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FacultyDepartment of Biotechnology and Chemistry / Graduate School of System Enginnering
PositionAssociate Professor
DegreePh.D. in Engineering
Commentator Guide
Last Updated :2020/09/01

Research Activities

Research Areas

  • Nanotechnology/Materials, Functional solid-state chemistry
  • Nanotechnology/Materials, Basic physical chemistry
  • Life sciences, Biomaterials
  • Life sciences, Biomedical engineering
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering), Applied biofunctional and bioprocess engineering

Published Papers

  • Biodegradable and Hollowed Micro-Scaffolds for Improved Modular Assembly-Based Tissue Engineering: Design, 3D Fabrication, and Feasibility in Randomly Packed Perfusion Culture, Y. Pang, S. L, U. Sutoko, Y. Horimoto, K. Montagne, K. Komori, K. Takano, R. Shirakashi, M. Anzai, T. Niino, Y. Sakai, Biochem. Eng. J., Biochem. Eng. J., 149, 107239, 2019 , Refereed
  • Integration of an Oxygen Sensor into a Polydimethylsiloxane Hepatic Culture Device for Two–Dimensional Gradient Characterization, S. Matsumoto, E. Leclerc, T. Maekawa, H. Kinoshita, M. Shinohara, K. Komori, Y. Sakai, T. Fujii, Sens. Actuators B, Sens. Actuators B, 273, 1062 - 1069, 2018 , Refereed
  • Enhanced Self-Organization of Size-Controlled Hepatocyte Aggregates on Oxygen Permeable Honeycomb Microwell Sheets, M. Shinohara, K. Komori, T. Fujii, Y. Sakai, Biomed. Phys. Eng. Express, Biomed. Phys. Eng. Express, 3(045016), 2017 , Refereed
  • Establishment of a New Physiologically-Relevant Liver Tissue Model Based on Hierarchically Coculturing Primary Rat Hepatocytes with Liver Sinusoidal Endothelial Cells on a Gas Permeable Membrane, W.-J. Xiao, G. Perry, K. Komori, Y. Sakai, Integr. Biol., Integr. Biol., 7, 1412 - 1422, 2015 , Refereed
  • Combination of Microwell Structures and Direct Oxygenation Enables Efficient and Size-Regulated Aggregate Formation of an Insulin-Secreting Pancreatic beta-Cell Line, Marie Shinohara, Hiroshi Kimura, Kevin Montagne, Kikuo Komori, Teruo Fujii, Yasuyuki Sakai, BIOTECHNOLOGY PROGRESS, BIOTECHNOLOGY PROGRESS, 30(1), 178 - 187, Jan. 2014 , Refereed
    Summary:Spherical three-dimensional (3D) cellular aggregates are valuable for various applications such as regenerative medicine or cell-based assays due to their stable and high functionality. However, previous methods to form aggregates have shown drawbacks, being labor-intensive, showing low productivity per unit area or volume and difficulty to form homogeneous aggregates. We proposed a novel strategy based on oxygen-permeable polydimethylsiloxane (PDMS) honeycomb microwell sheets, which can theoretically supply about 80 times as much oxygen as conventional polystyrene culture dishes, to produce recoverable aggregates in controllable sizes using mouse insulinoma cells (MIN6-m9). In 48 hours of culture, the PDMS sheets produced aggregates whose diameters were strictly controlled (?32, 60, 90, 150 and 280 mm) even at an inoculum density eight times higher (8.0x105 cells/cm(2)) than that of normal confluent monolayers (1.0x105 cells/cm(2)). Measurement of the oxygen tension near the cell layer and glucose/lactate analysis clearly showed that cells exhibit aerobic respiration on the PDMS-based culture system. Glucose-responsive insulin secretion of the recovered aggregates showed that the aggregates around 90 mm in diameter secreted the largest amounts of insulin. This confirmed the advantages of 3D cellular organization and the existence of a suitable aggregate size, above which excess organization leads to a decreased metabolic response. These results demonstrated that this microwell-based PDMS culture system provides a promising method to form size-regulated and better functioning 3D cellular aggregates of various kinds of cells with a high yield per surface area. (c) 2013 American Institute of Chemical Engineers Biotechnol. Prog., 30:178-187, 2014
  • Formation and harvesting of thick pancreatic β-cell sheets on a highly O2-permeable plate modified with poly(N-isopropylacrylamide), Kikuo Komori, Mari Udagawa, Marie Shinohara, Kevin Montagne, Tatsuro Tsuru, Yasuyuki Sakai, Biomaterials Science, Biomaterials Science, 1(5), 510 - 518, May 2013 , Refereed
    Summary:Producing sheet-like tissues is a promising strategy for implantable engineered tissues, because in vitro pre-vascularization is dispensable in this configuration. We developed a simple methodology for the formation and non-destructive harvesting of a thick pancreatic β-cell sheet consisting of mouse insulinoma MIN6-m9 cells and mouse NIH3T3 fibroblasts using an O 2-permeable polydimethylsiloxane plate modified with poly(N-isopropylacrylamide) (O2+/PNIPA-PDMS plate). Owing to the direct oxygenation of the cells through the PNIPA-modified PDMS plate, a viable, metabolically active sheet 5-6 cell layers thick (ca. 60 μm thick) was formed spontaneously in the absence of direct oxygenation, only a thin cell sheet could be formed consisting of at most 2 layers (ca. 20 μm thick) with mainly anaerobic metabolism. Consequently, the net density of MIN6-m9 cells under direct oxygenation was about twice as high as in the absence of direct oxygenation. Accordingly, the insulin secretion for 10 to 60 min after glucose stimulation was also about 1.5 times higher with oxygenation. Furthermore, the thick cell sheet was successfully harvested from the O2+/PNIPA-PDMS plate surface in a non-destructive manner by inducing a phase transition of PNIPA by lowering the temperature below the lower critical solution temperature. Thus, the present report shows a promising and simple method to produce thick sheet-like engineered tissues for transplantation that could be used as a treatment for type 1 diabetes. © 2013 The Royal Society of Chemistry.
  • Prediction of Phthalate Permeation Through Pulmonary Alveoli Using a Cultured A549 Cell-Based in Vitro Alveolus Model and a Numerical Simulation, K. Iwasawa, G. Tanaka, T. Aoyama, M. M. Chowdhury, K. Komori, T. Tanaka-Kagawa, H. Jinno, Y. Sakai, AATEX, AATEX, 18, 19 - 31, 2013 , Refereed
  • Efficient Formation of Endothelialized Rat Hepatocyte Aggregates in a PDMS Microwell Device and their Immobilization with Biodegradable Fibers in Perfusion Culture, Y. Pang, K. Montagne, M. Shinohara, K. Komori, Y. Sakai, Biofabrication, Biofabrication, 4(045004), 2012 , Refereed
  • Microfluidic Device with Integrated Glucose Sensor for Cell-based Assay in Toxicology, H. Kimura, H. Takeyama, K. Komori, T. Yamamoto, Y. Sakai, T. Fujii, J. Robotics Mech., J. Robotics Mech., 22, 594 - 600, 2010 , Refereed
  • Rapid and Direct Cell-to-Cell Attachment Using Avidin-Biotin Binding System: Large Aggregate Formation in Suspension Culture and Small Tissue Element Formation Having a Precise Microstructure Using Optical Tweezers, N. Kojima, K. Miura, T. Matsuo, H. Nakayama, K. Komori, S. Takeuchi, Y. Sakai, J. Robotics Mech., J. Robotics Mech., 22, 619 - 622, 2010 , Refereed
  • Mechanical Characterization of a Cell-loaded Elastin Film Prepared by Use of a Novel Cross-linker, Dode-DSP, K. Komori, S. Takamiya, N. Kojima, O. Kuwazuru, N. Yoshikawa, K. Furukawa, K. Miyamoto, Y. Sakai, Chem. Lett., Chem. Lett., 38, 878 - 879, 2009 , Refereed
  • Development of a Multi-Compartment Micro-Cell Culture Device as a Future on-Chip Human: Fabrication of a Three-Compartment Device and Immobilization of Rat Mature Adipocytes for the Evaluation of Chemical Distributions, H. Nakayama, H. Kimura, K. Komori, T. Fujii, Y. Sakai, J. Robotics Mech., J. Robotics Mech., 19, 544 - 549, 2007 , Refereed
  • Electrochemiluminescence Reactions of Metal Complexes Immobilized on Surface of a Magnetic Microbead, N. Oyama, K. Komori, O. Hatozaki, Stud. Surf. Sci. Catal., Stud. Surf. Sci. Catal., 132, 427 - 430, 2001 , Refereed
  • Disposable test plates with tyrosinase and beta-glucosidases for cyanide and cyanogenic glycosides, T Tatsuma, K Komori, HH Yeoh, N Oyama, ANALYTICA CHIMICA ACTA, ANALYTICA CHIMICA ACTA, 408(1-2), 233 - 240, Mar. 2000 , Refereed
    Summary:Colorimetric methods for the determination of cyanide and cyanogenic glycosides (amygdalin and linamarin) are developed. In the presence of dissolved oxygen, tyrosinase catalyzes the oxidation of L-tyrosine to dark melanin via red dopachrome. This coloring reaction is inhibited by cyanide, which is added or Liberated from a cyanogenic glycoside as a result of hydrolysis catalyzed by a beta-glucosidase. This inhibition is utilized to determine cyanide and the cyanogenic glycosides. A spectrophotometric method is quantitative, and its typical dynamic range is 3 mu M to 0.1 mM. Test plates that are coated by the films containing tyrosinase, a beta-glucosidase, L-tyrosine, and poly(ethyleneoxide) are also prepared as semi-quantitative devices, and their typical dynamic range is 10 mu M to 10 mM. This is expected to be an inexpensive, safe, and convenient method for end-users. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Controlled direct electron transfer kinetics of fructose dehydrogenase at cup-stacked carbon nanofibers, K. Komori, J. Huang, N. Mizushima, S. Ko, T. Tatsuma, Y. Sakai, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 19(40), 27795 - 27800, Oct. 2017 , Refereed
    Summary:Graphene edge sites not only facilitate heterogeneous electron transfer reactions of redox species because of localization of electrons, but also allow sensitivities and selectivities to be tuned by controlling the atomic oxygen/carbon (O/C) ratio. Here, we immobilized fructose dehydrogenase (FDH) onto the surface of cup-stacked carbon nanofibers (CSCNFs), which provide highly ordered graphene edges with a controlled O/C ratio, and investigated the direct electron communication with FDH. As the O/C ratio decreased at the CSCNF surface, the negative zeta potential was mitigated and the electrochemical communication with FDH was facilitated. This is likely due to improved orientation of FDH molecules on the CSCNF surface. CSCNFs with a controlled O/C ratio could be applied to FDH-based D-fructose biosensors with tunable dynamic range and fructose biofuel cells with a controlled maximum current.
  • Amperometric pH Sensor Based on Graphene-Polyaniline Composite, Rinky Sha, Kikuo Komori, Sushmee Badhulika, IEEE SENSORS JOURNAL, IEEE SENSORS JOURNAL, 17(16), 5038 - 5043, Aug. 2017 , Refereed
    Summary:Here, we report a grapheme-polyaniline (Gr-PANi) composite modified glassy carbon electrode (GCE) as an amperometric pH sensor. Gr-PANi composite was synthesized by electrodeposition of PANi on the surface of Gr modified GCE using the cyclic voltammetry technique. XRD and Raman analysis confirmed high crystallinity of Gr-PANi composite. FESEM analysis revealed that Gr flakes are surrounded by PANi film because of the heterogeneous nucleation and growth of PANi during electro-polymerization. In acidic region, current of the composite-based pH sensor increased with decreasing pH values of the solution, whereas in alkaline region, current increased with the increasing pH values of the solution. The as-fabricated pH sensor exhibits shorter response time with an excellent sensitivity of -50.14 mu A pH(-1) cm(-2) in the range of pH 1-5 and 139.2 mu A pH(-1) cm(-2) in the range of pH 7-11. The composite-based sensor showed enhanced sensitivity compared with pure Gr-based pH sensor because unlike pristine Gr-based pH sensor, it utilizes both charge-storage mechanisms in EDLCs and pseudo-capacitors, thereby resulting in excellent synergy between Gr and PANi. Reproducibility of the pH sensor was also examined between three different electrodes in the solution of pH 5. Insignificant variation in the current response suggested excellent reproducibility of pH sensor. To the best of our knowledge, no other studies have been reported on the Gr-PANi composite-based pH sensor over wide pH range. This Gr-PANi-based pH sensor offers a simple, low-cost, promising, real-time amperometric pH sensor in chemistry, clinical diagnostics, bio-sensing, and environmental monitoring applications.
  • Graphene-Polyaniline composite based ultra-sensitive electrochemical sensor for non-enzymatic detection of urea, Rinky Sha, Kikuo Komori, Sushmee Badhulika, ELECTROCHIMICA ACTA, ELECTROCHIMICA ACTA, 233, 44 - 51, Apr. 2017 , Refereed
    Summary:Detection of urea is of prime importance in food and water safety, dairy industries and environmental monitoring. Traditional methods to detect urea are either expensive and involve sophisticated instrumentation or are based on enzymatic approach of detection. Herein, we report a Graphene-Polyaniline (Gr-PANi) based electrochemical sensor for non-enzymatic detection of urea. Gr-PANi composite was synthesized by electro-deposition of PANi on the surface of Gr modified GCE using cyclic voltammetry (CV) technique. The presence of Gr and PANi in the composite was confirmed using a multitude of characterization techniques which included FESEM, XRD and Raman spectroscopy. The electrochemical behavior of urea at the surface of Gr-PANi modified GCE was studied by CV whereas urea sensing was performed by using simple current-potential (I-V) technique. The current response of the as fabricated urea sensor was similar to 4.74 folds greater than that of pure PANi based sensor and similar to 67.2 times greater than that of pure Gr based sensor. The sensing performance of the composite based urea sensor was optimized by varying the thickness of PANi film. The optimized sensor exhibited lower limit of detection (5.88 mu M), excellent reproducibility, selectivity and stability with an enhanced sensitivity of 226.9 mu A/mu M cm(2) (R-2 = 0.993) in the range of 10 mu M-200 mu M. The reliability of the as-fabricated sensor was successfully investigated by using it to detect urea concentrations in samples of tap water and milk samples. This highly-sensitive Gr-PANi composite based urea sensor provides a simple, low cost, non enzymatic approach for detection of urea that find numerous applications in clinical diagnostics, dairy industries, fertilizer plants and environmental monitoring. (C) 2017 Elsevier Ltd. All rights reserved.
  • Electrochemical properties of seamless three-dimensional carbon nanotubes-grown graphene modified with horseradish peroxidase, Kikuo Komori, Trupti Terse-Thakoor, Ashok Mulchandani, BIOELECTROCHEMISTRY, BIOELECTROCHEMISTRY, 111, 57 - 61, Oct. 2016 , Refereed
    Summary:Horseradish peroxidase (HRP) was immobilized through sodium dodecyl sulfate (SDS) on the surface of a seamless three-dimensional hybrid of carbon nanotubes grown at the graphene surface (HRP-SDS/CNTs/G) and its electrochemical properties were investigated. Compared with graphene alone electrode modified with HRP via SDS (HRP-SDS/G electrode), the surface coverage of electroactive HRP at the CNTs/G electrode surface was approximately 2-fold greater because of CNTs grown at the graphene surface. Based on the increase in the surface coverage of electroactive HRP, the sensitivity to H2O2 at the HRP-SDS/CNTs/G electrode was higher than that at the HRP-SDS/G electrode. The kinetics of the direct electron transfer from the CNTs/G electrode to compound I and II of modified HRP was also analyzed. (C) 2016 Elsevier B.V. All rights reserved.
  • Direct Electron Transfer Kinetics of Peroxidase at Edge Plane Sites of Cup-Stacked Carbon Nanofibers and Their Comparison with Single-Walled Carbon Nanotubes, Kikuo Komori, Tetsu Tatsuma, Yasuyuki Sakai, LANGMUIR, LANGMUIR, 32(36), 9163 - 9170, Sep. 2016 , Refereed
    Summary:Electron transfer kinetics at the graphene edge site is of great interest from the viewpoints of application to sensing and energy conversion and storage. Here we analyzed kinetics of direct electron transfer of horseradish. peroxidase (HRP) adsorbed through surfactant sodium dodecyl sulfate,at cup-stacked carbon nanofibers (CSCNFs), which provide highly ordered graphene edges, and compared it with that at single-walled carbon nanotube (SWCNTs), which consist of a rolled-up basal plane graphene. The heterogeneous electron transfer rate constant of the Fe2+/(3+) couple of the HRP reaction center at CSCNFs (ca. 34.8 s(-1)) was an order of magnitude larger than that at SWCNTs (ca. 4.7 s(-1)). In addition, the overall rate constant of the electron transfer reaction from CSCNFs to HRP oxidized by H2O2 was higher than that from SWCNTs by a factor of 3. CSCNFs also allowed enhancement of the complex-formation reaction rate of HRP with H2O2, in comparison with that at SWCNTs. CSCNFs would therefore be applied to not only biosensors but also biofuel cells with enhanced performance.
  • Novel integrative methodology for engineering large liver tissue equivalents based on three-dimensional scaffold fabrication and cellular aggregate assembly, Y. Pang, Y. Horimoto, S. Sutoko, K. Montagne, M. Shinohara, D. Mathiue, K. Komori, M. Anzai, T. Niino, Yasuyuki Sakai, BIOFABRICATION, BIOFABRICATION, 8(3), Sep. 2016 , Refereed
    Summary:A novel engineering methodology for organizing a large liver tissue equivalent was established by intergrating both 'top down' and 'bottom up' approaches. A three-dimensional (3D) scaffold was engineered comprising 43 culture chambers (volume: 11.63 cm(3)) assembled in a symmetrical pattern on 3 layers, a design which enables further scaling up of the device to a clinically significant size (volume: 500 cm(3)). In addition, an inter-connected flow channel network was designed and proved to homogenously deliver culture medium to each chamber with the same pressure drop. After fabrication using nylon-12 and a selective laser sintering process, co-cultured cellular aggregates of human hepatoma Hep G2 and TMNK-1 cells were loosely packed into the culture chambers with biodegradable poly-L-lactic acid fibre pieces for 9 days of perfusion culture. The device enabled increased hepatic function and well-maintained cell viability, demonstrating the importance of an independent medium flow supply for cell growth and function provided by the current 3D scaffold. This integrative methodology from the macro- to the micro-scale provides an efficient way of arranging engineered liver tissue with improved mass transfer, making it possible to further scale up to a construct with clinically relevant size while maintaining high per-volume-based physiological function in the near future.
  • Oxygenated Cup-Stacked Carbon Nanofibers/TiO2 Composite Films with Enhanced Photocatalytic Currents, Kikuo Komori, Kentaro Yamura, Atsushi Kogo, Yusuke Takahashi, Tetsu Tatsuma, Akiyoshi Sakoda, Yasuyuki Sakai, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN, 89(5), 603 - 607, May 2016 , Refereed
    Summary:Oxygenated cup-stacked carbon nanofibers (ox-CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were introduced to a nanoporous TiO2 photoelectrode for enhanced photocatalytic currents. The ox-CSCNFs are characterized by good electric conductivity and high dispersibility in solvents. Under UV irradiation, short-circuit photocurrents based on water oxidation at the photoelectrode and oxygen reduction at a counter electrode were enhanced by about 15 times by introduction of the ox-CSCNFs. The oxygen-containing functional groups, which may facilitate good contact between the ox-CSCNFs and TiO2, are essential for the dramatic enhancement in the photocurrent. Recombination efficiency between excited electrons and generated holes may be reduced by facilitated electron transport from excited TiO2 to a substrate electrode via ox-CSCNFs. Photo currents for photocatalytic oxidation of glucose were also enhanced by about 20-fold. The present composite materials would be applied to photocatalytic and photovoltaic cells with enhanced performances.
  • Electrochemically Functionalized Seamless Three-Dimensional Graphene-Carbon Nanotube Hybrid for Direct Electron Transfer of Glucose Oxidase and Bioelectrocatalysis, Trupti Terse-Thakoor, Kikuo Komori, Pankaj Ramnani, Ilkeun Lee, Ashok Muchandani, LANGMUIR, LANGMUIR, 31(47), 13054 - 13061, Dec. 2015 , Refereed
    Summary:Three-dimensional seamless chemical vapor deposition (CVD) grown graphene-carbon nanotubes (G-CNT) hybrid film has been studied for its potential in achieving direct electron transfer (DET) of glucose oxidase (GOx) and its bioelectrocatalytic activity in glucose detection. A two-step CVD method was employed for the synthesis of seamless G-CNT hybrid film where CNTs are grown on already grown graphene film on copper foil using iron as a catalyst. Physical characterization using SEM and TEM show uniform dense coverage of multiwall carbon nanotubes (MWCNT) grown directly on graphene with seamless contacts. The G-CNT hybrid film was electrochemically modified to introduce oxygenated functional groups for DET favorable immobilization of GOx. Pristine and electrochemically functionalized G-CNT film was characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry, X-ray photoelectron-spectroscopy, and Raman spectroscopy. The DET between GOx and electrochemically oxidized G-CNT electrode was studied using cyclic voltammetry which showed a pair of well-defined and quasi-reversible redox peaks with a formal potential of -459 mV at pH 7 corresponding to the redox site of GOx. The constructed electrode detected glucose concentration over the clinically relevant range of 2-8 mM with the highest sensitivity of 19.31 mu A/mM/cm(2) compared to reported composite hybrid electrodes of graphene oxide and CNTs. Electrochemically functionalized CVD grown seamless G-CNT structure used in this work has potential to be used for development of artificial mediatorless redox enzyme based biosensors and biofuel cells.
  • Bioelectrochemistry of Heme Peptide at Seamless Three-Dimensional Carbon Nanotubes/Graphene Hybrid Films for Highly Sensitive Electrochemical Biosensing, Kikuo Komori, Trupti Terse-Thakoor, Ashok Mulchandani, ACS APPLIED MATERIALS & INTERFACES, ACS APPLIED MATERIALS & INTERFACES, 7(6), 3647 - 3654, Feb. 2015 , Refereed
    Summary:A seamless three-dimensional hybrid film consisting of carbon nanotubes grown at the graphene surface (CNTs/G) is a promising material for the application to highly sensitive enzyme-based electrochemical biosensors. The CNTs/G film was used as a conductive nanoscaffold for enzymes. The heme peptide (HP) was immobilized on the surface of the CNTs/G film for amperometric sensing of H2O2. Compared with flat graphene electrodes modified with HP, the catalytic current for H2O2 reduction at the HP-modified CNTs/G electrode increased due to the increase in the surface coverage of HP. In addition, microvoids in the CNTs/G film contributed to diffusion of H2O2 to modified HP, resulting in the enhancement of the catalytic cathodic currents. The kinetics of the direct electron transfer from the CNTs/G electrode to compound I and II of modified HP was also analyzed.
  • The Importance of Physiological Oxygen Concentrations in the Sandwich Cultures of Rat Hepatocytes on Gas-Permeable Membranes, Wenjin Xiao, Marie Shinohara, Kikuo Komori, Yasuyuki Sakai, Hitoshi Matsui, Tomoharu Osada, BIOTECHNOLOGY PROGRESS, BIOTECHNOLOGY PROGRESS, 30(6), 1401 - 1410, Nov. 2014 , Refereed
    Summary:Oxygen supply is a critical issue in the optimization of in vitro hepatocyte microenvironments. Although several strategies have been developed to balance complex oxygen requirements, these techniques are not able to accurately meet the cellular oxygen demand. Indeed, neither the actual oxygen concentration encountered by cells nor the cellular oxygen consumption rates (OCR) was assessed. The aim of this study is to define appropriate oxygen conditions at the cell level that could accurately match the OCR and allow hepatocytes to maintain liver specific functions in a normoxic environment. Matrigel overlaid rat hepatocytes were cultured on the polydimethylsiloxane (PDMS) membranes under either atmospheric oxygen concentration [20%-O-2 (+)] or physiological oxygen concentrations [10%-O-2 (+), 5%-O-2 (+)], respectively, to investigate the effects of various oxygen concentrations on the efficient functioning of hepatocytes. In parallel, the gas-impermeable cultures (polystyrene) with PDMS membrane inserts were used as the control groups [PS-O-2 (-)]. The results indicated that the hepatocytes under 10%-O-2 (+) exhibited improved survival and maintenance of metabolic activities and functional polarization. The dramatic elevation of cellular OCR up to the in vivo liver rate proposed a normoxic environment for hepatocytes, especially when comparing with PS-O-2 (-) cultures, in which the cells generally tolerated hypoxia. Additionally, the expression levels of 84 drug-metabolism genes were the closest to physiological levels. In conclusion, this study clearly shows the benefit of long-term culture of hepatocytes at physiological oxygen concentration, and indicates on an oxygen-permeable membrane system to provide a simple method for in vitro studies. (c) 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1401-1410, 2014
  • Oxygen-permeable membrane-based direct oxygenation remarkably enhances functions and gene expressions of rat hepatocytes in both 3D and sandwich cultures, Wenjin Xiao, Makoto Kodama, Kikuo Komori, Yasuyuki Sakai, BIOCHEMICAL ENGINEERING JOURNAL, BIOCHEMICAL ENGINEERING JOURNAL, 91, 99 - 109, Oct. 2014 , Refereed
    Summary:Although there have been remarkable progresses in hepatocytes cultures in terms of mimicking microenvironments of in vivo liver, oxygen supply is still a critical issue. In this study, we investigated the effect of direct oxygenation through oxygen-permeable membranes on functionalities of hepatocytes in two widely accepted advanced culture models, sandwich culture and 3D culture. Rat hepatocytes were cultured on the polydimethylsiloxane (PDMS) membranes for 14 days in monolayer culture, sandwich culture with Matrigel and 3D culture with microporous expanded polytetrafluoroethylene (ePTFE) membranes in the presence and absence of direct oxygenation from the other side of the membranes. The present results showed remarkable enhancement of hepatocytes duration and their functions by oxygen transfer through PDMS membranes in all these three cultures. The hepatocytes cultured in sandwich with oxygen exhibited extended survival and highest maintenance of metabolic activities, such as albumin productivity and Cyp1 a1/2 activity. Additionally, the expression levels of various drug-metabolism genes, as examined by PCR arrays, were also closest to those of freshly isolated hepatocytes. As the cellular maintenance has been greatly improved by microporous ePTFE membranes, the hepatocytes in 3D culture performed increased functions that comparable to those in sandwich culture. This study clearly illustrates that oxygenation is a critical factor to be considered in optimization of the microenvironments of hepatocytes cultures. (C) 2014 Elsevier B.V. All rights reserved.
  • Electrochemical properties of oxygenated cup-stacked carbon nanofiber-modified electrodes, Seongjae Ko, Tetsu Tatsuma, Akiyoshi Sakoda, Yasuyuki Sakai, Kikuo Komori, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 16(24), 12209 - 12213, 2014 , Refereed
    Summary:Oxygenated cup-stacked carbon nanofibers (CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were investigated as electrode materials by using typical redox species in electrochemistry, Fe2+/(3+), [Fe(CN)(6)] (3-)/(4-), and dopamine. The electron transfer rates for these redox species at oxygenated CSCNF electrodes were higher than those at edge-oriented pyrolytic graphite and glassy carbon electrodes. In addition, the oxygen-containing functional groups also contributed to the electron transfer kinetics at the oxygenated CSCNF surface. The electron transfer rate of Fe2+/(3+) was accelerated and that of [Fe(CN)(6)] (3-)/(4-) was decelerated by the oxygen-containing groups, mainly due to the electrostatic attraction and repulsion, respectively. The electrochemical reaction selectivities at the oxygenated CSCNF surface were tunable by controlling the amount of nanofibers and the oxygen/carbon atomic ratio at the nanofiber surface. Thus, the oxygenated CSCNFs would be useful electrode materials for energy-conversion, biosensing, and other electrochemical devices.
  • Direct Synthesis of Cup-Stacked Carbon Nanofiber Microspheres by the Catalytic Pyrolysis of Poly(ethylene glycol), Seongjae Ko, Yusuke Takahashi, Akiyoshi Sakoda, Yasuyuki Sakai, Kikuo Komori, LANGMUIR, LANGMUIR, 28(23), 8760 - 8766, Jun. 2012 , Refereed
    Summary:Uniformly sized microspheres tangled with cup-stacked carbon nanofibers (CSCNFs) were directly synthesized by the pyrolysis of poly(ethylene glycol) (PEG) with a nickel catalyst. A PEG/Ni membrane was prepared on a silicon wafer surface by heating it to 750 degrees C at a heating rate of 15 degrees C min(-1). The wafer was heated to a temperature of 400 degrees C and was held at that temperature for 1 h before raising the temperature to 750 degrees C for 10 min to form the CSCNF microspheres. The final CSCNF microspheres and the intermediates were evaluated using scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and Raman spectroscopy to elucidate the growth mechanism. Furthermore, the CSCNF microspheres were successfully dispersed and maintained their spherical shape in an aqueous solution containing 0.5% Nafion. The CSCNF microspheres have the potential to work as a sophisticated carrier with high adsorption and fast electron-transfer exchange properties based on the graphene edges of the nanofiber surface.
  • Development of a well-of-the-well system-based embryo culture plate with an oxygen sensing photoluminescent probe, Kikuo Komori, Sho Fujii, Kevin Montagne, Hiroko Nakamura, Hiroshi Kimura, Katsuto Otake, Teruo Fujii, Yasuyuki Sakai, SENSORS AND ACTUATORS B-CHEMICAL, SENSORS AND ACTUATORS B-CHEMICAL, 162(1), 278 - 283, Feb. 2012 , Refereed
    Summary:In this study, we developed a well-of-the-well (WOW) system-based embryo culture plate with an oxygen sensing photoluminescent probe (OSPP). This system can incubate single embryos in an array of microwells and continuously and non-invasively monitor their morphology by microscopy and respiration metabolic activity based on the quenching of photoexcited platinum octaethylporphyrin by oxygen. Although the development rate to the blastocyst stage obtained in the WOW embryo culture plate with the OSPP was about 11% lower than that obtained with the conventional drop culture method because of the absence of paracrine effects due to the size of the microwells, the average cell number in the embryo at the blastocyst stage was not significantly different between the two culture systems. However, the present embryo culture plate enabled the selection and harvest of high quality blastocysts by monitoring both their morphology and their oxygen consumption rate, making it suitable for the high throughput evaluation of embryos. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.
  • Peroxidase-modified cup-stacked carbon nanofiber networks for electrochemical biosensing with adjustable dynamic range, Seongjae Ko, Yusuke Takahashi, Hirotaka Fujita, Tetsu Tatsuma, Akiyoshi Sakoda, Kikuo Komori, RSC ADVANCES, RSC ADVANCES, 2(4), 1444 - 1449, 2012 , Refereed
    Summary:Cup-stacked carbon nanofibers (CSCNFs) were treated with ozone to introduce oxygen-containing groups to the edges of the graphene cups. The O/C atomic ratio at the surface was estimated to be 5.3 x 10(-2). The hydrophilic CSCNFs were used for constructing a three-dimensional network that works both as an electrical nanowire and an enzyme support. Horseradish peroxidase (HRP) molecules were immobilized onto the network for amperometric sensing of H2O2 and inhibition-based sensing of cyanide. Both the upper sensing limit of H2O2 and the upper and lower sensing limits of cyanide were controlled by about two orders of magnitude by changing the HRP coverage.
  • Cytotoxicity evaluation of reactive metabolites using rat liver homogenate microsome-encapsulated alginate gel microbeads, Naoko Yamamoto, Kikuo Komori, Kevin Montagne, Hitoshi Matsui, Hidenari Nakayama, Shoji Takeuchi, Yasuyuki Sakai, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, JOURNAL OF BIOSCIENCE AND BIOENGINEERING, 111(4), 454 - 458, Apr. 2011 , Refereed
    Summary:We present an improved cytotoxicity test for reactive metabolites, in which the 59 microsomal fraction of rat liver homogenate is encapsulated in alginate gel microbeads to avoid cytotoxic effects of 59-self-generated toxicants, microsomal lipid peroxides. The 59-encapsulated gel microbeads were prepared by a coaxial two-fluid nozzle and surfaces of the microbeads were coated with poly-L-lysine (PLL). Although the initial metabolic rate of the 59-encapsulated gel microbeads was about 20% slower than that of bare 59, the microbeads prevented the leakage of microsomal lipid peroxides thanks to the dense alginate and PLL polymer networks. In fact, the half maximal effective concentration of the indirect mutagen cyclophosphamide on NIH3T3 cells in the presence of the 59-encapsulated gel microbeads was about 5 times higher than that in the presence of bare S9. Use of the S9-encapsulated gel microbeads enabled the more accurate evaluation of the cytotoxicity of the reactive metabolites without the S9-based cytotoxicity. (C) 2010, The Society for Biotechnology, Japan. All rights reserved.
  • Phthalocyanine-based fluorescence probes for detecting ascorbic acid: phthalocyaninatosilicon covalently linked to TEMPO radicals, Kazuyuki Ishii, Kensuke Kubo, Tomoya Sakurada, Kikuo Komori, Yasuyuki Sakai, CHEMICAL COMMUNICATIONS, CHEMICAL COMMUNICATIONS, 47(17), 4932 - 4934, 2011 , Refereed
    Summary:We have applied phthalocyaninatosilicon (SiPc) covalently linked to one or two tetramethyl-1-piperidinyloxyl (TEMPO) radicals as fluorescence probes for detecting ascorbic acid in biological systems.
  • Electrochemical biosensor for the detection of H2O2 from living cancer cells based on ZnO nanosheets, Qi Rui, Kikuo Komori, Yang Tian, Haiqing Liu, Yongping Luo, Yasuyuki Sakai, ANALYTICA CHIMICA ACTA, ANALYTICA CHIMICA ACTA, 670(1-2), 57 - 62, Jun. 2010 , Refereed
    Summary:In this work, direct electron transfer of cytochrome c (cyt. c)-a model for studying the electron transfer of enzymes is achieved at hexagonal ZnO nanosheets by one-step electrodeposition. UV-vis spectra and electrochemical data demonstrate that such ZnO nanosheets can supply a bio-compatible surface to keep the bioactivity of cyt. c. The redox formal potential (E-0') of cyt. c is estimated to be 338.2 +/- 4.3 mV (vs. Ag vertical bar AgCl) at the nanostructured ZnO surface. This value is much more positive than those of enzymes previously obtained at other metal oxides and zeolite surfaces. Experiment data show, under the optimized potential of 0.0V (vs. Ag vertical bar AgCl), the electrochemical determination of H2O2 is free from not only anodic interferences like ascorbic acid (AA) and dopamine (DA), but also a cathodic interference-O-2. Such an excellent selectivity enable the present H2O2 biosensor determine the extracellular H2O2 released from living human hepatoma cells. (C) 2010 Elsevier B.V. All rights reserved.
  • A rapid and simple evaluation system for gas toxicity using luminous bacteria entrapped by a polyion complex membrane, Kikuo Komori, Shotaro Miyajima, Tatsuro Tsuru, Takao Fujii, Shino Mohri, Yoshiro Ono, Yasuyuki Sakai, CHEMOSPHERE, CHEMOSPHERE, 77(8), 1106 - 1112, Nov. 2009 , Refereed
    Summary:We have developed a rapid and simple gas toxicity evaluation system based on bioluminescence inhibition of a marine-derived wild luminous bacterium, Vibrio fischeri. The luminous bacteria were trapped using a thin polyion complex membrane in order to allow semi direct contact between the bacteria and toxic gases. Bioluminescence inhibition ratios of the present system to six reference gases, including benzene, trichloroethylene. acetone, NO2. SO2, and CO, were evaluated, and dose-response relationships were successfully obtained after 15 min of gas exposure, except for CO gas. The sensitivity to the five gases except for CO gas of the present system was 1-3 orders of magnitude higher than that in acute animal tests. The present system also allowed for the evaluation of overall toxicity of some environmental gases containing various chemicals. These results clearly demonstrated that the present system would be a valuable prototype for rapid and on-site acute toxicity detection of a gas mixture, such as environmental gases. (C) 2009 Elsevier Ltd. All rights reserved.
  • Simultaneous evaluation of toxicities using a mammalian cell array chip prepared by photocatalytic lithography, Kikuo Komori, Jun Nada, Masaki Nishikawa, Hideo Notsu, Tetsu Tatsuma, Yasuyuki Sakai, ANALYTICA CHIMICA ACTA, ANALYTICA CHIMICA ACTA, 653(2), 222 - 227, Oct. 2009 , Refereed
    Summary:A prototype of a mammalian cell array chip was developed on a flat glass surface. A superhydrophilic (water contact angle=5 degrees)/highly hydrophobic (120 degrees) pattern was prepared on a fluorinated polymer-coated glass surface by means of photocatalytic lithography, and A549 (a human alveolar epithelial cell line), Hep G2 (a human hepatoma cell line) and mouse fibroblast 3T3 cells were inoculated onto the superhydrophilic regions. The cell populations were confined in the superhydrophilic regions for at least 24h and separated from each other for at least one week. Organ-specific toxicity of aflatoxin B(1) and non-specific toxicity of adriamycin were successfully detected by using the cell array chip. (c) 2009 Elsevier B.V. All rights reserved.
  • A micropatterned cell array with an integrated oxygen-sensitive fluorescent membrane, Kevin Montagne, Kikuo Komori, Fei Yang, Tetsu Tatsuma, Teruo Fujii, Yasuyuki Sakai, PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, 8(11), 1529 - 1533, 2009 , Refereed
    Summary:We propose a simple method for producing micropatterned cell spots by photocatalytic lithography on a Pt porphyrin-based oxygen-sensitive polystyrene membrane that enables real-time imaging of oxygen consumption of patterned cell spots with sub-millimetre resolution.
  • Development of an in vitro batch-type closed gas exposure device with an alveolar epithelial cell line, A549, for toxicity evaluations of gaseous compounds, Kikuo Komori, Kenji Murai, Shotaro Miyajima, Takao Fujii, Shino Mohri, Yoshiro Ono, Yasuyki Sakai, ANALYTICAL SCIENCES, ANALYTICAL SCIENCES, 24(8), 957 - 962, Aug. 2008 , Refereed
    Summary:To simply evaluate toxicity for various types of exhaust-gas samples collected in various locations, we developed a small-scale (150 mL) batch-type completely closed gas exposure device incorporated with an air-liquid interface culture of a human alveolar epithelial cell line, A549. On the basis of cell viability tests using an acid phosphatase assay after 48 h of gas exposure, the developed device was able to measure clear dose-response relationships for volatile organic and inorganic compounds, such as benzene, trichloroethylene (TCE), acetone, SO2 and NO2 gases, but not CO gas. Although the 50% effective concentration values in the device were much higher than 50% lethal concentration values reported in animal experiments, the tendency of the toxic intensity observed in the former was roughly consistent with that of the acute toxicity in the latter. We further applied the device to evaluate the toxicity of cigarette smoke as an example of actual environmental gases, and successfully measured acute cell death from the gas after 48 h of exposure. The present small device is expected to be one of good tools not only in simultaneously assessing various gaseous chemicals or samples, but also in studying acute toxicity expression mechanisms in human lung epithelia.
  • Stable immobilization of rat hepatocytes as hemispheroids onto collagen-conjugated poly-dimethylsiloxane (PDMS) surfaces: Importance of direct oxygenation through PDMS for both formation and function, Masaki Nishikawa, Takatoki Yamamoto, Nobuhiko Kojima, Komori Kikuo, Teruo Fujii, Yasuyuki Sakai, BIOTECHNOLOGY AND BIOENGINEERING, BIOTECHNOLOGY AND BIOENGINEERING, 99(6), 1472 - 1481, Apr. 2008 , Refereed
    Summary:The highly oxygen-permeable material, polydimethylsiloxane (PDMS), has the potential to be applied to cell culture microdevices,"but cell detachment from PDMS has been a major problem. In this study, we demonstrate that a combination of collagen covalently immobilized PDMS and an adequate oxygen supply enables the establishment of a stable, attached spheroid (hemispheroid) culture of rat hepatocytes. The bottom PDMS surfaces were first treated with oxygen plasma, then coupled with aminosilane followed by a pbotoreactive crosslinker, and they were finally reacted with a collagen solution. X-ray photoelectron spectroscopy (XPS) and contact angle measurements showed that the covalent immobilization of collagen on the surface occurred only where the crosslinker had been introduced. On the collagen-conjugated PDMS surface, rat hepatocytes organized themselves into hemispheroids and maintained the viability and a remarkably high albumin production at least for 2 weeks of culture. In contrast, hepatocytes on the other types of PDMS surfaces formed suspended spheroids that had low albumin production. In addition, we showed that blocking the oxygen supply through the bottom PDMS surface inhibited the formation of hemispheroids and the augmentation of hepatocellular function. These results show that appropriate surface modification of PDMS is a promising approach towards the development of liver tissue microdevices.
  • Enhanced maintenance and functions of rat hepatocytes induced by combination of on-site oxygenation and coculture with fibroblasts, Masaki Nishikawaa, Nobuhiko Kojimaa, Kikuo Komoria, Takatoki Yamamoto, Teruo Fujii, Yasuyuki Sakai, JOURNAL OF BIOTECHNOLOGY, JOURNAL OF BIOTECHNOLOGY, 133(2), 253 - 260, Jan. 2008 , Refereed
    Summary:In in vivo liver tissue, each hepatocyte has intimate interactions not only with adjacent hepatocytes but also with nonparenchymal cells in a three-dimensional (3D) manner. We recently reported that hepatic function is highly maintained on collagen covalently immobilized polydimethylsiloxane (PDMS) membranes through which oxygen is supplied directly to the cells. In this study, to further enhance performances of hepatocytes culture, we investigated cocultivation of rat hepatocytes with a mouse fibroblast, NIH/3T3 (M) in the same PDMS membranes. Various functions of hepatocytes were better maintained on the membrane at remarkably higher levels, particularly albumin secretion on such coculture was about 20 times higher than that in conventional coculture on tissue-culture-treated polystyrene (TCPS) surfaces. The remarkable functional enhancements are likely to be explained by the net growth of hepatocytes (from 1.2- to 1.4-fold inoculated number) and very intimate contact between hepatocytes and 3T3 cells in almost continuous double-layered structures under the adequate oxygen supply. The results demonstrate that simultaneous realization of different requirements toward mimicking in vivo liver tissue microstructure is effective in improving performance of hepatocytes culture system. (c) 2007 Elsevier B.V. All rights reserved.
  • Electrochemiluminescence of Ru(II) complexes immobilized on a magnetic microbead surface: Distribution of magnetic microbeads on the electrode surface and effect of azide ion, Kikuo Komori, Kazutake Takada, Osamu Hatozaki, Noboru Oyama, LANGMUIR, LANGMUIR, 23(11), 6446 - 6452, May 2007 , Refereed
    Summary:The electrochemiluminescence (ECL) of magnetic microbeads modified with tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)(3)](2+)) was studied in the presence of tri-n-propylamine (TPA) to develop highly sensitive ECL detection system, where the employed microbead has a diameter of 4.5 mu m. The ECL signal of the [Ru(bpy)(3)](2+) derivative-modified magnetic microbeads was found to be affected by the geometrical distribution of the magnetic microbeads on the electrode surface. The ECL peak intensity increased with increasing the number of the beads on the electrode surfaces up to 1.6 x 10(6) beads cm(-2), although above 1.6 x 10(6) beads cm(-2), it decreased. The ECL decrease arises from the physical prevention of the ECL from reaching the photomultiplier tube by the excessive beads. The observed peak ECL signal of the [Ru(bpy)(3)](2+) derivative-modified magnetic microbeads in the presence of NaN3, which serves as a preservative substance, mainly appeared at a potential of +0.90 V vs Ag/AgCl where [Ru(bpy)(3)](2+) is hardly oxidized, whereas the ECL signal in the absence of NaN3 appeared at a potential of +1.15 V. The presence of NaN3 on the electrode surface retards formation of an oxide layer on the electrode surfaces and promotes TPA oxidation. The ECL response at +0.90 V was mainly attributed to ECL reaction of excited-state [Ru(bpy)(3)](2+*) formed by oxidation of [Ru(bpy)(3)](+) with TPA radical cation, where the [Ru(bpy)(3)](+) was generated by reduction of [Ru(bpy)(3)](2+) with TPA radical.
  • Electrodes modified with the phase transition polymer and heme peptide: Biocatalysis and biosensing with tunable activity and dynamic range, K Komori, K Takada, T Tatsuma, LANGMUIR, LANGMUIR, 22(1), 478 - 483, Jan. 2006 , Refereed
    Summary:An electrode was modified with a phase transition polymer, poly(N-isopropylacrylamide), and the polymer was further modified with a peroxidase model compound, heme peptide (HP). As the polymer layer shrank at temperatures above 30-40 degrees C, the catalytic activity of the HP molecules for H2O2 reduction improved, and simultaneously, the number of HP molecules that can communicate electrochemically with the electrode increased. As a result, the catalytic current for H2O2 reduction in the shrunken state was 4 times larger than that in the swollen state. This reversible change was exploited for tuning the sensitivity and dynamic range of the HP electrode in H2O2 biosensing. The dynamic range in inhibition-based biosensing of imidazole derivatives was also tunable.
  • Peroxidase model electrodes: Self-mediation of heme peptide multilayer-modified electrodes and its application to biosensing with adjustable dynamic range, K Komori, K Takada, T Tatsuma, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, JOURNAL OF ELECTROANALYTICAL CHEMISTRY, 585(1), 89 - 96, Nov. 2005 , Refereed
    Summary:Electrochemical communication between an electrode and a multilayered enzyme model based on "self-mediation" without a mediator was demonstrated as one of the advantages of using enzyme models instead of natural enzymes for the fabrication of biosensors. Heme undecapeptide (HP), as a peroxidase model, was immobilized on the indiumi-tin oxide (ITO) electrode as a multilayer and its elect rocatalytic reduction for H2O2 was studied. The cathodic current of the HP multilayer-modified electrode was found to be one order of magnitude larger than that of a HP monolayer-modified electrode, in which the surface coverage of HP was one order of magnitude smaller than that of the multilayer. Since direct electron transfer between upper HP molecules and the electrode is difficult, H2O2 was reduced via an electron self-exchange between the lower HP molecules. On the basis of the self-mediation, the overall catalytic reaction rate of the HP electrode was changed by simply varying the surface coverage of HP without a mediator. Taking advantage of this system, dynamic ranges for the detection of HP inhibitors such as cyanide, imidazole and histamine were adjusted. (c) 2005 Elsevier B.V. All rights reserved.
  • Toward selectivity control of a heme peptide electrode by modification with a phase-transition polymer, K Komori, K Takada, T Tatsuma, ANALYTICAL SCIENCES, ANALYTICAL SCIENCES, 21(4), 351 - 353, Apr. 2005 , Refereed
    Summary:Reduction currents for H2O2 at a heme peptide (HP)-modified electrodes are suppressed by inhibitors, such as imidazole derivatives. Although this inhibition effect allows determinations of the total inhibition ability of imidazole derivatives, it has no selectivity. In this study the selectivity control of HP-modified electrodes for imidazole derivatives was performed utilizing the thermoresponsive phase transition of poly(N-isopropylacrylamide), which was chemically immobilized on HP-modified electrodes. The inhibition ratios for imidazole derivatives appeared to be small at temperatures below the lower critical solution temperature (LCST), and to be large above the LCST. This change was ascribed to a steric hindrance caused by a phase transition of the polymer. On the other hand, the inhibition ratio for histamine, which has a larger molecular size relative to imidazole, was not significantly changed by the phase transition. Thus, the selectivity of the HP-modified electrode was found to be controllable using an immobilized phase-transition polymer.
  • Control of heme peptide activity by using phase transition polymers modified with inhibitors, K Komori, H Matsui, T Tatsuma, BIOELECTROCHEMISTRY, BIOELECTROCHEMISTRY, 65(2), 129 - 134, Feb. 2005 , Refereed
    Summary:Catalytic activity of a heme peptide (HP) modified-electrode for H2O2 reduction was controlled by use of poly(N-isopropylacrylamide) modified with an inhibitory moiety, imidazole group. The polymers inhibited the catalytic activity below their lower critical solution temperature (LCST) where the polymers were dissolved and did not inhibit the activity above the LCST where the polymers were precipitated. A polymer with a longer side chain connecting with the imidazole group was more inhibitory than a polymer with a shorter side chain at temperatures below the LCST. Formation constants of dissolved HP-imidazole complexes were evaluated by spectroscopic means, and it was found that the polymers were more inhibitory than the corresponding monomers. (c) 2004 Elsevier B.V. All rights reserved.
  • Activity regulation of tyrosinase by using photoisomerizable inhibitors, K Komori, K Yatagai, T Tatsuma, JOURNAL OF BIOTECHNOLOGY, JOURNAL OF BIOTECHNOLOGY, 108(1), 11 - 16, Feb. 2004 , Refereed
    Summary:Enzymatic activity of tyrosinase was controlled on the basis of cis-trans photoisomerization of inhibitors, 4-azobenzene carboxylic acid (ACA) and 4,4'-azobenzene dicarboxylic acid (ADCA). In the case of ACA, the cis form inhibited tyrosinase-catalyzed oxidation of L-tyrosine more strongly than the trans form. On the contrary, in the case of ADCA, the cis form was less inhibitory. The oxidation rate was controlled reversibly by light irradiation in the course of the reaction. In the presence of ACA, UV light irradiation, which isomerized trans to cis form, decelerated the tyrosine oxidation, while visible light irradiation, which isomerized backward, accelerated the reaction. In contrast, in the presence of ADCA, UV light accelerated and visible light decelerated the reaction. (C) 2003 Elsevier B.V. All rights reserved.
  • Interference-based electrochemical biosensor for the measurement of the concentration and isomer ratio of urocanic acid, T Tatsuma, K Okamura, K Komori, A Fujishima, ANALYTICAL CHEMISTRY, ANALYTICAL CHEMISTRY, 74(19), 5154 - 5156, Oct. 2002 , Refereed
    Summary:Urocanic acid (UCA) is known to be synthesized as the trans isomer (trans-UCA) in the skin, and trans-UCA is transformed by UV light to the cis isomer (cis-UCA), which may be involved in photoimmunosuppression. An electrochemical method has been developed for the measurement of the concentration and isomer ratio of UCA. A heme peptide-modified electrode (HP electrode) reduces hydrogen peroxide at +150 mV vs Ag\AgCl, and the reduction current is inhibited by UCA. Since cis-UCA is a stronger inhibitor than trans-UCA, irradiation of a sample solution with UV light increases the percent inhibition. The concentration and isomer ratio of UCA in the sample solution can be estimated from the values of percent inhibition before and after the UV irradiation.

Books etc

  • In Vivo Inhalation Toxicity Screening Methods for Manufactured Nanomaterials, K. Komori, K. Iwasawa, R. Ogasawara, A. Suwabe, Y. Sakai, Contributor, In Vitro Alveolar Epithelial Models toward the Prediction of Cytotoxicity Tests and Translocation Studies of Nanoparticles, Springer,   2019