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Arrays with cell aggregations and single-cell arrays embedded in hydrogel sheets were fabricated by negative dielectrophoretic (n-DEP) cell-manipulation techniques and hydrogel gelation. Cells suspended randomly in a prepolymer solution were rapidly manipulated to form an island-like organization of cells through the repulsive force of n-DEP by using a DEP device consisting of grid electrodes. The cell patterns were retained by irradiating ultraviolet (UV) light so as to urge gelation. Moreover, control of the optical transparency of the grid electrode allows for the fabrication of cubes with single cells and cell aggregation.

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A graphene quantum dots (GQDs) and horse radish peroxidase (HRP) hybrid system was designed for the sensing of alkaline phosphatase (ALP) activity and inhibitor screening. We found that the photoluminescence (PL) intensity of GQDs could be quenched efficiently in the presence of phenol, H₂O₂ and HRP. Moreover, ALP could hydrolyze disodium phenyl phosphate (DPP) to produce phenol, and also could result in the photoluminescence quenching of GQDs. The decrease in the PL intensity was linear to the activity of ALP in the concentration range of 0.02 – 0.8 U/L, with a detection limit of 0.008 U/L. The proposed GQDs/HRP hybrid system was successfully applied to ALP determination in human serum samples. The inhibition study was further analyzed, and Na₃VO₄ (as an ALP inhibitor) showed a clear inhibition effect. The results suggest that the GQDs/HRP hybrid system has good potential applications for the assay of ALP activity and inhibitors screening in related biochemical fields.

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There has been considerable discussion of the speed performance of HPLC separation, especially regarding the relationship between theoretical plates and hold-up time. The fundamental discussion focuses on the optimal velocity, u_0,opt, which gives a minimal height equivalent to a theoretical plate of the van Deemter plot. On the other hand, Desmet’s method, using the kinetic performance limit (KPL), calculates the highest performance with a constant pressure drop, without focusing solely on the optimal velocity. In this paper, a precise method based on the KPL is proposed, to understand how increasing pressure enhances both theoretical plates and hold-up time. A three-dimensional representation method that combines the pressure drop with two axes of time and theoretical plates will be useful for discussing the effect of pressure in pressure-driven chromatography. Using three dimensions, the methods based on u_0,opt and the KPL can be combined, because u_0,opt can be visualized three-dimensionally, including the neighbor of u_0,opt; and the question of whether the KPL is an asymptotic or effective limit can be investigated. Three performances of high resolution, high speed, and low pressure can be understood on different packing supports at a glance.

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Previously, we reported that ε-poly-L-lysine (25 – 35 residues) significantly promoted a glucose oxidase enzymatic (GOx) reaction using ferricyanide ion as the oxidant, and that the effect was due to the formation of a polyion complex between anionic GOx and protonated (polycationic) ε-poly-L-lysine. Here, we show that streptothricins (STs), which have an L-β-lysine oligomer (1 – 7 residues) and possess only several positive charges at most, also effectively promote the GOx enzymatic reaction. Interestingly, the promotion effect increased with the size of the lysine oligomer of STs, suggesting that the ionic valence is a key factor determining the degree of the promotion effect. The GOx enzymatic reaction is accompanied by a color change due to the reduction of yellow ferricyanide ion to a colorless reductant. A more distinctive color change can be achieved by the addition of Fe(III) ions due to the formation of Prussian blue. Thus, the promotion effect allowed for colorimetric detection of STs at the 1 mg/L level. The detection method was simple and easy to carry out, and would become a helpful tool for the detection of STs.

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The detection of disease-related DNA is of great significance for early and accurate diagnosis and therapy. In this work, we successfully achieved the sensitive detection of target DNA based on a thioflavin T (ThT)-induced G-quadruplex fluorescent biosensor. ThT, a water-soluble fluorescent dye, can induce G-rich sequences to form G-quadruplexes and obtain an obviously enhanced fluorescence. In this work, it was employed to construct a biosensor for the detection of HIV. When the target HIV existed, the hairpin DNA probes would be opened in succession and release the completely exposed G-rich sequence to combine with ThT. The simple and rapid biosensor performed satisfactory selectivity; it also exhibited sensitivity with a detection limit of 2.4 nM. With good performance in human serum, we believe that this optical biosensor has the potential to be applied to the practical detection of target DNA.

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In this study, nanocomposites of ligand-free gold nanoparticles that are anchored onto the graphene surface (Graphene/AuNPs) were synthesized by a sonochemical method in a single reaction step. A highly sensitive amperometric sensor using Graphene/AuNPs is proposed for the determination of trace hexavalent chromium Cr(VI) in environmental water samples. Compared with a gold electrode, a glassy carbon electrode and a AuNPs modified glassy carbon electrode, the Graphene/AuNPs modified glassy carbon electrode exhibits the highest electrocatalytic activity and stability towards the reduction of Cr(VI), based on the results by cyclic voltammetry and electrochemical AC impedance studies. This study shows that the Graphene/AuNPs-based sensor can detect Cr(VI) with a low detection limit of 10 nM (∼0.5 μg/L), a wide dynamic range of 0 to 20 μM (R = 0.999) and very good selectivity and reproducibility. The electrode is applied to the determination of Cr(VI) in river samples with satisfactory recovery values.

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A microfluidic method with front-face fluorometric detection was developed for the determination of total inorganic iodine in drinking water. A polydimethylsiloxane (PDMS) microfluidic device was employed in conjunction with the Sandell–Kolthoff reaction, in which iodide catalyzed the redox reaction between Ce(IV) and As(III). Direct alignment of an optical fiber attached to a spectrofluorometer was used as a convenient detector for remote front-face fluorometric detection. Trace inorganic iodine (IO₃⁻ and I⁻) present naturally in drinking water was measured by on-line conversion of iodate to iodide for determination of total inorganic iodine. On-line conversion efficiency of iodate to iodide using the microfluidic device was investigated. Excellent conversion efficiency of 93 – 103% (%RSD = 1.6 – 11%) was obtained. Inorganic iodine concentrations in drinking water samples were measured, and the results obtained were in good agreement with those obtained by an ICP-MS method. Spiked sample recoveries were in the range of 86%(±5) – 128%(±8) (n = 12). Interference of various anions and cations were investigated with tolerance limit concentrations ranging from 10⁻⁶ to 2.5 M depending on the type of ions. The developed method is simple and convenient, and it is a green method for iodine analysis, as it greatly reduces the amount of toxic reagent consumed with reagent volumes in the microfluidic scale.

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A new design of membraneless gas-diffusion unit with dual acceptor channels for separation, collection and simultaneous determination of two volatile analytes in liquid sample is presented. The unit is comprised of three parallel channels in a closed module. A sample is aspirated into the central channel and two kinds of reagents are introduced into the other two channels. Two analytes are isolated from the sample matrix by diffusion into head-space and absorbed into the specific reagents. Non-absorbed vapor is released by opening the programmable controlled lid. The unit was applied to liquors for measurement of ethanol and acetaldehyde using reverse flow injection. Dichromate and nitroprusside were exploited as reagents for colorimetric detection of ethanol and acetaldehyde, respectively. Good linearity ranges (r² >0.99) with high precision (RSD <2%) and high accuracy (recovery: 90 – 105%) were achieved. The results were compared to the results by GC-FID and no significant difference was observed by paired t-test (95% confidence).

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A simple sample preparation method for eicosanoid was developed by the combination of deproteinization and nanoLC-ESI-MS/MS. Eicosanoids are a group of bioactive lipid mediators, present in trace amounts in the body. Therefore, an analytical method for eicosanoids requires superior sensitivity. The method described in this report, which takes advantage of the highly sensitive power of nanoLC-ESI-MS/MS, enabled a simplification of the sample-preparation process. Eicosanoid extraction was performed just by homogenization in methanol with subsequent phospholipid removal, and then the liquid phase was directly subjected to nanoLC-ESI-MS/MS analysis without a condensation process. The quantitation range achieved 0.01 – 100 ng/mL for thromboxane B₂, and 0.05 – 100 ng/mL for prostaglandin E₂, prostaglandin D₂, prostaglandin F₂, leukotriene B₄, 6-keto prostaglandin F_1α and 11-dehydro thromboxane B₂. Rat brain sample analyses demonstrated the feasibility of the quantification of those seven eicosanoids from biological samples.

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We demonstrated that a cost-efficient, easy to prepare, hybrid SERS substrate-gold nanoparticles (AuNPs) on untreated Al foil (AlF) can effectively detect pharmaceuticals, such as paracetamol and clinical biomarkers, like urea in artificial urine. The limit of detection (LOD) for paracetamol on AuNPs on AlF is superior (0.1 vs. 1 mM ) to the LOD reported for SERS detection of paracetamol in the literature. For SERS detection of urea in urine, AuNPs on both Al foil and Au film performed much better than AuNPs on glass, in terms of the concentration range, linearity and LOD. However, assay on AuNPs on AlF showed a better semi-logarithmic trendline with R² = 0.98 than an assay on AuNPs on Au film with R² = 0.94. They have comparable sensitivity with LOD 0.024 and 0.017 M, respectively. The limit of quantification (LOQ) of the former is 0.026 M, which makes it sufficient for the quantification of urea in urine at both normal and pathophysiological (0.03 – 0.15 M) concentration.

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The solvent-extraction behavior of Li⁺ and Na⁺ with a Li⁺ selective metallacrown, [{Ru(η⁶-3,5-dimethylanisole)(2,3-pyridinediolate)}₃], was investigated in the presence of organic dye anions, 3′,3″,5′,5″-tetrabromophenolphthalein ethyl ester ([TBPE]⁻), 2,6-dichloroindophenolate, and picrate ([pic]⁻). Each alkali metal ion was extracted as a 1:1:1 ternary complex of the metal ion, metallacrown, and anion. The Li⁺/Na⁺ extraction selectivity is anion dependent and highest with [pic]⁻. Therefore, we devised an extraction–spectrophotometric determination method for Li⁺ in saline water based on the extraction of Li⁺ using the metallacrown and [pic]⁻ for high selectivity and subsequent replacement of [pic]⁻ in the extracted species with [TBPE]⁻ for high sensitivity. When applying this to artificial seawater samples containing known concentrations of Li⁺, a linear relationship was observed between the absorbance at 571 nm of the organic phase and the Li⁺ concentration in the samples. By this method, the determination of Li⁺ at the sub-ppm level in natural seawater is possible.

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A new microfluidic polymer chip with an embedded cationic surfactant (CS) ion-selective optode (CS-optode) as a detector of flow-injection analysis (FIA) for the determination of CSs was developed. The optode sensing membrane is based on a poly(vinyl chloride) membrane plasticized with 2-nitrophenyl octyl ether containing tetrabromophenolphthalein ethyl ester. Under the optimal flow conditions of the FIA system, the CS-optode showed a good linear relationship between the peak heights in the absorbance, and the concentrations of CS in a concentration range from 50 to 400 μmol dm⁻³. The sample throughput of the present system for the determination of a CS ion (300 μmol dm⁻³ zephiramine) was ca. 11 samples h⁻¹. The proposed FIA system was applied to determine the level of CS in dental rinses.

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A purge-and-trap method using a needle-type extraction device and a gas chromatography–barrier discharge ionization detector for the analysis of formic (FA) and acetic acids (AA) in aqueous samples is presented. An activated carbon-based adsorbent, Carboxen 1000, was employed as the extraction medium for the needle-type extraction device. The sampling time was 5 min for collecting headspace gas in a glass vial, including 10 mL of an aqueous sample. The detection limits for FA and AA with a headspace sampling volume of 100 mL were 3.3 and 2.0 mg L⁻¹, respectively. Since the proposed method was based on purge-and-trap collection, it was suitable for the determination of aqueous FA and AA in complex matrices with simple and rapid sample preparation steps. The proposed method was applied to the determination of FA and AA in fruit juice samples and FA generated by the electrochemical reduction of carbon dioxide.

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Herbal medicine (HM) formulae are the combinations of two or more types of constituting herbs. This study has proposed a novel approach to efficiently develop HPLC methods for HM formulae, which take advantage of the mutual retention rules between HM formulae and their constituting herbs. An HM formula composed of two herbs, Radix Salviae Miltiorrhizae and Rhizoma Chuanxiong, was taken as a case study. Based on design of experiments and stepwise multiple linear regression, models relating the analytical parameters to the chromatographic parameters were built (correlation coefficients >0.9870) for chemical compounds in the two herbs. These models representing the retention rules were utilized to predict the elution profile of the formula. The analytical parameters were numerically optimized to ensure adequate separation of the analytes. In validation experiments, satisfactory separations were achieved without any pre-experiments on the formula. The approach can significantly increase the HPLC method development efficiency for HM formulae.

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Moment equations were developed for quantitatively studying the separation characteristics of micellar electrokinetic chromatography (MEKC). They explain how the first absolute and second central moments of elution peaks are correlated with some fundamental parameters of the partition equilibrium and mass transfer kinetics in MEKC systems. In order to discuss the influence of the mass transfer kinetics on peak broadening, the moment equations were used to analyze the separation behavior in MEKC systems. Separation conditions were chosen on the basis of practical MEKC experiments previously conducted. It was quantitatively clarified that both the solute permeation at the interfacial boundary of surfactant micelles and axial diffusion of solute molecules in a capillary had a predominant contribution to the spreading of the elution peaks in MEKC systems. This is a preliminary study for the analytical determination of rate constants concerning solute permeation at the interface of surfactant micelles from elution peak profiles measured by MEKC. In addition, it was also indicated that the experimental conditions of MEKC systems could be controlled so that the interfacial solute permeation would have a predominant role for the band broadening. For example, the contribution of the interfacial permeation was about 33 times larger than that of the axial diffusion of solute molecules under the MEKC conditions in a previous study. This means that the rate constants could appropriately be determined for the interfacial solute permeation.

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Food additives generally used in carbonated drinks, such as 4-methylimidazole (4MI), caffeine (Caf?), citric acid (CA), and aspartame (Apm), were measured by matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) using nanometer-sized particles of iron oxide (Fe₂O₃ NPs). The quantification of 4MI in Coca Cola (C-cola) was carried out. In order to improve the reproducibility of the peak intensities, Fe₂O₃ NPs loaded on ZSM5 zeolite were used as the matrix for quantification. By using 2-ethylimidazole (2EI) as the internal standard, the amount of 4MI in C-cola was determined to range from 88 to 65 μg/355 mL. The results agree with the published value (approx. 72 μg/355 mL). It was found that MALDI using Fe₂O₃ was applicable to the quantification of 4MI in C-cola.

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For determination of methylmercury (MeHg) and ethylmercury (EtHg) in seawater and industrial wastewater, a simple and robust analytical method was developed based on phenylation and solvent extraction followed by GC-MS measurement. Alkylmercury compounds were directly phenylated with sodium tetraphenylborate in water and extracted into toluene. The method detection limits obtained for MeHg and EtHg in pure water were 53.3 and 33.5 ng Hg L⁻¹, respectively, which are almost 10 times lower than the environmental quality standards for water pollution in Japan (EQSJ): 0.5 μg Hg L⁻¹. The recoveries of alkylmercury compounds from seawater and four kinds of industrial wastewater except for EtHg from treated wastewater of an optic lens factory were satisfactory (>90%) at 1- or 4-fold concentrations of the EQSJ. Contrarily, the low recovery of EtHg from the treated wastewater (75.4 ± 4.7%) was found to be caused by the rapid decomposition of EtHg into inorganic mercury.

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The keto-enol tautomerism of phenylpyruvic acid (PPA) has been studied by temperature-variable 9.4 T nuclear magnetic resonance (NMR) spectroscopy. It was found that PPA favored its existence in the enol form in dimethyl sulfoxide (DMSO) solvent, 93.5% of the enol and 6.5% of the keto tautomer was present in DMSO at room temperature. Increasing the temperature increased the percentage of the keto form. The experimental thermodynamic parameters for the tautomerism were successfully obtained from the spectral data.

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Tube radial distribution chromatography based on tube radial distribution flow, or annular flow, in an open-tubular capillary has been reported. The chromatographic system requires specific instruments and treatments for microfluidic flow in the capillary tube. In this study, we have developed a new model of tube radial distribution chromatography, which is comprised of a commercially available HPLC system without any packed separation columns. Separation is performed in an open-tubular pipe (100-μm inner diameter and 350-cm length; temperature, 5°C) connected between the pump and the detector in the HPLC system. An analyte solution is introduced with a sample injector (2-μL volume) and a ternary water/acetonitrile/ethyl acetate mixed solution (volume ratio of 3:8:2) is delivered as an eluent solution into the pipe at a flow rate of 10-μL min⁻¹. Fused silica and stainless pipes can separate 1-naphthol and 2,6-naphthalenedisulfonic acid, but a polyetheretherketone pipe cannot. The obtained data provides an important clue to practical developments in separation science.

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A new microtitration system based on the counting of titrant droplets has been developed for precise on-site analysis. The dropping rate was controlled by inserting a capillary tube as a flow resistance in a laboratory-made micropipette. The error of titration was 3% in a simulated titration with 20 droplets. The pre-addition of a titrant was proposed for precise titration within an error of 0.5%. The analytical performances were evaluated for chelate titration, redox titration and acid-base titration.

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