This review addresses recent studies of newly developed carbon-based electrode materials and their use for DNA electroanalysis. Recently, new carbon materials including carbon nanotubes (CNT), graphene and diamond-based nanocarbon electrodes have been actively developed as sensing platforms for biomolecules, such as DNA and proteins. Electrochemical techniques using these new material-based electrodes can provide very simple and inexpensive sensing platforms, and so are expected to be used as one of the “post-light” DNA analysis methods, which include coulometric detection, amperometric detection with electroactive tags or intercalators, and potentiometric detection. DNA electroanalysis using these new carbon materials is summarized in view of recent advances on electrodes.
Polychlorinated biphenyls (PCBs) are persistent organic pollutants that are present in the insulating oil inside a large number of transformers. To aid in eliminating PCB-contaminated transformers, PCBs in oil need to be measured using a rapid and cost-effective analytical method. We previously reported a pretreatment method for the immunoassay of PCBs in oil using a large-scale multilayer column and a microchip with multiple microrecesses, which permitted concentrated solvent extraction. In this paper, we report on a more rapid and facile pretreatment method, without an evaporation process, by improving the column and the microchip. In a miniaturized column, the decomposition and separation of oil were completed in 2 min. PCBs can be eluted from the capillary column at concentrations seven-times higher than those from the previous column. The total volume of the microrecesses was increased by improving the microrecess structure, the enabling extraction of four-times the amount of PCBs achieved with the previous system. By interfacing the capillary column with the improved microchip, PCBs in the eluate from the column were extracted into dimethyl sulfoxide in microrecesses with high enrichment and without the need for evaporation. Pretreatment was completed within 20 min. The pretreated oil was analyzed using a flow-based kinetic exclusion immunoassay. The limit of detection of PCBs in oil was 0.15 mg kg−1, which satisfies the criterion set in Japan of 0.5 mg kg−1.
The heterodyne transient grating (HD-TG) method was first applied to the curing dynamics measurement of photopolymers. The curing dynamics for various monomers including an initiator (2.5 vol%) was monitored optically via the refractive index change after a single UV pulse irradiation. We could obtain the polymerization time and the final change in the refractive index, and the parameters were correlated with the viscosity, molecular structure, and reaction sites. As the polymerization time was longer, the final refractive change was larger, and the polymerization time was explained in terms of the monomer properties.
Inorganic-binding peptides, which exhibit specific binding affinity to an inorganic material, are versatile building blocks in the construction of novel bio-conjugated materials. However, very little knowledge regarding their adsorbed structures on the target material is currently available. In this article, we report on the single-molecule analysis of such polypeptides by scanning tunneling microscopy (STM). The adsorbed structure of a gold-binding peptide (GBP) on Au(111) was observed at the single-molecule level. FTIR spectroscopy revealed the helical structure of the GBP, and ab initio calculations confirmed the correlation between the observed STM image and a sample helical structure. It has been demonstrated that the conformational structure of the polypeptide is highly pre-organized, allowing favorable binding onto the gold surface. Gaining such an insight into the relation between the structure and the binding function of the peptide leads to a fundamental understanding of inorganic-binding peptide, and, consequently, to a rational design of these peptides.
A new microspectroscopic technique was applied to the analysis of occluding deposits in xylem elements of Quercus serrata. The production of this substance is believed to be a defense response of the sapwood against fungal infection. An occluding substance about 10 μm across was analyzed by Infrared-Scanning Near-field Optical Microscopy (IR-SNOM), which allows for the measurement of IR spectrum with high spatial resolution. The near-field IR spectrum of an occluding substance was different from those of xylem elements and featured a lack of the clear C–H absorption band that should appear at 3000 – 2850 cm−1. On the other hand, the absorption band of ester bond exhibited a very strong peak. Among the near-field IR spectra of related compounds, a similar ester absorption peak was observed in the spectrum of pectin and tannic acid. The presence of a C–H absorption band as a very week peak was similar to (+)-catechin and tannic acid.
Hybrid materials using a macroporous sponge and spherical microporous adsorbents have been developed for an effective rapid pretreatment of water samples. Various adsorbents, including methacrylate series, divinylbenzene (DVB), and graphite particles, were utilized for hybridization with a macroporous sponge consisting of polyethylene and polyvinyl acetate, EVA resin. Both the EVA resin and each of the particles were thermally blended at 150°C with water-soluble pore templates, pentaerythritol and poly (oxyethylene, oxypropylene) triol. After molding as a columnar shape, the hybrid materials were observed by a scanning electron microscope both before and after washing with water/methanol sonication. Only methacrylate series could be effectively fixed onto the pore surface of sponge, whereas DVB and graphite particles were incorporated to the EVA matrix. We assume that the chemical interactions between EVA and adsorbents are very important for effective hybridization to fix the adsorbents onto the pore surface. Furthermore, we demonstrated the hybridization of ion-exchange resin and sponge for a high throughput purification of ionic compounds. The ion-exchangeable polymers prepared by methacrylic acid, 4-vinylpiridine, and p-styrene sulfonic acid with ethyleneglycol dimethacrylate could be fixed at a given ratio of “20, wt%”, and its effective adsorption based on the ion-exchange ability was observed under rapid elution (3 mL min−1).
Inorganic anions were separated on a chemically bonded 18-crown-6 ether (18C6E) stationary phase in capillary ion chromatography. In this study 18C6E groups were chemically bonded on silica gel via reaction with 3-glycidyloxypropyltrimethoxysilane, followed by reaction with 2-aminomethyl-18C6E. Analyte anions were separated in the ion-exchange mode based on the fact that the eluent cation was trapped on the 18C6E and it worked as the anion-exchange site. The eluent cation and eluent anion as well as the eluent concentration affected the retention of the analyte anions. Different selectivity was achieved by using an acetonitrile-rich eluent. The present stationary phase was applied for the determination of UV-absorbing anions contained in saliva samples.
Two-dimensional (2D) mapping using different chromatographic separations coupled with mass spectrometry is a rapid and simple method for the analysis of a mixture using conventional liquid chromatography mass spectrometry. The 2D map could be created from two different chromatograms obtained with the same detector and different columns or separation methods. In this study, 2D mapping was applied to the analysis of components contained in Panax ginseng, and was evaluated in terms of its effectiveness in the separation of these components. The several glycosides included in Panax ginseng could not be sufficiently separated by one-dimensional chromatography with a reverse phase or a hydrophilic interaction chromatography (HILIC) column, but the components of Panax ginseng could be separated and visualized as a component pattern by 2D mapping. We showed that the components contained in the calli and their quantities were altered by the culture conditions in which the calli were grown by 2D mapping. 2D mapping is expected to be a useful method for visualizing complex component patterns found in glycosides and unknown compounds in foods.
The interaction of quinine sulfate (QS) and DNA has been investigated by spectra methods including fluorescence spectroscopy and resonance light scattering (RLS) technique in aqueous solutions. The QS showed an obvious decrease of fluorescence intensity upon the addition of trace amounts of DNA, and the quenching mechanism was suggested to be static quenching according to the Stern–Volmer equation. Under the acidic condition of pH 2.5, the quenched fluorescence intensity of the QS–DNA system was linearly dependent on the concentration of ctDNA ranging from 0.02 to 2.5 mg/L. The interaction between QS and DNA as well as the detection of DNA was further confirmed by RLS technique, and the results showed that enhanced RLS intensity was linearly related to the concentration of ctDNA from 0.01 to 3.5 mg/L. Therefore, two spectral methods for the detection of ctDNA have been established with the use of a QS small molecular probe.
In this work, the effects of ammonium fluoride on the decomposition of geochemical samples were investigated by analyzing some certified reference materials (CRM). The major and minor elements were detected by inductively coupled plasma optical emission spectrometry (ICP-OES), while trace and ultra-trace elements were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Decomposition time, temperature and the amount of ammonium fluoride were studied in detail. In the process of sample decomposition, on one hand, ammonium fluoride was used as the fluorinating agent because ammonium fluoride can be dissociated under acid medium to yield fluoride ions to attack silicon compound effectively. On the other hand, ammonium fluoride was used as a latent solvent since ammonium salt may dissolve insoluble fluorine compounds. The removal of insoluble fluorine compounds decreased the memory effect on digestion vessels caused by fluoride coprecipitation. By testing CRMs and many real samples, it was found that trace and ultra-trace elements could be digested using ammonium fluoride instead of hydrofluoric acid and the dissolution ratios of major and minor elements, for example Al, Ca, Mg, Fe, Na and K, improved noticeably. Moreover, the use of ammonium fluoride instead of hydrofluoric acid contributes to a greener environment and safer for operators.
The isomerization reaction of the β-form of 12-molybdophosphate ([PMo12O40]3−: PMo12) into the α-form in aqueous-organic mixed media containing various salts was extensively investigated with cyclic voltammetry. It was found that the concentration and type of organic solvent and salt strongly affected the rate of the isomerization reaction. When organic solvents with lower permittivity than water were used as auxiliary solvents, and high concentrations of salts were added to the reaction mixture, the β-form of PMo12 (β-PMo12) became more stable, leading to slow isomerization into the α-form (α-PMo12). Based on the results of this study, it is proposed that the isomerization reaction of β-PMo12 into α-PMo12 is caused by the attack of a proton on a corner-shared oxygen atom. Also, the variation of its reaction rate upon the addition of organic solvents and salts is due to interactions between both the protons and the solvents or anions, and between the cations and the PMo12 anion.
A simple spectrophotometric method for the assay of steroid 5α-reductase (5α-SR) was developed in which 5α-dihydrotestosterone (5α-DHT) and 5α-androstane-3α,17β-diol (5α-diol), metabolites formed in the NADPH-dependent reduction of testosterone with enzyme sources of 5α-SR, were measured by enzymatic cycling using 3α-hydroxysteroid dehydrogenase in the presence of excess thionicotinamide-adenine dinucleotide (thio-NAD) and NADH. It was found that 5α-SR activity was proportional to the accumulated thio-NADH having an absorption maximum at 400 nm. Because of the high cycling rate (> 600 cycle per min) and no interference from testosterone, enzymatic cycling can determine the sum of 5α-DHT and 5α-diol at the picomole level without separation from excess testosterone. The present method was readily applicable to the assay of 5α-SR activity of rat liver and prostate microsomes as well as to the assay of inhibitory activity of finasteride, a synthetic inhibitor of 5α-SR.
The plant toxin ricin is a lectin that binds to D-galactose or lactose moieties by multivalent interactions. In the present work, this avidity was used to develop a novel sandwich glyco-immunoassay using a carbohydrate microarray. For realization, 6-azidohexyl-lactose was immobilized on an alkyne silane surface by Cu(I) catalyzed click chemistry. This procedure is fast, and prevents any nonspecific binding on the microarray surface. Ricin binds via its B-chain to the lactose moieties, and is detected by the biotinylated anti-ricin A-chain. By adding a horseradish peroxidase-labeled streptavidin, a chemiluminescence signal can be generated. This method is described as a sandwich-type glyco-immunoassay. The signal on the glyco-chip can be regenerated for at least 10 measurements. The limit of detection was estimated to be 80 ng mL−1. The assay was carried out on the automated microarray readout platform MCR 3. In this way, it took 20 min for one measurement, including regeneration of the chip surface.
This study was concerned about an estimation of molecular diffusivity (Dm) in liquid phase systems. An equation based on the absolute rate theory of diffusion was derived by considering the aggregation of not only solvent molecules, but also solute molecules. It was also studied how the replacement of the molar volume of a solvent with its molecular weight influences the accuracy in estimating Dm. The values of Dm estimated by the equation were compared with those experimentally measured. The mean square deviation for the estimation of Dm was calculated as being about 14% for 217 Dm data measured in aqueous solutions of methanol and acetonitrile, which is comparable to that obtained by the Wilke–Chang equation. However, Dm of some solutes in carbon tetrachloride was more accurately estimated by this equation than by the Wilke–Chang equation. It is expected that the equation proposed in this study is effective for estimating Dm in liquid phase systems.
An amperometric biosensor for the determination of catechol was developed by immobilizing tyrosinase (tyr) on gold nanoparticles (AuNPs) and a (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel three-dimensional network film-modified gold electrode. The AuNPs self-assembled in a sol-gel network provided an excellent microenvironment for an enzymatic reaction between tyrosinase and the substrate. It was found that the AuNPs could significantly affect the electron-transfer kinetics of the enzyme reaction, and remarkably enhance the electrochemical reduction of the corresponding o-quinones at the electrode surface. The nanostructured electrode showed high sensitivity (306.7 mA M−1 cm−2) toward catechol, with an amperometric detection limit of 0.56 μM. The catalytic current of the biosensor was linear with the catechol concentration ranging from 1.7 to 96 μM with a correlation coefficient of 0.9992. The proposed biosensor exhibited a short response time, good anti-interferent ability, and excellent operational and storage stability.
Fine aerosol particles were analyzed by time-of-flight secondary ion mass spectrometry with high lateral resolution. After sulfate particles with a diameter of about 1 μm were sputtered by gallium primary ions (a gallium focused ion beam), solid materials with a diameter of about 100 nm were occasionally found inside the particles. Since the mass spectrum for the solid material was almost the same as that of graphite, we concluded that the solids were black carbon. It was also found that the black carbon located at the surface of the sulfate core, and they were usually surrounded by organic matter.
A disk-type solid-phase extraction method for simultaneous extraction of a wide range of semi-volatile organic compounds in water samples was developed. The developed method could extract 186 out of 202 model compounds from spiked environmental samples (0.1 μg/L) with 94% average recovery (50 – 111%). Compared with the previous cartridge-type method, the extraction time was reduced to approximately 1/6. Applying the combination of the developed method and the database system to environmental samples for non-target analyses, 39 micro-pollutants with a wide range of physicochemical properties were determined.