Herein, we describe the development of a novel material, “enzyme-responsive fluorescent ionic liquid”, which enabled a highly sensitive detection of alkaline phosphatase (ALP). We prepared a plasticized poly(vinyl chloride) (PVC) membrane using this new material as a plasticizer and quantified ALP in aqueous solutions. Preliminary results suggested that the PVC membrane responded to ALP at an interface between the membrane and the sample solution with anion extraction to maintain electroneutrality in the membrane phase. The developed PVC membrane showed an approximately six-times higher sensitivity than the conventional membrane, thereby demonstrating highly sensitive ALP detection. These results suggested the potential applicability of the proposed membrane for highly sensitive protein detection by using ALP-labeled antibodies.

Taste is of five basic types, namely, sourness, saltiness, sweetness, bitterness and umami. In this review, we focus on a potentiometric taste sensor that we developed and fabricated using lipid polymer membranes. The taste sensor can measure the taste perceived by humans and is called an electronic tongue with global selectivity, which is the property to discriminate taste qualities and quantify them without discriminating each chemical substance. This property is similar to the gustatory system; hence, the taste sensor is a type of biomimetic device. In this paper, we first explain the sensing mechanism of the taste sensor, its application to beer evaluation and the measurement mechanism. Second, results recently obtained are introduced; i.e., the application of the senor to high-potency sweeteners and the improvement of the bitterness sensor are explained. Last, quantification of the bitterness-masking effect of high-potency sweeteners is explained using a regression analysis based on both the outputs of bitterness and sweetness sensors. The taste sensor provides a biomimetic method different from conventional analytical methods.

Low aspect ratio nanopores are expected to be applied to the detection of viruses and bacteria because of their high spatial resolution. Multiphysics simulations have revealed that the ion current–time waveform obtained from low aspect ratio nanopores contains information on not only the volume of viruses and bacteria, but also the structure, surface charge, and flow dynamics. Analysis using machine learning extracts information about these analytes from the ion current–time waveform. The combination of low aspect ratio nanopores, multiphysics simulation, and machine learning has made it possible to distinguish different types of viruses and bacteria with high accuracy.

Nanometer-sized clay, allophane, was used as the matrix for matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) and applied to the ionization of small molecules. First, the laser desorption ionization mass spectrum of cation-exchanged allophane was measured, and it was found that the cation exchange proceeded smoothly with increasing atomic number of alkali metals in the periodic table. This phenomenon was explained by considering the size of the counter anion on the allophane surface. Then, fructose was measured as the analyte using each alkali-cation-exchanged allophane as the matrix. Contrary to the measurements using allophane itself, the peak intensity of fructose decreased with increasing atomic number of alkali metals in the periodic table. This phenomenon was clarified by considering the stability of alkali cation in the presence of a surface anion, the desorption energy, and the solvation enthalpy of each alkali cation. The applicability of allophane to high molecular weight compounds was also confirmed by measuring cyclodextrin, angiotensin II, and insulin. Finally, a combination of allophane and zeolite was examined by assuming proton relay among allophane, zeolite, and analyte. As a result of proton supply from zeolite to allophane, the peak intensity of the proton sponge (1,8-bis(dimethylamino)naphthalene) was enhanced by almost 2.2 times.

A fluorescence quenching study of the fluorescent probes L-tryptophan and indole by anions (NO₃⁻, Cl⁻, SO₄²⁻) was carried out in an aqueous system. The ions NO₃⁻, Cl⁻ and SO₄²⁻ showed very good quenching of both the probes. Quenching of L-tryptophan by all the anions studied was higher as compare to the quenching of indole. The data was fitted with the Stern–Volmer equation. Stern–Volmer constants were observed in the order NO₃⁻ > Cl⁻ > SO₄²⁻. Stern–Volmer constants reflect the sensitivity of the method for the studied anions. Limit of detection (LOD) was calculated as three times the standard deviation of the blank for n = 10 (3 × SD) while the limit of quantification (LOQ) was calculated as ten times the standard deviation of the blank for n = 10 (10 × SD). In the case of L-tryptophan LOD and LOQ varied from 4.08 × 10⁻⁵ – 4.56 × 10⁻⁴ mol L⁻¹, while in the case of indole the values ranged from 3.87 × 10⁻⁵ – 6.59 × 10⁻⁴ respectively. Fluorescence quenching of L-tryptophan and indole by the studied anions showed good reproducibility and the method could be very effective for the determination of anions.

Porous glass frits are frequently used to contain the salt bridges through which reference electrodes interface samples. Prior work with widely used glass frits with 4 – 10 nm diameter pores showed that, when samples have a low electrolyte strength, electrostatic screening of sample ions by charged sites on the glass surface occurs. This creates an ion-specific phase-boundary potential at the interface between the sample and frit, and it biases the potential of the reference half-cell. Use of frits with much larger pores eliminates this problem but results in the need for frequent replenishing of the bridge electrolyte. A methodical study to determine the optimum pore size has been missing. We show here that charge screening of sample ions occurs when the pore size of nanoporous glass frits is on the order of 1 – 50 nm and samples have a low electrolyte strength. An increase in pores size to 100 nm eliminates charge screening in samples with ionic strengths in the 1.0 M to 3.3 × 10⁻⁴ M range. However, the rates of electrolyte solution flow through frits with 1, 5, 20, 50, and 100 nm pores are still low, which makes diffusion the dominant mode of ion transport into and out of these frits. Consequently, the flow of bridge electrolyte into samples is not fast enough to prevent diffusion of ions and electrically neutral components from the sample diffusing into the salt bridge, which can result in cross contamination among samples.

A novel approach to building a membrane-based disposable well-plate, here applied to cyanide detection, is described. Chitosan encapsulated CdTe quantum dots with a maximum emission at 520 nm (CS-QD520) were used as fluorophores. The CS-QD520 nanoparticle was specifically quenched by copper(II), and the quenched CS-QD520 (Cu-CS-QD520) was deposited onto a glass microfiber filter (GF/B). Subsequent introduction of cyanide ion resulted in fluorescence recovery. The “signal-ON” fluorescence linearly correlated to cyanide concentrations in the range of 38.7 to 200 μM with a limit of detection of 11.6 μM. The assay was incorporated into a membrane-based well-plate format to enhance sample throughput. A three-layer paper/glass microfiber well plate design was cut using a laser cutter and assembled using a polycaprolactone (PCL) as a bonding agent in a low-cost laminator. The experimental conditions were optimized and applied to detect cyanide in drinking water with rapid, high-throughput, low-cost analysis.

A phosphate ion-selective electrode using molybdenum metal was constructed. The modified molybdenum electrode responded to HPO₄²⁻ in the presence of molybdenum dioxide and molybdophosphate (PMo₁₂O₄₀³⁻) on the surface. The electrode exhibited a linear response to HPO₄²⁻ in the concentration range between 1.0 × 10⁻⁵ and 1.0 × 10⁻¹ M (mol dm⁻³) in the pH range from 8.0 to 9.5 with a detection limit of 1.0 × 10⁻⁶ M. The sensor showed near Nernstian characteristics (27.8 ± 0.5 mV dec⁻¹) at pH 9.0. Since the responding potential was attributed to the activity of HPO₄²⁻, the potential at a given concentration of phosphate depended on the pH. The electrode indicated a good selectivity with respect to other common anions such as NO₃⁻, SO₄²⁻, Cl⁻, HCO₃⁻ and CH₃COO⁻. The modified molybdenum electrode can be continuously used for over a 1 month with good reproducibility. The feasibility of the electrochemical sensor was proved by successful for the detection of phosphate in real samples.

A simple and rapid solid phase extraction (SPE) procedure has been developed for the extraction and determination of uranium in water samples. The method is based upon the adsorption of uranium(VI)-2,3-dihydroxynaphthalene complex on microcrystalline naphthalene at the pH range 10 – 12 in the presence of a counter cation cetyltrimethylammonium ion. The solid mass consisting of uranium-2,3-dihydroxynaphthalene-CTA complex and naphthalene is ignited in the furnace at a temperature of 700°C for 1 h and then digested in dil. HNO₃ solution. Uranium is then determined by LED fluorimetry using fluorescence enhancing pyrophosphate buffer. The effects of different variables like pH of the solution, reagent concentrations, counter cations, stirring time, interfering ions etc. have been investigated thoroughly for the quantitative recovery of uranium. The accuracy of the developed method has been ascertained by standard addition method as well as conventional pellet fluorimetry method involving co-precipitation of uranium using aluminum phosphate as a carrier.

In immunosensing, immobilization of the antibody on the sensing platform significantly influences the performance of the sensor. Herein, we propose a novel antibody-immobilization method based on a protein-polymer chain containing multiple copies of an antibody-binding protein, the Z-domain. In our approach, the Z-domain-containing polymer is prepared on the surface of the sensing platform with a biotinylation reaction from the archaeon Sulfolobus tokodaii. Biotinylation from S. tokodaii has a unique property by which biotin protein ligase (BPL) forms an extremely stable complex with its biotinylated substrate protein (BCCP). Here, we employed two types of engineered proteins: one was the fusion protein of BCCP with the Z-domain (BZB), in which BCCP was genetically attached to the N- and C-termini of the Z-domain; the other was a BPL dimer prepared by connecting two BPL molecules with a cross-linking reagent. We applied these two engineered proteins alternately onto the BPL-modified solid support of the surface plasmon resonance sensor chip, and succeeded in growing polymer chains comprising multiple units of BZB and the BPL dimer. The antibody-binding capability of the Z-domain-containing polymer thus prepared is adjustable by controlling the number of cycles of protein addition and the surface density of the polymer on the solid support.

In this article, an alterable structural color in the reflected light of a chiral nematic imprinted film was fabricated. Bio-template nanocrystalline celluloses were applied as structural oriented templates. Selectivity of the sensor was endowed by the molecular imprinting process which applied sulfamethoxazoles (SMXs) as template molecules, urea and phenol as double functional monomers, and formaldehyde as cross-linkers. The sensor exhibited a chiral nematic blue mesoporous structure, which could selectively recognize SMXs on account of the abundant predetermined rebinding sites. Once SMXs were detected, the sensor showed a visible color variance from blue to yellow and the sensitive concentration range was from 3.9 × 10⁻³ to 3.9 mmol L⁻¹. Both quantitative analyses, selective testing and recycling performance of the sensor were demonstrated. This optical response to SMXs can provide a portable, low-cost and easy-to-use strategy for the convenient detection of SMXs.

Propoxur insecticide as a thermally unstable compound (decomposed at its boiling point) could not be analyzed by traditional sample introduction systems based on the thermal desorption. In this study, an ultrasonic piezoelectric nebulizing injection port was applied for evaporating this compound prior to its determination by corona discharge ionization ion mobility spectrometry (CD-IMS). The target analyte was extracted from different water samples by using the extraction method of dispersive liquid–liquid microextraction. Methanol and trichloromethane were utilized as the disperser and extraction solvents, respectively. The effective variables included the volume of the disperser and the extraction solvents, the pH, and the centrifugation time were studied by a Fractional Factorial Design to identify the important parameter(s) and their interaction. To that end, a Central Composite Design was performed to achieve optimum levels of each effective parameter. The results showed that the optimum conditions were 78 μL of the extraction solvent, and 1.2 mL for the disperser solvent; centrifugation time was 1 min at 1010g, and finally pH 7. A detection limit of 2.1 μg L⁻¹, a linear range of 2.5 – 80 μg L⁻¹, and a relative standard deviation of 7% were obtained. Different water samples were analyzed by the proposed technique, and the propoxur amounts were successfully determined. The obtained results revealed satisfactory relative recovery values of between 91 and 105%.

An inter-laboratory study was carried out to characterize a candidate hijiki seaweed for its concentrations of total arsenic and water-soluble arsenic compounds, particularly arsenosugar compounds. The candidate material, a dried hijiki seaweed powder, was analyzed by individual techniques in two laboratories. The water-soluble arsenic compounds were separated by anion exchange, and reversed-phase columns, and As(V), DMA and four kinds of arsenosugars, namely glycerol (–OH), phosphate (–PO₄), sulfonate (–SO₃), and sulfate (–SO₄) types were detected by HPLC-ICP-MS. The methods applied were validated by analyzing a second sample, the NMIJ CRM 7405-a hijiki seaweed, which is certified for both total arsenic and As(V). Techniques for the inter-laboratory study, extraction efficiencies under different extraction conditions, some chromatographic techniques and sequential extraction were investigated. The results from the two laboratories for the candidate hijiki material showed good agreement within the measurement uncertainties for total and water-soluble arsenic compounds.

To investigate the effective separation of actinides (Ans) from lanthanides (Lns), single-stage batch extraction experiments were performed with a novel extractant, tetradodecyl-1,10-phenanthroline-2,9-diamide (TDdPTDA) with various diluents such as 3-nitrobenzotrifluoride (F-3), nitrobenzene, and n-dodecane for Am, Cm, and Lns. The extraction kinetics with TDdPTDA was rapid enough to perform continuous extraction experiments using mixer-settler extractors. The slopes of the distribution ratio versus the TDdPTDA concentration and the distribution ratio versus the nitric acid concentration were similar for F-3 and nitrobenzene systems, but different from the n-dodecane system. These differences were attributed to the characteristics of the diluents. This study revealed high distribution ratios of Am (D_Am) and Cm (D_Cm) for TDdPTDA, with the high separation factors (SFs) of Am from Lns enough for their separation.

For accurately determining nutrients in seawater by continuous flow analysis (CFA), the characteristic of the calibration curve was examined in detail. Under absorbance below 0.8, the calibration curve and the bracketing methods showed more accurate results that the bias fell below 0.5%. The analytical results of dissolved silica in seawater from the nutrient maximum layer of the Pacific Ocean obtained by the proposed methods showed good agreement with those obtained by an ion exclusion chromatography postcolumn absorption spectrophotometry (IEC-postcolumn) and an ion exclusion chromatography isotope dilution ICP mass spectrometry (IEC-ID-ICP-MS). From the results, the analysis of nutrients in seawater could be accurately carried out by CFA with an expanded uncertainty of below 1% using both the calibration curve and the bracketing methods with an appropriate absorbance range.

Small molecular biothiols, such as cysteine (Cys), homocysteine (Hcy), reduced glutathione (GSH), and hydrogen sulfide (H₂S), play crucial parts in regulating the redox balance of life activities, regulating normal physiological activities and preventing various diseases. Quantitative analysis of these important small molecular substances is very important for revealing their diverse physiological and pathological effects. Although many fluorescent probes have been reported to detect biothiols in cells, it is still not sufficiently advanced to detect biothiols with separated fluorescence emission peak by same wavelength excitation. In our work, we designed a simple conjugate of Nile red and NBD (7-nitro-1,2,3-benzoxadiazole) as long-wavelength fluorescent probe NR-NBD for the simultaneous discrimination of these biothiols at single wavelength excitation. Probe NR-NBD could efficiently discriminate Cys/Hcy, GSH and H₂S by two separated fluorescence emission channels and absorption spectra. Importantly, probe NR-NBD has excellent specificity and sensitivity towards the monitoring of endogenous/exogenous Cys/Hcy and GSH/H₂S in living cells and zebrafish.

Epithelial-mesenchymal transition (EMT), a qualitative change in cell migration behavior during cancer invasion and metastasis, is becoming a new target for anticancer drugs. Therefore, it is crucial to develop in vitro assays for the evaluation of the abilities of drug candidates to control EMT progression. We herein report on a method for the quantification of the EMT based on particle image velocimetry and correlation functions. The exponential fitting of the correlation curve gives an index (λ), which represents transforming growth factor (TGF)-β1-induced EMT progression and its suppression by inhibitors. Moreover, real-time monitoring of the λ value illustrates a time-dependent EMT progressing process, which occurs earlier than the bio-chemical changes in an EMT marker protein expression. The results demonstrate the usefulness of the present method for kinetic studies of EMT progression as well as EMT inhibitor screening.

This study describes a direct analysis of oxygenated organic compounds, such as ketones, esters and ethers, rapidly and easily using a soft plasma ionization (SPI) source combined with a Q-mass spectrometer. A related molecular ion, [2M+H]⁺, in which a sample molecule (M) can undergo protonation via water clusters, such as [(H₂O)_n+H]⁺ and [N₂(H₂O)_n+H]⁺, in an ambient air glow discharge plasma, can be dominantly detected as a base peak with little or no fragmentation at a pressure of several kPa. Oxygenated organic compounds with high proton affinity were found to generate their dimers through the hydrogen bonding interaction at higher pressures. A deuterated solvent was used to examine whether or not the adduct ion of analyte was derived from the solvent. The formation of [2M+H]⁺ strongly depended on the time. A two-dimensional spectrometer was used to obtain the distribution of several excited species and then to confirm the ionization reactions of the analyte in the SPI source. The sample molecule would be readily ionized through Penning-type collisions with excited N₂, which causes fragmentation for oxygenated compounds due to the lower pressures (approx. 1.0 kPa) while it is ionized by an attachment with protons from water clusters at higher pressures (several kPa). The SPI source can be a new and powerful tool for soft ionization in direct analysis of volatile organic compounds (VOCs).

A novel extraction medium was developed by packing polyethylene terephthalate (PET) nanofiber sheet having a diameter of 500 nm into a stainless-steel capillary of 0.8 mm inner diameter. The nanofiber was prepared by a carbon dioxide (CO₂) laser supersonic multi-drawing method, which has a significantly higher surface area than the original PET fiber. A nanofiber sheet was prepared by winding the nanofibers. Extraction of phthalates in water samples by a PET nanofiber-packed extraction capillary was investigated using a conventional high-performance liquid chromatography (HPLC). Water samples were introduced into the extraction capillary with a low pressure. After extracting the water sample, the extraction capillary was directly connected to a six-port valve of HPLC with a PEEK nut, and the extracted analytes were desorbed, followed by injection to an HPLC system using a small amount of organic solvent. In this manuscript, the fundamental performance of the nanofiber sheet-packed extraction capillary for the extraction of organic compounds in water samples is quantitatively evaluated using a conventional HPLC system.