Multiple unknown high-order cluster ions were observed as the results of ion-molecule reactions between strontium ions and fluoromethane molecules in the reaction-cell of an inductively coupled plasma tandem quadrupole mass spectrometer (ICP-QMS/QMS). In order to elucidate the structures of these unknown cluster ions, isotope-enriched fluoromethane (CD3F) was used as the reaction-cell gas compared to natural fluoromethane (CH3F). As results, SrF(CH3F)0-4+ and SrF(H2O)(CH3F)0-3+ cluster ions were experimentally confirmed in the present work, while SrF(H2O)(CH3F)0-3+ cluster ions in the reaction-cell of ICP-QMS/QMS were observed and confirmed for the first time in the world.
A fiber-optic sensor capable of real-time monitoring of biofilm formation in water was developed. The sensor can be easily fabricated by removing the cladding of a multimode fiber optic to expose the core. The sensing action is based on the penetration of an evanescent wave through a biofilm formed on the surface of the exposed fiber core during total internal reflection. The proposed setup can be used to analyze the transmittance response over a wide wavelength range using a white-light source and a spectroscopy detector. The change in transmittance with respect to the biofilm formation on the fiber core surface was observed. The findings from this study showed that the sensor detection had better sensitivity at near-infrared wavelengths than at visible-light wavelengths. Moreover, the sensitivity of this sensor could be controlled by surface modifications of the core surface through electrostatic interactions, involving a silane coupling layer, polyanions, and polycations. The developed sensor was successfully applied to evaluating of the effectiveness of a commercial biofilm inhibitor.
A developed Christmas-tree derived immunosensor based on a gold label silver stain (GLSS) technique was fabricated for a highly sensitive analysis of Vibrio parahaemolyticu (VP). In this strategy, captured VP antibody (cAb) was immobilized on a solid substrate; then, the VPs were sequentially tagged with a signal probe by incubating the assay with a detection VP antibody (dAb) conjugated gold nanoparticles (AuNPs)-labeled graphite-like carbon nitride (g-C3N4). Finally, the attached signal probe could harvest a visible signal by the silver meal deposition, and then followed by homebrew Matlab 6.0 as a grey value acquisition. In addition, the overall design of the biosensor was established in abundant AuNPs and g-C3N4 with a two-dimensional structure, affording a bulb-decorated Christmas-tree model. Moreover, with the optimized conditions, the detection limit of the as-proposed biosensor is as low as 102 CFU (Colony-Forming Units) mL−1, exhibiting an increase of two orders of magnitude compared with the traditional immune-gold method. Additionally, the developed visible immunosensor was also successfully applied to the analysis of complicated samples.
Labeling with fluorescent proteins is now widely exploited for elucidating the functions and roles of target proteins in living cells. Previously, we developed a protein labeling method by combining a fluorescent protein with a biotinylation reaction from archaeon Sulfolobus tokodaii. Biotinylation from S. tokodaii has a unique property that biotin protein ligase (BPL) forms a stable complex with its biotinylated substrate protein (BCCP). By taking advantage of this unique property, a target protein carrying BCCP in living cells can be labeled through biotinylation with BPL carrying a fluorescent protein. In the present work, to demonstrate the utility and performance of this labeling system in more detail, the cytoskeletal proteins β-actin and α-tubulin were selected as target proteins and labeled in living cells. With this approach, we succeeded in fluorescent imaging of actin filaments and microtubules in living cells, and shows the advantages of our approach over the conventional labeling methods with fluorescent proteins.
We were able to fill 1 – 10 nm-scale silica pores with water by vapor condensation, and examined the freezing phenomena, structures, and molecular motions of the confined water in the temperature range from 293 to 188 K by 1H-NMR spectroscopy. The results showed that almost all water molecules confined in 10 nm-scale pores were frozen and that approximately half of the water confined in 1 nm-scale pores existed in the liquid state even below the freezing point. The water adsorbed on the pore surfaces was estimated as a monolayer in 2.58 nm pores and bi- and tri-layers in 6.48 nm and larger pores, respectively. Furthermore, it was clarified from the proton relaxation rate (1H-1/T1) measurements that the molecular motions of adsorbed water itself were restricted by nanoconfinement and were extremely dependent on the conditions of proton exchange and hydrogen bond rearrangements of the adsorbed water.
We have developed an electrochemical reactive oxygen/nitrogen species sensor that can detect superoxide anion radicals (O2−•) and nitric oxide (NO). The reactive oxygen/nitrogen species sensor was fabricated by surface modification of an electrode with polymerized iron tetrakis(3-thienyl)porphyrin (FeT3ThP), and it can detect either O2−• or NO by switching the applied potential. Furthermore, we fabricated a sensor with improved selectivity by coating a Nafion® film onto the poly(FeT3ThP)-modified electrode. An interference current caused by NO2− was seen for the poly(FeT3ThP)-modified electrode, while the interference current was significantly reduced at the Nafion®/poly(FeT3ThP)-modified electrode, leading to improved selectivity for NO detection. The current response at the Nafion®/poly(FeT3ThP)-modified electrode exhibited good linearity in the O2−• and NO concentration ranges 1.3 – 4.1, and 0.5 – 10 μM, respectively. The Nafion®/poly(FeT3ThP)-modified and poly(FeT3ThP)-modified electrodes are highly versatile, because these electrodes can detect either O2−• or NO by switching the applied potential. Since the Nafion®/poly(FeT3ThP)-modified and poly(FeT3ThP)-modified electrodes contain no bio-derived compounds, the reactive oxygen/nitrogen species sensor should be safe even when it is used in vivo.
The simultaneous and sensitive electrochemical detection of dihydroxybenzene isomers (hydroquinone, HQ; catechol, CC; resorcinol, RS) is of great significance because such isomers can be awfully harmful to the environment and human health. In this paper, by preparing poly(L-arginine) modified glassy carbon electrode (P-L-Arg/GCE) with a simple method, a highly sensitive electrochemical sensor for simultaneously detecting HQ, CC and RS was constructed successfully due to the large surface area, good electronic properties and catalytic ability of P-L-Arg/GCE and the electrostatic action between P-L-Arg (positive) and targets (negative). Under the optimized conditions, the results show that the P-L-Arg/GCE has a wide linear range from 0.1 to 110.0 μM for HQ ,CC and RS. The detection limits for HQ, CC and RS are 0.01, 0.03 and 0.1 μM, respectively. Finally, the proposed sensor was successfully applied in real sample analysis.
In the present study, we found that phenylboronic acid derivatives including benzene-1,4-diboronic acid (BDBA) and mercaptophenyl boronic acid (MPBA) can induce the aggregation of citrate-capped gold nanoparticles (Au NPs). However, the speed of Au NP aggregation induced by MPBA was much faster than that of BDBA. The reaction between MPBA and Hg2+ ions resulted in the formation of MPBA-Hg2+-MPBA, which was similar to BDBA having two free boronic acid groups. Based on the above phenomenon, a sensitive and selective colorimetric method for the detection of mercury ions (Hg2+) in aqueous solution was developed. The linear range for the detection of Hg2+ ions was from 0.08 to 1.25 μmol dm−3 with a detection limit of 37 nmol dm−3. The strategy offered excellent selectivity toward Hg2+ against other metal ions. Meanwhile, this simple and cost-effective sensor was applied to determine the Hg2+ in the lake water samples with satisfactory recoveries (91.3 – 100.7%).
Direct chemiluminescence emission from the reaction of acidic permanganate and organic compounds was employed for determining the chemical oxygen demand (COD) in water (1-step CL COD). Due to the diversity of organic pollutants in water, there are no standards for COD measurements, and many compounds do not show any chemiluminescence signal in the 1-step CL COD method. As a result, this method shows a low correlation with the conventional CODMn method. In this study, a new 3-step CL COD method was developed to overcome these drawbacks. The basic principle of the 3-step CL COD method is based on the principle of “back titration” in the CODMn method: (i) the sample is treated with permanganate under heating, (ii) the excess permanganate is treated with pyrogallol, and (iii) the excess pyrogallol is measured by the chemiluminescence reaction with permanganate. The reagent concentration, sample volume, and heating temperature were optimized, and the 3-step CL COD method successfully obtained the signal from some samples that cannot be detected by 1-step CL COD method. The calibration graph is linear in the range of 0 – 12.86 mg/L with a detection limit of 0.082 mg/L. This method is continuous, sensitive and low cost compared with the conventional method, and is applicable for on-site monitoring. The effect of the chloride ion was investigated, and showed an insignificant effect after two-times dilution of high-salinity samples. The correlation with the CODMn method for various organic compounds showed a good coefficient of determination, R2 = 0.9773 (n = 16).
Herein, we propose a concept for sensing based on density changes of microparticles (MPs) caused by a biochemical reaction. The MPs are levitated by a combined acoustic–gravitational force at a position determined by the density and compressibility. Importantly, the levitation is independent of the MPs sizes. When gold nanoparticles (AuNPs) are bound on the surface of polymer MPs through a reaction, the density of the MPs dramatically increases, and their levitation position in the acoustic–gravitational field is lowered. Because the shift of the levitation position is proportional to the number of AuNPs bound on one MP, we can determine the number of molecules involved in the reaction. The avidin–biotin reaction is used to demonstrate the effectiveness of this concept. The number of molecules involved in the reaction is very small because the reaction space is small for an MP; thus, the method has potential for highly sensitive detection.
Room-temperature type H2S sensing devices that use Au-doped ZnFe2O4 yolk-shell microspheres as the active material have been fabricated using a solvothermal method as well as subsequent annealing and a chemical etching process. The samples are characterized using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), field-emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the doping of Au does not change the spinel structure of the products, which were yolk-shell microspheres, while the particle size varied with the Au doping concentration. Also, the as-fabricated sensor device exhibited excellent selectivity toward H2S gas at the room temperature; the gas-sensing property of 2 wt% Au-doped ZnFe2O4 microspheres was the best. The Au-doped ZnFe2O4 yolk-shell microspheres can be promising as a sensing material for H2S gas detecting at room temperature.
Developing blood substitutes is in urgent demand for chronic blood shortage all over the world. In this connection, the oxygen binding behavior of hemoglobin-based oxygen carriers (HBOCs) is one of the most important characteristics. However, present methods available for estimating oxygen binding behavior have need of expensive apparatus, and also are not suitable for high-throughput and the time-course analysis. To overcome these problems, we proposed a simple analysis method for the time-course oxygen binding behavior of HBOCs, which employs a general UV-Vis microplate reader and a common reagent, sodium dithionite, as a reductant for HBOCs and an oxygen scavenger. Our method enabled time-course oxygen binding behavior analysis of HBOCs in a simple manner, and obtained data corresponding with those by the conventional method. Thus, our developed method will accelerate the development of HBOCs due to easy oxygen binding analysis.
In this paper, quantum dot (QD)-based molecularly imprinted polymer (MIP) was fabricated and successfully utilized as a fluorescent probe for highly selective and sensitive detection of carbofuran in water samples. The MIPs were synthesized followed by a multi-step swelling and polymerization method, and then labeled with CdSe/ZnS QDs via gradual solvent evaporation. Then the prepared QDs-MIP microspheres were introduced to flow cytometry by virtue of their good dispersibility in water, and fast adsorption and desorption. Under optimized conditions, the fluorescence intensity of QDs-MIP decreased linearly with the increasing of carbofuran in the concentration range of 1 – 20 μg L−1 (R2 > 0.99) and it can detect down to 0.2 μg L−1 of carbofuran. This method was simple, selective and applied successfully to the optosensing of trace carbofuran in water samples with good recoveries ranging from 94.1 ± 3.7 to 98.4 ± 4.5%.
Au nanoparticles (AuNPs) dispersed in water were stabilized by tripolyphosphate (P3O105−). When Cr2O72− (Cr(VI)) was present, the AuNPs did not change; when Cr3+ (Cr(III)) was present, the AuNPs would aggregate because of cooperative metal-ligand reaction. Aggregated AuNPs showed different color from the non-aggregated ones. Thus, a simple colorimetric assay was made using AuNPs-Cr(VI) to detect ascorbic acid (AA). Upon introducing AA to the AuNPs-Cr(VI) system, Cr(VI) was reduced to Cr(III), and the aggregation of AuNPs occurred. This colorimetric assay performed high selectivity and a linear concentration response in the range of 0.2 to 10 μM; its limit of detection was 0.15 μM.
In this study, a fast and easy-to-use capillary-type microdevice for competitive bioassay is proposed. The device is composed of polydimethylsiloxane (PDMS) microchannel arrays that separately immobilize polyethylene glycol (PEG) coating, which contained graphene oxide (GO)–analyte conjugates and fluorescently-labelled receptor proteins. The working principle of the device involved the spontaneous dissolution of the PEG coating, subsequent mixing and reaction with analyte to give fluorescence response, triggered by the capillary action-mediated introduction of a sample solution. For principle verification, a competitive biotin assay was successfully demonstrated within 20 s in a single-step operation by detecting the change in fluorescence via microscopy.
Optimized Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) pretreatment methods for determination of six polychlorinated biphenyls (PCBs) residues in fish and aquatic invertebrates samples were investigated. Large volume injection (LVI) coupled gas chromatography tandem mass spectrometry (GC-MS/MS) with selected reaction monitoring (SRM) was used to provide a very sensitive and selective means of analyzing PCBs via internal calibration. Three analytical processes were validated and compared, and the florisil Celite®545 pretreatment method was selected. Performance characteristics, such as linearity, limit of detection (LOD), limit of quantization (LOQ), recovery and precision (relative standard deviation, RSD) were studied. The method was applied to 233 samples obtained from local markets, which was useful and thus suggested that the method could serve as a screening model for PCB residues analysis.
Stable hydrogen and oxygen isotopic compositions (δD and δ18O values, respectively) were analyzed for “sake,” a traditional Japanese alcohol beverage, to assess these values for the identification of its geographic origin. We collected sake (Junmai-shu; made of only rice, water, and koji) and its source water (i.e., brewing water) from breweries in Niigata Prefecture, Japan, and measured the isotopic compositions of water in these samples. The δD and δ18O values for the sake are well correlated with their respective values for the corresponding brewing water (δD; r = 0.92, δ18O; r = 0.80). Furthermore, based on the δD–δ18O cross plot, sake brewed in Niigata Prefecture is distinguishable from that brewed in countries other than Japan. These results imply that this dual isotope (δD and δ18O) analysis is potentially useful in identifying the geographic origin of sake.