Shewanella oneidensis MR-1 is a facultative anaerobic bacterium that is known to transfer electrons generated during metabolism to various metal ions and produce nanoparticles on the bacterial surface. In this study, we tracked the formation of gold nanoparticles (Au NPs) on the S. oneidensis cell surfaces and investigated the roles of membrane proteins and extracellular polysaccharides in this process by spectrometry, zeta potential analysis, and electron microscopy.
In the present work, a simple design of a “label-free” fluorescence method for kanamycin was developed and explored based on a specific DNA aptamer as a recognizer and a NMM/G-quadruplex DNA system as a reporter. The titration experiment showed a linear detection range of 0.5 to 100 nM with a low detection limit of 0.5 nM. It also showed excellent selectivity in a selectivity experiment. It was then successfully employed to detect kanamycin in milk with a excellent reliability.
The steady state and time-resolved photoluminescence quenching of streptavidin modified CdSe/ZnS quantum dots (QDs) instigated by biotin-peptide-BHQ-1 (biotin-pep-BHQ-1) molecule was investigated. Here, we have achieved an efficient photoluminescence (PL) quenching of QDs with the conjugation of dark quencher (black hole quencher-BHQ) molecules intermediated with the GPLGVRGK peptide. The luminescence of streptavidin-QDs585 was decreased upon titration with a nano molar concentration of the biotin-GPLGVRGK-BHQ-1 molecule. It has been suggested that the decrease of QDs PL occurred through a Förster resonance energy transfer (FRET) mechanism from the analysis of steady state photoluminescence intensity measurements as well as time resolved lifetime measurements of streptavidin-QDs and QDs-(pep-BHQ-1)n conjugates. The sequence of intermediate peptide GPLG↓VRGK can act as a target material for matrix metalloproteinases-2 (MMP-2) produced by cancer cells at its Gly and Val region, shown by the down-headed arrow. Interestingly, here the reported self-assembled QDs-(pep-BHQ-1)n conjugates could detect the presence MMP-2 at a detection limit of 1 ng/mL with a clear luminescence recovery.
We investigated the transduction function of a cationic dextran hydroxypropyltrimethyl ammonium chloride-coated magnetic iron oxide nanoparticle (TMADM-03) for transducing quantum dots (QDs) into adipose tissue-derived stem cells (ASCs). As a result, the fluorescence intensity of ASCs labeled with QDs using TMADM-03 was much higher than that of QDs only labeling. These data suggest that TMADM-03 can be useful as a transduction agent for QDs in stem-cell imaging.
Gas sampling bags have been used for collecting air samples. Tedlar bags are most commonly used, but bleed background chemicals such as N,N-dimethylacetamide and phenol. It is often necessary to remove the contaminant by flushing the bags with pure nitrogen or air. In this study, we identified four chloroprene dimerization products as background contaminants emitted from ALTEF bags that are made of a proprietary polyvinylidene difluoride (PVDF). No monomer chloroprene was detected in the bags analyzed. All of the dimers gradually increased once bags were filled with nitrogen due to diffusion from the bag surface. Flushing the bags with nitrogen reduced their concentrations, but was not effective for removing the contaminants. When the bags that had been flushed with nitrogen 5 times were left for 24 h, they increased again, indicating that the dimers were constantly emitted from the ALTEF bag surface. To our knowledge, these compounds have never been demonstrated in ALTEF or other PVDF bags. Our finding indicates that ALTEF might be incorporated with Neoprene (chloroprene-based polymer) during its manufacturing process.
A sensitive method was developed for the determination of ammonium in an aqueous solution based on gas phase light scattering. In a stream of carrier gas, the gaseous ammonia from the alkalized solution formed a volatile ammonium chloride derivative by reacting with gaseous hydrogen chloride; the gaseous ammonium chloride was analyzed by nondispersive atomic fluorescence spectrometry. The mechanisms of the method are elucidated based on evaporative light scattering detection. Parameters such as temperature, amount of sodium hydroxide, and carrier gas flow rate were studied. Under optimal conditions, the detection limit of ammonium-nitrogen was 0.045 μg. The method was successfully applied to the determination of ammonium in certified reference materials, and tap and seawater samples.
The selectivity coefficients reported for perchlorate of the high selectivity on anion exchange resins (AXRs) have not been consistent with one another. Possible errors by the unique use of four parameters (concentrations of two anions in two phases) were experimentally verified. The concentrations of perchlorate buffered at low levels (10−6 – 10−4 mol L−1) by two forms of AXRs were successfully determined by potentiometry with a perchlorate ion-selective electrode. This gave reasonable coefficients. The coefficients for perchlorate on several AXRs were independent of the relative exchange (RE), in contrast to the previous reports. On the other hand, the coefficients for fluoride of the low selectivity that were examined for comparison decreased with an increase in RE, and the dependency was more remarkable for the resins of large exchange capacity.
In the present work, a simple design of “turn-on” fluorescence method for mercury ion was developed and explored based on specific T-Hg-T mismatches as a recognizer and N-methyl mesoporphyrin IX (NMM)/G-quadruplex DNA system as a reporter. The titration experiment showed that the mercury-ion concentration and the fluorescence intensity signal change exhibited a consistent linear correlation within the 50 to 500 nM range with a detection limit down to 12.9 nM. In a selectivity experiment, our method showed obvious selectivity against other metal ions, being consistent with other reported detection methods of mercury ion based on the specific reactivity of T-Hg-T mismatches. Our method was then successfully employed to detect mercury ion in pond water with excellent reliability.
MicroRNAs (miRNAs) are attracting considerable attention as potential biomarkers for the early diagnosis of cancer. We have been developing a detection method for miRNAs on a microfluidic chip with external-power-free fluid pumping and enzyme-free amplification. The assay is completed within 20 min. Here, we describe the specificity of this miRNA detection method. First, the specificity against mismatched sequences was investigated. The nonspecific detection of a 2-nucleotide mismatched sequence was negligible, while that of a 1-nucleotide mismatched sequence was observed to a reasonable extent. Next, the disturbance in mature miRNA detection by existence of its precursor miRNA was evaluated. One precursor miRNA out of four tested showed significant nonspecific responses at 1 nM or higher concentrations. However, those responses were much lower than that of the target mature miRNA at 0.1 nM. Finally, we tried to detect three endogenous miRNAs, which are known to be potential cancer biomarkers, in human leucocyte total RNA. The measured concentraions of these miRNAs agreed well with those obtained by quantitative reverse transcription polymerase chain reaction. These results indicate that the on-chip miRNA detection method has good specificity, which is promising for applications to real biological samples.
A micrometer-sized spherical silica gel microparticle (pore diameter, ∼7 nm) was injected into an aqueous rhodamine 6G solution using microcapillary manipulation-injection technique, and the dye distribution in the single microparticle was measured as the fluorescence depth profile by confocal fluorescence microspectroscopy. The fluorescence depth profile was simulated by the convolution and deconvolution methods to correct the contribution of the spatial resolution of the experimental system. The dye homogeneously or heterogeneously distributed in the microparticle at the adsorption equilibrium, dependent on the type of silica gel. The intraparticle diffusion coefficient of the dye distributed homogeneously in the silica gel was analyzed by the simulations of the time dependence of the fluorescence depth profile based on the external and intraparticle diffusion model. The results indicated that the intraparticle diffusion of the dye in the silica gel is governed by the pore diffusion.
Aluminum (Al) has been well known as an environmental factor that may affect several enzymes and other biomolecules related to Alzheimer’s disease. The increasing use of Al in the preparation and storage of food currently represents the main form of Al exposure for the general public. The present study was aimed to develop a household procedure for the rapid test determination of Al in edible jellyfish. The method was developed based on the reaction of Chrome Azurol S with Al in acidic medium, forming a colored compound on the surface of filter paper. Experimental design methodologies were used to optimize the measurement conditions. The proposed method was applied successfully to the analysis of Al in edible jellyfish products in clinical laboratory and household settings.
This study aimed to develop a label-free, sensitive, selective, and environment-friendly fluorescent peptide probe His-His-Trp-His (HHWH) for determining the concentration of copper ion (Cu2+) in aqueous solutions. The results demonstrated that the designed HHWH has a high selectivity and sensitivity for monitoring the concentration of free Cu2+via quenching of the probe fluorescence upon a binding of Cu2+. The fluorescence intensity of the HHWH had a linear relationship with the concentration of Cu2+ between 10 nM and 10 μM, and the detection limit was 8 nM. Furthermore, HHWH could be regenerated with sulfide ions at least five times. The concentrations of Cu2+ in three different real water samples were detected using this probe, and the results were consistent with the one detected using an atomic absorption spectrometer. Thus, HHWH can be used as an accurate and feasible fluorescent peptide probe for detecting Cu2+ in aqueous solutions.
We propose an easy microchannel surface functionalization method for a poly(dimethylsiloxane) (PDMS) microchip that utilizes electron beam-induced graft polymerization (EIGP) as a platform for microchip-based biomarker analysis. Unlike other grafting techniques, EIGP enables rapid surface modification of PDMS without initiator immobilization. The grafted microchip is preservable, and can be easily functionalized for versatile applications. In this study, the surface-functionalized power-free microchip (SF-PF microchip) was used for the detection of microRNA (miRNA), which is a biomarker for many serious diseases. The EIGP enables high-density three-dimensional probe DNA immobilization, resulting in rapid and sensitive miRNA detection on the portable SF-PF microchip. The limit of detection was 0.8 pM, the required sample volume was 0.5 μL, and the analysis time was 15 min. The SF-PF microchip will be a versatile platform for microchip-based point-of-care diagnosis.
DNA-templated copper nanoparticles (CuNPs) have recently received considerable interest as functional fluorescent probes for biochemical analysis. In this work, a novel ATP-dependent ligation reactions (ATP-DLR) based ATP assay strategy was proposed by using hairpin-shaped (HS) DNA templated CuNPs as a fluorescent probe. Nick sealing by T4 DNA ligase leads to the formation of intact HS DNA, which can resist the exonuclease cleavage and be taken as the template for CuNPs formation, resulting in strong fluorescence. The proposed ATP detection is label free, sensitive and highly selective, and it has good linearity from 0.02 to 4 μM and a detection limit of 7 nM. This strategy is expected to promote the exploitation and application of DNA-templated CuNPs in biochemical and biomedical studies, and holds great promise in fluorescence detection for other ligation-related biomolecules.
Inductively coupled plasma tandem quadrupole mass spectrometry (ICP-QMS/QMS) measurements after xylene dilution were investigated as a method for determining the elements (Na, Mg, K, Ca, P, and S) in a biodiesel fuel (BDF) candidate reference material (RM). Optimizations were respectively carried out for the following parameters to obtain the best performance for measurements: O2 flow rate (additional gas to the carrier gas) to ensure complete combustion of the xylene solvent in the plasma, plasma power to obtain lower background signal intensities for Na and K, O2 flow rate (reaction cell gas) to remove any spectral interference with the S, H2 flow rate so as to remove spectral interference with Ca. After optimization, the lower detection limits of Na, Mg, K, Ca, P, and S were 0.0004, 0.00004, 0.0003, 0.00012, 0.00005, and 0.002 mg kg−1, respectively. Typical relative standard deviations were 2.1, 2.0, 1.7, 1.1, 2.5, and 2.5% for Na, Mg, K, Ca, P, and S, respectively, where the elemental concentrations in the BDF sample were, respectively, ca. 1 mg kg−1 each for Na, Mg, K and Ca, ca. 2 mg kg−1 for P, and ca. 6 mg kg−1 for S. The established method was applied to the homogeneity assessment of a candidate RM of BDF made from palm oil. The relative uncertainties of the homogeneity were 0.3, 0.4, 0.6, 0.3, 1.6, and 0.6% for Na, Mg, K, Ca, P, and S, respectively.
We investigated a simultaneous internal standard method in flame atomic absorption spectrometry (FAAS), in order to better the analytical precision of 3d-transition metals contained in steel materials. For this purpose, a new spectrometer system for FAAS, comprising a bright xenon lamp as the primary radiation source and a high-resolution Echelle monochromator, was employed to measure several absorption lines at a wavelength width of ca. 0.3 nm at the same time, which enables the absorbances of an analytical line and also an internal standard line to be estimated. In considering several criteria for selecting an internal standard element and the absorption line, it could be suggested that platinum-group elements: ruthenium, rhodium, or palladium, were suitable for an internal standard element to determine the 3d-transition metal elements, such as titanium, iron, and nickel, by measuring an appropriate pair of these absorption lines simultaneously. Several variances of the absorption signal, such as a variation in aspirated amounts of sample solution and a short-period drift of the primary light source, would be corrected and thus reduced, when the absorbance ratio of the analytical line to the internal standard line was measured. In Ti-Pd, Ni-Rh, and Fe-Ru systems chosen as typical test samples, the repeatability of the signal respnses was investigated with/without the internal standard method, resulting in better precision when the internal standard method was applied in the FAAS with a nitrous oxide–acetylene flame rather than an air–acetylene flame.
A simple and sensitive method to determinate glucose content was developed based on single plasmonic nanoparticles by conventional dark-field microscopy (DFM). An enzyme-responsive plasmonic Ag/Au bilayer of rods was designed and prepared. Their localized surface plasmon resonance (LSPR) could be tailored by the enzyme reaction of glucose oxidase (GOx) by finely tuning the morphology and plasmonic optical response of the hybrid nanostructure. It was found that the plasmon resonance scattering (PRS) spectra peak (λmax) shifted to longer wavelengths under enzyme reactions, and the degree of the shift were proportional to the content of glucose. This approach is convenient to study the local concentration of glucose in real time.
Based on the tunability of ionic liquids (ILs) according to the specific requirement of an application, 1-dodecylimidazolium chloride with amphiphilic structures was chemically fabricated on the surface of filter papers (DIL-FPs) for the first time. After synthesis, DIL-FPs was characterized by scanning electronic microscopy, energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy. DIL-FPs was used as a novel thin-film microextraction (TFME) phase for the preconcentration of amphiphilic bisphenol A from plant oil samples. The related extraction variables were studied in a spiked sunflower seed oil. Under the optimal conditions, the linear range was 5.0 – 1000 μg L−1 with a correlation coefficient of 0.9976. The limit of detection (S/N = 3) and the enrichment factor of the proposed method were 2.7 μg L−1 and 118, respectively. The intra-day precision and inter-day precision for six repeated determinations were 2.3 and 4.9%, respectively. These plant oil samples used in this work were free of bisphenol A contaminations. The recovery study carried out in different plant oil samples and mean recoveries ranged from 77.16 to 97.10%. The developed DIL-FPs extraction film phase followed by HPLC-UV provides a potential pretreatment strategy for the analysis of weak organic acid compounds in plant oil samples.
An analytical method to determine the residual lactide in polylactide (PLA) was proposed using an internal standard method of gas chromatography (GC). PLA samples and diphenyl ether (DPE) as an internal standard were dissolved in dichloromethane, then PLA was precipitated in anhydrous alcohol. The residual lactide and DPE were extracted to alcohol for GC analysis. At room temperature, lactide could react with alcohol and change into ethyl lactoyl lactate (ELL), but the relative response factor of lactide versus DPE could be obtained through a numerical analysis method. Therefore, the residual lactide content could be quantitatively calculated in PLA. The relative standard deviation (RSD) of the measurements is not more than 7.0%, indicating that the method is suitably precise.
Alkyl diamide amine (ADAAM), a new high-performance reagent with a simple structure, was examined for the mutual separation of Am(III) and Cm(III). The combination of ADAAM and N,N,N′,N′-tetraethyldiglycolamide (TEDGA) as a masking agent shows selectivity for Am(III) over Cm(III) in highly acidic media with separation factors of up to 41.
Acridine orange (AO) is widely applied as an organic fluorescent probe. In this work, AO was reacted with sunset yellow (SY) to form an ion-association complex in pH 3.4 Britton–Robinson (BR) buffer solution medium. This resulted in the fluorescence quenching of the former and helped to detect the latter with the maximum excitation wavelengths (λex) and emission wavelengths (λem) near 490 and 530 nm, respectively. The assay exhibits high sensitivity and selectivity with a detection limit of 0.002 μmol L−1 and the remarkable quenching of fluorescence was proportional to the concentration of SY in the range of 0.008 – 9.0 μmol L−1. Herein, this finding was utilized to develop a new strategy for simple, rapid, sensitive and selective detection of SY by combining AO based on fluorescence quenching. In addition, the optimum reaction conditions and the effect of foreign substances were studied. The reasons for fluorescence quenching were also investigated, which showed the quenching of fluorescence of AO with SY was a static quenching process. Furthermore, the proposed method was applied in a real sample analysis with satisfactory results.
The luminol chemiluminescence (CL) profile of an oil-in-water (O/W) emulsion during thermal oxidation (60°C) was assessed using the luminol-K3[Fe(CN)6] assay, in which the oxidation species produced by the autoxidation of an O/W emulsion generated CL emission. Increased CL intensity was observed for O/W emulsions prepared using either linseed or corn oil, which was increased by the addition of Fe2+ to the O/W emulsion. The relationship between the CL profile and results obtained by conventional approaches, such as the peroxide value (PV) and thiobarbituric acid (TBA) methods, were compared. Owing to good correlation between the CL intensity and results obtained by the methods, the CL method might be applicable for estimating the oil oxidizing of an emulsion in thermal oxidation.
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