Published papers

© 2019, Springer Science+Business Media, LLC, part of Springer Nature. Dendrimers can provide unique reaction space for sub-nano sized materials. Recently, we have demonstrated a luminous bismuth dendrimer and the on/off switching by stepwisely assembled bismuth units in a phenylazomethine dendrimers. In addition, formation of bismuth clusters was also demonstrated by the reduction of the bismuth salts assembled in the dendrimer. In this study, we have revealed the atomicity dependency about the reduction and oxidation potentials of the assembled bismuth complexes and clusters, respectively. The measurements were conducted by the electrochemical process of the bismuth assembled dendritic poly-phenylazomethines.

© 2019 Elsevier B.V. Palmitic acid, a model compound for palm oil mill effluent (POME), was eliminated from a water–ethanol solution using electrochemical oxidation with a boron-doped diamond (BDD) electrode. For a palmitic acid solution in a water–ethanol solution, chronoamperometry with a potential of +3.0 V (vs Ag/AgCl) showed a decrease in chemical oxygen demand (COD) of ~85.75% in 4 h, whereas at a higher potential (+10.0 V), the COD decreased to 75.76% in 1 h. It was noticed that the use of high potentials for up to 4 h caused the structure damaged of the BDD.

© the Owner Societies. Since a boron-doped diamond (BDD) exhibits excellent electrode properties such as wide potential window, low back-ground current, and high physical and chemical durability, it has been studied as an electrode material for various electrochemical applications. The electrochemical behavior of BDD depends on the surface termination, which can be easily converted by chemical reactions. Fluorine termination has attracted interest because it exhibits unique surface properties such as high hydrophobicity and a low coefficient of friction, and the electrochemical properties also drastically change. However, so far, it has not been elucidated why fluorinated BDD exhibits specific electrochemical properties. In this article, fluorine-terminated BDD was fabricated by a fluorine-containing plasma treatment, and the electrochemical properties were systematically investigated. Together with experiments, we have calculated the interfacial structures and electronic states of hydrogenated, oxygenated, and fluorinated BDD electrodes. As a result, fluorinated BDD showed lower electrochemical reactivity than hydrogenated and oxygenated BDD. Especially, electron transfer between anionic compound and fluorinated BDD was significantly suppressed. Considered together with theoretical calculations, this reactivity could be attributed to the larger interfacial band bending in fluorinated BDD and electrostatic interactions between BDD and redox species.

Copyright © (2018) by Chemical and Biological Microsystems Society. All rights reserved. Here we report an improved μTAS based on electrochemical measurements and microbeads sorting for screening of NAD(P)-dependent oxidoreductases. By using this system, we measured the activity of model enzymes immobilized on microbeads by detection of NADH with a boron-doped diamond (BDD) electrode in each compartment (∼30 nL) of the microfluidic system. Then, we recovered the magnetic microbeads or the droplets containing genes of enzymes with higher activity by magnetophoretic or dielectrophoretic sorting, respectively. Our μTAS should be useful for directed evolution of various NAD(P)-dependent oxidoreductases with high activity and stability in the future.

The electrogenerated chemiluminescence of luminol is a process by which light generation is triggered by adding hydrogen peroxide and then applying a suitable electrode potential. Here, we take this phenomenon one step forward by avoiding the addition of hydrogen peroxide using a smart combination of a boron-doped diamond electrode and a carbonate electrolyte to generate the hydrogen peroxide directly in situ. The reaction occurs because of the carbonate electrochemical oxidation to peroxydicarbonate and the following hydrolysis to hydrogen peroxide, which triggers the emission from luminol. The electrogenerated chemiluminescence emission has been optimized by an investigation of the applied potentials, the carbonate concentration, and the pH. Furthermore, these results have been used to shine a light on the reaction mechanisms. Because this method does not require the addition of hydrogen peroxide, it might find application in efforts to avoid instability of hydrogen peroxide or its interference with the analytes of interest.

Silicon carbide (SiC) has excellent properties such as chemical and physical stability, biocompatibility, and high thermal conductivity. However, electrical conductivity of SiC is not high enough for electrochemical applications, which has been a major challenge. Here, in order to improve the conductivity, we prepared boron-doped SiC (SiC:B) and evaluated the electrochemical properties. SiC and SiC:B were fabricated by a microwave plasma chemical vapor deposition method. Structural characterization revealed that the main phase of SiC:B is 3C–SiC where the concentration of doped boron could be controlled by tuning the growth conditions. Electrochemical properties were evaluated by cyclic voltammetry measurements, indicating that the reactivity and sensitivity of the SiC:B electrode was comparable of that of the glassy carbon electrode.

The oxidation of dopamine (DA) on a boron-doped diamond (BDD) electrode was investigated using in situ attenuated total reflection infrared spectroscopy (ATR-IR) and infrared reflection absorption spectroscopy (IRAS). Voltammogram showed multiple anodic/cathodic peaks for the oxidation/reduction of DA and its oxidized derivatives on the BDD electrode. The oxidation/reduction species on the surface and in solution were assigned using ATR-IR and IRAS, respectively. The anodic oxidation of DA promoted polymerization, and the polymerized DA (PDA) was continuously deposited on BDD without being reduced by potential cycles, which resulted in the irreversible behavior of the voltammogram. A decrease in the oxidation current of DA by potential cycles was due to the deposition of PDA. Some intermediate quinone species, such as dopaminequinone and dopaminechrome, were reversibly reduced to hydroquinone.

Methylcobalamin, which is used for the clinical treatment of patients with neuropathy, can have an impact on the sensorineural components associated with the cochlea, and it is possible that the auditory threshold in a certain population of patients with deafness may be recovered. Nonetheless, it remains uncertain whether the action site of methylcobalamin is localized inside or outside the cochlea and which cellular or tissue element is targeted by the drug. In the present work, we developed a method to realize in vivo real-time simultaneous examination of the drug kinetics in two separate locations using boron-doped diamond microelectrodes. First, the analytical performance of methylcobalamin was studied and the measurement protocol was optimized in vitro. Then, the optimized protocol was applied to carry out real-time measurements inside the cochlea and the leg muscle in live guinea pigs while systemically administering methylcobalamin. The results showed that the methylcobalamin concentration in the cochlea was below the limit of detection for the microelectrodes or the drug did not reach the cochlea, whereas the compound clearly reached the leg muscle.

Controlled surface functionalization of electrode materials is an important technique in various fields such as analytical chemistry, molecular electronics, and molecular recognition in biological systems. In this work, we report the control decoration of boron-doped diamond (BDD) electrodes by electrochemically driven copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition of alkyne and azide (e−CLICK) in which the catalyst is produced by electroreduction of copper(II) species. As the e−CLICK strategy enabled to tune the produced amount of the copper(I) catalyst electrochemically, the alkyne-terminated BDD electrodes were decorated with azide-terminated ferrocene in a controlled manner.

A stereoselective and electrocatalytic coupling reaction of isoeugenol has been reported for the first time in a 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)/boron-doped diamond (BDD) electrode system. This particular C-C bond formation and diastereoselectivity is driven by a solvate interaction between the radical species and another isoeugenol molecule. Due to an electrocatalytic cycle, only understoichiometric amounts of charge are necessary. Since electric current is directly employed as the oxidant, the reaction is metal and reagent-free. In addition, the electrolysis can be conducted in a very simple undivided beaker-type cell under constant current conditions. Therefore, the protocol is easy to use, suitable for scale-up, and inherently safe.

© 2018 Elsevier Ltd The electrochemical nitrate reduction by using boron-doped diamond (BDD) and copper (Cu) electrodes was investigated at various potentials. Product selectivity of nitrate reduction was strongly dependent on the applied potential for both electrodes. The highest selectivity of nitrogen gas production was obtained at −2.0 V (vs. Ag/AgCl) by using a BDD electrode with a faradaic efficiency as high as 45.2%. Compared with Cu electrode, nitrate reduction on BDD electrode occurred at more positive potential, and the production of nitrogen gas was larger. The transformation of surface-adsorbed nitrate into molecular nitrogen would be accelerated on BDD electrode with hindering nitrite production. In addition, low concentration of surface-adsorbed hydrogen on the BDD would also retard the ammonia generation, leading to increase in the selectivity of nitrogen gas formation. Meanwhile, BDD electrode could hinder the hydrogen evolution reaction, which enhanced the efficiency for nitrate reduction and decreased energy consumption. BDD electrode has excellent stability to remain better performance for reducing nitrate during electrolysis without any variation of surface morphology or chemical components.

© 2019 The Royal Society of Chemistry. Conductive diamond possesses unique features as compared to other solid electrodes, such as a wide electrochemical potential window, a low and stable background current, relatively rapid rates of electron-transfer for soluble redox systems without conventional pretreatment, long-term responses, stability, biocompatibility, and a rich surface chemistry. Conductive diamond microcrystalline and nanocrystalline films, structures and particles have been prepared using a variety of approaches. Given these highly desirable attributes, conductive diamond has found extensive use as an enabling electrode across a variety of fields encompassing chemical and biochemical sensing, environmental degradation, electrosynthesis, electrocatalysis, and energy storage and conversion. This review provides an overview of the fundamental properties and highlights recent progress and achievements in the growth of boron-doped (metal-like) and nitrogen and phosphorus-doped (semi-conducting) diamond and hydrogen-terminated undoped diamond electrodes. Applications in electroanalysis, environmental degradation, electrosynthesis electrocatalysis, and electrochemical energy storage are also discussed. Diamond electrochemical devices utilizing micro-scale, ultramicro-scale, and nano-scale electrodes as well as their counterpart arrays are viewed. The challenges and future research directions of conductive diamond are discussed and outlined. This review will be important and informative for chemists, biochemists, physicists, materials scientists, and engineers engaged in the use of these novel forms of carbon.

© 2020 The Royal Society of Chemistry. Stable and continuous biosensing of electroactive species in vivo has been achieved by using boron-doped diamond (BDD) electrodes owing to their outstanding electrochemical properties. However, the present problem in biosensing using BDD electrodes is how to specifically measure/detect the target molecules, including electrochemically inactive species. A possible solution is to fabricate an electrochemical aptamer-based (E-AB) sensor using a BDD electrode. In a preliminary investigation, we found that DNA aptamers strongly adsorb on the BDD surface and the aptamer-adsorbed BDD apparently worked as an E-AB sensor. The present study reports the performance of the aptamer-adsorbed BDD electrode as an E-AB sensor. Doxorubicin (DOX), a widely used chemotherapeutic, was chosen as a target molecule. The sensor could be prepared by just dipping BDD in an aptamer solution for only 30 min, and the electrochemical signals were dependent on the DOX concentration. The adsorption of DNA was strong enough for continuous measurements and even a sonication treatment. Such behaviors were not observed when using gold and glassy carbon electrodes. In a kinetic measurement, distortion by a sluggish response was observed for both association and dissociation phases, indicating that the interaction between DOX and the aptamer involves several kinetic processes. By fitting to a Langmuir isotherm, a limit of detection of 49 nM and a maximum detectable concentration of 2.3 μM were obtained. Although the sensitivity was lower than those of the well-established E-AB sensors of gold, the values are within a drug's therapeutic range. Overall, the present work demonstrates that a DNA aptamer and a BDD electrode is an effective combination for an E-AB sensor with stable sensitivity, and a wide variety of DNA aptamers can be applied without any special treatment.

Copyright © 2020 American Chemical Society. The development of a simple detection method with high sensitivity is essential for the diagnosis and surveillance of infectious diseases. Previously, we constructed a sensitive biosensor for the detection of pathological human influenza viruses using a boron-doped diamond electrode terminated with a sialyloligosaccharide receptor-mimic peptide that could bind to hemagglutinins involved in viral infection. Circulation of influenza induced by the avian virus in humans has become a major public health concern, and methods for the detection of avian viruses are urgently needed. Here, peptide density and dendrimer generation terminated on the electrode altered the efficiency of viral binding to the electrode surface, thus significantly enhancing charge-transfer resistance measured by electrochemical impedance spectroscopy. The peptide-terminated electrodes exhibited an excellent detection limit of less than one plaque-forming unit of seasonal H1N1 and H3N2 viruses. Furthermore, the improved electrode was detectable for avian viruses isolated from H5N3, H7N1, and H9N2, showing the potential for the detection of all subtypes of influenza A virus, including new subtypes. The peptide-based electrochemical architecture provided a promising approach to biosensors for ultrasensitive detection of pathogenic microorganisms.

© 2018 The Chemical Society of Japan It is well known that “diamond” has ultra-high hardness and low electrical conductivity. However, introducing dopants such as boron into the diamond lattice during growth can increase its conductivity. Boron-doped diamond (BDD) with high conductivity is attracting increasing attention as one of the next-generation of superior electrode materials. In particular, it is expected that BDD electrodes can help solve some of our environmental problems and also improve our quality of life through their use in biomedical devices. Here, in this article, recent developments in the electrochemical applications of boron-doped diamond (BDD) electrodes are introduced.

© 2019, Japanese Pharmacological Society. All rights reserved. Continuous and real-time measurement of local concentrations of systemically administered drugs in vivo must be crucial for pharmacological studies. Nevertheless, conventional methods require considerable samples quantity and have poor sampling rates. Additionally, they cannot determine how drug kinetics correlates with target function over time. Here, we describe a system with two different sensors. One is a needle-type microsensor composed of boron-doped diamond with a tip of ~40 μm in diameter, and the other is a glass microelectrode. We first tested bumetanide. This diuretic can induce deafness. In the guinea-pig cochlea injected intravenously with bumetanide, the changes of the drug concentration and the extracellular potential underlying hearing were simultaneously measured in real time. We further examined an antiepileptic drug lamotrigine in the rat brain, and tracked its kinetics and at the same time the local field potentials representing neuronal activity. The action of the anticancer reagent doxorubicin was also monitored in the cochlea. This microsensing system may be applied to analyze pharmacokinetics and pharmacodynamics of various drugs at local sites in vivo, and contribute to promoting the pharmacological researches.

© 17CBMS-0001. Here we report the development of a flow injection analysis system based on electrochemical measurements and dielectrophoresis for screening of NAD(P)-dependent oxidoreductases. In this system, the activity of enzyme which is immobilized on microbeads together with its encoding DNA can be measured with a boron-doped diamond (BDD) electrode in each compartment (~30 nL) of the microfluidic system, and the large droplets (~30 nL) containing genes of enzymes with higher activity can be recovered by dielectrophoretic sorting.

Nitrate contamination in groundwater requires efficient remediation to prevent adverse environmental impacts. This study illustrates the improvement in nitrate reduction process using copper modified BDD (Cu-BDD) with higher stability after annealing treatment. The highest values for nitrate reduction and the selectivity of nitrogen gas were about 71% and 45%, respectively, which were obtained using annealed Cu-BDD electrode. Annealing process promoted the homogeneity of copper oxides that consolidated the electrodeposited copper oxides on the surface of Cu-BDD to enhance the stability of electrode. Meanwhile, annealed Cu-BDD exhibited higher conductivity to facilitate nitrate reduction initiating at a more positive potential. Furthermore, cuprous ions and metallic Cu were formed during the annealing treatment, and had active chemical reaction with nitrate and excellent catalytic capability for the reaction, which efficiently enhanced either the nitrate reduction efficiency or the selectivity of nitrogen gas. The findings advance the current understanding on the enhancement of electrochemical stability and nitrate reduction performance using Cu-BDD after the annealing treatment, and also offer a promising technology for remediation of nitrate-contaminated groundwater.

The progression of corrosion in polycrystalline boron-doped diamond (BDD) thin film electrode is explored as the electrode undergoes high-current density anodic treatments with organic compounds. Micro-Raman spectroscopy and spectral mapping indicate that anodic corrosion is initiated by the conversion of sp3 diamond to amorphous sp2 carbon at the surface, which are then removed after longer anodic treatment. Polarized Raman analysis reveals that corrosion-induced changes on the surface are specific to (100)-grain facets and (111)-grain edges. X-ray photoelectron spectroscopic measurements suggest that carbonyl groups consequently form on these specific sites and act as an intermediate toward the etching of the surface. This process exposes and subsequently removes the subsurface boron atoms, thus reducing the doping density. The observed crystal grain orientation dependence of the corrosion process provides new insights toward a better understanding of degradation in BDD electrodes.