Published papers

Sensors rely on a plurality of transduction methods, and among the available selections, electrochemical techniques offer the peculiar advantage of an easy interfacing between biological recognition elements and electronic signal transduction processes. Furthermore, electrochemical devices are qualified for decentralized point-of-care testing as they can be easily downsized and made at low cost for a wide range of potential applications, for example biomedical or environmental. Electrochemical methods of transduction differ for the technique used, as it can be voltammetry, chronoamperometry, impedance spectroscopy, or electrochemiluminescence. The latter is peculiar among electrochemical techniques since in electrochemiluminescence the analytical signal is light emission, and this offers several advantages, mainly related to background suppression and detection limit, combined with fast measurement. This review introduces the principles of enzyme biosensors coupled with electrochemiluminescence transduction, summarises the research, and finally highlights the strategies to take full advantage of this detection method.

The detection of dopamine in the presence of norepinephrine using nafion-coated boron doped diamond (Nafion-BDD) electrodes was presented. An increase current signal for dopamine could be observed at around 0.75 V using Nafion-BDD, while a change in the current signal of norepinephrine that appears at similar potential was not observed. This might be due to electronegativity of the norepinephrine that is not positive enough to be attracted towards the nafion membrane, albeit neutral enough to pass through the membrane and undergo electrochemical oxidation. An optimization process including accumulation time of dopamine inside the nafion layer, solution of the pH, and nafion thickness was conducted to exploit the difference electrochemical behavior between those two catecholamines at the Nafion-BDD. Using an accumulation time of 300 s, solution pH of 7, and nafion thickness of 1.1 μm, dopamine's LOD was found to be 0.966 μM. Low-interference signal of norepinephrine to the dopamine could be observed with an excellent %recovery of dopamine in 5% range when the concentration of norepinephrine was 10 times lower compared to dopamine concentration.

Electrogenerated chemiluminescence, or electrochemiluminescence (ECL), is nowadays a powerful transduction method in electroanalysis, in particular regarding the application in clinical diagnostics. Indeed, its superior capability relies in the fruitful combination of electrochemical and photoluminescence properties. The research on efficient ECL luminophores has brought a wide range of molecules, form organic systems to inorganic complexes, however, despite this large pool of luminophores available, tris(2,2′-bipyridine)ruthenium (II) [Ru(bpy)3]2+ is still leading since the first report in 1972, in both academic research and commercially available systems. To acknowledge the outmost importance of this inorganic complex, here we report the photophysical and electrochemical properties of [Ru(bpy)3]2+ and its derivatives obtained by ligand design for application in ECL.

By means of an initial electrochemical carbon dioxide reduction reaction (eCO2RR), both the reaction current and Faradaic efficiency of the eCO2RR on boron-doped diamond (BDD) electrodes were significantly improved. Here, this effect is referred to as the self-activation of BDD. Generally, the generation of carbon dioxide radical anions (CO2•-) is the most recognized pathway leading to the formation of hydrocarbons and oxygenated products. However, the self-activation process enabled the eCO2RR to take place at a low potential, that is, a low energy, where CO2•- is hardly produced. In this work, we found that unidentate carbonate and carboxylic groups were identified as intermediates during self-activation. Increasing the amount of these intermediates via the self-activation process enhances the performance of eCO2RR. We further evaluated this effect in long-term experiments using a CO2 electrolyzer for formic acid production and found that the electrical-to-chemical energy conversion efficiency reached 50.2% after the BDD self-activation process.

Monitoring drug concentration in blood and reflecting this in the dosage are crucial for safe and effective drug treatment. Most drug assays are based on total concentrations of bound and unbound proteins in the serum, although only the unbound concentration causes beneficial and adverse events. Monitoring the unbound concentration alone is expected to provide a means for further optimisation of drug treatment. However, unbound concentration monitoring has not been routinely used for drug treatment due to the long analysis time and the high cost of conventional methods. Here, we have developed a rapid electrochemical method to determine the unbound concentration in ultrafiltered human serum using boron-doped diamond (BDD) electrodes. When the anticancer drug doxorubicin was used as the test drug, the catalytic doxorubicin-mediated reduction of dissolved oxygen provided a sensitive electrochemical signal, with a detection limit of 0.14 nM. In contrast, the sensitivity of glassy carbon (GC) was inferior under the same conditions due to interference from the dissolved oxygen reduction current. The signal background ratio (S/B) of BDD and GC was 11.5 (10 nM doxorubicin) and 1.1 (50 nM), respectively. The results show that a fast measurement time within ten seconds is possible in the clinical concentration range. Additionally, in the ultrafiltered human serum, the obtained values of unbound doxorubicin concentration showed good agreement with those quantified by conventional liquid chromatography-mass spectrometry. This approach has the potential for application in clinical settings where rapid and simple analysis methods would be beneficial.

The electrochemical reduction of carbon dioxide (CO2) has been attracting great interest in these days. In particular, the electrochemical production of formic acid from carbon dioxide in a halogen-free electrolyte is practically important for recently developed applications such as hydrogen carriers and fuel cells. In the present work, we have demonstrated highly selective electrochemical CO2 reduction in a halogen-free electrolyte by an "activation"process which involves an initial electrochemical CO2 reduction reaction at a boron-doped diamond (BDD) electrode. The BDD activation increased the Faradaic efficiency of formic acid from 10 to 90%. A mechanistic study on the BDD activation is presented, which can explain the drastic change of reaction selectivity from the perspective of reducing the energy of electron transfer from the BDD electrode and the mass transport of CO2 molecules to the electrode surface.

Carbon capture, utilization, and storage (CCUS) have been attracting much attention as an initiative to achieve carbon neutrality. In the capture and storage strategy, amines are widely used for highly efficient separation and capturing of CO2since amines react with CO2to form carbamates. In the utilization strategy, CO2electroreduction is a promising method to convert CO2into value-added compounds because reaction conditions are relatively mild and easily controlled. In this work, toward combining CO2capture and storage technologies and CO2electroreduction, we focused on amine modification of the electrode surface, in which boron-doped diamond (BDD) was chosen as a sustainable electrode material. CO2electroreduction using the amine-modified BDD was performed, and an applied potential dependence of the product selectivity was examined. In situ attenuated total reflectance-infrared measurements showed that the peak intensity of the stretching vibration of the carbonyl group at around 1640 cm-1decreased as applied potentials became more negative. The effect of amine modification of the BDD surface lies in the formation of a C-N bond during CO2electroreduction, resulting in the enhancement of the selectivity of CO production up to 8 times compared to the unmodified BDD.

Boron-doped diamond (BDD) electrodes have been attracting attention as superior electrode materials for electrochemical sensing applications. Here, we focused on applications of the BDD electrodes to electrochemical gas sensing especially dissolved gas in aqueous solution. This article discusses arsine, hydrogen sulfide, nitrogen dioxide gas for environmental sensing, and oxygen in the blood for biomedical sensing. The analytical performances suggest that BDD electrodes are more than adequate for determining the concentration of these gas species.

Boron-doped diamond (BDD) electrodes are next generation electrode materials and their electrochemical applications have been actively developed in recent years. They are expected to be useful electrode materials for improving the environment and for bio-medical applications. Here, examples of practical applications as electrochemical sensors, the development of in vivo real time measurements, and electrochemical organic synthesis using BDD electrodes are briefly introduced. In the second part, our recent work on the production of useful chemicals by means of the electrochemical reduction of CO2 using BDD electrodes is described. The work has attracted particular attention for its potential contribution to carbon neutrality and carbon recycling.

As a working electrode, boron-doped diamond (BDD) has been studied in detail in electrochemical processes because of its superior electrochemical properties. However, these characteristics have rarely been mentioned when BDD is used as a quasi-reference electrode (QRE). Herein, we conducted a systematic investigation on BDD electrodes, with different boron-doping levels (1 and 0.1%) and different surface terminations (hydrogen and oxygen) for their application as a QRE. A BDD electrode with 1% boron and a hydrogen-terminated surface achieved the best stability. Its open-circuit potential (OCP) exhibited less than 100 mV of potential drift over 6000 s and showed a minuscule half-wave potential difference (E1/2) of 0.0037 V in 0.1 mM K3[Fe(CN)6]/1 M KCl solution before and after the OCP measurement. Based on these observations, anions are found to contribute to the potential, which we preliminarily speculate as related to the capacitance caused by electrostatic adsorption on the positively charged hydrogen-terminated surface. The repeatability of measurement was verified through continuous cyclic voltammetry tests in 0.1 mM K3[Fe(CN)6]/1 M KCl, showing a maximum E1/2 difference of 0.042 V. The contribution of the redox couples was excluded, and the repeatability was considered to originate from its surface stability. Finally, a linear response of the optimized BDD as a QRE was validated (R2 > 0.99) by determination of free chlorine and dopamine concentrations, respectively. These results consolidate the existing fundamental research on BDD electrodes and promote the possibility of its application as a QRE in harsh environments or in vivo biological monitoring.

We report on the first observation of the production of C2/C3 species from the electrochemical reduction of CO2 at the surfaces of copper-modified boron-doped diamond (Cu-BDD) electrodes in aqueous media at room temperature and ambient pressure. The product distribution is dependent on the amount of deposited Cu and the applied potential. At low potential, −1.0 V (vs. Ag/AgCl), ethanol was observed as the main product with acetaldehyde and acetone as side products. The highest faradaic efficiencies obtained for ethanol, acetaldehyde and acetone were 42.4%, 13.7% and 7%, respectively. The Cu particles on the surfaces of the BDD electrodes remained stable, showing insignificant differences after the CO2 electroreduction process under these particular conditions. The efficiency dropped with increasing Cu deposition time and at high reduction potentials. Moreover, we present comparisons with a Cu plate and Cu-modified glassy carbon as working electrodes under the same conditions, which explains the specific behavior of the CO2 reduction process on the Cu-BDD electrode.

High faradaic efficiencies can be achieved in the production of formic acid (HCOOH) by metal electrodes, such as Sn or Pb, in the electrochemical reduction of carbon dioxide (CO2). However, the stability and environmental load in using them are problematic. The electrochemical reduction of CO2 to HCOOH was investigated in a flow cell using boron-doped diamond (BDD) electrodes. BDD electrodes have superior electrochemical properties to metal electrodes, and, moreover, are highly durable. The faradaic efficiency for the production of HCOOH was as high as 94.7%. Furthermore, the selectivity for the production of HCOOH was more than 99%. The rate of the production was increased to 473μmolm-2s-1 at a current density of 15mAcm-2 with a faradaic efficiency of 61%. The faradaic efficiency and the production rate are almost the same as or larger than those achieved using Sn and Pb electrodes. Furthermore, the stability of the BDD electrodes was confirmed by 24h operation.

© 2019 American Chemical Society. The main product obtained by electrochemical reduction of CO 2 depends on the electrode material, and in many cases the Faradaic efficiency for this is determined by the electrolyte. Only a few investigations in which attempts to produce different products from the same electrode material have been done so far. In this work, we focus on boron-doped diamond (BDD) electrodes with which plentiful amounts of formic acid and small amounts of carbon monoxide have been produced. By optimizing certain parameters and conditions used in the electrochemical process with BDD electrodes, such as the electrolyte, the boron concentration of the BDD electrode, and the applied potential, we were able to control the selectivity and efficiency with which carbon monoxide is produced. On one hand, with a BDD electrode with 1% boron used for the cathode and KClO 4 for the catholyte, the selectivity for producing carbon monoxide was high. On the other hand, with a BDD electrode with 0.1% boron used for the cathode and KCl for the catholyte, the production of formic acid was the most evident. In situ attenuated total reflectance-infrared (ATR-IR) measurements during electrolysis showed that CO 2·- intermediates were adsorbed on the BDD surface in the KClO 4 aqueous solution. Here, switchable product selectivity was achieved when reducing CO 2 using BDD electrodes.

© 2018 Elsevier Ltd Transmission electron microscopy (TEM) coupled with electron energy loss spectroscopy (EELS), and first principles calculations of EEL spectra were utilized to elucidate the relationship between the microscopic structure and the electrochemical properties of heavily boron-doped diamond (h-BDD). The electrochemical properties of h-BDD containing 1 at.% and 3 at.% boron are very different. TEM observations showed that 1 at.% h-BDD consists of small densely packed diamond crystallites, while 3 at.% h-BDD contains small voids and a graphite phase partly along the grain boundaries. The EEL spectrum of the grain interior in 1 at.% h-BDD and comparison of this with a theoretical spectrum shows that the boron atoms are mostly dispersed as single isolated substitutional atoms on diamond lattice sites in the grain interior and that only a small amount of sp2-bonded carbon is present. In contrast, in the grain interior of 3 at.% h-BDD, the boron atoms are mostly associated with nearest neighbor boron pairs, and consequently sp2-bonded carbon is formed. Thus, the local structure has a significant effect on the amount of sp2-bonded carbon. The quite different electrochemical properties of the samples are ascribed to the amount of sp2-bonding arising from the different local structures.

© The Electrochemical Society of Japan, All rights reserved. The utilization of boron doped diamond (BDD) as an electrode material for the electrochemical reduction of CO 2 has been studied in recent decades. Its stability and ability to suppress hydrogen evolution makes it an attractive choice for the electrochemical reduction of CO 2 . It has been confirmed that, when using a bare BDD electrode, very high selectivity and productivity can be achieved in the production of formic acid. Moreover, by modifying the surface of a BDD electrode with copper (Cu) particles, we have been able to produce compounds with a high number of carbon atoms. In this article, we summarize the results of our work on the electrochemical reduction of CO 2 using BDD electrodes, with the specific aim of the producing compounds with a high number of carbon atoms.

© 2019 The Royal Society of Chemistry. The electrochemical oxidation of hydroxide ions using boron-doped diamond (BDD) electrodes in weak basic solutions was examined. Using simple linear sweep voltammetry (LSV), a well-shaped peak originating from the oxidation of hydroxide ions involving a CE mechanism was observed at ∼1.30 V versus a Ag/AgCl reference electrode in 20 mM H3PO4 solutions with hydroxide ion concentrations ranging from 0.1 to 10 mM. Compared to a NaOH solution with the same hydroxide ion concentration, the peak current in the phosphate solution was found to be higher due to the buffering capability of the phosphate solution, which maintains the hydroxide ion concentration, making it possible to provide more hydroxide ions to the surface of the electrode. The peak was found to depend not only on the hydroxide ion concentration, but also on the phosphate concentration, confirming that the origin of the peak was due to oxidation of the hydroxide ions enhanced by the buffering capability of the weak basic solution. These results further promote the use of BDD electrodes for measuring hydroxide ion concentration, and offer the possibility of directly measuring the buffer capacity of a solution.

© 2020 Elsevier B.V. We studied an oxidation reaction of dissolved hydrogen sulfide using boron doped diamond (BDD) electrodes and 0.1 mol Lˉ1 KClO4 as an electrolyte. Oxidation of H2S and HSˉ started at potentials of +1.7 V and + 0.5 V (vs. Ag/AgCl), respectively. In order to study the oxidation behavior, the effects of pH and the scan rate were investigated. Moreover, as demonstrated by X-ray photoelectron spectroscopy, no sulfur fouling was detected on the BDD surface. A linear calibration curve was observed in the concentration range of 0.08–2.34 mg Lˉ1 (r2 = 0.99) with a detection limit of 0.82 μg Lˉ1 (S/N = 3). In addition, an interference test with CO2 was performed, which showed there was no significant interference to the sensor.

Copyright © 2020 American Chemical Society. Unexpected phenomena displayed by low-boron-doped diamond (BDD) electrodes are disclosed in the present work. Generally, the presence of sp2 nondiamond carbon impurities in BDD electrodes causes undesirable electrochemical properties, such as a reduced potential window and increased background current, etc. However, we found that the potential window and redox reaction in normally doped (1%) BDD and low-doped (0.1%) BDD exhibited opposite tendencies depending on the extent of sp2 carbon. Moreover, we found that contrary to the usual expectations, low-doped BDD containing sp2 carbon hinders electron transfer, whereas in line with expectations, normally doped BDD containing sp2 exhibits enhanced electron transfer. Surface analyses by X-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) and electrochemical methods are utilized to explain these unusual phenomena. This work indicates that the electrochemical properties of low-doped BDD containing sp2 might be due partially to the high level of surface oxygen, the large work function, the low carrier density, and the existence of different types of sp2 carbon.

Boron-doped diamond (BDD) is most often grown by chemical vapor deposition (CVD) in polycrystalline form, where the electrochemical response is averaged over the whole surface. Deconvoluting the impact of crystal orientation, surface termination, and boron-doped concentration on the electrochemical response is extremely challenging. To tackle this problem, we use CVD to grow isolated single-crystal microparticles of BDD with the crystal facets (100, square-shaped) and (111, triangle-shaped) exposed and combine with hopping mode scanning electrochemical cell microscopy (HM-SECCM) for electrochemical interrogation of the individual crystal faces (planar and nonplanar). Measurements are made on both hydrogen- (H-) and oxygen (O-)-terminated single-crystal facets with two different redox mediators, [Ru(NH3)6]3+/2+ and Fe(CN)64-/3-. Extraction of the half-wave potential from linear sweep and cyclic voltammetric experiments at all measurement (pixel) points shows unequivocally that electron transfer is faster at the H-terminated (111) surface than at the H-terminated (100) face, attributed to boron dopant differences. The most dramatic differences were seen for [Ru(NH3)6]3+/2+ when comparing the O-terminated (100) surface to the H-terminated (100) face. Removal of the H-surface conductivity layer and a potential-dependent density of states were thought to be responsible for the behavior observed. Finally, a bimodal distribution in the electrochemical activity on the as-grown H-terminated polycrystalline BDD electrode is attributed to the dominance of differently doped (100) and (111) facets in the material.

Nickel hydroxide nanoparticles [Ni(OH)2-NPs] synthesized by a complexation-precipitation method under hydrothermal conditions were employed as a probe in immunochromatographic strip tests for the selective detection of melamine. The characterization of Ni(OH) -NPs and their conjugation to anti-melamine antibody (anti-MEL) were performed using a UV- visible spectrophotometer, Fourier transform infrared (FTIR) spectroscopy, and TEM. On the basis of the green line intensity, the strip test can selectively detect melamine at a minimum concentration of 25 ppm. Our results suggest that this system is promising for the quantitative detection of melamine. 2