This review describes advancements toward the development of a capillary-assembled microchip (CAs-CHIP) for simultaneous multiple analyte sensing and microchip capillary electrophoresis. Development of such an advanced system relies on several factors such as improving the fluid handling technique, creating new biosensing mechanisms, and integrating different functional capillaries into a single CAs-CHIP system. Furthermore, we provide an overview of various functional capillaries that have been established for valving and biosensing applications such as ions, metabolites, proteins, and enzyme activities. We also highlight future prospects for CAs-CHIP development as related to high-throughput systems, facile fluid handling, and mass production.

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This article describes new analytical methods for studying biopolymer ε-poly-L-lysine (εPL). The produced amount of εPL in culture broth can be determined based on the precipitation of polycationic εPL with a colored heteropolymolybdate anion and the color change of the supernatant. The product can be separated and purified by precipitation with the tetraphenylborate anion and reprecipitation in the form of the hydrochloride salt. These methods have been applied advantageously to the screening of εPL-synthetase. Also, pyrophosphate can be determined colorimetrically based on the formation of 18-molybdopyrophosphate species. The pyrophosphate determination has been successfully applied to the assay of adenylation enzyme, which plays important roles in the biosynthetic mechanism. Under certain conditions, εPL associates with a redox enzyme, glucose oxidase. The effect of the adduction on the stability and reaction rate of the enzyme can be evaluated by measuring the bioelectrocatalytic current, which is related to the enzyme activity. Electrochemical studies showed new applications of εPL as an enzyme stabilizer and a reaction enhancer.

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Our modern society has created a large number of chemicals that are used for the production of everyday commodities including toys, food packaging, cosmetic products, and building materials. We enjoy a comfortable and convenient lifestyle with access to these items. In addition, in specialized areas, such as experimental science and various medical fields, laboratory equipment and devices that are manufactured using a wide range of chemical substances are also extensively employed. The association between human exposure to trace hazardous chemicals and an increased incidence of endocrine disease has been recognized. However, the evaluation of human exposure to such endocrine disrupting chemicals is therefore imperative, and the determination of exposure levels requires the analysis of human biological materials, such as blood and urine. To obtain as much information as possible from limited sample sizes, highly sensitive and reliable analytical methods are also required for exposure assessments. The present review focuses on effective analytical methods for the quantification of bisphenol A (BPA), alkylphenols (APs), phthalate esters (PEs), and perfluoronated chemicals (PFCs), which are chemicals used in the production of everyday commodities. Using data obtained from liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS analyses, assessments of the risks to humans were also presented based on the estimated levels of exposure to PFCs.

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This article presents an overview of our recent progress on the development of chelating materials. Carboxymethylated pentaethylenehexamine (CM-PEHA) and polyethyleneimine (CM-PEI) as chelating ligands show excellent performance for the solid-phase extraction of trace elements. Chelating resins immobilizing these ligands can be readily prepared by immobilizing PEHA and PEI on methacrylate resins and then carboxymethylating them. Chelating fiber can also be prepared with a wet spinning technique using a mixture of a viscose solution and a solution containing fine particulate CM-PEHA resin or CM-PEI. The potentials of these chelating materials for the separation and preconcentration of trace elements are outlined.

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Ice plays an important role for the circulations of some compounds in the global environment. Both the ice surface and the liquid phase developed in a frozen solution are involved in such reactions of the molecules of environmental importance. This leads to the idea that ice can be used to design novel analytical reaction systems. We devised ice chromatography, in which ice particles are used as the liquid chromatographic stationary phase, and have subsequently developed various analytical systems utilizing the functionality of ice. This review focuses our attention on the analytical facets of ice containing impurities such as salts; hereinafter, we call this “doped ice”. The design of novel separation systems and use as microreactors with doped ice are mainly discussed.

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The research activities by the author’s group to elucidate the chemical states of ions within the ion exchange resin phase are summarized. The resin with the higher exchange capacity has the smaller space available for ion exchange, and the higher cross linking degree interferes more with swelling of the resin. As a result, diverse secondary interactions between exchanged ions are observed on the resins of high exchange capacities and high cross linking degrees: the van der Waals contact results in incomplete exchange or enhanced dehydration of ions, hydrogen bond formation between acidic anions, and coadsorption of anions with metal ions. Contribution of the simple ion exchange mechanism to the reactions of iminodiactate-type chelating resins with metal ions in the acidic media is quantitatively discussed. The resulting complexes were successfully applied to preconcentration and separation of anions.

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Rolling circle amplification (RCA) catalyzed by φ29 DNA polymerase offers a simple method for DNA amplification in the presence of a circular DNA template and its complimentary primer. RCA continuously produces long single-strand DNA using the strand displacement activity of polymerase during DNA synthesis. This property allows one to monitor the progress of a reaction by means of electrophoresis or fluorescence measurements, and has eventually allowed the application of RCA to signal increments in the sensing of a variety of molecular species. Originally, RCA was successfully applied for the detection of specific DNA, such as single nucleotide polymorphisms. In addition, the conjugation of an antibody with a primer achieves efficient signal enhancement in antigen detection, and mRNA can also be specifically detected. Since RCA is a carry-over contamination-resistant, cost-effective, and user-friendly method of DNA amplification, RCA could be a universal technology for biosensing in fields of medical- and food-related industries.

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The author herein reviews a specific microfluidic behavior exhibited by mixed-solvent solutions in a microspace, coined as the tube radial distribution phenomenon (TRDP). The specific fluidic behavior was observed in the following solution systems: ternary water–hydrophilic/hydrophobic organic solvents, water–surfactant, water–ionic liquid, and fluorous/organic solvents. When the mixed homogeneous solutions were delivered into a microspace under certain conditions, the solvent molecules were radially distributed in the microspace, generating inner and outer phases with a kinetic liquid–liquid interface. The TRDP was fundamentally evaluated by fluorescence microscopy, phase diagrams construction, and the elution behaviors of solutes in a capillary tube. A TRDP-based capillary chromatography, referred to as tube radial distribution chromatography (TRDC), where the outer phase serves as a pseudo-stationary phase under laminar flow conditions, has been developed as one of the applications of TRDP. We have also investigated TRDP-based extraction, chemical reaction, and mixing processes, coined as tube radial distribution extraction (TRDE), tube radial distribution reaction (TRDR), and tube radial distribution mixing (TRDM), respectively. The concept and experimental findings regarding TRDP, TRDC, TRDE, TRDR, and TRDM are described in this review.

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We present a novel, cavity-enhanced spectroscopic technique based on a phase-matched Raman process to detect trace quantities of gas. The essence of this technique is the careful control of cavity dispersion to satisfy the phase-matching condition of coherent anti-Stokes Raman scattering (CARS) enhanced in a high-finesse optical cavity. A 6000-fold improvement of the CARS signal is observed under optimized conditions, indicating that this is a promising tool to quantify Raman-active molecules with an extremely low detection limit.

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This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics.

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The fabrication of electronic devices using individual molecules necessitates an adept control of the placement of molecules and tuning the space between them. This paper provides an overview of sensing using molecularly bridged gold nanoparticles (AuNPs) with nanometer-sized space. We have attempted to form a nanometer-sized space in a two-dimensional network consisting of a repeated sequence of an AuNP–molecule–AuNP junction. It is possible to evaluate electron tunneling or electron transfer in an AuNP–molecule–AuNP junction by directly measuring the electrical resistivity of the two-dimensional network. The resistivity of the two-dimensional sequence, in turn, depends on the size and conducting states of the molecules in each junction. The molecular junction in such nanometer-sized structures can be moved and rearranged to any location, enabling the rapid development of miniaturized compact electronic devices.

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This review describes the development of molecularly imprinted materials for selective separation and/or concentration of environmental pollutants, the quantitative concentration of which is usually difficult to determine because of their low level of concentration and existence of a large number of contaminants in environmental water. The fragment imprinting technique allowed for the selective separation of endocrine disrupters and halogenated aromatic compounds, including bisphenol A, and chlorinated/brominated aromatic compounds by the specific structural recognition based on the breeds, position, and number of the substituents. Also, the interval immobilization technique provided the specific materials enabling selective concentration based on the interval recognition of ionic functional groups in the targeting compounds, so that the effective determinations were achieved for natural toxins and pharmaceuticals in environmental water. Additionally, a selective photodegradation of toxins and a stimulus responsible hydrogel by the similar molecular recognition ability were successfully carried out. We have summarized these techniques including our recent studies.

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A needle-type extraction device is one of the promising sample preparation devices for the gas chromatographic (GC) analysis of various organic compounds. The most remarkable advantage of this device is a simple and rapid desorption of the analytes by direct insertion of an extraction needle into a conventional GC injection port. In this review, fundamental aspects of the needle-type extraction devices and its applications for the determination of trace organic compounds, especially volatile organic compounds (VOCs), in several sample matrices are described.

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Phenylboronic acid (PBA) derivatives are known to form reversible complexes with polyols, including sugars. This unique chemistry has provided many useful molecular bases for analytical and therapeutic applications. This mini-review highlights some new aspects of related research efforts with a special focus on the interaction with sialic acid as a new class of molecular targets and other PBA-based strategies for drug delivery applications.

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Pore-forming compounds are attracting much attention due to the signal transduction ability for the development of highly sensitive biosensing. In this review, we describe an overview of the recent advances made by our group in the design of molecular sensing interfaces of spherical and planar lipid bilayers and natural bilayers. The potential uses of pore-forming compounds, such as gramicidin and MCM-41, in lipid bilayers and natural glutamate receptor channels in biomembrane are presented.

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Microfluidic devices are an attractive choice for meeting the requirements of point-of-care microRNA detection. A method using a microfluidic device can drastically shorten the incubation time because the device conveys sample molecules right straight to the surface-immobilized probe DNAs by hydrodynamic force. In this review, we present an overview of a new method for rapid and sensitive microRNA detection from a small sample volume using a power-free microfluidic device driven by degassed poly-dimethylsiloxane (PDMS). Two key technologies for this detection method are summarized. One of the methods relies on the coaxial stacking effect of nucleic acids during sandwich hybridization. This effect is also efficient for stabilizing sandwich hybridization consisting of small DNA and microRNA. The other is the laminar flow-assisted dendritic amplification, which increases the fluorescent signal by supplying two amplification reagents from laminar streams to surface-bound molecules. Utilizing both technologies, microRNA detection is possible with a 0.5 pM detection limit from a 0.5 μL sample corresponding to 0.25 attomoles, with a detection time of 20 min. Since microRNAs are associated with various human diseases, future studies of these technologies might contribute to improved healthcare and may have both industrial and societal impacts.

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This review addresses our recent efforts to design AP site-binding small ligands for SNP (single-nucleotide polymorphisms) typing. First, we present a surface plasmon resonance (SPR) biosensor carrying a derivative of 3,5-diaminopyrazines. Comparison with a bulk assay based on 3,5-diaminopyrazines-DNA binding shows that the immobilization of 3,5-diaminopyrazines on the SPR sensor allows a more sensitive detection of the target DNA, and binding selectivity can be tuned by controlling salt concentrations of the sample solutions. We also present a ratiometric fluorescent probe, in which an environmentally sensitive fluorescent dye, a benzofurazan derivative, is linked through an alkyl spacer to a 2-amino-1,8-naphthyridine derivative. The binding and sensing properties of these systems are discussed as a basis for the advanced design of DNA-binding small molecules for gene detection.

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The purpose of this review article is to outline the recent progress in near-infrared (NIR) imaging technology with particular emphasis on new instrumentation. Superior features of NIR imaging such as suitability for nondestructive and in-situ analysis, transmission ability, availability of optical fibers, high-speed monitoring and stability are very attractive not only for laboratory-based studies but also for diverse practical applications. In this review, introduction to chemical imaging is described, and then, a comparison among NIR, infrared (IR) and Raman imaging are made. Furthermore, the features of new NIR imaging instruments developed by our research group in collaboration with Yokogawa Electric Corporation and Sumitomo Electric Industries, Ltd. are discussed. Finally, some examples of applications of NIR imaging are introduced. Particularly, the performance and usefulness of the newly-developed imaging devices are demonstrated through their applications to pharmaceutical tablets and polymers.

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This review highlights work using the author’s method for the preparation of highly aligned metallic nanofibers with one-dimensional aggregates of metal nanoparticles (MNPs) and their utilization in surface enhanced Raman scattering (SERS) analysis. The preparation method, which is based on the process of evaporation-induced self-assembly with DNA and a drying front movement, eliminates the need for lithography and an external field; it is also fast, cheap and easy. Dark-field scattering spectroscopy was used to study the strong plasmon coupling of MNPs in metallic nanofibers. Furthermore, Raman spectral imaging of the metallic nanofibers revealed the existence of intense hot spots localized along their axes, which played a significant role in the intensity of SERS signals from DNA bases and rhodamine B in the metallic nanofibers. Our results demonstrate the use of evaporation-induced self-assembly with DNA as a straightforward method to produce the one-dimensional coupling of localized plasmons with a longer scale, and to facilitate the fabrication of optical sensor chips for single-molecule detection via SERS.

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High-sensitivity nuclear magnetic resonance (NMR) of gaseous atoms realized by using a hyperpolarization technique is an attractive research tool used in a wide range of areas, such as physics, chemistry, material science and biomedical imaging. One of the most promising applications of this technology is the use as a noninvasive diagnostic tool for pulmonary diseases, where hyperpolarized (HP) noble gases, ³He and ¹²⁹Xe, play a role as gaseous (i.e. inhalable) contrast agents of magnetic resonance imaging (MRI). During the last two decades, lung MRI with HP gases has become widely applicable from mouse to human. In this review we present a brief overview of recent progress made by our group in the development of HP ¹²⁹Xe MR measurements, while focusing on the methodology for probing pulmonary dysfunctions in mice.

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Polymers that respond to small changes in environmental stimuli with large, sometimes discontinuous changes in their physical state or properties, are often called “smart” polymers. Poly(N-isopropylacrylamide), PNIPAAm, is one of the most representative smart polymer that exhibits a thermally reversible soluble-insoluble change in the vicinity of its lower critical solution temperature (LCST) at 32°C in aqueous solution. Temperature-responsive chromatography for the separation of biomolecules utilizing the poly(N-isopropylacrylamide) (PNIPAAm)-modified stationary phase is performed with an aqueous mobile phase without using an organic solvent. The surface properties and function of the stationary phase are controlled by external temperature changes without changing the mobile-phase composition. The separation of the biomolecules, such as nucleotides, was achieved by a dual temperature- and pH-responsive chromatography system. The electrostatic and hydrophobic interactions could be modulated simultaneously with the temperature in an aqueous mobile phase. Additionally, we also prepared functional copolymers composed of N-isopropylacrylamide (NIPAAm) and amino acid derivative or naphthyl alanine derivative, which have temperature-responsiveness and molecular recognition. These separation systems would have potential applications in the separation of biomolecules.

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Inductively coupled plasma mass spectrometry (ICP-MS) is of great value to researchers concerned with inorganic analytical chemistry as well as to engineers performing elemental analysis. However, the effects of the plasma reactions on ICP spectrometry are still incompletely understood and they sometimes introduce severe problems for measurements, such as spectral interferences. When we determine arsenic (As) by ICP-MS or ICP-AES, we observe two interesting plasma phenomena; one is the incoherent molecular formation (IMF) effect in the plasma, and the other the selective and partial oxygenation of ions with O₂ gas in a dynamic reaction cell. The mechanisms of the IMF effect and selective oxygenation of As with a reaction gas were investigated and the techniques to remove their influence on As determination are discussed.

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This mini-review introduces a general understanding of the use of a milli-whistle as a gas chromatography (GC) detector in gas analysis, including our research on the methodology and theory associated with a number of different related applications. The milli-whistle is connected to the outlet of a GC capillary, and when the eluted gases and the GC carrier gas pass through it, a sound with a fundamental frequency is produced. The sound wave can be picked up by a microphone or an accelerometer, and after a fast Fourier transform, the online data obtained for frequency-change vs. retention time constitute a new method for detecting gases. The first part of this review discusses the fundamentals of the milli-whistle. Some modifications are also discussed, including various types of whistles and an attempt to maximize the sensitivity and stability of the method. The second part then focuses on several practical applications, including an analysis of hydrogen released from ammonia borane, inorganic gases produced from fireworks, the CO₂/O₂ ratio from expired human breath and a purity test for alcohols. These studies show that the GC-whistle method has great potential for use as a fast sampling ionization method, and for the direct analysis of biological and chemical samples at under ambient conditions.

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