Direct and quick molecular analysis of live plant single cells viewed under a video-microscope has been developed in their intact undamaged environment using nano-electrospray tip and mass spectrometers. This method has been successful in identifying specific molecules in plant live single-cell analysis by mass spectrometry, and opens the possibility to compare different cell types from different tissues with morphological evidence in undamaged plants.
A thermal desorption (TD)-GC/MS method was applied for the determination of phthalates in plastic children's toys. The method, which does not need any cumbersome sample pretreatment such as solvent extraction, filtration and derivatization, has been proved to be useful not only as a sensitive analytical method to evaluate phthalate concentration in the toys, but also as a rapid and practical screening method to check whether the concentration exceeds the regulatory limit.
Spectroscopic measurements and applications to analytical sciences utilizing strong interactions between photons and molecules will be described. In particular, this report demonstrates high-sensitivity analysis of chemical species in solution through laser multiphoton ionization, and selective detection and characterization of the molecules located at solid surfaces and phase boundaries by using the method of second harmonic generation. Furthermore, new spectroscopic methods and sensitivity improvements utilizing the resonance of incident light photons with surface plasmons emerging on the surfaces of gold nanoparticles and nanostructures are presented. In addition, applications of surface plasmon resonance to spatio-selective plating to microscopic sites and to the field of nanobiotechnology are described, with special focusing on controlling biomolecules.
A weak laser irradiation (523 − 785 nm, 5 − 60 mW) onto an Au electrode surface of a 27-MHz quartz crystal microbalance (QCM) caused a frequency increase (a mass decrease) in the air phase. These frequency changes depended on the wavelength of the irradiated laser in the order of 523 nm > 636 nm > 785 nm, which corresponds to the light absorbance of the Au electrode of the QCM. The laser response increased linearly with increasing laser power (5 − 60 mW). In addition, the laser response showed a maximum at the incidence angle of 72 degrees when the P-polarized 636 nm laser was irradiated on the Au surface, due to the evanescent effect. These laser responses were also observed in the humid air of H2O, D2O, and in the vapors of various alcohols. Based on these findings, the observed frequency increase (mass decrease) can be explained by the photo-induced reversible desorption of water molecules from the Au electrode surface of the QCM due to the interfacial property changes.
It has been shown that polyammonium cations comprising quaternary ammonium and hydrophilic groups such as amide and hydroxyl groups stabilize a redox enzyme bilirubin oxidase (BOD). The BOD catalyzes the reaction: 4[Fe(CN)6]4− + 4H+ + O2 → 4[Fe(CN)6]3− + 2H2O, and has been a promising enzyme for use as a cathode catalyst in biofuel cells. In this study, the stabilizing effect of poly[oxyethylene(dimethylimino)propyl(dimethylimino)ethylene] (PA1) on BOD has been investigated. The sample solution containing BOD and the PA1 salt was kept at a given temperature, and the loss of the enzymatic activity was detected after given stored times. The activity decreased exponentially with stored time so that the first-order rate-constant of inactivation was determined. The inactivation rate-constant lowered with increasing the concentration of the PA1 salt, suggesting that BOD was stabilized by the association with the PA1 cation. The PA1 cation may act like a protective colloid or decrease the local disorder of BOD by its wrapping. A membrane-covered electrode containing BOD, PA1, and [Fe(CN)6]4−/3− in the internal solution phase was examined in air-saturated aqueous solution. The electrode gave a well-defined current-potential curve with a steady state limiting current due to the PA1-[Fe(CN)6]4−/3− polyion complex-mediated bioelectrocatalytic current for the reduction of O2. The decreasing of the steady state limiting current became slower in the presence of the PA1 salt, indicating again the stabilizing effect of PA1 cation on BOD.
An amperometric biosensor was constructed by using ZnO nanorod clusters as platforms for immobilizing tyrosinase on the nanocrystalline diamond (NCD) electrodes. The results showed that ZnO nanorod clusters provided an advantageous microenvironment due to their favorable isoelectric point (IEP) for tyrosinase loading; immobilized tyrosinase generally retained its activity. The tyrosinase/ZnO/NCD electrode showed a linear response range of 1 − 210 and sensitivity of 179.9 μA mmol−1 cm−2 for p-cresol. The corresponding values were 1 − 190 and 90.2 for phenol, and 1 − 250 and 121.3 for 4-chlorophenol. The low detection limits were estimated to be 0.2 μM for p-cresol, 0.5 μM for phenol, and 0.4 μM for 4-chlorophenol (S/N = 3). The prepared enzyme electrode could keep 85% of its original activity after intermittent use for 4 weeks when stored in a dry state at 277 K. Therefore, the ZnO nanorod cluster thin films have potential applications as platforms to immobilize other enzymes and bioactive molecules in biosensors.
Molecularly imprinted polymers (MIPs) were applied as molecular recognition elements to an electrochemical sensor for phenylephrine. A MIPs membrane was created on a glassy carbon electrode. SEM revealed a gradual change on the morphology of modified electrodes as the ratios of function monomer and cross-linking varied. When the ratio was 4:40, the surface morphology between the imprinted electrode (M-electrode) and the control electrode (N-electrode) became unambiguously different. This artificial receptor exhibited high selectivity for the template compared to closely related analogue. The response of the sensor varied in different concentration range might due to the heterogeneity of the MIPs membrane. This sensor was also used to determine phenylephrine in tablet samples.
Benzaldehyde (Bz) is a typical fragrant compound for peach-flavored beverages. In the food and beverage industries there is great demand for a sensitive and easy detection system of Bz in order to ensure product quality control and to avoid contamination. For the noncompetitive detection of Bz, we applied an open-sandwich enzyme-linked immunosorbent assay (OS-ELISA) utilizing an antigen-dependent reassociation of antibody variable region fragments, VH and VL. We cloned the VH and VL genes of an anti-Bz monoclonal antibody, and the fragments were individually expressed and purified as a bacterial alkaline phosphatase (BAP)-conjugated form for VH and as a thioredoxine (Trx)-fused form for VL, respectively. Using these VH and VL fragments, we successfully constructed the OS-ELISA system for Bz detection. The Bz-induced formation of a trimolecular complex composed of VH-BAP/Bz/Trx-VL was readily detected by a dose-dependent increase in the BAP activity of the VH-fusion protein.
With a specific and strong molecular-recognition capability cultivated in humoral acquired immunity, an antibody has been extensively utilized in various applications, such as diagnostics and therapy. However, so far most of its uses have been limited to be in the liquid phase. In view of its potential uses, such as a gas-phase biosensor or a high-performance air filter, we have tried to verify a previously undescribed binding reaction between protein antigens and corresponding antibodies immobilized on a solid surface by using fluorescence resonance energy transfer between the two. Our data showed that the antibody on a solid surface specifically reacted with a protein antigen supplied from the gas phase under the normal ambient condition. Also discovered was that the reaction occurred even faster than that in the liquid phase under several assay conditions.
Butyl methacrylate-based reversed phase capillary monolithic columns were prepared using ultraviolet (UV) photo-polymerization. The effects of two photo-polymerization conditions (UV irradiation intensity and polymerization temperature) on the column characteristics were investigated. Both the higher UV irradiation intensity and the lower polymerization temperature lead to the superior column efficiency. The column prepared under the optimized conditions was evaluated through the separation of the uracil and five alkylbenzenes in the linear flow rate range of 1 − 110 mm/s. At 1 mm/s, all analytes were well separated (N = 36000 − 45000 plates/m). The high speed separation within 8 s was performed at 110 mm/s (back pressure, 33 MPa) at room temperature, whereas the peaks eluted earlier were overlapped partially. The relationship between the flow rate and the back pressure indicated that some kind of structural change of the monolith might occur in 50 − 110 mm/s, although no visible or hysteresis changes of the monolith were observed after the measurement.
We report here on the results of a procedure for the determination of amphetamine drugs in hair. The procedure is simple and sensitive. The results from the procedure using small-volume extraction matches perfectly with those either from using the derivatization method or selected ion monitoring (SIM) detection. We validated our method using four different amine drugs, including amphetamine, methamphetamine, methylenedioxy-amphetamine and methylenedioxy-methamphetamine. The detection limit for these drugs is about 50 ± 7.5 pg/mg in hair and the intra-day and inter-day reproducibility are within 15% at most drug concentrations. Moreover, we also showed the utility of the procedure in analyses of authentic hair samples taken from amphetamine abusers, and demonstrated that the method meets the requirement for the analysis of a trace amounts of amphetamines in human hair.
A capillary electrophoresis (CE)-potential gradient detection (PGD) method was developed for quick and sensitive determinations of puerarin, farrerol and baicalin. The flavonoids were baseline separated in 1.9 min with a buffer comprised of 20 mM tris(hydroxymethyl)aminomethane (Tris) and 3 mM HCl at pH 8.69. The analysis time is, to the best of our knowledge, the shortest for the CE analysis of flavonoids. The association constants, determined by affinity CE, suggested an ion-dipole or ion-induced dipole interaction between Tris and flavonoid molecules. The detection limits, in the range of 0.068 and 0.116 mg L−1, were lower than the early reported UV and chemiluminescence detection techniques. A solvent-extraction method was coupled to CE to determine baicalin in a Chinese herbal preparation Scutellaria Baicalensis Georgi. The concentration of baicalin in the sample was determined to be 5.1%. Validation of the method suggested its applicability in real sample analysis.
This study intended to develop a robust and sensitive method for simultaneous determination of polycyclic musks (HHCB and AHTN) and nitro musks (musk xylene (MX) and musk ketone (MK)) in water samples using optimized solid-phase extraction (SPE) by gas chromatography and mass spectrometry (GC-MS). The SPE procedure was optimized in terms of selections of SPE cartridge, sample pH, elution process, etc. The method detection limits (MDLs) were from 0.09 to 0.18 ng L−1 for the analytes. The recoveries ranged from 88.3 to 104.1% in spiked deionized water and from 86.4 to 106.8% in groundwater samples, respectively. The proposed approach was also validated by detecting real samples. The results revealed that HHCB and AHTN were ubiquitous in the local aquatic matrices. Furthermore, nitro musks were found in some aquatic matrices, which is consistent with the fact that nitro musks are still being produced and applied in China.
A pH electrode for the selective determination of H+ was introduced. Both phosphorated calixarene and a N,N′-bisethoxycarbonyl-1,10-diaza-4,7,13,16-tetraoxacyclo-octadecane (DZCE) were used as new H+-ionophores. The calibration graphs of the obtained electrodes exhibits satisfactory Nernstian slopes. The electrodes were compared to blank membranes (without any ionophoric substances) for the first time. Selectivity coefficients of the studied electrodes towards several inorganic cations were calculated. The relative selectivity coefficient (RSC) was applied for evaluating the selectivity properties of H+-electrode using a mathematical equation. The electrodes were applied for the determination of different inorganic and organic acids.
The main aim of the present work was development of a quantitative structure-property relationship method using an artificial neural network (ANN) for predicting gas-to-olive oil partition coefficients of organic compounds. As a first step, a multiple linear regression (MLR) model was developed; the descriptors appearing in this model were considered as inputs for the ANN. These descriptors are: solvation connectivity index χ−1, hydrophilic factor, conventional bond-order ID number, dipole moment and a total size index/weighted by atomic masses. Then a 5-5-1 neural network was generated for the prediction of gas-to-olive oil partition coefficients of 179 organic compounds including hydrocarbons, alkyl halides, alcohols, ethers, esters, ketones and benzene derivatives. The values of standard error for training, test and validation sets are 0.127, 0.122 and 0.162, respectively for ANN model. Comparisons between these values and other obtained statistical values reveal the superiority of the ANN model over the MLR one.
This paper reports on the construction of an efficacious model for a non-invasive identification of traditional Chinese medicines, Liuwei Dihuang pills from different manufacturers, on the basis of near-infrared spectra (NIRS) coupled with moving window partial least-squares discriminant analysis (MWPLSDA). Considering the continuity of near-infrared spectral measurements, MWPLSDA is used to identify continuous and highly classification-related information intervals, a simple, yet effective classification model that can be developed for identifying accurate 150 Liuwei Dihuang pills from five different manufacturers. Meanwhile, the method is compared with some traditional pattern-recognition methods including principal component analysis (PCA), linear discriminant analysis (LDA) and partial least-squares discriminant analysis (PLSDA). The obtained results show that the method not only can reduce the operation time, but also significantly improves the classification accuracy. Hence, the nondestructive method can be expected to be promising for more practical applications on quality control and the discrimination of traditional Chinese medicine.
A technique to detect residual tetracyclines (TCs) in honey by HPLC and derivative UV-Vis spectra is examined in this study. Chromatograms of honey products often experience overlapped peaks and sloping background due to similar retention properties of components or to the presensce of impurities. The derivatives provide resolution of overlapped peaks in an UV-Vis spectrum and eventually bring chromatograms that show pure elution behavior of TCs. Calibration models for oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC) are built out of the derivative spectra of standard solutions of honey and their prediction abilities are examined. The results show that the calibration models for OTC, TC and CTC can yield sufficient levels for the determination. The technique reported here may be effectively used for quantitative determination of TCs.
The high performance liquid chromatography-electrospray ionization-mass spectrometry method has been applied to the measurement of bile acid transport activities in membrane vesicles obtained from a human bile salt export pump expressing Sf9 cells. The amounts of bile acids transported using the human bile salt export pump expressing Sf9 cells were determined using liquid chromatography-electrospray ionization-mass spectrometry method and the values of the kinetic parameters were determined to be comparable with those obtained using radioisotope-labeled substrates. The developed method was highly useful for the measurements of bile acid transport activities.
Poly(dimethylsiloxane) (PDMS)-coated platinum electrodes modified with glucose oxidase (GOx) have been prepared from poly(L-lysine) (polymer backbone), glutaraldehyde (cross-linking agent) and poly(ethylene glycol) units. To fabricate a GOx layer by applying cross-linking chemistries, the PDMS layer was treated with oxygen plasma to replace silane groups with silanol groups. Optimization for the chemical fabrication of a GOx layer resulted in a simple preparation of sensors with a wide detectable range (0.1 − 6.0 mM) and without interference from hydrogen peroxide produced by a GOx reaction and the other in biological samples.
4-Iodophenol was applied to an enhancer in the direct detection of horseradish peroxidase (HRP) encapsulated in liposomes by using luminol chemiluminescence (CL). Luminol, 4-iodophenol and hydrogen peroxide permeate into the inner phase of liposomes containing HRP, resulting in the progress of 4-iodophenol-enhanced luminol CL catalyzed by HRP in liposomes. The CL intensity observed in liposomes was a factor of 150 greater than that observed in a lipid-free bulk solution. The detection limit in the direct detection of HRP encapsulated in liposomes was sensitive by a factor of 30 compared with that in a lipid-free bulk solution. 4-Iodophenol effectively functioned as an enhancer in HRP-catalyzed luminol CL in liposomes.
The extraction behavior of new bi-functional ligands containing sulfoxide and amide groups viz. N,N′-dibutyl carbamoyl methyl phenyl sulfoxide (L1) and N,N′-dibutyl carbamoyl methyl benzyl sulfoxide (L2) towards the U(VI), Pu(IV) and Am(III) ions from nitric acid was studied. Both of these extractants showed appreciable extractions for U(VI) and Pu(IV) from 1 to 9.5 M nitric acid concentrations. Am(III) did not show an appreciable extraction under the conditions studied. The species extracted from a nitric acid medium correspond to the compositions of [UO2(NO3)2·2L] and [Pu(NO3)4·2L] for L1 and a mixture of [UO2(NO3)2·2L], [UO2(NO3)2·L] and [Pu(NO3)4·2L] for the L2. The conditional extraction constant (Kex) values for the Pu(IV) with L1 and L2 were estimated for the first time, and found to be 6.21 × 102 and 5.64 × 102 mol−4 dm, respectively.