hooke's time (1672). BLMs have been used in a number of applications, ranging from basic membrane biophysics studies to the conversion of solar energy via water photolysis, and to biosensor development using supported bilayer lipid membranes (s-BLMs and sb-BLMs). This paper briefly summarizes the past research on the use of BLMs as models of biological membranes and describes some details of our current work on supported BLMs as practical biosensors. Additionally, experiments carried out in close collaboration with others on s-BLMs and sb-BLMs are presented.     

十二烷基磺基甜菜碱与铂电极支撑的磷脂双层膜作用的电化学研究

以铂电极支撑的磷脂双层膜(Supported Bilayer Lipid Membrane,s-BLM)作为生物膜的模型,以Fe(CN)36-和Fe(CN)64-为探针分子,利用循环伏安法(CV)和交流阻抗谱(EIS)研究两性表面活性剂十二烷基磺基甜菜碱(Dodecyl Sulfobetaine,DSB)对s-BLM相互作用。结果显示,DSB可以嵌入到s-BLM的疏水区,容易使其表面分子的排列发生变化,产生缺陷或孔洞,探针分子Fe(CN)63-和Fe(CN)64-可以通过这些微孔接近电极,产生氧化还原响应。并且作用时间、DSB的浓度以及胆固醇的存在与否对二者的相互作用有直接影响。此外作用后的双层膜在0.1mol/LKCl溶液中能够自我修复,这表明DSB与s-BLM的相互作用是可逆的。     

Flow Injection Analysis of Mixtures of Dopamine,Adrenaline and Ephedrine in Human Biofluids Using Stabilized after Storage in Air Lipid Membranes with a Novel Incorporated Resorcin[4]arene Receptor

This work describes a technique for the rapid, selective and sensitive electrochemical flow injection analysis of mixtures of the stimulating compounds adrenaline, dopamine, and ephedrine using stabilized after storage in air bilayer lipid membranes (BLMs) with incorporated resorcin[4]arene receptor. Injections of the stimulating compounds were made into flowing streams of a carrier electrolyte solution and a transient current signal, with duration of seconds, reproducibly appeared in less than two min after exposure of the lipid membranes to the compounds. The magnitude of this signal was linearly related to the concentration of the compound, which could be determined at micromolar levels. Repetitive cycles of injection of stimulating compounds have shown no signal degradation during each cycle (30 sequential injections). The time of appearance of the transient response was different for each stimulating compound and increased in the order of adrenaline, dopamine and ephedrine. The difference in time of response has allowed selective detection and analysis of these compounds in mixtures. The investigation of the effect of potent interferences included a wide range of compounds usually found in human biofluids, as well as proteins and lipids. The results showed that only proteins (most common in lipid film based biosensors) pose a problem that can be eliminated by modulation of the carrier solution to flow rates that do not allow adsorption of these compounds in the lipid films. The technique was applied in human urine samples.     

Electrochemical characterization of pore formation by bacterial protein toxins on hybrid supported membranes

The interaction of pore-forming streptolysin O (SLO) with biomimetic lipid membranes has been studied by electrochemical methods. Phosphatidylcholine lipid vesicles were deposited onto gold electrodes modified with supporting layers of hexyl thioctate (HT) or thioctic acid tri(ethylene glycol) ester (TA-TEGE), and integrity and permeability of the resulting membranes were characterized by cyclic voltammetry and impedance spectroscopy. Both positively and negatively charged electrochemical probes, potassium ferrocyanide, hexaammineruthenium(III) chloride, and ferrocene carboxylic acid (FCA), were employed to evaluate their suitability to probe the membrane permeability properties, with FCA exhibiting ideal behavior and thus employed throughout the work. Fusion of vesicles incubated with SLO on the electrodes yielded membranes that showed a distinctive response pattern for FCA as a function of SLO concentration. A direct dependence of both the currents and peak separation of FCA in the cyclic voltammograms was observed over a concentration range of 0-10 hemolytic units (HU)/microL of the toxin. The interaction of SLO with preformed supported lipid membranes was also investigated, and much lower response was observed, suggesting a different extent of membrane-toxin interactions on such an interface. Nonionic surfactant Triton was found to disrupt the vesicle structure but could not completely remove a preformed membrane to fully restore the electrode response. The information reported here offers some unique insight into toxin-surface interactions on a hybrid membrane, facilitating the development of electrochemically based sensing platforms for detecting trace amounts of bacterial toxins via the perforation process.     

The lipid bilayer concept and its experimental realization: from soap bubbles,kitchen sink,to bilayer lipid membranes

The inspiration for lipid bilayer research, without question, comes from the biological world. Although self-assembled bilayer lipid membranes (BLMs) in vitro, were first reported in 1961, experimental scientists have been dealing with BLM-type interfacial adsorption phenomena since Robert Hooke’s time (1672). BLMs (of planar lipid bilayers) have been used in a number of applications ranging from basic membrane biophysics including transport, practical AIDS research, and ‘microchips’ studies, to the conversion of solar energy via water photolysis, to biosensor development using supported bilayer lipid membranes (s-BLMs), and to photobiology comprising apoptosis and photodynamic therapy. This paper presents an overview of the origin of the lipid bilayer concept and its experimental realization, as well as the studies of our laboratory and recent research of others on the use of BLMs as models of certain biomembranes. In addition, we describe briefly our present work on supported BLMs as biosensors and molecular devices; the experiments carried out in close collaboration with colleagues on s-BLMs are delineated.     

Lipid Specific Spin-Labeling of Erythrocyte Membranes: Development and Characterization of a new Labeling Procedure for a Cationic Spin Label,CAT-16

Abstract

A new method for spin labeling the lipid bilayer component in erythrocyte membranes at low hematocrit with extremely low concentration of 4-(N,N-dimethyl-l-n-hexadecyl)ammonium-2,2,6,6-tetramethylpiperidine-l-oxyl iodide, (CAT-16) is described. Characterization of the motional determinants of CAT-16 in erythrocyte membranes at 20°C is presented from which it is deduced that protein-lipid interactions in the lipid bilayer arc primary.     

Rapid Electrochemical Detection of Propranolol and Metoprolol in Pharmaceutical Preparations Using Stabilized Lipid Films

This work reports a technique for the rapid electrochemical detection of propranolol and metoprolol in pharmaceutical preparations using stabilized lipid films. Microporous filters composed of glass fibers (nominal pore sizes 0.7 and 1.0 μm) were used as supports for the formation and stabilization of these devices. The lipid film is formed on the filter by polymerization prior to its use. This stabilized after storage in air. Lipid films composed of phosphatidylcholine were used for the detection of propranolol and metoprolol in pharmaceutical preparations. The stabilized lipid membranes provided artificial ion gating events in the form of transient signals within about 60 and 34 s after exposure of the membranes to propranolol and metoprolol, respectively. The magnitude of the transient current signal was related to the concentration of propranolol and metoprolol in bulk solution in the micromolar range. The mechanism of signal generation was investigated by differential scanning calorimetric studies. These studies revealed that the adsorption of the drug is through the hydrophobic aryl terminal of the compound, whereas the hydrophilic groups were directed towards the electrolyte solution. This adsorption caused a rapid alteration of the electrochemical double layer of the lipid film (i.e., capacitance changes) that resulted in the transient ion current signal. The present technique was used for the rapid detection of propranolol and metoprolol in pharmaceutical preparations and can function for repetitive uses after storage in air. Future research is targeted to the determination of these chemicals in human biofluids such as urine of athletes.     

Photoelectric measurements of self-assembled and supported planar lipid bilayers: a new technique for studying apoptosis

A new method based on photoelectrochemistry for analyzing apoptosis of bilayer lipid membranes (s-BLMs) containing MCF-7 nuclei is reported. The s-BLM cell responded to white light (200–800 nm). During the apoptosis induced by Taxol, the photoelectric current of the cell decreased, suggesting degradation of the nuclear DNA. Electron transfer along the DNA double helix and along the nuclear skeleton is assumed in the interpretation. This novel photoelectric analytical method may provide a rapid and sensitive technique to evaluate apoptosis.     

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.     

Electrochemical Red Blood Cell Counting: One at a Time

We demonstrate that the concentration of a red blood cell solution under physiological conditions can be determined by electrochemical voltammetry. The magnitude of the oxygen reduction currents produced at an edge‐plane pyrolytic graphite electrode was diagnosed analytically at concentrations suitable for a point‐of‐care test device. The currents could be further enhanced when the solution of red blood cells was exposed to hydrogen peroxide. We show that the enhanced signal can be used to detect red blood cells at a single entity level. The method presented relies on the catalytic activity of red blood cells towards hydrogen peroxide and on surface‐induced haemolysis. Each single cell activity is expressed as current spikes decaying within a few seconds back to the background current. The frequency of such current spikes is proportional to the concentration of cells in solution.     

Drug-liposome distribution phenomena studied by capillary electrophoresis-frontal analysis

The potential of using CE frontal analysis (CE-FA) for the study of low-molecular-weight drug-liposome interactions was assessed. The interaction of bupivacaine, brompheniramine, chlorpromazine, imipramine, and ropivacaine with net negatively charged 80/20 mol% 1-oleoyl-2-palmitoyl-sn-glycero-3-phosphocholine/egg yolk phosphatidic acid liposome suspensions in HEPES buffer at pH 7.4 was investigated. The fraction of free drug as a function of lipid concentration was measured and apparent liposome - buffer distribution coefficients were determined for the basic drug substances. The distribution coefficients increased in the order ropivacaine, bupivacaine, brompheniramine, imipramine, and chlorpromazine. The developed CE method was relatively fast allowing estimates of drug-liposome affinity to be obtained within 15 min. CE-FA may have the potential to become a valuable tool for the characterization of drug-liposome interactions in relation to estimation of drug lipophilicity and for the evaluation of drug distribution in liposomal drug delivery systems.     

Preparation of a Selective Receptor for Ephedrine for the Rapid Electrochemical Detection of Ephedrine in Human Urine Using Stabilized in Air Lipid Films with Incorporated Ephedrine Receptor

The present technique describes the preparation of a selective receptor for ephedrine and a technique for the rapid electrochemical detection of ephedrine in human urine using lipid films with incorporated receptor that are synthesized by a chemical reaction with a methacrylate polymer on a glass fiber filter. The selective receptor was synthesized using a resorcin[4]arene receptor and by transforming all the ? OH groups into methoxy groups. Injections of ephedrine were made into flowing streams of a carrier electrolyte solution and a transient current signal, with duration of seconds, appeared in less than two minutes after exposure of the lipid membranes to the compound. The magnitude of this signal was linearly related to the concentration of this stimulant, which could be determined at micromolar levels. The effect of potent interferences including a wide range of compounds usually found in human urine (i.e., ascorbic aid, glucose, leucine, glycine, tartrate, citrate, bicarbonate and caffeine) was examined. Also, the effect of proteins and lipids was investigated. The results showed that there were no interferences from all these constituents in concentration levels usually found in human urine samples. Dopamine was also investigated as a potent interferent. The results have shown that the transformation of the hydroxy to methoxy groups has increased the selectivity of the receptor towards ephedrine and decreased it towards dopamine which does not cause and interference at concentration levels lower than of 10^?3 M. Urine samples provided similar results and allowed the development of a technique for the rapid electrochemical detection of this stimulant in human urine at the levels of 10^?6 M concentrations. The reproducibility of the method was checked in about 100 samples.