Published papers

A novel method has been developed to immobilize macroscopic two-dimensional arrays of Au nanoparticles (AuNPs) onto the surfaces of boron-doped diamond (BDD) electrodes. These AuNP-modified surfaces are prepared by self-assembly of differently sized colloidal Au particles onto the BDD surfaces. A dense and well-distributed AuNP monolayer onto the BDD surfaces was obtained by pretreating the BDD surface with allylamine by photochemical reaction. These modified surfaces have been characterized by XPS, SEM, and electrochemical cyclic voltammetry (CVs). SEM data indicated that the AuNPs are immobilized and well-dispersed, forming a uniform monolayer on the amine-terminated activated BDD surfaces in two dimensions. Cyclic voltammtric (CV) results indicate that the immobilized AuNPs monolayer onto BDD electrode shows excellent electrochemical properties, implying facile electrochemical communication between the AuNPs monolayer and BDD substrate through the amine linkers. © 2006 American Chemical Society.

The electrochemical analysis of tetracyclines was investigated using nickel-implanted boron-doped diamond thin film electrode (Ni-DIA) by cyclic voltammetry and high performance liquid chromatographic with amperometry. Cyclic voltammetry was used to study the electrochemical oxidation of tetracyclines. Comparison experiments were carried out utilizing as-deposited BDD and glassy carbon electrodes. Ni-DIA electrode provided well-resolved oxidative irreversible cyclic voltammograms and the highest current signals among the electrode studied. High performance liquid chromatography (HPLC) with amperometric detection was also studied. The chromatography was performed using a commercially available Inertsil C18 column, with the mobile phase being: 80% phosphate buffer (pH 2.5)-20% acetonitrile and detected at 1.55 V. The methods were validated over the concentration range 0.05-100 ppm with the overall average recoveries from 83.3 to 102.5% and R.S.D. of less than 10%. The proposed method was further applied to analyse shrimp samples. © 2005 Elsevier B.V. All rights reserved.

The phenylazomethine dendrimer (DPA) with amino groups at the terminal (end-amine dendrimer) was synthesized by the convergent method without protection from 4,4′-diamino-3,3′,5, 5′-tetramethylbenzophenone (DTB) as the raw material. The amino groups enabled the periphery of the dendrimer (DPA) to be modified by functional molecules, and we succeeded in the synthesis of the end-ferrocene dendrimer (A), which was perfectly modified by the ferrocenes, in one step with high yields. The stepwise metal complexation from the core was also observed in A G2 and A G3. The equilibrium constant K of the terminal imine connected with ferrocnes was determined to be 10 times smaller than that of the N-diphenylmethylene imine (ca. 105 [M-1]); however, it was strong enough for metal assembling. We found that A G3 showed redox switching by the addition of metal ions. The potential jump of the modified ferrocenes from 0.32 to 0.42 V was observed, when the complexation of Fecl3, which started from the first layer, reached the third-layer imines next to the ferrocenes. This behavior was reversible based on the encapsulation reversibility and releasing of iron ions. © 2006 American Chemical Society.

We have observed size-reduction induced ferromagnetism and significant photo-magnetic effects in azobezene-thiol-modified gold nanoparticles. When the particle size was reduced to 1.7 nm, ferromagnetism even at room temperature was observed while diamagnetism was dominating with the particle size of 5.0 nm. Furthermore, reducing the particles size to 1.7 nm also gave rise to photo-magnetic properties because the decrease in particle size provided free volume between each of the azobenzene ligands. This photo-magnetic effect could be attributed to photo-induced changes in the values of d-charge losses due to the photoisomerization of azo-ligands, which were accompanied by the inversion of surface dipole values to the opposite sign. © 2008 Elsevier Ltd. All rights reserved.

A non-enzymatic glucose sensor, consisting of a regular array of nickel microdisks on a diamond electrode substrate designed to control the diffusion processes of glucose and interfering species such as ascorbic acid and uric acid, was fabricated. Each nickel microdisk acts as a microelectrode for glucose (hemispherical diffusion) due to the inactive diamond surface for glucose oxidation while interfering species are oxidized at the diamond surface (linear diffusion). The difference in diffusion profiles gives a difference in the time dependence of the amperometric response. That is, the glucose concentration gives rise to a constant amperometric response whereas the concentration of mixed interfering species gives rise to a time dependent response, because the hemispherical diffusion profile yields a constant response and the linear diffusion profile yields a transient current following Cottrell's equation. The results show that the fabricated electrodes exhibit a high selectivity for glucose in solutions containing ascorbic and uric acids. © 2009 Elsevier B.V. All rights reserved.

The differential pulse voltammetric (DPV) peak for dopamine (DA) oxidation was found to be highly amplified by the addition of ascorbic acid (AA) when carboxyl-terminated boron-doped diamond (BDD) electrodes were used as the working electrode. The DP voltammogram for a solution containing DA and AA obtained using a 4-pentenoic acid-modified BDD (4PA-BDD) electrode showed well-separated oxidation peaks for DA and AA at 0.4 and 0.6 V vs. Ag/AgCl, respectively. In addition, as the DA concentration increased at constant AA concentration, a simultaneous increase in the DA peak current density and decrease in the AA peak current density were observed. The slope of the calibration curve for the [DA] range of 1-10 μM in the presence of AA (500 μM) was seven times larger than that obtained in the absence of AA. Such an enhancement was found to be more efficient at 4PA-BDD than at oxidized-BDD, partly due to simple electrostatic effects and partly due to suppression of the polymerization of DA oxidation products by the terminal carboxyl groups. The enhanced detection method using a carboxyl-terminated BDD electrode should be an effective analytical tool, especially for determining low concentrations of DA in the presence of high concentrations of AA. © 2008 Elsevier Ltd. All rights reserved.

Getting organized: Assemblies of ferromagnetic FePt nanoparticles were generated with large perpendicular magnetic anisotropy by a magnetic-field- assisted layer-bylayer method, and subsequently layer-by-layer films consisting of L10-FePt nanoparticles and organic polymers were prepared. These films are phototunable when photochromic molecules are used as polymer layers. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

In this paper, the simplest methods developed so far for the analyses of pH and acid concentrations in acid solution are described, using a technique based on highly boron-doped diamond (BDD) electrodes. These simple analyses take advantage of a very attractive electrochemical property of BDD electrodes, i.e., a very wide potential window. It transpires that the value of the current generated by hydrogen evolution during the reduction of an acid when measured by linear sweep voltammetry (LSV) measurements accurately reflects the proton concentration (pH) when using a BDD macroelectrodes (hereafter designated as BDD-M), whereas accurate measurements are impossible when using conventional electrode materials such as glassy carbon, metal etc because of their narrow potential windows. Furthermore, the measurements of weak acid concentrations [HA] were also possible by using both the pH value (obtained by BDD-M) and the limiting current value obtained by using BDD microelectrodes (hereafter designated as BDD-m). © 2008 Elsevier B.V. All rights reserved.

How low can you go? An Fell4 square was prepared by self-assembly and exhibits both thermally induced and photoinduced spin crossover from a system with four high-spin (HS) centers to one with two high-spin and two low-spin (LS) centres. The spin-crossover sites are located on the same side of the square, and the spin transition and magnetic interactions (see picture) are synergistically coupled. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.

We have observed the emergence of a large anisotropic magnetization and significant photoinduced changes in the magentization that appear at the interface between a gold film and an azobenzene-containing self-assembled monolayer. The magnetization value was extremely high, up to 50 μB per adsorbed molecule. These photomagnetic effects can be attributed to a photoinduced change in the loss of d charge due to photoisomerization of the azobenzene monolayer, which is accompanied by inversion of the surface dipoles. Furthermore, we have also observed reversible changes in the work function of the gold film by alternating UV and visible light, showing that the value of the surface dipole moment is changed as a result of photoisomerization. This allowed us to control the magnetization by alternating the photoillumination between UV and visible light, and we have clarified the mechanism for these photomagnetic effects. A novel strategy such as this, which enables significant reversible phototuning of the magnetic order, has great potential for applications in future magneto-optical devices. © 2009 American Chemical Society.

Out of nowhere: Significant photoinduced changes in ferromagnetism have been observed at the interfaces between gold nanoparticles (Au NPs) and azobenzene-derivatized thiols. These photomagnetic effects could be attributed to photoinduced changes in d-charge losses resulting from the photoisomerization of the azo ligands (see picture), which are accompanied by the inversion of surface dipoles to the opposite sign. (Figure Presented) © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.

A three-dimensional mixed-valence iron complex with NiAs-type topology, [(FeIII 3O)FeII(TA)6(H 2O)3]•(ClO4)2(NO 3)(EtOH)(H2O)2 (1, HTA = tetrazole-1H-acetic acid), shows spin-crossover behavior that was characterized via variable-temperature crystal structures, Mössbauer spectra and magnetic susceptibilities, the pressure effects on the transition behavior were also studied. © The Royal Society of Chemistry.

Boron-doped diamond (BDD) surfaces were photochemically modified with vinylferrocene (VFC), and the modified surfaces were analyzed both qualitatively and quantitatively by electrochemical techniques. VFC-modified BDD (VFC-BDD) was prepared by ultraviolet (254 nm) irradiation of hydrogen-terminated BDD in mesitylene, acetonitrile, or n-alkane solutions of VFC. Cyclic voltammetry (CV) results indicated facile electron transfer between ferrocenyl groups and the BDD substrate. The surface coverage of VFC-modified polycrystalline and single-crystal (100) BDD was also estimated by CV and was found to reach saturation at a value possibly corresponding to monolayer coverage by ferrocenyl groups. The electrochemical stability of VFC-BDD to successive potential cycling in acetonitrile was found to be much higher than that of a self-assembled ferrocenylalkanethiol monolayer on an Au electrode surface. This study is the first to show that appropriate solutions of a terminal alkene can be used in the photochemical modification of diamond, yielding monolayer coverage of the surface. © 2008 American Chemical Society.

Nanosized ε-Fe2O3 crystals with a diameter below 20 nm were successfully prepared at 600°C in a mesoporous silica matrix. The formation of the metastable iron oxide occurred through nanoscale segregation in an immiscible SiO2-Fe2O3 system having a mesoporous structure. The nanocrystals incorporated into ca. 50nm-size particles of the mesoporous silica exhibited a coercive field up to 8 kOe. Copyright © 2008 The Chemical Society of Japan.

In this report, we established a new electrochemical method for the detection of conformational changes in large, non-metalloproteins such as bovine serum albumin, using flow injection analysis coupled with hydrogen-terminated, boron-doped diamond electrodes. The oxidation current was used as a signal reporter in the monitoring of urea-induced BSA denaturation. In the denatured state at high urea concentrations, the electrochemical signal increased, and the amperometric responses for the oxidation potential at 1300 mV were consistent with the results of conventional methods of denaturation monitoring using fluorescence spectroscopy. The oxidation involved at least five redox-active species (cysteine, tryptophan, tyrosine, methionine, and disulfide bonds). Furthermore, the method also showed high sensitivity for quantitative analysis of protein. A linear dynamic in the concentration range 50-400 μg/mL (r 2 = 0.977) with a lower detection limit of 190 ng/mL was achieved for BSA. Direct electrochemical detection of conformation changes of proteins using BDD electrodes can be performed with advantages in terms of simplicity and sensitivity. © 2008 American Chemical Society.

Allyltriethylammonium bromide (ATAB) was covalently attached to the surface of hydrogen-terminated boron-doped diamond (BDD) thin films using a photochemical method to fabricate positively charged electrode surfaces. The anodic current for oxalate oxidation both in cyclic voltammetry and in flow-injection analysis with amperometry was found to be up to two times larger at ATAB-modified BDD (ATAB-BDD) than at an unmodified BDD electrode, which may be based on the electrostatic interaction between the oxalate anion and the electrode surface. In addition, the stability of the electrochemical detection of oxalate was improved at the ATAB-BDD electrode compared to the unmodified electrode. © 2008 Wiley-VCH Verlag GmbH&Co. KGaA.

Crystal-face-selective adsorption of Au nanoparticles (AuNPs) was achieved on polycrystalline boron-doped diamond (BDD) surface via the self-assembly method combined with a UV/ozone treatment. To the best of our knowledge, this is the first report of crystal-face-selective adsorption on an inorganic solid surface. Hydrogen-plasma-treated BDD samples and those followed by UV/ozone treatment for 2 min or longer showed almost no adsorption of AuNP after immersion in the AuNP solution prepared by the citrate reduction method. However, the samples treated by UV/ozone for 10 s showed AuNP adsorption on their (111) facets selectively after the immersion. Moreover, the sample treated with UV/ozone for 40-60 s showed AuNP adsorption on the whole surface. These results indicate that the AuNP adsorption behavior can be controlled by UV/ozone treatment time. This phenomenon was highly reproducible and was applied to a two-step adsorption method, where AuNPs from different batches were adsorbed on the (111) and (100) surface in this order. Our findings may be of great value for the fabrication of advanced nanoparticle-based functional materials via bottom-up approaches with simple macroscale procedures. © 2008 American Chemical Society.

The ability to generate small-scale structures and assemble functional substances in the fields of micro electronics and optoelectronics continues to support advances in information technology. Here we present a novel type of "layer-by-layer" assembled films, whose surface properties can be controlled by UV irradiation in aqueous solution. We have designed a photochromic multilayer film of Preyssler-type polyoxometalate, (NaP5W30) and polyethyleneimine (PEI) by using the layer-by-layer method. We found that the outermost PEI layer could be detached by UV irradiation in aqueous solution, and that this process could then cause inversion of the zeta potential. Furthermore, we achieved reversible-control of the surface properties first by UV irradiation, which induced the detachment of the outermost PEI layer, and by subsequent dipping into a PEI solution, which attached a new PEI layer. Finally, we successfully prepared photopatterned films with highly site-selective adsorption abilities by image-wise UV exposure. © 2008 American Chemical Society.

A novel spin-crossover molecular conductor, [Fe(qnal)2][Pd(dmit)2]5·acetone, was prepared and characterized. The crystal structural analyses of both the low- and high-temperature phases revealed that the supramolecular π-π interactions between the spin-crossover Fe(qnal)2 cations as well as the cation contraction play an important role in the uniaxial lattice deformation which will modulate the electrical conductivity of the conducting Pd(dmit)2 layer. Copyright © 2008 American Chemical Society.

Negatively charged gold nanoparticles (AuNPs) and a polyelectrolyte (PE) have been assembled alternately on a polystyrene (PS) colloid by a layer-by-layer (LBL) self-assembly technique to form three-dimensional (Au/PAH)4/(PSS/PAH)4 multilayer-coated PS spheres (Au/PE/PS multilayer spheres). The Au/PE/PS multilayer spheres have been used to modify a boron-doped diamond (BDD) electrode. Cyclic voltammetry is utilized to investigate the properties of the modified electrode in a 1.0M KCl solution that contains 5.0 × 10-3 M K3Fe(CN)6, and the result shows a dramatically decreased redox activity compared with the bare BDD electrode. The electrochemical behaviors of dopamine (DA) and ascorbic acid (AA) on the bare and modified BDD electrode are studied. The cyclic voltammetric studies indicate that the negatively charged, three-dimensional Au/PE/PS multilayer sphere-modified electrodes show high electrocatalytic activity and promote the oxidation of DA, whereas they inhibit the electrochemical reaction of AA, and can effectively be used to determine DA in the presence of AA with good selectivity. The detection limit of DA is 0.8 × 10-6M in a linear range from 5 × 10-6 to 100 × 10-6M in the presence of 1×10-3M AA. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.