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ABSTRACT: This paper reports on the reconstitution of human ether-a-go-go-related gene (hERG) channels in artificial bilayer lipid membranes (BLMs) formed in micropores fabricated in silicon (Si) chips. The hERG channels were isolated from Chinese hamster ovary (CHO) cell lines expressing the channels and incorporated into the BLMs formed by a process in which the two lipid monolayers were folded into the micropores. The characteristic features of hERG channels reported by the patch-clamp method, including single-channel conductance, voltage dependence, sensitivity to typical drugs and dependence on the potassium concentration, were investigated in the BLM reconstitution system. The BLM with hERG channels incorporated exhibited a lifetime of ~65 h and a tolerance to repetitive solution exchanges. Such stable BLMs containing biological channels have the potential for use in a variety of applications, including high-throughput drug screening for various ion-channel proteins.
Analytical Chemistry 03/2013; · 5.86 Impact Factor
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ABSTRACT: In this review, we will discuss our recent approaches for the formation of mechanically stable bilayer lipid membranes (BLMs) by combining with BLM formation and micro- and nano-fabrication techniques. BLMs were prepared across a microaperture fabricated in silicon (Si) chips or nanoporous alumina films using a minimized amount of organic solvent. Although BLMs spanned over the porous alumina film showed better electrical properties, such as background current noise and current transient, BLMs suspended in a thin Si(3)N(4) septum showed a much superior BLM stability. The BLMs showed tolerance to a high voltage of ±1 V, a membrane lifetime of >40 h, and tolerance to repetitive solution exchanges. Application to a drug screening system has been examined by using the human ether-a-go-go-related gene (hERG) potassium channel as an illustrative example. The potentiality of the present system as a platform of the high-throughput analysis for ion-channel protein is also discussed.
Analytical Sciences 01/2012; 28(11):1049-1057. · 1.25 Impact Factor
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ABSTRACT: In this review, we will discuss our recent approaches for improving the mechanical stability of free-standing bilayer lipid membranes (BLMs) by combining with BLM formation and micro- and nano-fabrication techniques. BLMs were prepared across a microaperture fabricated in silicon (Si) chips or nanoporous alumina films, and their mechanical stability and electric properties were investigated. BLMs spanned over the porous alumina showed background noise currents small enough for recording activities of low-conductance channels, though further stability enhancement of porous alumina films was necessary. BLMs suspended in a thin Si3N4 septum showed a dramatic improvement of BLM stability. The BLMs were resistant to a voltage of ± 1 V and the membrane lifetime was 15–43 h with and without incorporated channels. The membrane containing gramicidin channel exhibited tolerance to repetitive solution exchanges, though the electric properties of the BLMs are necessary to be improved. The realisation of BLMs having both mechanical stability and proper electric properties will open up a variety of applications including highly sensitive biosensors and high-throughput drug screenings for ion channels.
Supramolecular Chemistry 07/2010; 22(Nos. 7–8):406-412. · 2.14 Impact Factor
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ABSTRACT: The lateral remote photocatalytic activity of TiO(2) nanotubes fabricated by anodic oxidation, was characterized by use of a 'silver nanosheet' as a marker. The silver nanosheet is a two-dimensional crystalline film composed of myristate-capped silver nanoparticles (d = 5 nm), which has a sharp localized plasmon absorption band at lambda(max) = 470 nm. A quartz substrate was coated with TiO(2) nanotubes to a coverage of 10% and then covered with a silver nanosheet. Upon UV irradiation a rapid decrease in the intensity of the 470 nm plasmon band and an increase in the long-wavelength absorption (550-1000 nm) band were clearly confirmed, indicating fusion of the nanoparticles due to decomposition of the myristate capping agent. Surface morphology measured by high-resolution scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed the decomposition and fusion of silver nanoparticles even in regions of the surface a micron away from the TiO(2) nanotubes.
Nanoscale 01/2010; 2:107-113. · 5.91 Impact Factor
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ABSTRACT: In the present study, we propose a method for preparing stable free-standing bilayer lipid membranes (BLMs). The BLMs were prepared in a microfabricated aperture with a smoothly tapered edge, which was prepared in a nanometer-thick Si(3)N(4) septum by the wet etching method. Owing to this structure, the stress on lipid bilayers at the contact with the septum was minimized, leading to remarkable membrane stability. The BLMs were not broken by applying a constant voltage of +/-1 V. The membrane lifetime was 15-45 h with and without an incorporated gramicidin channel. Gramicidin single-channel currents were recorded from the same BLM preparation when the aqueous solutions surrounding the BLM were repeatedly exchanged, demonstrating the tolerance of the present BLM to repetitive solution exchanges. Such stable membranes enable analysis of channel functions under various solution conditions from the same BLM, which will open up a variety of applications including a high throughput drug screening for ion channels.
Langmuir 10/2009; 26(3):1949-52. · 4.19 Impact Factor
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ABSTRACT: Self-formation process of bilayer lipid membranes (BLMs) cushioned on agarose-coated Si surfaces was in situ monitored by simultaneous electrophysiological and infrared absorption spectroscopic (IRAS) measurements using IRAS with the multiple internal reflection geometry. IRAS signals corresponding to self-thinning of lipid solution to form BLMs were demonstrated. It was found that the appearance of IRAS bands due to C = O modes of phosphstidylcholine is related to formation of BLMs with a gigaohm seal. The functionality of the present BLM system was also demonstrated by incorporating gramicidin into the BLMs and recording its channel activities.
Applied Physics Letters 07/2009; · 3.84 Impact Factor
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ABSTRACT: This paper reviews our recent approaches for in situ label-free detection of biomolecules and their interactions by using infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry. Biomolecular interactions, such as DNA hybridization, DNA hydration, protein-protein interaction, cell growth and cell death, were characterized and monitored in situ both in D <sub>2</sub> O and H <sub>2</sub> O media. Combination of MIR-IRAS and various sensing platforms, such as Si, GaAs, porous Si, and porous amunina, was also discussed in terms of sensitivity and applicability to chip analysis. It is demonstrated that MIR-IRAS is a promising tool not only for the label-free detection of biomolecules but also for the accurate discrimination between specific and nonspecific interactions, which is critically important when we are monitoring complex and dynamic biological samples.
Journal of Applied Physics 06/2009; · 2.17 Impact Factor
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ABSTRACT: Nearly perfect pentacene single crystals with wide terraces several micrometers in width were grown by crystallization from a pentacene-containing trichlorobenzene solution. Organic field-effect transistors (OFETs) were fabricated with the pentacene single crystals and characterized for their electrical properties. The field effect mobility was found to be in the range of 0.4-0.6 cm(2)/V x s, which is comparable to that of OFETs fabricated with pentacene single crystals prepared by a physical vapor-phase growth method. The results described in this paper clearly demonstrate that the crystallization of organic semiconductors from solution is a promising chemical method for device processing of OFETs.
Langmuir 06/2009; 25(9):4861-3. · 4.19 Impact Factor
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ABSTRACT: Nearly perfect pentacene single crystals with wide terraces several micrometers in width were grown by crystallization from a pentacene-containing trichlorobenzene solution. Organic field-effect transistors (OFETs) were fabricated with the pentacene single crystals and characterized for their electrical properties. The field effect mobility was found to be in the range of 0.4−0.6 cm2/V·s, which is comparable to that of OFETs fabricated with pentacene single crystals prepared by a physical vapor-phase growth method. The results described in this paper clearly demonstrate that the crystallization of organic semiconductors from solution is a promising chemical method for device processing of OFETs.
04/2009;
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ABSTRACT: We have investigated in situ real-time monitoring of apoptosis on human promyelocytic leukemia (HL-60) cells using infrared absorption spectroscopy with the multiple internal reflection (MIR-IRAS) geometry. Actinomycin D (Act D)-induced apoptosis on HL-60 cells was monitored for 24 h. Apoptotic cells showed two strong peaks around the protein amide I and amide II bands probably due to the leakage of cytoplasmic proteins, while growing viable cells showed a peak corresponding to the secretion of metabolites and two downward peaks corresponding to uptake of nutrients from culture media. In addition, IR absorption peak intensity of the amide I and amide II bands was proportional to the extracellular concentration of lactate dehydrogenase, a marker protein for cell damage. These results demonstrate that our MIR-IRAS method is useful for discrimination of apoptotic cells from viable ones and cell apoptotic processes can be monitored in situ by analyzing the amide I and amide II peak intensity.
Journal of Applied Physics 02/2009; · 2.17 Impact Factor
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IEICE Transactions. 01/2009; 92-C:1475-1478.
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ABSTRACT: In this study, we have investigated in-situ the process of antigen immobilization and subsequent antigen-antibody interaction on solid surfaces by using infrared absorption spectroscopy in the multiple internal reflection (MIR-IRAS) geometry. Three kinds of MIR substrates, Si, GaAs and SiO2-deposited GaAs, were investigated in terms of transparency to the IR light and immobilization performance of antigen peptides, which was evaluated by using MIR-IRAS and enhanced chemiluminescence (ECL) assay. The SiO2-deposited GaAs prism provides the highest peptide immobilization efficiency that is compatible with MIR-IRAS measurements in the mid-infrared region. By using Pluronic F-127 as a blocking agent to inhibit nonspecific protein binding to the surfaces, we observed an antiserum-induced increase in the peak intensity corresponding to the amide I and amide II bands, which was selective for the antigen-antibody interaction. The present results show that MIR-IRAS is a promising tool not only for the characterization of the peptide-immobilized surface but also for the label-free detection of antigen-antibody interactions on solid surfaces.
Sensor Letters 07/2008; 6(4):613-617. · 0.82 Impact Factor
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ABSTRACT: It is important to precisely estimate values of all solar cell parameters in order to analyze the performance of a solar cell. We have proposed a stable method for the derivation of solar cell parameters from a single I-V curve under only the valid assumption for a general solar cell. Our method was applied to experimental I-V curves of a selection of solar cells, comprising of silicon, organic, and dye-sensitized solar cells, which were previously reported. Each I-V curve was calculated using the values of parameters derived from our method, and was found to be in good agreement with the experimental I-V curves, compared to previous work. Our extensively valid and stable method can be applied to for the analysis of all kinds of solar cells showing various characteristics that follow the single diode model and is very useful for improving the performance of developing solar cells.
Journal of Applied Physics 06/2008; · 2.17 Impact Factor
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ABSTRACT: In this study, we report on an in situ monitoring system of living cultured cells using infrared absorption spectroscopy in the geometry of multiple internal reflections (MIR-IRAS). In order to observe living cultured cells, the temperature in the sample chamber of a FT-IR spectrometer was maintained at 37 degrees C and a humidified gas mixture containing 5% CO(2) was introduced into the sample chamber. Human breast cell line MCF-7 cultured on Si MIR prisms were placed in the sample chamber and infrared spectra of MCF-7 cells were collected for 5 h. It was found that the adhesion and metabolism of MCF-7 cells could be monitored by the absorption intensity of amide-II protein band (1,545 cm(-1)) and also by the absorption intensities of CH( x ) bands (2,700-3,100 cm(-1)). These results suggest that our system is useful for a nondestructive and non-label monitoring of cell viability. Our method based on infrared absorption spectroscopy has a potential for bioscreening application.
Cytotechnology 01/2008; 55(2-3):143-9. · 1.21 Impact Factor
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ABSTRACT: We have synthesized anodic titanium oxide nanotubes with a high aspect ratio by anodizing a metallic titanium sheet in a perchloric
acid based electrolyte, and fabricated a dye-sensitized solar cell (DSSC) by using the nanotubes as its negative electrode.
Rapid and homogeneous anodization has been accomplished using a mixture of perchloric acid and ethanol as the electrolyte.
Furthermore, it was demonstrated that the diameter of anodic titanium oxide nanotubes could be varied by adjusting the anodization
conditions, such as the electrolyte and the anodic potential. The measured characteristic of the DSSC showed that anodic titanium
oxide nanotubes have a potential for improving the performance of a DSSC.
Journal of The Electrochemical Society. 12/2007; 155(1):K10-K14.
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ABSTRACT: Here, we propose a label-free detection of protein-protein interactions that enables simultaneous qualitative analysis of target proteins by using Fourier transform infrared (FTIR) absorption spectroscopy in multiple internal reflection geometry (MIR-FTIR). Using this method, the target proteins were detected based on the peak height of the amide I and amide II bands, while discrimination of specific and nonspecific signals is made based on the secondary structure of the analytes, which is determined through second-derivative analysis of the amide I band. As a model system, an antigen peptide was immobilized on the surface of GaAs, which was transparent to mid-infrared light, and the interaction with its antibody was examined in aqueous media. We demonstrated that the binding of the antibody to the antigen immobilized on a GaAs surface selectively gave rise to beta-sheet amide I vibrations (1639 and 1690 cm-1), while no structurally related signals were induced by nonspecifically adsorbed proteins. The peak height of the beta-peak (1639 cm-1) in the amide I band linearly increased with the antiserum concentration as well as that of the amide II band. The detection limit (S/N = 3) was a 1:36 000 dilution for the amide I signal. In addition, through the use of surface-sensitive MIR-FTIR, the present sensor selectively detected the antigen-antibody interactions at the surfaces without being affected by the presence of bulk species, enabling rapid and wash-free detection. Our method provides not only rapid label-free detection of protein-protein interactions but a more accurate discrimination between specific and nonspecific interactions through the use of the secondary structure of the target proteins as a measure for the specific signals.
Langmuir 12/2007; 23(24):12287-92. · 4.19 Impact Factor
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ABSTRACT: An aluminum nanodot was self-organized between two electrodes using the anodization process of an aluminum microelectrode of 3 μm in width. The authors observed a clear Coulomb staircase with a very large Coulomb energy of about 2 eV at room temperature. This very large Coulomb energy is attributed to the device structure which depends strongly on the aluminum nanodot formation mechanism. The authors’ results indicate that a single electron transistor operating at room temperature can be fabricated at an appropriate position using both bottom-up and top-down processes.
Applied Physics Letters 02/2007; 90(9):093119-093119-3. · 3.84 Impact Factor
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ABSTRACT: We have investigated in situ the hybridization and denaturation of DNA in aqueous solution using infrared absorption spectroscopy (IRAS) in the multiple internal reflection (MIR) geometry. We demonstrate that conformational changes of DNA strands due to hybridization (binding of two complementary single-stranded DNAs) and denaturation (separation of double helix at elevated temperatures) are reflected in the infrared absorption spectra in the frequency region where vibrational modes of the bases of DNA appear. Comparison with results of ab initio cluster calculation shows that hybridization produces the specific C O carbonyl stretching vibration modes in the hydrogen-bonded base pairs. The ratio of absorbance of the C O stretching peak at 1690 cm <sup>-1</sup> to the absorbance at 1660 cm <sup>-1</sup> provides a definitive metric for determining DNA hybridization. We also reveal that the C O stretching vibration modes of the bases of a single strand is strongly influenced by the surrounding water molecules that may interact with the C O groups of the bases. The present results suggest that MIR-IRAS is applicable to label-free, high-sensitive biosensors that provide insight about the gene expression and a variety of biological interactions such as DNA-protein interactions.
Journal of Applied Physics 06/2006; · 2.17 Impact Factor
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ABSTRACT: It is widely accepted that atmospheric oxygen can work as an electron-accepting dopant mainly to p-type organic semiconductors. We have examined the effect of oxygen on a pentacene field effect transistor (FET) with and without exposure to light using the displacement current measurement. Under vacuum conditions, the change in the displacement current due to hole injection from the source and drain electrodes to the pentacene layer is clearly observed, suggesting that the origin of the mobile carriers in the pentacene FET is carrier injection. When the FET is exposed to oxygen under dark conditions, a very small change in the threshold gate voltage for hole injection is observed. In contrast, with exposure to both oxygen and light, we observed that the threshold voltage is lowered and shifted across the zero bias and even to the polarity against hole injection. This photoinduced doping effect induces a distinct increase in the drain current of the FET, and it is maintained for at least several hours even after the irradiation is turned off. This finding suggests that the performance of organic semiconductor devices is affected not only by atmospheric oxygen but also by ambient light even during the processing and storage of the devices.
Applied Physics Letters 06/2005; 86(25):252104-252104-3. · 3.84 Impact Factor
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ABSTRACT: We propose a method of in situ (in vitro) analysis of the chemical bonding state of DNA in aqueous solution by infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS) in conjugation with electrophoresis. We demonstrate that MIR-IRAS is capable of detecting in vitro DNA hybridization. In our method, a Si prism, through which infrared lights penetrate and are also internally reflecting, also serves as the electrode for electrophoresis. We show that with a positive or negative potential being applied to the electrode (prism), DNA molecules are concentrated on or expelled from the electrode, respectively, leading to highly sensitive detection and manipulation of DNA in aqueous solution.
Applied Physics Letters 02/2005; · 3.84 Impact Factor
