Electroanalysis is a way to detect analytes by measuring the current or potential on an electrode interface during a redox reaction. However, analytes that can be detected by the methods at conventional electrode materials have been limited due to a narrow measurable potential range and insufficient sensitivity for trace analytes. This article reviews our recently developed nanocarbon film electrodes for detecting trace amounts of various analytes. We have been studying nanocarbon film electrodes formed by electron cyclotron resonance sputtering or an unbalanced magnetron sputtering method. The film provides a nanocrystalline sp2 and sp3 mixed bond structure with an atomically flat surface (surface roughness of 0.05 – 0.1 nm) and high conductivity without doping. The film electrode has excellent properties, including a low background current, a wide electrochemical potential window, and little surface fouling, while maintaining relatively high electrode activity. These characteristics allow the detection of various analytes, especially ultratrace amounts of biomolecules. The nanocarbon film surface can be also easily modified with other atoms (oxygen or fluorine) without losing its ultraflatness that provides various nanocarbon film electrodes with hydrophilic and/or hydrophobic surfaces. For example, the hydrophilic nanocarbon film electrode can quantitatively measure various biomolecules (e.g., all DNA bases and cerebral gliotransmitter), which are difficult to measure at conventional carbon electrodes. In contrast, a fluorinated nanocarbon film is successfully used for the selective detection of lipophilic antioxidants (vitamin E) in combination with bicontinuous microemulsion. Moreover, we developed a new carbon film electrode material with surface nanostructures to realize efficient direct electron transfer (DET) with enzymes that can construct DET-type biosensors. Our study has expanded the possibility using electrochemical methods, and is expected to be applied to many practical measurement devices. These could find applications in various fields, such as drinks, foods, environmental and biochemical substances.
In organic semiconductor materials, investigating the energy levels is very important. For example, the combination of the donor’s and acceptor’s energy levels affects the performance of organic solar cells (OSCs). The HOMO and LUMO levels are generally determined by cyclic voltammetry or differential plus voltammetry, which require the solution state. However, these methods are influenced by the purity, solvent, solubility, vibration, and temperature. In this work, we employed photoemission yield spectroscopy and UV-vis-NIR spectroscopy in the thin-film state to measure the energy levels of magnesium porphyrin derivatives for OSCs. The results explained that the energy levels were correlated with a substituent introduced in the porphyrin core. In the case of electron-withdrawing substituent porphyrin, the HOMO and LUMO levels were lowest and the HOMO-LUMO gap was narrowest. On the other hand, electron-donating substituent porphyrin showed high-energy levels and a wide energy band gap. It is noteworthy that the energy levels were lower and the band gaps were narrower in the thin-film state compared with the solution state. This result explains that strong π-stacking derived from intermolecular interaction in thin films. We concluded that measurements of the energy levels in thin film state by PYS and UV-vis-NIR spectroscopy are beneficial for investigating organic semiconductor materials.
Scanning electrochemical microscopy allows for the detection and mapping of redox species near sample surfaces. In this paper, studies on the electrochemical characterization of embryos, embryoid bodies, and multicellular spheroids are reviewed. The mass-transfer rate on a spherical sample was evaluated based on spherical diffusion theory to study respiration activity and enzymatic activities including alkaline phosphatase and beta- galactosidase. The respiration rate of a single embryo has been applied for monitoring the developmental process and characterization of the embryo quality of individual samples, by combining time-laps microscopic observation and high-throughput gene-expression analysis. The respiration and alkaline phosphatase activities of individual embryoid body samples have been measured to evaluate the developmental potentials of individual samples. Electrochemically monitored beta galactosidase activity was applied to characterize the senescence of a multi-cellular spheroid.
Electrogenerated chemiluminescence can be seen because of radiative transitions from excited states, which are formed through homogeneous electron transfer between the electrochemically generated oxidized and reduced form of a light-emitting material. Therefore, photophysical and electrochemical properties with homogeneous electron transfer processes can affect the ECL properties. Although the ECL spectra and intensities (efficiencies) are the main concern as the ECL properties, by analyzing the ECL properties while considering the photophysical and electrochemical properties with the electronic states, it is possible to understand the ECL properties deeply. Here the ECL properties of some light-emitting molecules, such as thermally activated delayed fluorescent molecules, a boron-dipyrromethene derivative, and liquid fluorescent molecules, are summarized along with their electronic states. The electronic states of Ru(bpy)32+ and its oxidized and reduced forms were estimated with density functional theory calculations to reveal the relationship between the electronic state and the redox behavior of the metal center and ligands. The kinetics for the formation of the lowest excited singlet and triplet states were estimated with the Marcus theory by considering the diffusion of the electrogenerated species. Moreover, simulating the ECL behavior with a coreactant, tripropylamine, based on a finite element method, was described.
This paper suggests a preparation procedure for the analysis of blast furnace slag, based on an idea of glass bead sample preparation for X-ray fluorescence (XRF) analysis, to determine all major constituents, including silicon at the same time, by using inductively coupled plasma - atomic emission spectrometry (ICP-AES). Differing from a conventional alkaline-fusion method, the slag sample was first fused with lithium tetraborate to prepare it in a glass bead specimen for XRF, and then a sample solution could be obtained without any loss of the silicic constituents by dissolving the glass bead with nitric acid and then adding hydrofluoric acid. The contents of Na, MgO, Al2O3, SiO2, P, K, CaO, TiO2, MnO, and total Fe in a slag sample could be simultaneously determined, while an additional procedure for separation of silicon from the other analytes was needed in a conventional ICP-AES. The suggested method would enable several kinds of blast furnace slag to be analyzed through easier sample preparation procedure.
Prior to the coating of a sample to a filament surface, a Joule-heating treatment of the filament was performed to remove any impurities from the filament and to minimize the influence of the background in thermal ionization mass spectrometry. In this work, the effect of the surface condition of the tungsten filament induced by the Joule-heating treatment on an uranium isotopic (235U/238U) measurement has been investigated. By the Joule-heating treatment, crystal grains were formed on the filament surface, and the filament surface became smooth. It was found that by extending the Joule-heating time, the surface became smoother and the precision of uranium isotopic (235U/238U) measurement was improved.
Aluminium tridecamer (Al13) has seemed to be stable in solutions because of its Keggin structure. Recently, some studies suggested that Al13 would be decomposed under specific conditions, especially under the sulfate ion’s existence. However, the fact is that the reason that the sulfate ion leads Al13 to be decomposed has not been clearly revealed yet. The main aim in this study was to evaluate the effect of the sulfate ion on Al13 with Electrospray Ionization Mass Spectrometry (ESI-MS). The sulfate ion, which is an oxidant, was added to Al solutions before and after Al13 formed. To discuss the results, the same experiments were carried out with ascorbic acid, which is a reductant, instead of the sulfate ion. As results of these experiments, it was deniable that a small amount of oxidation could deprive the Keggin structure of electrons, and thus caused the decomposition of Al13. On the contrary, a much greater amount of ascorbic acid than that of sulfate ion would cause the decomposition of Al13 by giving electrons into the Keggin structure. From these results, the Al Keggin structure maintains its itself even under the existence of a reductant.
Nanographenes have now become one of the most promising candidates for new functional materials because of their high fluorescence properties, electronic properties and opt-electric properties. Therefore, nanographenes have been mostly studied in the field of organic solar cells and organic light emitter diodes. Despite the importance of understanding their electronic character, their exact HOMO-LUMO energy levels were poorly understood. This is because of the difficulty in size and composition selective syntheses of nanographenes. In this study, we synthesized three nanographenes with different sizes of π conjugate systems and molecular distortion by using a bottom-up method. We conducted Photoemission yield spectroscopy in air to measure their HOMO levels directly. By combining those data with the HOMO-LUMO gap energy derived from the UV-Vis absorption spectra, we revealed energy diagrams of nanographenes. We found that the HOMO-LUMO gap energy becomes smaller by extending the π conjugate systems, and the energy levels of HOMO and LUMO become lower by introducing molecular distortion.