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ABSTRACT: In an effort toward determining the feasibility of single molecule analysis, we describe a case whereby the binding of one biotinylated DNA to one streptavidin molecule via electrostatic interactions was controlled by altering in pH 4.0-9.0 and 0.16 of the ion strength. The quantitative analysis of immobilized probe ssDNA was realized in real-time via a quartz crystal microbalance (QCM) and electrochemical (EC) measurement in the range 100 pM to 50 microM of probe oligonucleotide concentration. The variation amount of biotinylated ssDNA immobilized on the streptavidin-modified surface at pH 7.5 was about 0.16 pmol, giving a ratio of streptavidin to biotinylated ssDNA of about 1:1.1. On the other hand, at pH 4.9, it was immobilized about 0.29 pmol. From the shape of the Langmuir plot and QCM, the immobilization efficiency of biotinylated DNA via streptavidin at pH 4.9 was approximately twofold that at pH 7.5. In view points of the reaction velocity, it was increased with decreasing buffer solution pH, indicating a strong interaction of negatively charged probe DNA with the positively charged streptavidin. And also the EC response value of deltaI/I(streptavidin) for the immobilized biotinylated ssDNA in pH 4.9 was about 49%, while the corresponding value for the pH 7.5 was approximately 34%. As DNA molecules possess negative charges, electrostatic repulsion occurred between streptavidin and biotinylated ssDNA at pH 7.5. At pH 4.9, the attraction between the biotinylated ssDNA and streptavidin resulted in increased adsorption which has an isoelectric point of about 5.9. It was deduced that the binding of biotinylated ssDNA to one or two of the four binding sites of streptavidin can be controlled by adjusting the pH-controlled electrostatic interaction.
Analytica chimica acta 12/2007; 603(1):76-81. · 4.31 Impact Factor
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ABSTRACT: Nanofabrication technologies should be useful for developing highly sensitive, reproducible nanobiosensors. This letter presents a nanometric system that is composed of well-oriented nanowells. The geometry permits only one or a few biomolecules to enter and become attached to nanosized gold dots. This nanoarray is easily fabricated using current nanolithography technology. When the authors applied this array to highly sensitive electrochemical DNA detection, they obtained a two-orders-of-magnitude enhancement in sensitivity. This nanometric system could be applied to numerous other integrated digital biosensors.
Applied Physics Letters 09/2006; 89(11):113901-113901-3. · 3.84 Impact Factor
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ABSTRACT: Tapping mode atomic force microscopy (TM-AFM) imaging of a phospholipid bilayer vesicle (liposome) immobilized on a gold surface was performed to investigate morphologies of the electrode surfaces produced through application of three different sample preparation methods. We compared both methods from a morphological viewpoint using TM-AFM images. Liposomes, composed of zwitterionic and anionic phospholipids, were prepared by extrusion. Results indicate that the surface with immobilized L1-liposome, which was fabricated by the amino coupling method, seemed to form large amounts of aggregated or fused liposomes. In contrast, L2-liposome-containing 1-octadecanthiol that was directly attached on the gold surface using thiol-gold binding force was immobilized as a uniform surface topology without liposome aggregation. Finally, we attempted to arrange individual L3-liposome, prepared by mixing zwitterionic and anionic phospholipids, onto the gold layer by electron-beam (e-beam) lithography technique. A third method, L3-liposome formation on the sensor surface, is greatly anticipated for biosensor applications.
Journal of Bioscience and Bioengineering 08/2006; 102(1):28-33. · 1.79 Impact Factor
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ABSTRACT: Nano-materials and devices designed by programmed self-organization processes are presented in a realistic style. The concept of programmed self-organization is the accumulation ofelemental self-assembling steps with the control of time, space, and geometry by sequential procedures, fusion of top-down and bottom up processes, and multi-dimensional crystal growth, respectively. Molecule-incorporated DNA was formed by specific molecular recognition through the use of triple hydrogen bonding. For the construction of network-based molecular-scale devices, we developed the DNA-templated arrangement of Au-nanoparticles and top-contact electrode using nano-transfer printing. We also found that self-organized positioning of functional lipid vesicles on nano-well electrodes is useful for electrochemical bio-sensing.
Hyomen Kagaku 01/2006; 27:151-156.
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ABSTRACT: We measured the electrical conductivity of a DNA network as a spatially-resolved current-image using point-contact current imaging atomic force microscopy (PCI-AFM) under various humidity conditions. The simultaneous observation of topography and current image by PCI-AFM can provide information pertaining to the electrical properties of biological and/or soft materials in the nano-scale range. Under dry condition (0% humidity), no difference was observed for the electrical current both of the DNA network and mica surface, whereas the electrical current along the DNA network was larger than that of the mica surface by 20 pA at a bias voltage of 5 V under high humidity conditions of 60%.
Applied Physics Letters 04/2005; · 3.84 Impact Factor
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ABSTRACT: The assay of DNA biosensor-based nucleic acid recognition using microfabrication technology provides for high sensitivity, good surface coverage and reproducibility. We have achieved efficient immobilization and hybridization of nonlabeled DNA using cyclic voltammetry (CV), square wave voltammetry (SWV) and scanning near-field optical microscopy (SNOM) techniques. The increased electrochemical response observed following the immobilization of biotinlyated ssDNA probe suggests that nucleic acid is a somewhat better medium for electronic transfer. We demonstrated the high coverage of immobilized FITC-labeled biotinylated DNA probe on a streptavidin-modified surface using SNOM imaging. SNOM imaging of FITC-labeled complementary DNA also exhibited fluorescent light spots of hybridization distributed throughout. No fluorescent light was observed with the hybridization of non-complementary DNA.
Journal of Nanoscience and Nanotechnology 10/2004; 4(7):882-5. · 1.56 Impact Factor
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ABSTRACT: Protein adsorption on a gold surface is investigated by comparing the results of quartz crystal microbalance method and atomic force microscopy. The adsorption of streptavidin on functional gold surfaces is directly monitored by a quartz crystal microbalance, and confirmed by atomic force microscopy. For this investigation, a modified gold substrate is fabricated to obtain a topographic image of streptavidin molecules. Both methods show a correlation in terms of the highly dense protein single-layer formation, and the modified gold electrode shows a slightly denser protein layer formation because of the difference in substrate geometry as compared with that of a mica surface.
Journal of Bioscience and Bioengineering 02/2004; 97(2):138-40. · 1.79 Impact Factor
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ABSTRACT: Scanning near-field optical microscopy (SNOM) imaging was performed to allow for the direct visualization of damaged sites on individual DNA molecules to a scale of a few tens of nanometers. Fluorescence in situ hybridization on extended DNA molecules was modified to detect a single abasic site. Abasic sites were specifically labelled with a biotinlylated aldehyde-reactive probe and fluorochrome-conjugated streptavidin. By optimizing the performance of the SNOM technique, we could obtain high contrast near-field optical images that enabled high-resolution near-field fluorescence imaging using optical fiber probes with small aperture sizes. High-resolution near-field fluorescence imaging demonstrated that two abasic sites within a distance of 120 nm are clearly obtainable, something which is not possible using conventional fluorescence in situ hybridization combined with far-field fluorescence microscopy.
FEBS Letters 01/2004; 555(3):611-5. · 3.54 Impact Factor
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ABSTRACT: The transverse current–voltage characteristics of Copper‐ phthalocyanine (CuPc)/Si, PbTe/Si, and PbTe/CuPc/Si junction have been observed in the dark and under illumination. The PbTe/CuPc/Si junction exhibits a strong photovoltaic response with quantum efficiency of 15.4% and power conversion efficiency of 3.46×10<sup>-2</sup>. The photocarrier is generated in CuPc layer and the carrier is well separated by the steep incline of the potential near the CuPc/PbTe interface. The CuPc/PbTe multilayers show large photoconduction effect in the in‐plane direction. © 1996 American Institute of Physics.
Journal of Applied Physics 10/1996; · 2.17 Impact Factor
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ABSTRACT: A LiYF4 single crystal was grown by the Czochralski technique in an Ar-gas atmosphere. The complex dielectric constants and complex impedances are measured in the range of 100 Hz–10 MHz and up to 200°C for a c-plate of a LiYF4 single crystal. The LiYF4 reveals a strong low frequency dielectric dispersion below 300 kHz, from room temperature to 200°C. It is believed that the strong dielectric dispersion is related to the ionic hopping conduction, which arises mainly from the jumping of Li+-ions between neighboring sites, with an activation energy of Δ=0.49 eV. The conduction mechanism seems to be the non-interacting Debye type and the relaxation times satisfy the Arrhenius relation.
Materials & Design. 21(6):567-570.
