A black-hole quencher (BHQ-2) labeled DNA (Q-DNA) with a phosphorothioate backbone was covalently conjugated to the CdTe QDs during the QDs synthesis procedure. The hairpin structure of Q-DNA shortened the distance of the CdTe QDs and the BHQ-2 group, which resulted in fluorescence quenching of the QDs. The addition of target DNA or deoxyribonuclease I (DNase I) could move the BHQ-2 group away from the QDs. As a result, the fluorescence of the CdTe QDs recovered. This work provides a new way for target DNA and DNase I detection.

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A label-free, highly selective, and highly sensitive fluorescent sensor to detect Hg²⁺ was developed using a water-soluble conjugated polymer with carboxylate groups (poly(2,5-bis(sodium 4-oxybutyrate)-1,4-phenylethynylene-alt-1,4-phenyleneethynylene, PPE-OBS) in this work. The fluorescence of PPE-OBS would be quenched because of the effect among the unique coordination-induced aggregation and electron transfers of PPE-OBS toward Hg²⁺. The linear relationship between the fluorescence intensity and concentration of Hg²⁺ was observed within the range from 6 × 10⁻⁸ to 8 × 10⁻⁵ mol L⁻¹ (R² = 0.9985), and the limit of detection was 2.10 × 10⁻⁹ mol L⁻¹. The proposed method was applied to detect Hg²⁺ in environmental water samples, and satisfactory results were obtained.

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The ecological functions of lactic acid bacteria (LAB) have been utilized in human life for food processing and probiotic therapy. Understanding the interaction mechanisms between LAB and food ingredients may help to clarify the fermentation process and physiological functions of LAB in the production of fermented foods made from plant materials and dairy products. However, the interaction mechanisms have yet to be fully clarified. Although laser diffraction was used for measuring the size changes of aggregates caused by the interaction between LAB and food ingredients, aggregate sizes could not be determined because of the precipitation of aggregates and its disruption from stirring. Therefore, a microscopy-based method for directly visualizing their interactions is required. We directly observed aggregation processes of LAB cells mediated by water-soluble polysaccharides, carboxymethyl cellulose (CMC), by dark-filed microscopy (DFM). DFM could visualize CMC-mediated cell aggregation with high contrast in real time, and revealed that the aggregates were formed by repeated collisions of LAB cells in a suspension. This suggests that our method can be used as a useful assay to directly visualize grain formation caused by interactions between LAB cells and various polysaccharides in food ingredients.

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A reduced graphene oxide (rGO)/Fe₃O₄ composites modified screen-printed carbon electrode (SPCE) was used to determinate As(III) in a HAc–NaAc buffer solution. The rGO/Fe₃O₄ composites were prepared by a simple and one-pot synthesis method, and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), FT-IR and Raman spectra. The electrochemical behaviors of the composite electrode were characterized by cycle voltammetry and electrochemical impedance spectroscopy. The experimental parameters, such as supporting electrolyte, solution pH, deposition potential, deposition time were optimized, respectively. The calibration curve for the detection of As(III) in the range of 2 to 20 ppb was I = –4.495 + 1.922C, with a coefficient of 0.994. The sensitivity was 1.922 μA/ppb, and with about twice Fe₃O₄ modified SPCE, a detection limit as low as 0.3 ppb was achieved. The proposed electrode was validated by analyzing the As(III) content in real water samples.

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Multiphoton ionization time-of-flight mass spectrometry was applied to the measurement of an oil-in-water emulsion that contained toluene as a dispersed phase. Before the measurement, the sample was sufficiently creamed, and then stirred for a short period of time for dispersion. As a result, several intense spikes appeared on the time profile constructed from the peak area for toluene. In the present study, an optical microscope was used to observe the capillary column for sample introduction, and small toluene droplets along with their aggregates were found in the images of the emulsion flowing through the capillary. The aggregates produced intense spikes comprised of multiple plots, which could be easily marked by applying a moving median filter. In the present study, droplets with minimum diameters as small as 2.9 μm, which corresponds to 13 fL, could be calculated as detectable spikes.

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We developed a novel Pb²⁺-sensor based on a microcantilever that was modified with a specific Pb²⁺-dependent DNAzyme molecule. This microcantilever sensor could detect Pb²⁺ sensitively and selectively in an aqueous solution. Upon complexation with Pb²⁺, the DNAzyme duplex unwinded and formed a G-quadruplex conformation, which led to an increase of repulsion between the DNAzyme molecules and a subsequent bending of the microcantilever. This microcantilever sensor could be regenerated, flowing through a strong Pb²⁺ chelator, 1,4,7,10-tetraazacyclododecane- 1,4,7,10-tetraacetic acid. The detection limit of the microcantilever sensor for Pb²⁺ ions is as low as 10⁻⁸ M. The microcantilever sensor also exhibited a high selectivity to Pb²⁺ over other metal ions such as Mg²⁺, Fe³⁺, Zn²⁺, Ca²⁺, and Cd²⁺.

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The interactions of polyacrylates (PAs with mean molecular weight of 4.5, 25, and 250 kDa; Na⁺,pa⁻) with anion exchange resins in the Br⁻ form (AXRs; -R⁺,Br⁻) were studied under practical conditions by reaction stoichiometry and spectroscopy. The stoichiometric or an excess amount of PA(4.5 kDa) completely replaced Br- in the AXRs of the cross-linking degree of 2 or 8%, respectively, to give (-R⁺,pa⁻), due to enhancement in selectivity of carboxylate group by multiple interactions. In contrast, PA(250 kDa) exchanged Br⁻ only on the surface of AXRs and did not penetrate into the resins; CO₂ was involved in the system to induce exchange with CO₃²⁻. Using the slightly acidic condition caused substantially no exchange by CO₃²⁻ but induced coextraction of PA with proton as free Hpa. PA(4.5 kDa) once penetrating into the resin phase as (-R⁺,pa⁻) or free Hpa was reversibly eluted under the appropriate conditions.

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In this paper, an egg-shell membrane has been used for efficient immobilization and stabilization of glucose oxidase. This membrane was used for developing a simple and reusable method for estimation of glucose in biological samples. The proposed sensor was effectively used in a wide glucose concentration range (1 – 1000 mM) with fast response time of 70 s for higher concentrations and 120 s for lower concentrations. The results of response study for the fabricated sensor show limit of detection of 4.761 mM with high sensitivity over the entire concentration range (1 – 1000 mM). Most interestingly, the membrane used in the fabricated sensor could be repeatedly used for glucose analysis 150 times and it exhibited a shelf-life of more than 6 weeks. The proposed sensor was also demonstrated for estimation of glucose in human blood samples.

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A novel dissolved carbon dioxide flotation after emulsification microextraction (DCF-EME) method was proposed for the determination of four triazole pesticides in water samples coupled with gas chromatography–mass spectrometry (GC-MS) in a home-made glass round flask. The DCF-EME method is based on a rapid and simple phase separation of low-density organic solvent (toluene) from the aqueous phase via introducing a saturated NaHCO₃ solution into the acidified sample (0.1 mol L⁻¹ HCl); then analytes were extracted in toluene. Various parameters affecting the extraction process were optimized. Under the optimal conditions, the recoveries for four pesticides ranged from 82.8 to 121.2%. Meanwhile the limits of detection were at the range of 0.14 – 1.04 μg L⁻¹, and the preconcentration factors were varied between 342 and 473 for different triazoles. The method is simple, fast and environmentally friendly, being successfully applied for the determination of triazole pesticides in water samples.

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In order to reveal the surface structures of large molecular ionic liquids (ILs), the near-surface elemental depth distributions of 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C_nC₁Im][Tf₂N], n = 2, 6, 10) were studied using high-resolution Rutherford backscattering spectroscopy (HRBS) in combination with high-resolution elastic recoil detection analysis (HR-ERDA). The elemental depth profiles of all constituent elements, including hydrogen, were derived from HR-ERDA/HRBS measurements, so that the profiles would reproduce both HR-ERDA and HRBS spectra simultaneously. The derived elemental depth profiles agree with state-of-the-art molecular dynamics simulations, indicating the feasibility of this method. A controversy concerning the preferential orientation of [C₂C₁Im] at the surface has been resolved by this new combination analysis; namely, the [C₂C₁Im] cation has a preferential orientation with the ethyl chain pointing towards the vacuum in the topmost molecular layer.

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A green extraction spectrophotometric method was presented for the determination of trace amounts of cadmium in soil and sediment samples. This method is based on the selective extraction of cadmium as its iodide complex by aqueous biphasic extraction composed of polyethylene glycol (PEG) and sodium sulfate, and a subsequent sensitive determination by spectrophotometry using 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol. This extraction method is simple and environmentally benign, since the organic solvents used for the traditional liquid–liquid extractions are replaced by the non-toxic polymer and inorganic salt. Cadmium can be selectively extracted from soil and sediment samples into the PEG-rich upper phase by an aqueous biphasic system containing potassium iodide and sulfuric acid. The proposed method was applied to the determination of cadmium in certified reference materials for soil and river sediment. The obtained results were in good agreement with the certified values.

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Our earlier method for the detection and separation of ε-poly-L-lysine using a yellow anionic dye, the dipicrylamine (DPA⁻) anion, was herein optimized for streptothricin antibiotics (ST), which contains the β-lysine oligopeptides moiety, H–[NH–(CH₂)₃–CH(NH₂)–CH₂–CO]_n–. We then applied this method to the detection and separation of ST in a commercially available nourseothricin, a mixture of ST species with n = 1, 2, 3, and 4. The ST species were precipitated with the DPA− anion. The precipitate was found to consist of the salts of the fully protonated ST species, ST^z+ (z = n + 1), with the DPA⁻ anion. The ST(DPA)_z precipitate was re-dissolved in acetonitrile. The solution was yellowish, and gave an absorption maximum at around 420 nm. Thus, the equivalent concentration of the ST species referred to the charge numbers of ST^z+ can be determined colorimetrically. By the addition of bis(triphenylphosphoranylidene)ammonium chloride, the ST species could be re-precipitated from the acetonitrile solution as hydrochloride salts. All of the ST species were found in the precipitate with high yields. The method was thus successfully applied to the detection and separation of ST species from the culture broth.

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A sensitive and disposable electrochemical impedance biosensor to detect Japanese encephalitis virus (JEV) was developed based on a gold nanoparticle (AuNP)-modified screen-printed carbon electrode (SPCE). A biosensor was fabricated through covalent grafting of a mixed self-assembled monolayer on AuNPs with a specific antibody. To detect JEV and achieve signal amplification, the horseradish peroxidase (HRP)-labeled second antibody was linked to the biosensor through a sandwich immunity reaction. HRP was used to catalyze 4-chloro-1-naphthol oxidation to produce an insoluble precipitate, which introduced a barrier to electron transfer on the electrode. Electrochemical impedance spectroscopy (EIS) was used to monitor the precipitation on the electrode. The electron-transfer resistance (R_et) of the biosensor was directly correlated with the concentration of JEV in the solution. Under optimal conditions, the method generated a linear response range between 500 and 5 × 10⁵ pfu mL⁻¹, and the detection limit was 167 pfu mL⁻¹. The biosensor exhibited good selectivity against other viruses.

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Direct analysis in real time mass spectrometry (DART-MS) was applied as a rapid method for the discrimination of the spices and traditional medicines cumin (Cuminum cyminum L.), caraway (Carum carvi L.), and fennel (Foeniculum vulgare Mill.). The seeds of these plants were analyzed without sample preparation by DART ion source coupled with quadrupole time-of-flight (QTOF) tandem mass spectrometry. The relatively clean DART spectra showed characteristic patterns, fingerprints, for each herb. It was found that a marker compound can be assigned to each species that can identify unambiguously these plants. Principal component analysis has also been used to analyze the DART-MS data of these seed herbs. Crispanone, carvone, and fenchone are the dominant compounds in the positive DART spectra of cumin, caraway, and fennel, respectively. Crispanone was first time identified as a constituent of cumin. Furthermore, the collision-induced dissociation (CID) behavior of the [M+NH₄]⁺ ion of crispanone was also described.

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Prostate-specific antigen (PSA) is a well-known biomarker for prostate-cancer diagnosis. However, the serum PSA measurement alone is insufficient for accurate diagnoses because the correlation with cancer is weak within the gray zone—the biomarker level range wherein a clear-cut diagnosis is impossible. As such, accurate prostate cancer diagnosis has been supplemented by measurements of the ratio of two types of PSA: free PSA (fPSA) and complexed PSA (cPSA; α-1-antichymotrypsin-bound PSA). Herein, we describe a new method for measuring the ratio of these two types of PSA by using gold nanoparticles (AuNPs) and biochips. Both types of PSA in a sample are captured by the antibody immobilized on a biochip based on self-assembled monolayers on gold. fPSA and cPSA on the biochip are then distinguished by AuNPs that present antibodies against fPSA and cPSA, respectively. The presence of PSAs in a sample is detected with laser desorption/ionization time-of-flight mass spectrometry by observing reporter molecules, called amplification tags (Am-tags), on the AuNPs. One of the reporter molecules is an Am-tag without isotope labeling, and the other is a deuterium-labeled Am-tag (dAm-tag). These tags amplify mass signals so as to enhance the sensitivity of the method. A comparison of the mass intensities between the Am-tag and dAm-tag signals allows the determination of the ratio between fPSA and cPSA. We validated the selective measurement of fPSA and cPSA at different ratios in 50, 75, and 100 pM of total PSA (fPSA + cPSA) solutions corresponding to the gray zone in prostate-cancer diagnosis (4 – 10 ng/mL). Finally, the two types of PSA were spiked in fetal bovine serum at various ratios, and our strategy greatly afforded their accurate ratios as spiked based on a constructed calibration curve. These results clearly indicate that the strategy is applicable to human serum as a diagnostic and prognostic assay for prostate cancer.

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A fast and sensitive ion chromatographic method for the simultaneous determinations of six inorganic anions [iodate (IO₃⁻), bromate (BrO₃⁻), bromide (Br⁻), nitrite (NO₂⁻), nitrate (NO₃⁻), and iodide (I⁻)] in seawater is described using dodecylammonium (DA⁺)-coated monolithic octadecylsilyl (ODS) columns, a concentrated aqueous NaCl mobile phase containing dodecylammonium chloride (DAC), and a UV detector. The DA⁺-coated monolithic ODS columns show greater retention for iodate and weaker retention for iodide, compared to dilauryldimethylammonium (DDA⁺)-coated monolithic ODS columns. Six anions were determined within 12 min with baseline separation without interferences by matrix ions, such as Cl⁻ and SO₄²⁻, in seawater, compared to a DA⁺-coated particulate ODS column (it took 25 min per sample) obtained previously. The detection limits (DLs) were comparable to the DA⁺-coated particulate ODS column: IO₃⁻ (7.7 μg L⁻¹), BrO₃⁻ (20), Br⁻ (88), NO₂⁻ (0.9), NO₃⁻ (1.9), and I⁻ (0.9) with a 100-μL sample injection. A larger sample volume injection lowered the DLs of IO₃⁻, BrO₃⁻, and I⁻. The good performance was maintained for ca. 2 years examined. The robust IC system developed in the present work was successfully applied to real seawater samples without sample dilution in the recovery rates of 93 – 104% for all ions.

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A method for determination of hydrogen sulfide in microsamples (200 μL) was developed by modifying the methylene blue method. Samples were collected using a micropipette and were combined with sulfide coloring reagent and 5 mL of 0.1 M HCl in test tubes. Absorbance of the solution was measured spectrophotometrically at 667 nm. This modified method did not require any special labware or technique, and can be used in a variety of research fields.

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