Kazuma Mawatari

The University of Tokyo, Tōkyō, Japan

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Publications (110)473.85 Total impact

  • Yutaka Kazoe, Kazuma Mawatari, Takehiko Kitamori
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    ABSTRACT: The transport and behavior of nanoparticles, viruses, and biomacromolecules in 10-1000 nm confined spaces (hereafter "extended nanospaces") is important for novel analytical devices based on nanofluidics. This study investigated the concentration and diffusion of 64-nm nanoparticles in a fused-silica nanochannel of 410 nm depth, using evanescent wave-based particle velocimetry. We found that the injection of nanoparticles into the nanochannel by pressure-driven flow was significantly inhibited and that the nanoparticle diffusion was hindered anisotropically. A 0.2-pN repulsive force induced by the interaction between the nanoparticles and the channel wall is proposed as the dominant factor governing the behavior of nanoparticles in the nanochannel, on the basis of both experimental measurements and theoretical estimations. The results of this study will greatly further our understanding of mass transfer in extended nanospaces.
    Analytical Chemistry 03/2015; 87(8). DOI:10.1021/acs.analchem.5b00485 · 5.83 Impact Factor
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    ABSTRACT: Understanding liquid structure and the electrical properties of liquids confined in extended nanospaces (10-1000 nm) is important for nanofluidics and nanochemistry. To understand these liquid properties requires determination of the dielectric constant of liquids confined in extended nanospaces. A novel dielectric constant measurement method has thus been developed for extended nanospaces using a streaming potential method. We focused on the non-steady-state streaming potential in extended nanospaces and successfully measured the dielectric constant of liquids within them without the use of probe molecules. The dielectric constant of water was determined to be significantly reduced by about 3 times compared to that of the bulk. This result contributes key information toward further understanding of the chemistry and fluidics in extended nanospaces.
    Analytical Chemistry 01/2015; 87(3). DOI:10.1021/ac504141j · 5.83 Impact Factor
  • Kazuma Mawatari, Takehiko Kitamori
    Israel Journal of Chemistry (Online) 11/2014; 54(11‐12). DOI:10.1002/ijch.201410014 · 2.56 Impact Factor
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    ABSTRACT: Nanostructured photoanodes based on well-separated and vertically oriented WO3 nanorods capped with extremely thin BiVO4 absorber layers are fabricated by the combination of Glancing Angle Deposition and normal physical sputtering techniques. The optimized WO3-NRs/BiVO4 photoanode modified with Co-Pi oxygen evolution co-catalyst shows remarkably stable photocurrents of 3.2 and 5.1 mA/cm2 at 1.23 V versus a reversible hydrogen electrode in a stable Na2SO4 electrolyte under simulated solar light at the standard 1 Sun and concentrated 2 Suns illumination, respectively. The photocurrent enhancement is attributed to the faster charge separation in the electronically thin BiVO4 layer and significantly reduced charge recombination. The enhanced light trapping in the nanostructured WO3-NRs/BiVO4 photoanode effectively increases the optical thickness of the BiVO4 layer and results in efficient absorption of the incident light.
    Small 09/2014; 10(18). DOI:10.1002/smll.201400276 · 7.51 Impact Factor
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    ABSTRACT: We present a novel method to analysis clenbuterol based on a competitive microfluidic immunoassay scheme with micro-ELISA system, and obtained a limit of detection that is less than 0.1 ng/ml and a quantitative working range of 0.1 ng/ml to 27.0 ng/ml. The approach was envisaged to be a promising method for efficient onsite clenbuterol control with good sensitivity and portability.
    RSC Advances 08/2014; 4(75). DOI:10.1039/C4RA05386A · 3.71 Impact Factor
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    ABSTRACT: The small length scales that make microfluidics attractive are also the source of some very stringent constraints, especially with respect to the detection approach used. The low concentrations often analyzed in microfluidic devices require highly sensitive detection methods that are effective even in vanishingly small sample volumes. Over the years many detection approaches have been developed for microfluidics. The majority of these methods rely upon optical phenomena, with the most common being fluorescence detection. Fluorescence detection is well suited to microfluidics because it is both flexible and sensitive, however, it does have shortcomings. Weak fluorescence of targets, autofluorescence of materials, and photobleaching are a few of the issues that have to be dealt with when working with fluorescence detection. Another option that eliminates all of these problems is thermal lens microscopy (TLM), a photothermal spectroscopy technique. TLM is a flexible, sensitive detection approach for non‐fluorescent molecules that is capable of carrying out single molecule detection to label free in vivo quantification. Despite the potential benefits of TLM, it is still an underutilized detection approach. We hope this review will help broaden the use of TLM for microchip‐based CE, as well as a host of other microfluidic applications. This article is protected by copyright. All rights reserved.
    Electrophoresis 08/2014; 35(16). DOI:10.1002/elps.201300430 · 3.16 Impact Factor
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    ABSTRACT: We demonstrate a new approach to plasmonic enhanced photocatalytic water splitting by developing a novel core-shell Ti@TiO2 brush nanostructure where an elongated Ti nanorod forms a plasmonic core that concentrates light inside of a nanotubular anodic TiO2 shell. Following the ubiquitous element approach aimed at providing an enhanced device functionality without the usage of noble or rare earth elements, we utilized only inexpensive Ti to create a complex Ti@TiO2 nanostructure with an enhanced UV and Vis photocatalytic activity that emerges from the interplay between the surface plasmon resonance in the Ti core, Vis light absorption in the Ti-rich oxide layer at the Ti/TiO2 interface and UV light absorption in the nanotubular TiO2 shell.
    Nanotechnology 07/2014; 25(31):315402. DOI:10.1088/0957-4484/25/31/315402 · 3.67 Impact Factor
  • T H H Le, K Mawatari, H Shimizu, T Kitamori
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    ABSTRACT: Nanofluidics in 10(1) nm space, whose scale is comparable to the electric double layer (EDL) and the size of biomolecules, promises novel functional analytical devices. However, the detection, which is indispensable to the integrated chemical system, is still challenging in such an ultra-small space. Previously, we reported a differential interference contrast thermal lens microscope (DIC-TLM) based on the photothermal interferometry principle and succeeded in detection of nonfluorescent molecules in 10(2) nm spaces. However, the thermal diffusion into substrates becomes a problem for detection in 10(1) nm spaces. The DIC-TLM signals are significantly cancelled out in spaces much smaller than the confocal length (∼10(2) nm), which makes DIC-TLM detection in 10(1) nm space quite difficult. To overcome this problem, we propose a new channel structure that benefits the thermal diffusion and sensitivity enhancement in DIC-TLM by employing TiO2 as a substrate material for compensating the signal cancellation effect. As a result, DIC-TLM detection of nonfluorescent molecules (800 molecules) was successfully demonstrated in a nanochannel with a depth of 50 nm. The developed detection method will contribute to the functional nanofluidic devices utilizing 10(1) nm spaces.
    The Analyst 04/2014; DOI:10.1039/c4an00344f · 3.91 Impact Factor
  • Kentaro Shirai, Kazuma Mawatari, Takehiko Kitamori
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    ABSTRACT: The growing need to optimize immunoassay performance driven by interest in analyzing individual cells has resulted in a decrease in the amount of sample required. Miniaturized immunoassays that use ultra-small femtoliter to attoliter sample volumes, a range known as the extended nanospace, can satisfy this analytical need; however, capturing every targeted molecule without loss in extended nanochannels for subsequent detection remains challenging. This is the first report of a successful extended nanofluidics-based quantitative immunochemical reaction capable of high capture efficiency using a femtoliter-scale sample volume. A novel patterning method using a photolithographic technique with vacuum ultraviolet light and low-temperature (100 °C) bonding enables patterning of functional groups for antibody immobilization before bonding, resulting in an immunochemical reaction space of only 86 fL. Reaction rate analyses indicate a decrease in the required sample volume to 810 fL and improvement in the limit of detection to 3 zmol, 5-6 orders of magnitude better than possible with the microfluidic immunoassay format. Highly efficient (near 100%) immunochemical reactions on a seconds time scale are possible due to the nm-scale diffusion length, which should be advantageous for the analysis of ultra-low-volume samples.
    Small 04/2014; 10(8). DOI:10.1002/smll.201302709 · 7.51 Impact Factor
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    ABSTRACT: Engineering using liquids confined in channels 10-1000 nm in dimension, or "extended-nanofluidics," is the next target of microfluidic science. Liquid properties at this scale were unrevealed until recently because of the lack of fundamental technologies for investigating these ultrasmall spaces. In this article, the fundamental technologies are reviewed, and the emerging science and technology in the extended-nanospace are discussed.
    Analytical Chemistry 04/2014; 86(9). DOI:10.1021/ac4026303 · 5.83 Impact Factor
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    ABSTRACT: The separation and sensitive detection of nonfluorescent molecules at the femtoliter (fL) scale has been achieved for the first time in a nanofluidic channel. Smaller sample volumes and higher separation efficiencies have been significant targets for liquid chromatography for many years. However, the use of packed columns hindered further miniaturization and improvement of separation efficiency. Our group recently developed a novel chromatographic method using an open nanofluidic channel to realize attoliter sample injection and a separation efficiency of several million plates per m. However, because of the extremely small optical path length, this detection method was limited to fluorescent molecules. Herein, we describe the combination of nanofluidic chromatography with differential interference contrast thermal lens microscopy (DIC-TLM), a sensitive detection method for nonfluorescent molecules developed by our group that has the ability to detect 0.61 zmol (370 molecules) with an optical path length of 350 nm. As a result, separation of a 21 fL sample containing 250 zmol was possible at the limit of detection (LOD).
    The Analyst 03/2014; 139(9). DOI:10.1039/c3an02353b · 3.91 Impact Factor
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    ABSTRACT: The surface modification is indispensable to facilitate new functional applications of micro/nanofluidics devices. Among many modification techniques developed so far, the photo-induced chemical modification is the most versatile method in terms of robustness, process simplicity, and feasibility of chemical functionality. In particular, the method is useful for closed spaces, such as post-bonded devices. However, the limitation by optical diffraction limit is still a challenging issue in scaling down the pattern sizes to nanoscale. Here, we demonstrated a novel surface modification on sub-100 nm scale utilizing the novel optical near-field (ONF) generated on nanostructures of photocatalyst (TiO2). The minimum pattern size of 40 nm, which was much smaller than diffraction limit, was achieved using a visible light source (488 nm) and a conventional irradiation setup. The controllability of pattern size by light intensity, the feasibility of functionality, and the non-contact working mode have impacts on surface patterning of post-bonded micro/nanofluidics devices. It is also worthy to note that our results verified for the first time the ONF on nanostructures of non-metal materials and its ability to manipulate the chemical reaction on nanoscale.
    Microfluidics and Nanofluidics 02/2014; 17(4). DOI:10.1007/s10404-014-1361-7 · 2.67 Impact Factor
  • Journal- Ceramic Society Japan 01/2014; 122(1426):393-397. DOI:10.2109/jcersj2.122.393 · 0.85 Impact Factor
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    ABSTRACT: The development of foot-and-mouth disease virus (FMDV) detection methods is crucial for animal food security, tackling regional FMDV epidemic, and global FMDV prognostic control. For these purposes, a fast and sensitive analysis method is required. In this study, we developed a microchip-based ELISA (enzyme-linked immunosorbent assay), micro-ELISA, to realize FMDV detection. Nickel(II) chelating chemistry was utilized to immobilize recombinant protein (antigen) on polystyrene micro-beads in order to determine FMDV antibodies in cattle serum samples. In addition, reaction protocol and conditions were investigated. As a result, the FMDV detection was successfully demonstrated with only a 10-μL sample volume in 25-minute assay time. Analytical sensitivity was evaluated by a maximum nominal positiveness percentage value (NPPV) of 303 and a dilution factor of 32×. The method's inter-run and intra-run CV (coefficients of variance) values were 15.5 and 17.1%, respectively, which were fully compatible with the OIE (World Organization for Animal Health) principle of validation of diagnosis assays for infectious diseases. The developed method should become a powerful tool for determining other animal contagious diseases and/or zoonosis.
    Analytical Sciences 01/2014; 30(3):359-63. DOI:10.2116/analsci.30.359 · 1.40 Impact Factor
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    ABSTRACT: Understanding fluid flows in 10-1000 nm space, which we call extended nanospace, is important for novel nanofluidic devices in analytical chemistry. This study therefore developed a particle tracking velocimetry for velocity distribution in nanochannel flows, by using the evanescent wave illumination. 64 nm fluorescent nanoparticles were used as flow tracer. The particle position was determined from fluorescent intensity by the evanescent wave field, with a spatial resolution smaller than light wavelengths. The time resolution of 260 μs was achieved to make error by the Brownian diffusion of the tracer small to be neglected. An image processing by multi-time particle tracking was established to detect the tracer nanoparticles of weak fluorescent intensity. Though the measurement region was affected by nonuniform particle distribution with the electrostatic interactions, pressure-driven flows of water in a nanochannel of 50 μm width and 410 nm depth were successfully measured. The results of the velocity distribution in the depth-wise direction approximately showed agreement with the fluid dynamics with the bulk liquid properties from the macroscopic view, however, suggested slip velocities even in the hydrophilic channel. We suggest a possibility for appearance of molecular behavior in the fluid near the wall within 10 nm-order scale.
    Analytical Chemistry 10/2013; 85(22). DOI:10.1021/ac401964h · 5.83 Impact Factor
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    ABSTRACT: Understanding the properties of liquid confined in extended nanospace (10-1000 nm) is crucial for nanofluidics. Due to confinement and surface effects, water may have specific structures and reveals unique physicochemical properties. Recently, our group has developed a super resolution laser-induced fluorescence (LIF) technique to visualize proton distribution with the electrical double layer (EDL) in fused-silica extended nanochannel (Kazoe, Y.; Mawatari, K.; Sugii, Y.; Kitamori, T. Anal. Chem. 2011, 83, 8152). In this study, based on the coupling of the Poisson-Boltzmann theory and site-dissociation model, effect of specific water properties in extended nanospace on formation of EDL was investigated by comparison of numerical results with our previous experimental results. The numerical results of the proton distribution with a lower dielectric constant of approximately 17 were shown to be in good agreement with our experimental results, which confirms our previous observation showing a lower water permittivity in extended nanochannels. In addition, the higher silanol deprotonation rate in extended nanospaces was also demonstrated, which is supported by our previous results of NMR and streaming current measurements. The present results will be beneficial for a further understanding of interfacial chemistry, fluid physics and electrokinetics in extended nanospace.
    Analytical Chemistry 04/2013; 85(9). DOI:10.1021/ac400001v · 5.83 Impact Factor
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    ABSTRACT: A technical bottleneck to the broadening of applications of glass nanofluidic chips is bonding, due to the strict conditions, especially the extremely high temperatures (∼1000 °C) and the high vacuum required in the current glass-to-glass fusion bonding method. Herein, we report a strong, nanostructure-friendly, and high pressure-resistant bonding method, performed at room temperature (RT, ∼25 °C) for glass nanofluidic chips, using a one-step surface activation process with an O(2)/CF(4) gas mixture plasma treatment. The developed RT bonding method is believed to be able to conquer the technical bottleneck in bonding in nanofluidic fields.
    Lab on a Chip 02/2013; 13(6). DOI:10.1039/c3lc41345d · 5.75 Impact Factor
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    ABSTRACT: Demand for analysis of rare cells such as circulating tumor cells in blood at the single molecule level has recently grown. For this purpose, several cell separation methods based on antibody-coated micropillars have been developed (e.g., Nagrath et al., Nature 450, 1235–1239 (2007)). However, it is difficult to ensure capture of targeted cells by these methods because capture depends on the probability of cell-micropillar collisions. We developed a new structure that actively exploits cellular flexibility for more efficient capture of a small number of cells in a target area. The depth of the sandwiching channel was slightly smaller than the diameter of the cells to ensure contact with the channel wall. For cell selection, we used anti-epithelial cell adhesion molecule antibodies, which specifically bind epithelial cells. First, we demonstrated cell capture with human promyelocytic leukemia (HL-60) cells, which are relatively homogeneous in size; in situ single molecule analysis was verified by our rolling circle amplification (RCA) method. Then, we used breast cancer cells (SK-BR-3) in blood, and demonstrated selective capture and cancer marker (HER2) detection by RCA. Cell capture by antibody-coated microchannels was greater than with negative control cells (RPMI-1788 lymphocytes) and non-coated microchannels. This system can be used to analyze small numbers of target cells in large quantities of mixed samples.
    Biomicrofluidics 12/2012; 6(4). DOI:10.1063/1.4771968 · 3.77 Impact Factor
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    ABSTRACT: Analytical technologies of ultrasmall volume liquid, in particular femtoliter to attoliter liquid, is essential for single-cell and single-molecule analysis, which is becoming highly important in biology and medical diagnosis. Nanofluidic chips will be a powerful tool to realize chemical processes for such a small volume sample. However, a technical challenge exists in fluidic control, which is femtoliter to attoliter liquid generation in air and handling for further chemical analysis. Integrating mechanical valves fabricated by MEMS (microelectric mechanical systems) technology into nanofluidic channels is difficult. Here, we propose a nonmechanical valve, which is a Laplace nanovalve. For this purpose, a nanopillar array was embedded in a nanochannel using a two-step electron beam lithography and dry-etching process. The nanostructure allowed precise wettability patterning with a resolution below 100 nm, which was difficult by photochemical wettability patterning due to the optical diffraction. The basic principle of the Laplace nanovalve was verified, and a 1.7 fL droplet (water in air) was successfully generated and handled for the first time.
    Analytical Chemistry 12/2012; 84(24). DOI:10.1021/ac3028905 · 5.83 Impact Factor
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    ABSTRACT: This is a response to the comment by Anzo and Okada on our recent article published in Analytical Chemistry. Anzo and Okada estimated our experimental results for proton distribution in a 400 nm nanochannel based on the Poisson-Boltzmann theory with the Gouy-Chapman model. We consider that their comment is very supportive and extends our report to conventional surface and solution chemistry. However, from our recent studies for 10-1000 nm (extended nanospace), we suggest an importance of near-field liquid structure and charge behavior at an interface region. The heterogeneity of aqueous liquid in extended nanospace should be taken into consideration, in order to predict the electric double layer. Our group is establishing a numerical approach for the proton distribution based on the Poisson-Boltzmann theory combined with the site dissociation model, which considers the specific properties in extended nanospace. This study will be published in the near future.
    Analytical Chemistry 11/2012; 84(24). DOI:10.1021/ac302482g · 5.83 Impact Factor

Publication Stats

850 Citations
473.85 Total Impact Points


  • 1998–2015
    • The University of Tokyo
      • Department of Applied Chemistry
      Tōkyō, Japan
  • 2010–2014
    • Japan Science and Technology Agency (JST)
      Edo, Tōkyō, Japan
  • 2006–2010
    • Kanagawa Academy of Science and Technology
      Kawasaki Si, Kanagawa, Japan
  • 2005
    • Asahi Kasei
      Edo, Tōkyō, Japan