A method for releasing the content of microdroplets by changing the channel wall wettability is proposed. The contents of aqueous droplets were released to the continuous phase by inverting 10-μm-sized W/O droplets into O/W ones in a 2-μm-deep hydrophilic channel. The combination of “encapsulation” and “release” in microdroplets facilitates micromixing and reaction.
We report on a chemical-sensing method based on the silica-micelle mesophase wherein both a fluoroionophore and a masking agent are embedded. Using this method, a highly selective detection of metal ions in an aqueous solution has been successfully demonstrated. Furthermore, simultaneous analyses of multisamples using a sensor array composed of functionalized mesoporous thin films were demonstrated for the first time.
Continuous extensive studies on thermophilic organisms have suggested that life emerged on hydrothermal systems on primitive Earth. Thus, it is well known that hydrothermal reactions are, therefore, very important to study fields deeply related to the origin-of-life study. Furthermore, the importance of hydrothermal and solvothermal systems is now realized in both fundamental and practical areas. Here, our recent investigations are described for the development of real-time and in situ monitoring systems for hydrothermal reactions. The systems were primarily developed for the origin-of-life study, but it was also applicable to fundamental and practical areas. The present techniques are based on the concept that a sample solution is injected to a narrow tubing flow reactor at high temperatures, where the sample is rapidly heated up in a very short time by exposure at to a high-temperature narrow tubing flow reactor with a very short time scale. This enables millisecond to second time-scale monitoring in real time and/or in situ at temperatures of up to 400°C. By using these techniques, a series of studies on the hydrothermal origin-of-life have been successfully carried out.
Many chemists are not familiar with the problem of the liquid junction potential (LJP) between electrolyte solutions in different solvents. Some even misunderstand it. Therefore, it seems worthwhile to write a review article on this subject. The LJP between electrolyte solutions in different solvents consists of three components: i.e., (a) a component related to electrolyte concentrations and ionic mobilities, (b) a component related to ion solvation (and ionic mobilities), and (c) a component related to solvent-solvent interactions. The characteristics of each of the three components have been discussed in detail, based on our old and new results. Components (a) and (b) are diffusion potentials but component (c) is a dipole potential.
The immobilization of biomolecules is an important technique for bio-analysis, and can be applied to biosensors with both high selectivity and high sensitivity. Many researchers have developed immobilization techniques to optimize these characteristics. In the last two decades, an immobilization technique that meets the desired requirements was developed by using polyelectrolytes to form complexes, based on the electrostatic binding between polycations and polyanions. This review summarizes the techniques used for the immobilization of biomolecules by polyelectrolyte complexes; it also discusses related subjects.
We describe the electrochemical determination of oxidative damaged DNA by using a nanocarbon film electrode combined with a high performance liquid chromatography (HPLC) system. The nanocarbon film was formed by employing the electron cyclotron resonance sputtering method, and has a nano-crystalline sp2 and sp3 mixed bond structure with an atomically flat surface. This film electrode provided the high electrode activity and stability needed to quantitatively detect oxidative damaged DNA, 8-hydroxy-2′-deoxyguanosine (8-OHdG), by direct electrochemical oxidation. The coefficient of variation (C.V.) value of 1 μM 8-OHdG at our film electrode was 0.75% (n = 12), which constitutes superior reproducibility to that of a conventional glassy carbon (GC) electrode (9.28%, n = 12) in flow-injection analysis. This was because the nanocarbon film suppressed fouling for the oxidized product of 8-OHdG owing to its hydrophilically ultraflat and chemically stable surface. We also investigated the performance of HPLC with an electrochemical detection (HPLC-ECD) system using our nanocarbon film electrode. The detection limit for 8-OHdG at the nanocarbon film electrode was 3 nM, which was superior to the detection limit of the GC electrode (7.2 nM). Furthermore, this electrode was more suitable for use in a urinary 8-OHdG experiment than the GC electrode. The concentration of urinary 8-OHdG in the urinary sample was 8.30 nM. These results indicate that this HPLC-ECD system with our nanocarbon film electrode enables us to realize an accurate, sensitive, reproducible and easy to use analysis technique.
A rapid determination method of 87Sr/86Sr and Pb isotope (204Pb, 206Pb, 207Pb, and 208Pb) ratios was applied to determining the geographic origin of grain crops. This new method is more economical in terms of both time and cost compared to conventional methods. We used samples of barley (n = 321), rice (n = 111), and wheat (n = 93) grown in various countries. 87Sr/86Sr versus Sr concentration plots for the barley and wheat showed differences between products from Australia and those from other countries. Graphs of the Pb isotope ratios, comprising 15 two-dimensional plots, gave rise to a particular distribution for each country of production. The presented method showed promise for determining the production countries of grains by using the isotope ratios of Sr and Pb.
We synthesized dextran-based macromolecular probes carrying multiple molecules of horseradish peroxidase (HRP) as a signal-trigger enzyme and of biotin as an assembly mediator without losing the enzymatic activity. Multiple attachments of HRP and biotin to the dextran backbone were readily accomplished after the formation of aldehyde groups into the dextran macromolecule by periodate oxidation. The synthesized macromolecular probe was successfully used for sensitive chemiluminescence (CL)-imaging detection of mouse recombinant prion protein on a nylon membrane. The prion protein at a small amount of 20 fmol blotted on a nylon membrane was specifically detected, indicating at least a 10-times higher sensitivity than that of a conventional biotinylated HRP probe. Therefore, the synthesized dextran-based probes containing HRP and biotin should be used for the sensitive high-throughput analysis of various proteins on a solid-phase membrane.
A method for the determination of the oxygen content in magnesium and magnesium alloys has been developed. Inert gas fusion-infrared absorptiometry was modified by introducing a multistep heating process; a sample containing oxygen is fused with tin to form an eutectic mixture at 900°C in a graphite crucible, followed by a subsequent gradual temperature increase of up to 2000°C, which enables the evaporation of magnesium from the mixture, and subsequent solidification at the rim of the crucible. Residual tin including magnesium oxide remained at the bottom of the crucible. The oxygen in the tin is measured by a conventional inert gas fusion (IGF) method. From a comparison with the results of charged particle activation analysis, the IGF method is considered to be an attractive candidate for measuring the oxygen content in Mg and its alloys.
A novel approach to fabricate a label-free amperometric immunosensor for the detection of carcinoembryonic antigen (CEA) was described. Herein, methylene blue (MB), gold nanoparticles (AuNPs) and carcinoembryonic antibody (anti-CEA) were layer-by-layer assembled on the graphene-Nafion nanocomposite film-modified electrode by means of a self-assembling technique and the opposite-charged adsorption. Subsequently, the stepwise self-assembling procedure of the immunosensor was further characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The factors influencing the performance of the resulting immunosensor were studied in detail. The developed procedure showed improved features, including larger amount and higher immunoactivity of the immobilized antibody and repeatable regeneration of the sensor, as well as direct, rapid and simple determination for the antigen without multiple separation and labeling steps. The immunosensor could detect the target protein in a range of 0.5 to 120 ng/mL with a limit of 0.17 ng/mL (at 3σ). Finally, the immunosensing system was evaluated on several clinical samples. Analytical results were found to be in satisfactory agreement with those detected by the enzyme-linked immunosorbent assay (ELISA) method, indicating that this new method was a promising alternative tool for clinical diagnosis.
In this work, a portable and reliable instrument based on manual hydride generation and subsequent ozone induced chemiluminescence analysis was developed and optimized for measurement of aqueous arsenic in drinking water. The aim was to develop a system for use in the field in villages in developing countries where water treatment systems have been installed. Consequently, it is beneficial that the system could be operated without reagent solutions or purified water. Arsenic trihydride (arsine) was generated by reaction with solid acid and solid borohydride, and then introduced to a chemiluminescence cell where the arsine was mixed with ozone to generate chemiluminescence. The measurement could be repeated with the throughput of 60 times h−1, and the limit of detection was 0.4 μg L−1. The measurable arsenic concentration was up to 1 mg L−1 for 2 mL samples. The system was evaluated for analysis of natural water samples, and the obtained data agreed well with those from ICP-MS and sequential hydride generation flow analysis. We expect this small and inexpensive instrument will be used in developing countries.
Herein we have demonstrated a novel protocol to integrating two immunoassay procedures for performing a sequential dual-protein determination, based on a chemiluminescence (CL) substrate-resolved technology. We evaluated our method for the sequential determination of S100β and neuron-specific enolase (NSE) by using alkaline phosphatase (ALP) and horseradish peroxidase (HRP) as two different labels. Especially sharply different and suitable linear ranges and detection limits were successfully obtained for these two markers. Briefly, a “sandwich-type” detection strategy is employed in our design, where capture antibodies against S100β and NSE were coupled to magnetic beads. The quantification of NSE was obtained by further reacting with ALP modified antibodies and measurements by catalyzed chemiluminescence while the determination of S100β was accomplished with HRP-labeled anti-rabbit IgG. A simple CL setup was employed to perform our novel multiplexed protein assays in a single experiment. No obvious cross-reaction was observed. S100β and NSE were found to be suitably assayed in the ranges of 0.02 – 1 and 1 – 20 ng/mL, and the limits of detection were 0.005 and 0.2 ng/mL for S100β and NSE, respectively. It is straightforward to adapt this strategy to detect a spectrum of other biomarkers, which can provide important information about the early-stage diagnosis of diseases.
The first-order multivariate calibration method was used for the simultaneous determination of the camptothecin derivative, CPT-11 and its main metabolite, SN-38. The method is based on the fluorescence emission of these compounds in acidic media (acetate buffer, pH 4.75) and in the presence of ethanol (50%). The experimental calibration matrix was constructed with 12 samples using a central composite design. The cross-validation method was used for selecting the optimum number of factors. The results showed that simultaneous determination could be performed in the range 0.08 – 1.50 and 0.10 – 0.40 μg mL−1 for CPT-11 and SN-38, respectively. The method was successfully applied to the simultaneous determination of both analytes in human urine and in serum samples previously extracted with chloroform.
A standard method for nanoparticle sizing based on the angular dependence of dynamic light scattering was developed. The dependences of the diffusion coefficients for aqueous suspensions of polystyrene latex on the concentration and scattering angle were accurately measured by using a high-resolution dynamic light-scattering instrument. Precise measurements of the short-time correlation function at seven scattering angles and five concentrations were made for suspensions of polystyrene latex particles with diameters from 30 to 100 nm. The apparent diffusion coefficients obtained at various angles and concentrations showed properties characteristic of polystyrene latex particles with electrostatic interactions. A simulation was used to calculate a dynamic structure factor representing the long-range interactions between particles. Extrapolations to infinite dilution and to low angles gave accurate particle sizes by eliminating the effects of long-range interactions. The resulting particle sizes were consistent with those measured by using a differential mobility analyzer and those obtained by pulsed-field gradient nuclear magnetic resonance measurements.
Fast and selective sorptions of Cr(VI) species from aqueous media onto tetraphenylphosphonium bromide (TPP+ · Br−) physically immobilized polyurethane foams (PUFs) sorbent were achieved. Based on the Scatchard model of binding sites of the PUFs and Langmuir and Dubinin–Radushkevich (D–R) adsorption models of Cr(VI) retention onto TPP+ · Br− immobilized PUFs, a dual retention mechanism involving absorption related to “weak-base anion ion exchange” and an added component for “surface adsorption” was proposed. Thus, the TPP+ · Br− loaded PUFs were successfully packed in column mode for preconcentration of trace and ultra trace concentrations of Cr(VI) as halochromates [CrO3C]−aq from aqueous HCl media. The retained [CrOCl3]−aq species were recovered with NaOH (1.0 mol L−1) and analyzed by flame atomic absorption spectrometry. Cr(III) species after oxidation to Cr(VI) with H2O2 in aqueous KOH (1.0 mol L−1) were also retained and could be recovered by the proposed method. The limits of detection (LOD) and quantification (LOQ) of Cr(VI) were 0.04 and 0.13 μg L−1, respectively. The chemical speciation of Cr(III, VI) species in various water samples at trace and ultra trace levels were carried out by TPP+ · Br− loaded PUFs packed column. The enhancement factor and sensitivity factor of [CrO3C]−aq sorption were 80.0 and 30.0, respectively.
A micellar electrokinetic chromatography (MEKC) method was applied for the identification of geographical origins of Chinese green teas. Under the optimized conditions, chromatographic profiling of collected Maojian tea samples was obtained. Based on MEKC-UV profiling, twenty-four tea samples were successfully differentiated according to the relative peak areas of selected peaks in the chromatograms. Tea samples from Hubei and Henan provinces were classified correctly by hierarchical cluster analysis model (HCA) and principal component analysis (PCA). The application of linear discriminant analysis (LDA) gave correct assignation percentages of 100% for the training set and the prediction set. The overall results demonstrated that MEKC with pattern recognition could be successfully applied to discriminate Maojian teas according to their geographical origins.