Published papers

Electrogenerated chemiluminescence (ECL) has recently become one of the most prominent and well-established transducers for immunoassay techniques. ECL relates a luminophore concentration in solution with the emission of light triggered by an electrochemical stimulus. ECL immunoassay (ECLIA) performance depends on the parameters of its light generation, including the luminophore, the species that emit light called labels in ECLIA; co-reactants, which are added reagents that support the luminophore to undergo the excited state; electrodes, which are the place for the ECL reactions to take place; and the format of the immunoassay. This review discusses the behaviour of ECLIA parameters, the required instrumentations, and some important examples of detections based on ECLIA.

Electrochemical CO2 reduction using an intermittent flow cell system with boron-doped diamond (BDD) as the working electrode is presented. A stop-start motion of the flow conditions in the intermittent cell is created using a piston pump, and this considerably increases the rate of electrochemical conversion of CO2 to HCOOH compared to a continuous flow system. The system works by stopping the flow of the electrolytes at a controlled frequency, which allows for sufficient time for more CO2 anion radicals (intermediate species) to be reduced into HCOOH instead of being washed away from the surface of the electrode. The findings presented here provide an important basis from which the design of CO2 reduction systems for industrial-scale applications can be started.

Doped diamond electrodes have attracted significant attention for decades owing to their excellent physical and electrochemical properties. However, direct experimental observation of dopant effects on the diamond surface has not been available until now. Here, low-temperature scanning tunneling microscopy is utilized to investigate the atomic-scale morphology and electronic structures of (100)- and (111)-oriented boron-doped diamond (BDD) electrodes. Graphitized domains of a few nanometers are shown to manifest the effects of boron dopants on the BDD surface. Confirmed by first-principles calculations, local density of states measurements reveal that the electronic structure of these features is characterized by in-gap states induced by boron-related lattice deformation. The dopant-related graphitization is uniquely observed in BDD (111), which explains its electrochemical superiority over the (100) facet. These experimental observations provide atomic-scale information about the role of dopants in modulating the conductivity of diamond, as well as, possibly, other functional doped materials.

The carbon-based electrode has been widely used for electrochemical analysis and synthesis. It is relatively inert for hydrogen evolution in the negative potential range, which is suitable for CO2 electrochemical reduction. In improving the catalytic activity, a modification of metal particles is commonly used on its surface. Various metal particles have been reported with multiple modification methods, including electrochemical and physical methods. In this report, the utilization of different metal particles, including metal oxide, metal hydroxide, and metal complexes, which are modified on carbon-based electrodes for CO2 electrochemical reduction application is specifically reviewed. This review is expected to provide comprehensive information on related topics.

A micro-band boron-doped diamond (BDD) electrode was prepared by sealing a piece of BDD film with an area of 1.11×10-7 m2 between two insulating plates, one Teflon and one silicon rubber, to form sandwich-like layers, so the surface area could be investigated. The micro-band BDD was combined with capillary zone electrophoresis as an electrode for the simultaneous detection of adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) in a solution. These adenosine phosphates can be separated with a 0.3 m-long fused silica capillary using Britton–Robinson buffers at pH 2.0. Current in the concentration range of 0.1 to 2.0 mM were linear with the limits of detection of 0.004 μM, 0.006 μM, and 0.011 μM for AMP, ADP, and ATP, respectively. A comparison with an unmodified BDD as the detector in the same electrophoresis system showed that the micro-band generated better limits of detection (LODs) than the macroelectrode. This method was successfully applied to human urine samples injected with three adenosine phosphates, as well as adenine and guanine, which can be well-separated with recovery percentages of adenine, guanine, AMP, ADP, and ATP of 99.2%, 102.5%, 107.4%, 107.7%, and 105.4%, respectively.

Modification of boron-doped diamond (BDD) with gold-palladium nanoparticles (Au@PdNPs) was successfully performed. Prior to the modification, BDD was modified with allylamine to provide active sites for the attachment of nanoparticles, while the synthesis of Au@PdNPs was performed by chemical reduction of a palladium salt solution in a colloidal solution of gold nanoparticles. Characterization using TEM images showed that by controlling the palladium concentration, flower and core-shell shaped Au@PdNPs can be prepared. XPS studies confirmed that the nanoparticles with a flower shape could be attached better on the BDD surface. The Au@PdNPs-modified BDD (Au@PdNPs-BDD) electrodes were then examined for the oxygen reduction reaction in comparison with gold and palladium-based electrodes. One order higher current response was observed at Au@PdNPs-BDD compared to AuNPs-BDD, indicating the contribution of palladium in the oxygen reduction reaction. Good linearity with comparable limits of detection suggested that Au@PdNPs-BDD electrodes are promising for use as oxygen sensors. Furthermore, their application as BOD sensors was demonstrated.

A series of [FeII(L)2](BF4)2 compounds were structurally and physically characterized (L = 2,6-bis(2-methylthiazol-4-yl)pyridine). A crystal structure phase transformation from dihydrate compound 1 to anhydrous compound 3 through partially hydrated compounds 2 and 2′ upon dehydration was found. Compounds 1 and 3 exhibited a gradual spin crossover (SCO) conversion, whereas compounds 2 and 2′ demonstrated two-step and one-step abrupt SCO transitions, respectively. An X-ray single-crystal structural analysis revealed that one-dimensional and two-dimensional Fe cation networks linked by π stacking and sulfur-sulfur interactions were formed in 1 and 3, respectively. A thermodynamic analysis of the magnetic susceptibility for 1, 2′, and 3 suggests that the enthalpy differences may govern SCO transition behaviors in the polymorphic compounds 2′ and 3. A structural comparison between 1 and 3 indicates that the SCO behavior variations and crystal structure transformation in the present [FeII(L)2](BF4)2 compounds can be interpreted by the relationship between the lattice enthalpies mainly arising from Coulomb interactions between the Fe cations and BF4 anions as in typical ionic crystals.

© 2018 Elsevier B.V. Boron-doped diamond (BDD) electrodes have been applied on the electrochemical reduction of CO2. Although boron doping level can strongly affect the electrochemical properties of BDD electrodes, there are, so far, no reports about the effect of doping level on the electrochemical reduction of CO2 using BDD electrodes. Here, we investigated the relationship between boron content of BDD electrodes and the products of CO2 reduction. We prepared five kinds of BDD electrodes with various boron contents (0.01%, 0.1%, 0.5%, 1%, and 2%). The highest faradaic efficiency for producing formic acid was achieved by using a BDD electrode with the boron content of 0.1%, and the faradaic efficiency for hydrogen evolution increased with increasing boron content due to narrower potential window of BDD with higher boron content. On the other hand, the faradaic efficiency for producing CO, which was a side product, slightly increased with increasing boron content. This trend suggested that the adsorbability of CO2 and its intermediates could be altered by controlling boron content. The research opens new insights for design and control of boron-doped diamond for the electrochemical reduction of CO2.

© 2019 The Royal Society of Chemistry. Ceria was deposited onto boron doped polycrystalline diamond (BDD) cathodes, through electrochemically induced precipitation from nitrate-based solutions. The deposits were characterized using SEM-EDS, HRTEM, XRD and XPS. The morphology, thickness and composition of ceria films, which besides CeO2 contained Ce(OH)3 when prepared at very negative potential, were controlled by tuning the deposition parameters. Thin Ce(OH)3-free ceria films allowed CO2 electrochemical reduction at overpotentials below 50 mV, yielding formic acid with faradaic yield higher than 40% and stable performance for many hours. Ceria seemed to act as a co-catalyst that activated CO2 for reduction at the H-terminated BDD surface, because comparable results were not obtained with ceria-coated glassy carbon electrodes.

© 2020 The Authors The effect of sp2 carbon within a boron-doped diamond (BDD) electrode on the electrochemical reduction of CO2 is investigated for the first time. With increasing sp2 content, the Faradaic efficiency for the production of hydrogen (H2) under constant current density increases while that for the production of formic acid (HCOOH) decreases. Moreover, favorable electrolysis conditions for producing HCOOH shift in the negative potential direction with increasing sp2 content. This phenomenon is ascribed to the presence of adsorption sites on the sp2 carbon. This work provides guidance for selectively controlling the reduction of CO2 by adjusting the distribution of carbonaceous species in the BDD electrode.

Natural products have played a significant role not only in discovery of drugs but also in development of organic chemistry by providing the synthetic challenges. Inspired by biosynthesis where enzymes catalyze a multi-step reaction, we have investigated the natural product synthesis utilizing electrochemical reactions as the key step. Electrochemical organic synthesis, so-called electro-organic synthesis, enables to control the reactivity of substrates simply by tuning electrolysis conditions. In this Personal Account, we overview the recent progress of our research projects about natural product synthesis, in which anodic oxidation of phenol compounds affords the important frameworks such as diaryl ether, spirodienone, and spiroisoxazoline.

We fabricated a CO2 electrolyzer in order to investigate the energy requirements and the electrical-to-chemical energy conversion efficiency obtained when using boron-doped diamond as the cathode. The main product in the electrochemical reduction of CO2 using a boron-doped diamond electrode is formic acid, with a faradaic efficiency of 96%. The electrical-to-chemical energy conversion efficiency was investigated at various bias voltages, and it reached 43%, very close to the predicted maximum value, at a cell voltage of 3 V. If the secondary products, hydrogen and carbon monoxide, are also considered, the total electrical-to-chemical energy conversion efficiency was as much as 45%. This journal is

Hearing loss affects >5% of the global population and therefore, has a great social and clinical impact. Sensorineural hearing loss, which can be caused by different factors, such as acoustic trauma, aging, and administration of certain classes of drugs, stems primarily from a dysfunction of the cochlea in the inner ear. Few therapeutic strategies against sensorineural hearing loss are available. To develop effective treatments for this disease, it is crucial to precisely determine the behavior of ototoxic and therapeutic agents in the microenvironment of the cochlea in live animals. Since the 1980s, a number of studies have addressed this issue by different methodologies. However, there is much less information on pharmacokinetics in the cochlea than that in other organs; the delay in ontological pharmacology is likely due to technical difficulties with accessing the cochlea, a tiny organ that is encased with a bony wall and has a fine and complicated internal structure. In this review, we not only summarize the observations and insights obtained in classic and recent studies on pharmacokinetics in the cochlea but also describe relevant analytical techniques, with their strengths, limitations, and prospects.

The electrochemical behavior of oxygen (O2) in blood was studied using boron-doped diamond (BDD) electrodes. Cyclic voltammogram of O2 in a 0.1 M phosphate buffer solution solution containing 1 × 10-6 M of bovine hemoglobin exhibits a reduction peak at -1.4 V (vs Ag/AgCl). Moreover, the scan rate dependence was investigated to study the reduction reaction mechanism, which was attributable to the reduction of O2 to H2O2 via two electrons. A linear calibration curve was observed in the concentration range of 86.88-314.63 mg L-1 (R2 = 0.99) with a detection limit of 1.0 mg L-1 (S/B = 3). The analytical performance was better than those with glassy carbon or platinum electrodes as the working electrode. In addition, an application to bovine blood was performed. The O2 concentration in the blood measured on the BDD electrodes was compared to that measured using an OxyLite Pro fiber-optic oxygen sensor device. Both methods gave similar values of the O2 concentration in the range of ∼40 to 150 mmHg. This result confirms that BDD electrodes could potentially be used to detect the O2 concentration in blood.

Boron-doped diamond (BDD) has attracted much attention in semi-/superconductor physics and electrochemistry, where the surface structures and electronic states play crucial roles. Herein, we systematically examine the structural and electronic properties of the unterminated and H-terminated diamond(111) surfaces by using density functional theory calculations, and the effect of the boron position on them. The surface energy increases compared to that of the undoped case when the boron is located at a deeper position in the diamond bulk, which indicates that boron near the surface can facilitate the surface stability of the BDD in addition to the H-termination. Moreover, the surface energy and projected density of state analyses suggest that the boron can enhance the graphitization of the pristine (ideal) unterminated (111) surface thanks to the alternative sp2-sp3 arrangement on that surface. Finally, we found that surface electronic states depend on the boron's position, i.e., the Fermi energy (EF) is located around the mid-gap position when the boron lies near the surface, instead of showing a p-type semiconductor behavior where the EF lies closer to the valence band maximum. This journal is

Electrochemiluminescence (ECL) is a powerful transduction technique where light emission from a molecular species is triggered by an electrochemical reaction. Application to biosensors has led to a wide range of electroanalytical methods with particular impact on clinical analysis for diagnostic and therapeutic monitoring. Therefore, the quest for increasing the sensitivity while maintaining reproducible and easy procedures has brought investigations and innovations in (i) electrode materials, (ii) luminophores, and (iii) reagents. Particularly, the ECL signal is strongly affected by the electrode material and its surface modification during the ECL experiments. Here, we exploit boron-doped diamond (BDD) as an electrode material in microbead-based ECL immunoassay to be compared with the approach used in commercial instrumentation. We conducted a careful characterization of ECL signals from a tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+)/tri-n-propylamine (TPrA) system, both homogeneous (i.e., free diffusing Ru(bpy)32+) and heterogeneous (i.e., Ru(bpy)32+bound on microbeads). We investigated the methods to promote TPrA oxidation, which led to the enhancement of ECL intensity, and the results revealed that the BDD surface properties greatly affect the ECL emission, so it does the addition of neutral, cationic, or anionic surfactants. Our results from homogeneous and heterogeneous microbead-based ECL show opposite outcomes, which have practical consequences in ECL optimization. In conclusion, by using Ru(bpy)32+-labeled immunoglobulins bound on microbeads, the ECL resulted in an increase of 70% and a double signal-to-noise ratio compared to platinum electrodes, which are actually used in commercial instrumentation for clinical analysis. This research infers that microbead-based ECL immunoassays with a higher sensitivity can be realized by BDD.

Bimetallic copper-gold (Cu@Au) nanoparticles were synthesized and utilised to modify boron-doped diamond (BDD) electrodes. Nanorod particles with a diameter size of around 10 nm and a length of around 20 nm were successfully synthesized. These nanoparticles were then attached to the BDD surface by using allylamine as the bridge. Comparison among the BDD modified with Cu@Au and individual gold nanoparticles showed that Cu@Au nanoparticles created around 3 times higher gold coverage on the BDD surface than normal gold nanoparticles. It was also found that the use of allylamine as the bridge can attach more gold than copper nanoparticles. Moreover, around two times higher current responses of oxygen reduction reaction were observed at Cu@Au-modified BDD. Good linearity in a concentration range from 2 to 9 ppm could be achieved with a sensitivity of 0.0138 mA ppm-1 and limit detection of 1.98 ppm. An application of the modified BDD for a biochemical oxygen demand (BOD) sensor using Rhodotorula mucilaginosa UICC Y-181 as the biosensing agent was also demonstrated with glucose solutions as the solution model. Sensitivity equivalent to 17.4 μA mM-1 BOD could be achieved. The system showed good stability with an RSD of 3.45% in 10 measurements. This journal is

Electrogenerated chemiluminescence (ECL) is a phenomenon of light emission from a molecular species that is triggered by an electrochemical reaction. As with many electrochemical systems, ECL is highly dependent on the electrode material and its surface state. Boron-doped diamond (BDD) has been applied for ECL, however, thoughtful investigation remains scarce. In particular, a peculiar feature of BDD is the tuning of its properties by changing the amount of boron doping which in turn affects the electrochemical response. Here, we summarize the results from the most important ECL systems, such as Ru(bpy)32+(bpy = 2,2′-bipyridine)/tri-n-propylamine (TPrA), Ru(bpy)32+/S2O82-, Ru(bpy)32+/SO42-, Ru(bpy)32+/CO32-, and the luminol/CO32-system, by using BDD and correlating the doping level to the ECL response. We showed that the most suitable boron doping level and surface state are highly dependent on the ECL system investigated, highlighting the importance of the right choice of the BDD electrode. While focused on ECL systems, these results offer a general interpretation and might be adapted to different electrochemical systems where BDD finds application.

Band engineering with a quantum size effect is proposed to be utilized to design photocatalytic activity for the conversion of organic compounds. Subnanometer WO3 quantum dots (QDs) are spontaneously produced with the enhancement of the photocatalytic activity in a mesoporous silica matrix by preliminary photochemical dissolution. An appropriate upshift of the conduction band of subnanometer WO3 QDs stabilized by the coverage with the surface WO bonds promotes the efficient conversion of benzene to phenol without decomposition of the product into CO2 under ultraviolet illumination.

Boron-doped diamond (BDD) electrodes are being increasingly investigated for application to electrochemical CO2 reduction. Previous, studies have mainly focused on microcrystalline (MC) BDD electrodes. In our study, we present an analysis of electrochemical CO2 reduction using sub-microcrystalline (SMC) BDD electrodes with different boron doping concentrations (0.28%, 0.11% and 0.03%). Unlike the microcrystalline case, these synthetic SMC BDD films with high sp2-bonded carbon do not show a boron-concentration dependence in terms of the activity of CO2 reduction to form formic acid (HCOOH). All the electrodes enabled efficient CO2 reduction at close to the maximum Faradaic efficiency for HCOOH in the range of 70% to 80%. From our observations, it is suggested that the sp2-bonded carbon should be crucial for the CO2 reduction. The results are hoped to enable a relaxation on the restrictions on the use of BDD electrodes towards industrial CO2 reduction application.