Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Ishimatsu Ryoichi Last modified date:2019.12.25

Assistant Professor / Molecular Information Systems / Department of Applied Chemistry / Faculty of Engineering


Papers
1. C. Malasuk, K. Nakakubo, R. Ishimatsu, Y. Nakashima, H. Yoshioka, K. Morita, Y. Oki, Compact and on-demand 3D-printed optical device based on silicone optical technology (SOT) for on-site measurement
Application to flow injection analysis, Review of Scientific Instruments, 10.1063/1.5118812, 90, 10, 2019.10, The current trend for analytical systems and devices is to be small, portable, and low in cost because of the flexibility required to ensure their availability for on-site measurement applications. Using the concept of silicone optical technology (SOT), we propose a fully flexible analytical system, and digital fabrication of a compact optical module for flow-injection analysis (FIA) is demonstrated. A simple structure composed of a transparent polydimethylsiloxane (PDMS) optical core with a carbon black-dispersed PDMS cladding acts as a tiny but straightforward optical filter and shows an ability to trap light at tilted incidence; this structure is embedded on a silicone 3D-printed optical module via a simple injection and coating method. The coating properties, the optical trapping performance, and the cross talk test performance of the device were evaluated. The SOT-FIA optical module successfully demonstrated a 99.8% undesired light trapping performance; cross talk of less than 0.5% was observed, illustrating the low-noise detection performance of the SOT-FIA optical system. Colorimetric determination of iron in natural water samples demonstrated excellent linearity, a wide chemical analysis range, and good percentage recovery performance. The results of the determination in real water samples using the proposed SOT-FIA optical device agreed well with the results from the conventional spectrophotometric method. With advantages that include simplicity, low cost, flexibility, portability, and high sensitivity, the proposed optical device will be potentially useful for on-site chemical analysis measurements..
2. Ryoichi Ishimatsu, Hirosato Shintaku, Yuto Kage, Misaki Kamioka, Soji Shimizu, Koji Nakano, Hiroyuki Furuta, Toshihiko Imato, Efficient Electrogenerated Chemiluminescence of Pyrrolopyrrole Aza-BODIPYs in the Near-Infrared Region with Tripropylamine
Involving Formation of S2 and T2 States, Journal of the American Chemical Society, 10.1021/jacs.9b05245, 141, 30, 11791-11795, 2019.07, Efficient electrogenerated chemiluminescences (ECLs) of three pyrrolopyrrole aza-BODIPYs in the near-infrared region by using tripropylamine as a coreactant are reported. Kinetic analysis based on Marcus theory indicates the direct formation of S2 and T2 states through the electron transfer reaction, which affects the ECL efficiencies..
3. Ryoichi Ishimatsu, Eri Kunisawa, Hirosato Shintaku, Koji Nakano, Toshihiko Imato, Portable Analytical Detection Systems Based on Light Emitting Devices, 2019 International Conference on Electronics Packaging, ICEP 2019 2019 International Conference on Electronics Packaging, ICEP 2019, 10.23919/ICEP.2019.8733418, 294-297, 2019.04, Portable analytical detection systems based on light emitting devices, organic light-emitting diode (OLED), and electrogenerated chemiluminescence (ECL) are described. The OLED is composed of an Eu(III) complex, whose emission spectrum is very sharp, was applied for fluorescence detection, and ECL of a boron-dipyrromethene derivative showing relatively sharp spectrum was used for the absorbance measurements..
4. Ryoichi Ishimatsu, Eri Kunisawa, Koji Nakano, Chihaya Adachi, Toshihiko Imato, Electrogenerated Chemiluminescence and Electronic States of Several Organometallic Eu(III) and Tb(III) Complexes
Effects of the Ligands, ChemistrySelect, 10.1002/slct.201900595, 4, 9, 2815-2831, 2019.03, We report the electrochemical properties, and electrogenerated chemiluminescence (ECL) of eight different organometallic complexes of Eu(III) and Tb(III), Eu(dbm) 3 phen, Eu(dbm) 3 bath, Eu(fod) 3 phen, Eu(tta) 3 phen, Tb(acac) 3 phen, Tb(acac) 3 bath, Tb(fod) 3 phen, and Tb(tmhd) 3 bpy in acetonitrile, where phen, bath, and bpy are 1, 10-phenanthroline, bathophenanthroline, 2,2′-bipyridyl, respectively, and the anionic ligands, acac , dbm , fod , and tta are the enolate forms of acetylacetone, dibenzoylmethanate, 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, and thenoyltrifluoroacetone, respectively. The electronic states of the neutral and some charged states of the complexes were clarified with density functional theory calculations. The ECL spectra were recorded by using S 2 O 8 2− as a coreactant, and for all complexes, sharp ECL spectra, which are attributable to the f-f transitions, were observed. On the potential-dependent ECL spectra, broad ECLs, which were originated from the ligands, were also detected. Based on the ECL behavior and the electronic states, the mechanisms of the intraconfigurational ECL were discussed..
5. Koji Nakano, Jun Horiuchi, Shingo Hirata, Makoto Yamanaka, Toshiki Himeno, Ryoichi Ishimatsu, Folding and Assembly of Vanilloid Receptor Secondary-Structure Peptide with Hexahistidine Linker at Nickel-Nitrilotriacetic Acid Monolayer for Capsaicin Recognition, Langmuir, 10.1021/acs.langmuir.8b03202, 35, 6, 2047-2054, 2019.02, Herein, we report the self-assembly of a synthetic vanilloid receptor (VR) peptide that selectively binds capsaicin. We synthesized a 26-mer peptide - YSEILFFVQS-HHHHHH-LAMGWTNMLY (S3HS4) - comprising two chemoreceptor domains of transient receptor potential channel (TRPV1) linked by a hexahistidine sequence. High-speed atomic force microscopy (AFM) imaging in water revealed that the peptide structures alternated rapidly between wedge shape and linear forms. Circular dichroism spectroscopy showed that 65% of the amide units in the peptide chain adopted an α-helix structure, which was ascribed to the chemoreceptor domains. S3HS4 developed well-packed monolayers at the Ni-treated thiolated nitrilotriacetic acid self-assembled monolayers by chelation of the hexahistidine segment, as characterized by infrared spectroscopy and AFM, which exhibited statistically constant specific height. Therefore, S3HS4 was expected to fold spontaneously upon chelation, and the resulting helix-turn-helix conformers developed films while uniformly oriented: the tilt angle was 69° from the surface normal to the substrate. According to microgravimetric analysis using a quartz crystal microbalance (QCM), the adsorption was 84 ± 47 pmol cm
-2
(n = 3), which was almost consistent with the saturation adsorption of an α-helix unit. We also used a QCM to investigate the host-guest reactions of S3HS4 and found that the S3HS4-attached QCM-chip-bound capsaicin with an apparent binding constant of (4.2 ± 3.6) × 10
4
M
-1
(n = 4), whereas there was no evidence of binding to vanillin or acetophenone. Two controls - a blank chip without S3HS4 and a chip modified with a single helical peptide (LAMGWTNMLY-HHHHHH) - produced no capsaicin response. To the best of our knowledge, S3HS4 is the first example of a synthetic VR mimic peptide. We believe that the present surface-directed structure-based design can be used to exploit the α-helix bundle in hexahistidine-linked bishelical peptides..
6. Eri Kunisawa, Ryoichi Ishimatsu, Koji Nakano, Toshihiko Imato, Electrogenerated chemiluminescence of tris(dibenzoylmethane)phenanthroline europium(III) as a light source
An application for the detection of PO4 3- based on the ion associate formation of phosphomolybdic acid and malachite green, analytical sciences, 10.2116/analsci.19N003, 35, 7, 799-802, 2019.01, We demonstrate that electorogenerated chemiluminescence (ECL) of an organometallic Eu(III) complex, tris(dibenzoylmethane)phenanthroline europium(III), whose emission spectra is very sharp with the maximum wavelength of 612 nm, can be used as a light source for the detection of PO4 3- based on changing the absorbance of the ion associate of malachite green (MG+) and phosphomolybdic acid. The ECL was also applied to measure the absorbance of MG+. With the detection system we established, absorbance up to ~1.6 with a change of ~0.1 could be detected..
7. Takashi Kasahara, Ryoichi Ishimatsu, Hiroyuki Kuwae, Shuichi Shoji, Jun Mizuno, Color-tunable microfluidic electrogenerated chemiluminescence cells using Y-shaped micromixer, Japanese Journal of Applied Physics, 10.7567/JJAP.57.128001, 57, 12, 2018.12, We proposed color-tunable microfluidic electrogenerated chemiluminescence (ECL) cells. A Y-shaped electro-microfluidic device, which consists of two inlet and one mixing channels, was fabricated to investigate variable multi-color emissions induced by mixing two different ECL solutions. 5,6,11,12-Tetraphenylnaphthacene (rubrene) and tetraphenyldibenzoperiflanthene (DBP)-doped rubrene solutions were used as liquid emitters. Yellow (rubrene) and red (DBP) ECL emissions were observed in the inlet channels before mixing, whereas the mixed solution exhibited orange emissions. This is because the DBP concentration was changed facilely in the mixing channel, which leads to the tunable ECL emission. The proposed device will be promising candidates for unique light-emitting applications..
8. Naofumi Kobayashi, Hiroyuki Kuwae, Juro Oshima, Ryoichi Ishimatsu, Shuya Tashiro, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, Jun Mizuno, A wide-energy-gap naphthalene-based liquid organic semiconductor host for liquid deep-blue organic light-emitting diodes, Journal of Luminescence, 10.1016/j.jlumin.2018.03.072, 200, 19-23, 2018.08, We developed a novel naphthalene derivative to function as a wide-energy-gap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene derivative 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ), which shows a low viscosity of 20 mPa·s at 25 °C, was synthesized as a LOS by introducing an ethylhexyl group into naphthalene. We doped 9,10-diphenylanthracene (DPA) into NLQ as a guest deep-blue dye. The highest occupied molecular orbital (HOMO) energy level of NLQ was estimated to be − 6.40 eV from photoelectron spectroscopy measurements in air. The energy gap of NLQ was estimated to be 4.08 eV from its absorption spectrum, indicating that NLQ has the widest energy gap of any such host material to date. The lowest unoccupied molecular orbital energy level of NLQ was calculated to be − 2.31 eV. Deep-blue electroluminescence emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Förster resonance energy transfer and direct recombination of trapped holes and electrons because the energy gap of DPA is straddled by the wider energy gap of NLQ..
9. Junichi Tanabe, Koji Nakano, Ryutaro Hirata, Toshiki Himeno, Ryoichi Ishimatsu, Toshihiko Imato, Hirotaka Okabe, Naoki Matsuda, Totally microperoxidase synthetic-11, Royal Society Open Science, 10.1098/rsos.172311, 5, 5, 2018.05, A totally synthetic microperoxidase-11 (MP-11) is reported. Accordingly, the undecapeptide (VQKCAQCHTVE) was synthesized by solid-phase peptide synthesis followed by the thiol-ene click reaction with haemin for reconstitution. High-speed atomic force microscopy measurement conducted in water confirmed the protein reconstitution by visualizing the morphological differences as animated molecular images. The synthetic MP-11 showed a considerable magnitude of catalytic activity (27%) against the natural MP-11 in the oxidation of 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide, whereas it showed very low (2.7%) activity of a synthetic variant with a point mutation (VQKCAQCMTVE, H8M). Slab waveguide spectroscopic measurements revealed that the ferrous/ferric redox reaction occurred by the direct electron transfer with specific spectral changes. Indeed, if hydrogen peroxide existed in the solution phase, the peroxidase-modified electrode showed catalytic current–voltage behaviour regardless of whether it was prepared using natural MP-11 or the synthetic MP-11. If a substrate recycling reaction was assumed, computer simulation well reproduced the experimental curves to give a global set of electrocatalytic reaction parameters. In any of the experiments, the synthetic MP-11 and natural MP-11 gave almost identical results. Our approach will be a convenient means of preparing MP-11, as well as its mutants, that does not rely on nature..
10. Koji Nakano, Takayuki Honda, Kanako Yamasaki, Yoshiki Tanaka, Keiichi Taniguchi, Ryoichi Ishimatsu, Toshihiko Imato, Carbon quantum dots as fluorescent component in peroxyoxalate chemiluminescence for hydrogen peroxide determination, Bulletin of the Chemical Society of Japan, 10.1246/bcsj.20180095, 91, 7, 1128-1130, 2018.01, Nitrogen-doped carbon quantum dots synthesized by onepot, microwave-assisted pyrolysis of citric acid in the presence of a small number of N-doping precursors, 1, 2-ethylenediamine, were found to be involved in the chemically initiated electron exchange luminescence enabling peroxyoxalate chemiluminescence assay of hydrogen peroxide in the concentration range of 101000 μM..
11. Koji Nakano, Junichi Tanabe, Ryoichi Ishimatsu, Toshihiko Imato, Monolithic Peptide-Nucleic Acid Hybrid Functioning as an Artificial Microperoxidase, Bioconjugate Chemistry, 10.1021/acs.bioconjchem.7b00216, 28, 8, 2031-2034, 2017.08, A new peptide nucleic acid (PNA) with an installed peroxidase function has been developed. Fmoc solid phase peptide synthesis prepared a PNA hybrid (VQKCAQCHTVE-(C2H4O)2CH2-[PNA(T)]6-G) that renders the microperoxidase backbone, followed by reconstitution with hemin. The resulting holocompound catalyzed the oxidation of 3,3′,5,5′-tetramthylbenzidine by H2O2 to 50% that of natural microperoxidase-11, whereas the apo-form and hemin gave no responses. The peroxidase domain was found to be active toward direct electrochemistry and the PNA hybrid served for gene sensor; in the presence of the target DNA (5′-CATGTATAAAAAA-3′), an electrode-attached DNA probe (5′-TsTsTsTsTsTCTCATACATG-3′) showed the ferric-to-ferrous quasi-reversible wave (-276 mV vs Ag/AgCl) through sandwich hybridization. Moreover, the hybridization product could accept H2O2 as an oxidant to enhance the reduction current, which occurred likely based on the iron(II)-center-recycling with specific rate constant of 0.19 s-1..
12. Naofumi Kobayashi, Hiroyuki Kuwae, Juro Oshima, Ryoichi Ishimatsu, Shuya Tashiro, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, Jun Mizuno, Deep-blue light emission with a wide-bandgap naphthalene-derivative liquid organic semiconductor host, Organic Photonic Materials and Devices XIX 2017 Organic Photonic Materials and Devices XIX 2017, 10.1117/12.2251640, 2017.01, We developed a novel naphthalene-derivative to function as a wide-bandgap liquid organic semiconductor (LOS) host material for the limited range of liquid deep-blue light-emitting materials that have been developed to date. The naphthalene-derivative, 1-naphthaleneacetic acid 2-ethylhexyl ester (NLQ) was synthesized as a LOS, by introducing an ethylhexyl group into naphthalene. 9,10-Diphenyl anthracene (DPA) was doped into NLQ as a guest deep-blue dye. From the absorption spectrum, the bandgap energy of NLQ was estimated to be 4.13 eV, indicating that NLQ has the widest bandgap energy of any such host material so far as we know. Deep-blue electroluminescence (EL) emission in a liquid state was obtained by doping DPA into NLQ. Light emission could be achieved by a combination of Förster resonance energy transfer and direct recombination of trapped holes and electrons because the bandgap energy of DPA is straddle by that of the wide-bandgap NLQ. Thus, NLQ is shown to be a promising wide-bandgap LOS host material, which allows deep-blue light emission and may have applications in liquid organic light-emitting diodes..
13. Ryoichi Ishimatsu, Hirosato Shintaku, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Electrogenerated Chemiluminescence of a BODIPY Derivative with Extended Conjugation, ChemistrySelect, 10.1002/slct.201702449, 2, 32, 10531-10536, 2017.01, The electrochemical properties and electrogenerated chemiluminescence (ECL) of a borondipyrromethane (BODIPY) derivative, 2,8-bis(4-isopropylphenyl)-difuro[2, 3-b][3, 2-g]-5,5-difluoro-5-bora-3a,4a-diaza-s-indacene (Derivative 1, Figure) are described. Derivative 1 emitted ECL in the range of 650∼800 nm by using tripropylamine (TPA) as a coreactant. In the cyclic voltammogram, Derivative 1 showed a reversible oxidation wave, whereas the reduction wave was irreversible. Energetically, it is likely that triplet-triplet annihilation is the main pathway to emit ECL through the ion annihilation of the radical anions and cations of Derivative 1 whereas the lowest excited singlet state of Derivative 1 is directly produced with TPA. The maximum ECL wavelengths (670 nm at 0.01 mM) were red-shifted with increasing the concentration of Derivative 1 because of the self-absorption resulted from a small Stokes shift (∼10 nm). Relative ECL efficiency of Derivative 1 was 0.13 compared to that of a Ru(bpy)2+/TPA system..
14. Anastasiia Petrova, Dmitriy Dar'in, Aleхander Ivanov, Leonid Moskvin, Ryoichi Ishimatsu, Koji Nakano, Toshihiko Imato, Andrey Bulatov, Determination of curcumin in biologically active supplements and food spices using a mesofluidic platform with fluorescence detection, Talanta, 10.1016/j.talanta.2016.06.046, 159, 300-306, 2016.10, A mesofluidic platform (MP) with fluorescence detection based on a stepwise injection analysis (SWIA) was used for the determination of curcumin in biologically active supplements and food spices. The main units of the MP are a mixing chamber (MC) and an optical channel with a quartz capillary inside. The MC provides rapid and complete mixing solutions by gas bubbling. The proposed method is based on the new rapid and sensitive reaction of curcumin with a fluorescence reagent – 4-(2,3,3-trimethyl-3H-indolium-1-yl)butane-1-sulfonate (TIBS). The fluorescence intensity of TIBS is greatly quenched in the presence of curcumin in an alkaline medium. The linear range was from 1 to 10 µM of curcumin, and the limit of detection, calculated as 3σ of a blank test (n=5), was found to be 0.3 µM. The sample throughput was 24 h−1. The proposed method was successfully applied for the determination of curcumin in biologically active supplements and samples of food spices. The obtained data were in good agreement with those measured by a HPLC-UV method..
15. Ryoichi Ishimatsu, Tomohiko Edura, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Photophysical Properties and Efficient, Stable, Electrogenerated Chemiluminescence of Donor-Acceptor Molecules Exhibiting Thermal Spin Upconversion, Chemistry - A European Journal, 10.1002/chem.201600077, 22, 14, 4889-4898, 2016.03, The photophysical properties and electrogenerated chemiluminescence (ECL) of three donor-acceptor molecules composed of dicyanobenzene and methyl-, tert-butyl-, and phenyl-substituted carbazolyl groups, 1,2,3,5-tetrakis(3,6-disubstituted-carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN-Me, 4CzIPN-tBu, and 4CzIPN-Ph, respectively) are described. These molecules show delayed fluorescence as a result of thermal spin upconversion from the lowest triplet state to the lowest singlet state at room temperature. The three molecules showed yellow to yellowish-red ECL. Remarkably, the ECL efficiencies of 4CzIPN-tBu in dichloromethane reached almost 40 %. Moreover, stable ECL was emitted from 4CzIPN-tBu and 4CzIPN-Ph. In case of 4CzIPN-Me, the ECL intensity decreased during voltage cycles because of polymerization. Quantum chemical calculations revealed that polymerization was inhibited by the steric hindrance of the bulky tert-butyl and phenyl groups on the carbazolyl moieties and lowered the spin density on the carbazolyl groups through electron conjugation for 4CzIPN-Ph. Delayed fluorescence: Because of thermal spin upconversion of donor-acceptor molecules, efficient electrogenerated chemiluminescence (ECL) was realized (see figure; ISC: Intersystem crossing, RISC: Reverse intersystem crossing). Moreover, methyl, tert-butyl, and phenyl substituents on the donor-acceptor molecule enhance the ECL stability..
16. A. V. Petrova, Ryoichi Ishimatsu, Koji Nakano, Toshihiko Imato, A. B. Vishnikin, L. N. Moskvin, A. V. Bulatov, Flow-Injection Spectrophotometric Determination of Cysteine in Biologically Active Dietary Supplements, Journal of Analytical Chemistry, 10.1134/S1061934816020118, 71, 2, 172-178, 2016.02, A procedure is developed for the flow-injection spectrophotometric determination of cysteine in dietary supplements based on the formation of a reduced phosphomolybdic complex by the analyte in mixing a sample solution with a solution of ammonium 18-molybdophosphate. For the flow-injection determination of cysteine, a polymethyl methacrylate chip is fabricated, in the channels of which the analytical form was obtained and detected. The detection limit for cysteine is 3 × 10–6 M and the throughput is 240 determinations per hour. The procedure was tested in the analysis of different samples of dietary supplements; the results obtained were verified by HPLC..
17. Jie Zhan, Koji Furui, Hizuru Nakajima, Noriaki Kaneki, Ryoichi Ishimatsu, Koji Nakano, Toshihiko Imato, Akihide Hemmi, Development of a portable surface plasmon resonance sensor with multi-sensing points based on the linear CCD sensor, analytical sciences, 10.2116/analsci.32.673, 32, 6, 673-679, 2016.01, A portable-type surface plasmon resonance (SPR) sensor, composed from a new optical system for multi-sensing, has been developed to apply to environment analysis, clinical diagnosis etc., where many samples are desired to be analyzed at high throughput. The optical system of the sensor consists of a light-emitting diode, a pair of cylindrical lenses, a pair of collimator lenses, a correction lens, a prism, a polarizer and a linear CCD sensor with 2048 pixels. Reflected light from a sensor chip of the width of 6 mm at a certain incident angle was detected by ca. 618 pixels of the linear CCD sensor as an SPR sensor signal. An SPR sensor signal at a specified incident angle is controllable for optimization by adjusting the position of the CCD sensor. A sensor chip having a 30-stripe linear pattern (100 μm width/stripe) was prepared. The spatial resolution as well as the performance of the sensor were evaluated by using sucrose solutions. As a result, the acquisition of SPR sensor signals from 30 sensing points was successfully achieved with a spatial resolution of 100 μm (distance between 2 sensing points). A lower detection limit of ca. 3.2-5.5 × 10-5 RIU with a standard deviation of ±4.5% was obtained by averaging the signals from 6-7 pixels of the CCD sensor per one sensing stripe. 2016..
18. Ryoichi Ishimatsu, Yuko Kirino, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Quenching behavior of thermally activated delayed fluorescence from a donor-acceptor molecule, 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene by O2, Chemistry Letters, 10.1246/cl.160561, 45, 10, 1183-1185, 2016.01, We describe the quenching behavior of thermally activated delayed fluorescence (TADF) from 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) by O2 in bis(2-ethylhexyl)sebacate (DOS). Importantly, the high quantum yield of photoluminescence (φPL = 0.93) with efficient TADF was dramatically decreased by O2. The quenching rate constants of the S1 and T1 states were estimated to be in the order of 109 and 108 s-1 M-1, respectively. A DOS-plasticized polystyrene film containing 4CzIPN was prepared for optical O2 sensing to determine O2 concentration..
19. Naofumi Kobayashi, Takashi Kasahara, Tomohiko Edura, Juro Oshima, Ryoichi Ishimatsu, Miho Tsuwaki, Toshihiko Imato, Shuichi Shoji, Jun Mizuno, Microfluidic White Organic Light-Emitting Diode Based on Integrated Patterns of Greenish-Blue and Yellow Solvent-Free Liquid Emitters, Scientific reports, 10.1038/srep14822, 5, 2015.10, We demonstrated a novel microfluidic white organic light-emitting diode (microfluidic WOLED) based on integrated sub-100-μm-wide microchannels. Single-μm-thick SU-8-based microchannels, which were sandwiched between indium tin oxide (ITO) anode and cathode pairs, were fabricated by photolithography and heterogeneous bonding technologies. 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ) was used as a solvent-free greenish-blue liquid emitter, while 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene (TBRb)-doped PLQ was applied as a yellow liquid emitter. In order to form the liquid white light-emitting layer, the greenish-blue and yellow liquid emitters were alternately injected into the integrated microchannels. The fabricated electro-microfluidic device successfully exhibited white electroluminescence (EL) emission via simultaneous greenish-blue and yellow emissions under an applied voltage of 100 V. A white emission with Commission Internationale de l'Declairage (CIE) color coordinates of (0.40, 0.42) was also obtained; the emission corresponds to warm-white light. The proposed device has potential applications in subpixels of liquid-based microdisplays and for lighting..
20. Naofumi Kobayashi, Takashi Kasahara, Tomohiko Edura, Juro Oshima, Ryoichi Ishimatsu, Miho Tsuwaki, Toshihiko Imato, Shuichi Shoji, Jun Mizuno, Microfluidic white organic light-emitting diode based on striped fine microchannels for greenish blue and yellow liquid emitters, 18th International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS 2015 2015 Transducers - 2015 18th International Conference on Solid-State Sensors, Actuators and Microsystems, TRANSDUCERS 2015, 10.1109/TRANSDUCERS.2015.7181359, 2049-2052, 2015.08, We demonstrated a microfluidic white organic light-emitting diode (microfluidic WOLED) with integrated patterns of greenish-blue and yellow. Sub-100-μm-wide microchannels were alternately filled with greenish-blue and yellow liquid emitters to generate the patterns. 1-Pyrenebutyric acid 2-ethylhexyl ester (PLQ) was used as the greenish-blue emitter, while 2,8-di-tert-butyl-5,11-bis(4-tert-butylphenyl)-6,12-diphenyltetracene (TBRb)-doped PLQ was applied as the yellow emitter. The microfluidic WOLED exhibited white electroluminescence (EL) emission under 100V, which covers the broad emission band ranging from 420 nm to 750 nm. The EL emission occurred from the simultaneous greenish-blue and yellow emissions. The white emission with Commission Internationale de l'Eclairage (CIE) color coordinates of (0.40, 0.42) was obtained, which corresponds to warm-white light. Our microfluidic WOLED technology opens up new possibilities for not only sub-pixels of microdisplays but also lightings..
21. Miho Tsuwaki, Takashi Kasahara, Tomohiko Edura, Juro Oshima, Eri Kunisawa, Ryoichi Ishimatsu, Shigeyuki Matsunami, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, Jun Mizuno, Fabrication of a portable electrochemiluminescence-induced fluorescence detection chip with microfluidic excitation source for point-of-care diagnostics, IEEJ Transactions on Sensors and Micromachines, 10.1541/ieejsmas.135.230, 135, 6, 230-235, 2015.06, In this study, we propose an electrochemiluminescence (ECL)-induced fluorescence detection chip toward portable point-of-care diagnostics. A prototype chip consists of polydimethylsiloxane (PDMS)-based flow channels for target samples and on-demand multi-color microfluidic excitation sources. The microfluidic ECL cells were fabricated via a heterogeneous bonding technique through the use of self-assembled monolayers. The flow channels for target samples, which were formed by soft lithography, were combined with the excitation source. A pink fluorescence of resorufin was successfully detected with yellow ECL emission of 5,6,11,12-tetraphenyltetracene (rubrene). The proposed principle can open a new possibility for on-onsite multiple fluorescence detections..
22. Poomrat Rattanarat, Prinjaporn Teengam, Weena Siangproh, Ryoichi Ishimatsu, Koji Nakano, Orawon Chailapakul, Toshihiko Imato, An Electrochemical Compact Disk-type Microfluidics Platform for Use as an Enzymatic Biosensor, Electroanalysis, 10.1002/elan.201400590, 27, 3, 703-712, 2015.03, A novel centrifuge-based microfluidic device coupled with an electrochemical detector for the determination of glucose in control human serum is described. The electrochemical compact disk (eCD) platform was based on a poly(dimethylsiloxane) (PDMS) material containing reservoir, a mixing chamber, a spiral channel, a carbon-paste electrode (CPE) detector, and a waste reservoir. For electrode fabrication, a mixture consisting of cobalt phthalocyanine (CoPC), graphite powder, PDMS, and mineral oil was printed and formulated into a PDMS-based electrode pattern. To enhance electrochemical sensitivity, a graphene-polyaniline (G-PANI) nanocomposite solution was cast onto the working electrode surface. During the rotation of the eCD platform at a rotation speed of ∼1000rpm, a glucose solution and a glucose oxidase solution in separated reservoirs were mixed in a spiral channel to produce hydrogen peroxide by an enzymatic reaction. The produced hydrogen peroxide was determined using the electrode detector set at an applied potential of +0.4V vs. CPE (pseudo reference electrode). Under optimal conditions, a linear calibration ranging from 1 to 10mM with a limit of detection (LOD) of 0.29mM (S/N=3) and a limit of quantitation (LOQ) of 0.97mM (S/N=10) was obtained. Various common interference compounds including ascorbic acid, uric acid, paracetamol, and L-cysteine were tested. Finally, glucose in control serum samples containing certified concentrations were amperometrically determined and validated. Glucose levels measured using the eCD system matched actual values for the certified reference serum samples with satisfactory accuracy..
23. Rong Liu, Ryoichi Ishimatsu, Masayuki Yahiro, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Fluorometric flow-immunoassay for alkylphenol polyethoxylates on a microchip containing a fluorescence detector comprised of an organic light emitting diode and an organic photodiode, Talanta, 10.1016/j.talanta.2014.10.055, 134, 37-47, 2015.03, A compact fluorescence detector was constructed on a microchip from an organic light emitting diode (OLED) as the light source and an organic photodiode (OPD) as the photo-detector and was used in an immunoassay for alkylphenol polyethoxylates (APE). The OLED based on a terbium complex emitted a sharp light at the main wavelength of 546 nm with a full width at half maximum of 9 nm. The incident photo-to-current conversion efficiency (IPCE) of the OPD fabricated with Fullerene 70 (C70) and tris[4-(5-phenylthiopen-2-yl)phenyl]-amine (TPTPA) was approximately 44% for light at a wavelength of 586 nm. The performance of the fluorescence detector was evaluated for the determination of resorufin (λem=586 nm) and the photocurrent of the OPD due to the fluorescence of resorufin was proportional to the concentration of resorufin in the range from 0 to 18 μM with a detection limit (S/N=3) of 0.6 μM. The fluorescence detector was successfully utilized in a competitive enzyme-linked immunosorbent assay for APE, where an anti-APE antibody was immobilized on the surface of the channel of the Polydimethylsiloxane (PDMS) microchip or on the surface of magnetic microbeads. After an immunoreaction with a sample solution of APE containing a horse radish peroxidase (HRP)-labeled APE, the fluorescence of resorufin generated just after introduction of a mixed solution of Amplex Red and H2O2 was measured using the fluorescence detector. The calibration curve for the photocurrent signals of the OPD due to the fluorescence of resorufin against the logarithmic concentration of APE was sigmoidal in shape. The detection limits defined as IC80 were ca. 1 ppb and ca. 2 ppb, respectively, for the methods using the anti-APE antibody immobilized on the surface of the microchannel and in the case where the antibody was immobilized on the surface of magnetic microbeads..
24. Anastasiia Petrova, Andrey Bulatov, Andrey Vishnikin, Leonid Moskvin, Ryoichi Ishimatsu, Koji Nakano, Toshihiko Imato, A miniaturized stepwise injection spectrophotometric analyzer, analytical sciences, 10.2116/analsci.31.529, 31, 6, 529-533, 2015.01, A novel micro-stepwise injection analyzer (μSWIA) has been developed for the automation and miniaturization of spectrophotometric analysis. The main unit of this device is a mixing chamber (MC) connected to the atmosphere. This part of the μSWIA provides rapid and effective homogenization of the reaction mixture components and completion of the reaction by means of gas bubbling. The μSWIA contained a rectangular labyrinth channel designed in way allowing one to eliminate bubbles by moving a solution from the MC to an optical channel. The light-emitting diode (LED) was used as a light emitter and the analytical signal was measured by a portable spectrophotometer. Fluid movement was attained via the use of a computer-controlled syringe pump. The μSWIA was successfully used for the spectrophotometric determination of cysteine in biologically active supplements and fodder by using 18-molybdo-2-phosphate heteropoly anion (18-MPA) as the reagent..
25. Shuai Guo, Ryoichi Ishimatsu, Koji Nakano, Toshihiko Imato, Automated chemiluminescence immunoassay for a nonionic surfactant using a recycled spinning-pausing controlled washing procedure on a compact disc-type microfluidic platform, Talanta, 10.1016/j.talanta.2014.06.075, 133, 100-106, 2015.01, A fully automated and integrated chemiluminescence immunoassay, carried out on a compact disc (CD)-type microfluidic platform, for the detection of alkylphenol polyethoxylates (APnEOs) is described. The pattern of the CD-type microchip was designed so as to permit the sequential solution delivery of the sample solution, the washing solution and the luminol solution, which are required in the chemiluminescence immunoassay process, along with a designed rotation program for spinning the CD-type microchip. The procedure for flowing the washing solution, the volume of which was limited on the CD-type microchip, was optimized by using a recycled spinning-pausing rotation program to overcome the non-specific adsorption of the horseradish peroxidase labeled APnEOs at the detection area. The detection limit of the immunoassay is about 10 ppb..
26. Takashi Kasahara, Shigeyuki Matsunami, Tomohiko Edura, Ryoichi Ishimatsu, Juro Oshima, Miho Tsuwaki, Toshihiko Imato, Shuichi Shoji, Chihaya Adachi, Jun Mizuno, Multi-color microfluidic organic light-emitting diodes based on on-demand emitting layers of pyrene-based liquid organic semiconductors with fluorescent guest dopants, Sensors and Actuators, B: Chemical, 10.1016/j.snb.2014.09.101, 207, Part A, 481-489, 2015.01, In this study, we propose on-demand multi-color microfluidic organic light-emitting diodes (microfluidic OLEDs) using fluorescent guest emitter-doped liquid organic semiconductors. We use 1-pyrenebutyric acid 2-ethylhexyl ester (PLQ) not only for a greenish-blue liquid emitter, but also for a liquid host. 5,12-Diphenyltetracene (DPT), 5,6,11,12-tetraphenyltetracene (rubrene), and tetraphenyldibenzoperiflanthene (DBP) are doped into PLQ to obtain green, yellow, and red liquid emitters, respectively. Single-micrometer-thick SU-8-based microchannels sandwiched between an indium tin oxide (ITO) anode and a 3-aminopropyltriethoxysilane (APTES)-modified ITO cathode are fabricated on a glass substrate using photolithography and heterogeneous bonding techniques, and emitting layers are formed on-demand by simply injecting liquid emitters into the target microchannels. The microfluidic OLEDs with liquid emitters successfully exhibited multi-color electroluminescence (EL) emissions. Furthermore, the maximum luminance reached 26.0 cd/m2 at 61 V for 2.5-μm-thick microfluidic OLED with PLQ, and the decreased EL luminance was recovered by replacing the degraded emitting layer with a fresh liquid emitter. We expect that on-demand multi-color EL emissions and refreshable luminance features of the proposed microfluidic OLEDs will be highly promising technologies for future long-life light-emitting device applications..
27. Rong Liu, Ryoichi Ishimatsu, Masayuki Yahiro, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Photometric flow injection determination of phosphate on a PDMS microchip using an optical detection system assembled with an organic light emitting diode and an organic photodiode, Talanta, 10.1016/j.talanta.2014.08.057, 132, 96-105, 2015.01, A compact photometric detector was constructed from an organic light emitting diode (OLED) based on a europium complex, europium(diben-zoylmethanato)3(bathophenanthroline) (Eu(DBM)3bath), as the light source and an organic photodiode (OPD) fabricated from a hetero-junction of two layers of copper phthalocyanine (CuPc)/fullerene (C60) as the photo-detector on a microchip prepared from poly(dimethylsiloxan) (PDMS) and was applied to the determination of phosphate. The OLED and the OPD were fabricated by a vapor deposition method on an indium tin oxide (ITO) coated glass substrate with the following layered structure; Glass (0.7 mm)/ITO (110 nm)/4,4′-bis[N-(1-naphthyl)-N-phenyl amino]-biphenyl (α-NPD) (30 nm)/4,4′-di(N-carbazolyl)biphenyl (CBP): Eu3+ (8 wt%, 30 nm)/bathocuproine (BCP) (30 nm)/aluminum tris(8-hydroxyquinoline) (Alq3) (25 nm)/magnesium and silver (MgAg) (100 nm)/Ag (10 nm) and Glass (0.7 mm)/ITO (110 nm)/CuPc (35 nm)/C60 (50 nm)/BCP (10 nm)/Ag (50 nm), respectively. The OLED based on the europium complex emitted a sharp light at the wavelength of 612 nm with a full width at half maximum (FWHM) of 8 nm. The performance of the photometric detector assembled was evaluated based on measurements of the absorbance of different concentrations of malachite green (MG) solutions for a batch system with 1 cm long path length. The molar absorptive coefficient of the MG solution, calculated from the photocurrent of the OPD, was in good agreement with the value reported in the literature. A microchip with two inlets and one outlet U-shaped channel was prepared by a conventional photolithograph method. The OLED and the OPD were configured so as to face each other through the PDMS microchip in parallel in order to align the light axis of the OLED and the OPD with the flow cell (optical path length of 5 mm), which was located at the end of outlet. For the determination of phosphate, an ion-association reaction between MG and a molybdenum-phosphate complex was utilized and a good linear relationship between the concentration and absorbance was observed in the concentration range 0-0.2 ppm, with a detection limit (S/N=3) of 0.02 ppm. The assembled photometric detector was also applied to the determination of phosphate by the flow injection of river water samples using the reagent solution containing MG and molybdenum ammonium in sulfuric acid. A good recovery (97-99%) for the river water samples, which had been spiked with the standard 0.08 ppm, with an RSD of ca 5% (n=5) was obtained using the constructed system..
28. Takashi Kasahara, Shigeyuki Matsunami, Tomohiko Edura, Ryoichi Ishimatsu, Juro Oshima, Miho Tsuwaki, Toshihiko Imato, Shuichi Shoji, Chihaya Adachi, Jun Mizuno, Multi-color microfluidic electrochemiluminescence cells, Sensors and Actuators, A: Physical, 10.1016/j.sna.2014.04.039, 214, 225-229, 2014.08, We demonstrated multi-color microfluidic electrochemiluminescence (ECL) cells. 5,6,11,12-Tetraphenylnaphthacene (rubrene), 9,10-diphenylanthracene (DPA), tetraphenyldibenzoperiflanthene (DBP)-doped rubrene, and 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) dissolved in a mixed organic solvent of 1,2-dichlorobenzene and acetonitrile in the ratio of 2:1 (v/v) were used as yellow, blue, red, and green ECL solutions, respectively. Light emissions were confirmed using simple-structured ECL cells consisting of two indium tin oxide (ITO) coated glass substrates with an SU-8 spacer of thickness varying from 0.9 to 6 μm. The SU-8-based microfluidic ECL cells were fabricated using photolithography and heterogeneous bonding techniques through the use of epoxy- and amine-terminated self-assembled monolayers. The emitting layers were formed on-demand by injecting the chosen ECL solutions into the microchannels sandwiched between ITO anode and cathode pairs. Multi-color ECL was successfully obtained at the light-emitting pixels. The microfluidic ECL cells with DBP-doped rubrene solution showed a maximum luminance of 11.6 cd/m2 and the current efficiency of ca. 0.32 cd/A at 8 V. We expect that the proposed microfluidic device will be a highly promising technology for liquid-based light-emitting applications..
29. Benjamin Kabagambe, Mohammed B. Garada, Ryoichi Ishimatsu, Shigeru Amemiya, Subnanomolar detection limit of stripping voltammetric Ca 2+-selective electrode
Effects of analyte charge and sample contamination, Analytical chemistry, 10.1021/ac501951m, 86, 15, 7939-7946, 2014.08, Ultrasensitive ion-selective electrode measurements based on stripping voltammetry are an emerging sensor technology with low- and subnanomolar detection limits. Here, we report on stripping voltammetry of down to 0.1 nM Ca2+ by using a thin-polymer-coated electrode and demonstrate the advantageous effects of the divalent charge on sensitivity. A simple theory predicts that the maximum concentration of an analyte ion preconcentrated in the thin membrane depends exponentially on the charge and that the current response based on exhaustive ion stripping from the thin membrane is proportional to the square of the charge. The theoretical predictions are quantitatively confirmed by using a thin ionophore-doped polymer membrane spin-coated on a conducting-polymer-modified electrode. The potentiostatic transfer of hydrophilic Ca2+ from an aqueous sample into the hydrophobic double-polymer membrane is facilitated by an ionophore with high Ca2+ affinity and selectivity. The resultant concentration of the Ca 2+-ionophore complex in the ∼1 μm-thick membrane can be at least 5 × 106 times higher than the aqueous Ca2+ concentration. The stripping voltammetric current response to the divalent ion is enhanced to achieve a subnanomolar detection limit under the condition where a low-nanomolar detection limit is expected for a monovalent ion. Significantly, charge-dependent sensitivity is attractive for the ultrasensitive detection of multivalent ions with environmental and biomedical importance such as heavy metal ions and polyionic drugs. Importantly, this stripping voltammetric approach enables the absolute determination of subnanomolar Ca2+ contamination in ultrapure water containing 10 mM supporting electrolytes, i.e., an 8 orders of magnitude higher background concentration..
30. Ryoichi Ishimatsu, Shigeyuki Matsunami, Takashi Kasahara, Jun Mizuno, Tomohiko Edura, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Electrogenerated chemiluminescence of donor-acceptor molecules with thermally activated delayed fluorescence, Angewandte Chemie - International Edition, 10.1002/anie.201402615, 53, 27, 6993-6996, 2014.07, The electrochemistry and electrogenerated chemiluminescence (ECL) of four kinds of electron donor-acceptor molecules exhibiting thermally activated delayed fluorescence (TADF) is presented. TADF molecules can harvest light energy from the lowest triplet state by spin up-conversion to the lowest singlet state because of small energy gap between these states. Intense green to red ECL is emitted from the TADF molecules by applying a square-wave voltage. Remarkably, it is shown that the efficiency of ECL from one of the TADF molecule could reach about 50 %, which is comparable to its photoluminescence quantum yield. Donor-acceptor molecules with thermally activated delayed fluorescence (TADF) at room temperature can emit efficient electrogenerated chemiluminescence (ECL). Efficient spin up-conversion from triplet to singlet excited states through thermal activation is required to break through the theoretical limitation according to spin statistics (25 % of the quantum yield of photoluminescence). The ECL efficiency one TADF molecule reached about 50 %..
31. Koji Nakano, Takayuki Kimura, Yusuke Kitamura, Toshihiro Ihara, Ryoichi Ishimatsu, Toshihiko Imato, Potentiometric DNA sensing platform using redox-active DNA probe pair for sandwich-type dual hybridization at indicator electrode surface, Journal of Electroanalytical Chemistry, 10.1016/j.jelechem.2014.03.029, 720-721, 71-75, 2014.04, A potentiometric sensing platform that enables real-time DNA hybridization detection is described. A model target DNA, t37s: 5′-AAA AAA AAA AAA-(TC)2-Ts5-(TC)2-GGA GCT GGT GGC-3′, which consist of a dodecamer polydeoxyadenylic acid and the human K-ras oncogene, and a five-successive deoxythymidine phosphorothioate (Ts) was designed. With the gold-phosphorothioate binding, the DNA could bind the complementarily sequences to concentrate them at the gold electrode surfaces. Accordingly, a dodecamer polydeoxythymidylic acid having ferroin-moiety (T12FeP) and a ferrocene-modified complementary of K-ras (KrasFc) were synthesized. Electrochemical quartz-crystal-microbalance (QCM) using Au-sputtered quartz chips that served as the indicator electrode collected the electrode responses. When the electrode surface was treated with the T12FeP-hybridized t37s, which were subsequently oxidized to the corresponding Fe(III) form, the emf developed in a buffer solution responded to KrasFc; with the electrode-attached t37s the redox-active DNAs could group into a pair to establish specific redox-titration equilibrium. A QCM confirmed the on-electrode titrimetry feasible by determining the initial concentration and the amount of hybridization along with the emf measurements. Although the present method is necessary for two-kinds of redox conjugation of the target DNA, it should be important as a novel framework of electrochemical gene sensing. Preliminary examples of real-time measurement were also demonstrated with the results of kinetics analysis data..
32. Jiyeon Kim, Anahita Izadyar, Mei Shen, Ryoichi Ishimatsu, Shigeru Amemiya, Ion permeability of the nuclear pore complex and ion-induced macromolecular permeation as studied by scanning electrochemical and fluorescence microscopy, Analytical chemistry, 10.1021/ac403607s, 86, 4, 2090-2098, 2014.02, Efficient delivery of therapeutic macromolecules and nanomaterials into the nucleus is imperative for gene therapy and nanomedicine. Nucleocytoplasmic molecular transport, however, is tightly regulated by the nuclear pore complex (NPC) with the hydrophobic transport barriers based on phenylalanine and glycine repeats. Herein, we apply scanning electrochemical microscopy (SECM) to quantitatively study the permeability of the NPCs to small probe ions with a wide range of hydrophobicity as a measure of their hydrophobic interactions with the transport barriers. Amperometric detection of the redox-inactive probe ions is enabled by using the ion-selective SECM tips based on the micropipet- or nanopipet-supported interfaces between two immiscible electrolyte solutions. The remarkably high ion permeability of the NPCs is successfully measured by SECM and theoretically analyzed. This analysis demonstrates that the ion permeability of the NPCs is determined by the dimensions and density of the nanopores without a significant effect of the transport barriers on the transported ions. Importantly, the weak ion-barrier interactions become significant at sufficiently high concentrations of extremely hydrophobic ions, i.e., tetraphenylarsonium and perfluorobutylsulfonate, to permeabilize the NPCs to naturally impermeable macromolecules. Dependence of ion-induced permeabilization of the NPC on the pathway and mode of macromolecular transport is studied by using fluorescence microscopy to obtain deeper insights into the gating mechanism of the NPC as the basis of a new transport model..
33. Miho Tsuwaki, Jun Mizuno, Takashi Kasahara, Tomohiko Edura, Eri Kunisawa, Ryoichi Ishimatsu, Shigeyuki Matsunami, Toshihiko Imato, Chihaya Adachi, Shuichi Shoji, Microfluidic electrochemiluminescence (ECL) integrated flow cell for portable fluorescence detection, 27th IEEE International Conference on Micro Electro Mechanical Systems, MEMS 2014 MEMS 2014 - 27th IEEE International Conference on Micro Electro Mechanical Systems, 10.1109/MEMSYS.2014.6765585, 108-111, 2014, We propose a portable electrochemiluminescence (ECL)-induced fluorescence chip which consists of flow channels for fluorescence sample and multi-color emitting ECL excitation source. A prototype ECL-induced fluorescence chip was fabricated by conventional photolithography and bonding technique. Device performance was evaluated using ECL of rubrene as excitation source and resorufin as fluorescent dye. Fluorescence of 500 μM resorufin (600 nm) was successfully detected using 10 mM rubrene solution (560 nm) under the applied voltage of 4 V. The proposed principle is applicable for portable and on-demand multi fluorescence detection device using its freedom of choice for combination of the ECL light source..
34. Ryoichi Ishimatsu, Shigeyuki Matsunami, Katsuyuki Shizu, Chihaya Adachi, Koji Nakano, Toshihiko Imato, Solvent effect on thermally activated delayed fluorescence by 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene, Journal of Physical Chemistry A, 10.1021/jp404120s, 117, 27, 5607-5612, 2013.07, Thermally activated delayed fluorescence (TADF) is fluorescence arising from a reverse intersystem crossing (RISC) from the lowest triplet (T 1) to the singlet excited state (S1), where these states are separated by a small energy gap (ΔEst), followed by a radiative transition to the ground state (S0). Rate constants relating TADF processes in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) were determined at four different solvent polarities (toluene, dichloromethane, ethanol, and acetonitrile). We revealed that the rate constant of RISC, kRISC, which is the most important factor for TADF, was significantly enhanced by a reduced ΔEst in more polar solvents. The smaller ΔEst was mainly attributable to a stabilization of the S1 state. This stabilization also induced a Stokes shift in fluorescence through a relatively large change of the dipole moment between S1 and S0 states (17 D). Despite of this factor, we observed a negative correlation between ΔEst and efficiency of the delayed fluorescence (pd). This was ascribed to a lower intersystem crossing rate, kISC, and increased nonradiative decay from S1, knrs, in polar solvents..
35. Ryoichi Ishimatsu, Azusa Naruse, Rong Liu, Koji Nakano, Masayuki Yahiro, Chihaya Adachi, Toshihiko Imato, An organic thin film photodiode as a portable photodetector for the detection of alkylphenol polyethoxylates by a flow fluorescence-immunoassay on magnetic microbeads in a microchannel, Talanta, 10.1016/j.talanta.2013.08.044, 117, 139-145, 2013.01, An organic thin film photodiode (OPD) was successfully employed as a portable photodetector in a competitive enzyme-linked immunosorbent assay (ELISA) of a class of nonionic surfactants, namely alkylphenol polyethoxylates (APnEOs) which are an environmental pollutant. Microbeads that were chemically immobilized with an anti-APnEOs antibody were used in the assay. The OPD consisted of a layer of copper phthalocyanine (CuPc), C60 and a second layer of bathocuproine (BCP) with a bulk heterojunction composed of CuPc and C60 prepared by a vapor deposition method on an indium-tin oxide coated glass substrate. The OPD showed an incident photon-current efficiency (IPCE) of approximately 19% for light at a wavelength of 585 nm. This relatively high IPCE at 585 nm makes it suitable for detecting the fluorescence of resorufin (λem=585 nm), the product of the competitive ELISA, produced through the enzymatic reaction of Amplex Red with horseradish peroxidase (HRP) and H2O2. A fluorometric detector was assembled on a microchip by combining the fabricated OPD and a commercial LED as a photodetector and a light source, respectively. The photocurrent of the OPD due to the fluorescence of resorufin was proportional to the concentration of resorufin in the concentration range from 0 to 8 μM. When the fabricated OPD was used as a portable photodetector, the competitive ELISA of APnEOs using HRP labeled APnEOs (HRP-APnEOs) was performed on magnetic microbeads on which surface an anti-APnEOs antibody had been immobilized. A typical sigmoidal calibration curve was obtained and the data were in good agreement with a numerical simulation, where the photocurrent of the OPD was plotted against the concentration of APnEOs, determined via the competitive ELISA. The detection limit of the immunoassay for APnEOs was approximately 2 and 4 ppb in batch and flow system, respectively..
36. Shuai Guo, Koji Nakano, Hizuru Nakajima, Katsumi Uchiyama, Akihide Hemmi, Yoshikazu Yamasaki, Shigeharu Morooka, Ryoichi Ishimatsu, Toshihiko Imato, Chemiluminescence immunoassay for a nonionic surfactant using a compact disc-type microfluidic platform, Pure and Applied Chemistry, 10.1351/PAC-CON-11-10-10, 84, 10, 2027-2043, 2012.10, A simple and pump-free chemiluminescence immunoassay based on a compact disc (CD)-type microfluidic platform for the determination of alkylphenol polyethoxylates (APnEOs) is described. The method is based on a competitive immunoreaction of the anti- APnEOs antibody immobilized on the magnetic microbeads between APnEOs and horseradish peroxidase (HRP)-labeled APnEOs in the sample solution. The luminol solution containing H 2O 2 and enhancer is caused to flow from one reservoir in the platform to another by appropriate adjustment of the speed of the rotation of the disc. The detection limit was similar to that reported in our previous paper, i.e., 10 ppb according to IC 80..
37. Mayo Miyake, Hizuru Nakajima, Akihide Hemmi, Masayuki Yahiro, Chihaya Adachi, Nobuaki Soh, Ryoichi Ishimatsu, Koji Nakano, Katsumi Uchiyama, Toshihiko Imato, Performance of an organic photodiode as an optical detector and its application to fluorometric flow-immunoassay for IgA, Talanta, 10.1016/j.talanta.2012.02.006, 96, 132-139, 2012.07, The performance of an organic thin film photodiode (OPD), fabricated from a hetero-junction comprised of two layers of C60 and a phthalocyanine-Cu(II) complex was evaluated by detecting the chemiluminescence generated from the reaction of luminol with horseradish peroxidase in the presence of H2O2, and the fluorescence from resorufin, as an optical detector. The photocurrent of the OPD was linear with respect to the power of light from a commercial LED. The sensitivity of the OPD was sufficient for detecting chemiluminescence with a power 0.1 μW/cm2. The OPD was successfully used in a flow-immunoassay for IgA, a marker of human stress, in which a sandwich immunoassay was carried out on the microchip and the fluorescence from resorufin, produced by the enzymatic reaction, was detected. The detection limits for resorufin and IgA were 5.0 μM and 16 ng/mL, respectively. The photosensitivity of the OPD remained relatively constant for a minimum of one year..
38. Mei Shen, Ryoichi Ishimatsu, Jiyeon Kim, Shigeru Amemiya, Quantitative imaging of ion transport through single nanopores by high-resolution scanning electrochemical microscopy, Journal of the American Chemical Society, 10.1021/ja3023785, 134, 24, 9856-9859, 2012.06, Here we report on the unprecedentedly high resolution imaging of ion transport through single nanopores by scanning electrochemical microscopy (SECM). The quantitative SECM image of single nanopores allows for the determination of their structural properties, including their density, shape, and size, which are essential for understanding the permeability of the entire nanoporous membrane. Nanoscale spatial resolution was achieved by scanning a 17 nm radius pipet tip at a distance as low as 1.3 nm from a highly porous nanocrystalline silicon membrane in order to obtain the peak current response controlled by the nanopore-mediated diffusional transport of tetrabutylammonium ions to the nanopipet-supported liquid-liquid interface. A 280 nm × 500 nm image resolved 13 nanopores, which corresponds to a high density of 93 nanopores/μm 2. A finite element simulation of the SECM image was performed to assess quantitatively the spatial resolution limited by the tip diameter in resolving two adjacent pores and to determine the actual size of a nanopore, which was approximated as an elliptical cylinder with a depth of 30 nm and major and minor axes of 53 and 41 nm, respectively. These structural parameters were consistent with those determined by transmission electron microscopy, thereby confirming the reliability of quantitative SECM imaging at the nanoscale level..
39. Daisuke Seto, Tomoharu Maki, Nobuaki Soh, Koji Nakano, Ryoichi Ishimatsu, Toshihiko Imato, A simple and selective fluorometric assay for dopamine using a calcein blue-Fe2+ complex fluorophore, Talanta, 10.1016/j.talanta.2012.02.025, 94, 36-43, 2012.05, A novel fluorimetric assay for dopamine using calcein blue (CB) complexed with Fe2+ ion as a chemical sensor is described. The fluorescence arising from CB of the CB-Fe2+ complex is quenched by the Fe 2+ ion. When dopamine is added to a solution of the CB-Fe 2+ complex, a dopamine-Fe2+ complex is formed as the result of a ligand exchange reaction between CB and dopamine which permits the fluorescence from CB to be recovered. The fluorescence intensity at the wavelength of 440 nm (at the excitation wavelength of 340 nm) was found to be proportional to the concentration of the dopamine added to the CB-Fe 2+ complex solution, which permits dopamine to be quantitatively determined. The selectivity for dopamine in the presence of other catecholamines and related compounds was good. The calibration curve for dopamine, determined using experimental data was successfully simulated based on the equilibrium of the ligand exchange reaction between CB and dopamine. The working range is from 50 μM to 1 mM and the limit of detection and limit of quantization are ca 10 μM and 50 μM, respectively. The assay is simple and economical, compared with conventional methods such as an enzyme-linked immunosorbent assay (ELISA)..
40. Hisao Yoshinaga, Koji Nakano, Nobuaki Soh, Ryoichi Ishimatsu, Toshihiko Imato, A pivot-hinge-style DNA immobilization method with adaptable surface concentration based on oligodeoxynucleotide-phosphorothioate chemisorption on gold surfaces, analytical sciences, 10.2116/analsci.28.1059, 28, 11, 1059-1064, 2012.01, The chemisorption of oligodeoxynucleotide phosphorothioate (s-oligo) is reported. A series of s-oligo DNAs was designed for use as capture probe DNA molecules. The s-oligo DNAs consist of the K-ras gene (5'-GGA GCT GGT GGC-3') and a dodecamer deoxyriboadenosine, both of which lie on either side of an s-oligo DNA sequence. By primarily focusing on the capture probe DNA having five-successive s-oligo sequences, e37, the immobilization chemistry of e37 was examined; atomic force microscopy achieved the direct visualization of individual molecules on Au(111) substrates, while a series of surface analyses, including IR, ellipsometry, and microgravimetry, showed that the s-oligo functional groups played a pivotal role in the surface-adlayer through the gold-thiol interaction. Interestingly, the amount of immobilization showed a definite relationship with the number of s-oligo linkages introduced, which should be important to regulate the concentration of the capture probe DNA molecules on the surface. Some preliminary studies using ferrocene-modified complementary sequences indicated that electrochemical labeling and readouts were possible..
41. Ryoichi Ishimatsu, Anahita Izadyar, Benjamin Kabagambe, Yushin Kim, Jiyeon Kim, Shigeru Amemiya, Electrochemical mechanism of ion-ionophore recognition at plasticized polymer membrane/water interfaces, Journal of the American Chemical Society, 10.1021/ja207297q, 133, 40, 16300-16308, 2011.10, Here, we report on the first electrochemical study that reveals the kinetics and molecular level mechanism of heterogeneous ion-ionophore recognition at plasticized polymer membrane/water interfaces. The new kinetic data provide greater understanding of this important ion-transfer (IT) process, which determines various dynamic characteristics of the current technologies that enable highly selective ion sensing and separation. The theoretical assessment of the reliable voltammetric data confirms that the dynamics of the ionophore-facilitated IT follows the one-step electrochemical (E) mechanism controlled by ion-ionophore complexation at the very interface in contrast to the thermodynamically equivalent two-step electrochemical-chemical (EC) mechanism based on the simple transfer of an aqueous ion followed by its complexation in the bulk membrane. Specifically, cyclic voltammograms of Ag +, K+, Ca2+, Ba2+, and Pb 2+ transfers facilitated by highly selective ionophores are measured and analyzed numerically using the E mechanism to obtain standard IT rate constants in the range of 10-2 to 10-3 cm/s at both plasticized poly(vinyl chloride) membrane/water and 1,2-dichloroethane/water interfaces. We demonstrate that these strongly facilitated IT processes are too fast to be ascribed to the EC mechanism. Moreover, the little effect of the viscosity of nonaqueous media on the IT kinetics excludes the EC mechanism, where the kinetics of simple IT is viscosity-dependent. Finally, we employ molecular level models for the E mechanism to propose three-dimensional ion-ionophore complexation at the two-dimensional interface as the unique kinetic requirement for the thermodynamically facilitated IT..
42. Ryoichi Ishimatsu, Jiyeon Kim, Ping Jing, Christopher C. Striemer, David Z. Fang, Philippe M. Fauchet, James L. McGrath, Shigeru Amemiya, Ion-selective permeability of an ultrathin nanoporous silicon membrane as probed by scanning electrochemical microscopy using micropipet-supported ITIES tips, Analytical Chemistry, 10.1021/ac1005052, 82, 17, 7127-7134, 2010.09, We report on the application of scanning electrochemical microscopy (SECM) to the measurement of the ion-selective permeability of porous nanocrystalline silicon membrane as a new type of nanoporous material with potential applications in analytical, biomedical, and biotechnology device development. The reliable measurement of high permeability in the molecularly thin nanoporous membrane to various ions is important for greater understanding of its structure-permeability relationship and also for its successful applications. In this work, this challenging measurement is enabled by introducing two novel features into amperometric SECM tips based on the micropipet-sup-ported interface between two immiscible electrolyte solutions (ITIES) to reveal the important ion-transport properties of the ultrathin nanopore membrane. The tip of a conventional heat-pulled micropipet is milled using the focused ion beam (FIB) technique to be smoother, better aligned, and subsequently, approach closer to the membrane surface, which allows for more precise and accurate permeability measurement. The high membrane permeability to small monovalent ions is determined using FIB-milled micropipet tips to establish a theoretical formula for the membrane permeability that is controlled by free ion diffusion across water-filled nanopores. Moreover, the ITIES tips are rendered selective for larger polyions with biomedical importance, i.e., polyanionic pentasaccharide Arixtra and polycationic peptide protamine, to yield the membrane permeability that is lower than the corresponding diffusion-limited permeability. The hindered transport of the respective polyions is unequivocally ascribed to electrostatic and steric repulsions from the wall of the nanopores, i.e., the charge and size effects..
43. Yushin Kim, Patrick J. Rodgers, Ryoichi Ishimatsu, Shigeru Amemiya, Subnanomolar ion detection by stripping voltammetry with solid-supported thin polymeric membrane, Analytical Chemistry, 10.1021/ac900995a, 81, 17, 7262-7270, 2009.09, Subnanomolar limits of detection (LODs) are obtained for stripping voltammetry based on ion transfer at the interface between the aqueous sample and the thin polymeric membrane supported with a solid electrode. It has been predicted theoretically that a lower LOD can be obtained for a more lipophilic analyte ion, which can be preconcentrated at a higher equilibrium concentration in the solid-supported thin polymeric membrane to enhance a stripping current response. This study is the first to experimentally confirm the general theoretical prediction for both cationic and anionic analytes. Proof-of-concept experiments demonstrate that a subnanomolar LOD of (8 ± 4) × 10-11 M tetrapropylammonium is significantly lower than a LOD of less lipophilic tetraethylammonium. Importantly, stripping voltammetry of the cationic analytes is enabled by newly introducing an oxidatively doped poly(3,4-ethylenedioxythiophene) film as the intermediate layer between a plasticized poly(vinyl chloride) membrane and a Au electrode. On the other hand, an undoped poly(3-octylthiophene) film is used as an intermediate layer for voltammetric detection of a lipophilic inorganic anion, hexafluoroarsenate, an arsenical biocide found recently in wastewater. A LOD of (9 ± 2) × 10-11 M hexafluoroarsenate thus obtained by ion-transfer stripping voltammetry is comparable to a LOD of 80 pM by inductively coupled plasma mass spectrometry with anion-exchange chromatography. Great sensitivity for a lipophilic ion is potentially useful for environmental analysis because high lipophilicity of an ion is relevant to its bioaccumulation and toxicity..
44. Ryoichi Ishimatsu, Yuki Kitazumi, Naoya Nishi, Takashi Kakiuchi, Phase transition of a binary room-temperature ionic liquid composed of bis(pentafluoroethanesulfonyl)amide salts of tetraheptylammonium and N-tetradecylisoquinolinium and its surface properties at the ionic liquid|water interface, Journal of Physical Chemistry B, 10.1021/jp9027035, 113, 27, 9321-9325, 2009.07, A binary room-temperature ionic liquid (RTIL) composed of bis(pentafluoroethanesulfonyl)amide (C2C2N-) salts of tetraheptylammonium (THpA+) and N-tetradecylisoquinolinium (C14Iq+) undergoes a phase transition upon increasing the mole fraction of C14Iq+ (x) in the bulk RTIL. The initial decrease with x of the interfacial tension (γ) at the interface between water (W) and the binary RTIL reaches a break point at x = 0.2 irrespective of the values of the phase-boundary potential. The surface tension at RTIL|air interface and the conductivity of the binary RTIL support that the break point at x = 0.2 at the RTIL|W interface is attributable to the change of the bulk property. However, unlike the micelle formation of a surfactant solution, a further increase in x gives rise to a further change in γ. Whereas the phase transition at x = 0.2 does not depend on the applied potential (E) across the RTIL|W interface, the mode of the change in γ at x > 0.2 strongly depends on E and the apparent deficit of C14Iq+ at the interface is more pronounced when E is closer to the point of zero charge..
45. Yukinori Yasui, Yuki Kitazumi, Ryoichi Ishimatsu, Naoya Nishi, Takashi Kakiuchi, Ultraslow response of interfacial tension to the change in the phase-boundary potential at the interface between water and a room-temperature ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, Journal of Physical Chemistry B, 10.1021/jp9006312, 113, 11, 3273-3276, 2009.03, Ultraslow response, on the order of minutes, of the interfacial tension to the change in the phase-boundary potential at the interface between water and a room-temperature ionic liquid, trioctylmethylammonium bis(nonafluorobutanesulfonyl)amide, has been demonstrated. This ultraslow relaxation, which is not observed at the interface between two immiscible electrolyte solutions made of molecular organic solvents, is likely to be due to the long-range and collective ordering of ions of the electrical double layer on the ionic liquid side of the interface..
46. Ryoichi Ishimatsu, Naoya Nishi, Takashi Kakiuchi, Wide polarized potential windows at the interface between water and an ionic liquid, tetraheptylammonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, Chemistry Letters, 10.1246/cl.2007.1166, 36, 9, 1166-1167, 2007.09, Wide polarized potential windows against interfacial ion transfer are available at the interface between a hydrophobic ionic liquid (IL), tetraheptylammonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate ([THpA +][TFPB-]) and an aqueous electrolyte solution (W) of MgSO4. The width of the potential window, 1.1V at 60°C, enables electrochemical studies of charge transfer at the IL/W interface for a variety of ions and redox couples..
47. Naoya Nishi, Ryoichi Ishimatsu, Masahiro Yamamoto, Takashi Kakiuchi, Orientation of 1-dodecyl-4-phenylpyridinium ions constituting an ionic liquid at the ionic liquid | water interface studied by second harmonic generation, Journal of Physical Chemistry C, 10.1021/jp071538v, 111, 33, 12461-12466, 2007.08, A hydrophobic room-temperature ionic liquid (RTIL) of 1-dodecyl-4- phenylpyridinium (C
12
ppy
+
) ions, the cations with high first hyperpolarizability, was prepared in combination with bis(pentafluoroethylsulfonyl)imide, and the orientation of C
12
ppy
+
at the RTIL|water and RTIL|air interfaces was analyzed using optical second harmonic generation (SHG). From polarization-dependence measurements and absolute phase measurements, it was found that C
12
ppy
+
ions at the RTIL|air interface are orientated with the main axis of 4-phenylpyridinium moiety (from phenyl to pyridinium direction) tilted at 53° from the surface normal (from RTIL to air direction) and that the dodecyl chain is protruding to the air. At the RTIL|water interface, it was suggested that C
12
ppy
+
is orientated at the tilt angle of 131° from the surface normal (from RTIL to water direction) with the dodecyl chain protruding away from the aqueous phase..
48. Ryoichi Ishimatsu, Naoya Nishi, Takashi Kakiuchi, Interfacial ion pairing at the interface between water and a room-temperature ionic liquid, N-tetradecylisoquinolinium bis(pentafluoroethylsulfonyl)imide, Langmuir, 10.1021/la700884q, 23, 14, 7608-7611, 2007.07, The specific interaction of N-tetradecylisoquinolinium (C 14Iq+) with Cl- and Br- has been detected in the voltammetry of ion transfer and electrocapillarity at the interface between an aqueous solution (W) and a room-temperature ionic liquid (RTIL), N-tetradecylisoquinolinium bis(pentafluoroethylsulfonyl)imide ([C 14Iq+][C2C2N-]). This specific interaction also makes the transfer of Cl- and Br - into [C14lq+][C2C 2N-] energetically more favorable in comparison with that of F- and SO42-. The width of the polarized potential window in ion-transfer voltammetry at the [C14Iq +][C2C2N-]|W interface is significantly narrower because of the transfer of anions from W to RTIL. The degree of affinity of the anion with C14Iq+ agrees with the Hofmeister series. Such an ion-pair formation of anions in W wth cations in the RTIL is much weaker when the cation constituting the RTIL is a symmetric tetraheptylammonium ion..
49. Ryoichi Ishimatsu, Fumiko Shigematsu, Takuma Hakuto, Naoya Nishi, Takashi Kakiuchi, Structure of the electrical double layer on the aqueous solution side of the polarized interface between water and a room-temperature ionic liquid, tetrahexylammonium bis(trifluoromethylsulfonyl)imide, Langmuir, 10.1021/la0623073, 23, 2, 925-929, 2007.01, The structure of the electrical double layer on the aqueous solution side has been studied by measuring electrocapillary curves at the polarized interface between a room-temperature ionic liquid (RTIL), tetrahexylammonium bis(trifluoromethylsulfonyl)imide, and water (W) at different concentrations of LiCl. Thermodynamic analysis of the electrocapillary curves indicates that Li+ ions negatively adsorb at the point of zero charge. The adsorption of Li+ and Cl- ions in the polarized potential window of about 200 mV can be explained by the Gouy's double layer model, and the specific adsorption of Li+ and Cl- ions at the RTIL|W interface is negligible within the polarized potential window..