As a tool to determine the magnetic susceptibility of a nano/microparticle in a liquid, a nano-gap magnetophoresis device was fabricated using tilted flat glass plates and a permanent magnet. The nano-gap device was not only used to determine the size of particles, but also directly provided measurements of Raman spectra of fractionally trapped particles in the nano-gap device. The performance of the new hyphenated method was demonstrated by an analysis of suspended particle matter in traffic air.
The present paper examines the efficiency of a complementary metal-oxide semiconductor (CMOS) using an indium nanoparticle (InNP) substrate for the high-sensitivity detection of antigen/antibody interactions at concentrations as low as 100 pg/ml under normal light. Metal NPs coated with antigen/antibody layers act as a dielectric layer on the conducting sphere, which enhances the number of photons hitting the sensor surface through a light-scattering effect. This photon number is proportional to the digital number observed with the CMOS sensor for detecting antigen/antibody interactions.
In this brief review, gold nanoparticles conjugated with functional polymers are described from the viewpoint of application to sensing materials. The optical properties of gold nanoparticles, the synthesis of polymer-functionalized gold nanoparticles, and their analytical applications are discussed. Polymer-functionalized gold nanoparticles are categorized into two classes: biopolymer-conjugated gold nanoparticles and artificial-polymer conjugated gold nanoparticles. Fluorometric and colorimetric sensing using gold nanoparticles are focused; fluorometric detection enables us to exploit sensitive assays for practical use. Furthermore, chemical amplification using gold nanoparticles is also discussed for the sensitive probing.
Surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF-MS) using nanoparticles (NPs) and nanostructured surfaces as the LDI-assisting nanomaterials is a soft ionization technique that features minimal fragmentation of analytes. As compared to traditional matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) using organic matrices, SALDI-MS affords several advantages, such as the ability to detect small molecules (<500 Da), easy sample preparation, low-noise background, high salt tolerance, and fast data collection without the use of an organic matrix. The performance of SALDI has been further improved recently in terms of the detection sensitivity, detection mass range from the low- to the high-mass region, a soft LDI process, the detection of both polar and nonpolar compounds, the selective detection of analytes from a complex mixture using functionalized NPs, and various applications, including imaging mass spectrometry. This review summarizes recent developments pertaining to various NPs and nanostructured surfaces for SALDI-MS.
We examined optical cavity effects on the 2-photon absorption efficiency of a dye (Rohdamine B; RhB) doped in polymer microspheres (ion-exchanging resin and poly(methyl methacrylate) (PMMA)). When 1064 nm pulsed-laser light was irradiated on single polymer microspheres doped with RhB under an optical microscope, we clearly observed dye fluorescence from individual microspheres, although the dye was transparent at 1064 nm. We confirmed that the fluorescence intensity was proportional to the square of the laser power for excitation. In contrast, such fluorescence was not observed from RhB doped in a PMMA film, in which the enhancement of a light electric field by an optical cavity effect was never expected. Theoretical calculations indicated that the microsphere possessed several peak values of the quality factor (Q = 102 − 105) at around certain particle diameters under 1064 nm irradiation. This means that the electromagnetic field of incident light is enhanced through light confinement in a microsphere. Based on these results, we conclude that the 2-photon absorption probability of RhB would be considerably enhanced by the optical cavity effects of the microsphere.
The acid-base behavior of rhodamine B (RB) in reversed micellar solutions of cetyltrimethylammonium chloride (CTAC) in 1-hexanol–cyclohexane/water was investigated through absorption and fluorescence measurements under varying the hydrogen-ion concentration in a water pool, the mole fraction of 1-hexanol in a bulk solvent and the water to surfactant molar concentration ratio. RB exhibited equilibria between the cationic, zwitterion and lactone forms of the dye as a cause of the spectral changes, indicating a change in the RB distribution among the reversed micellar water pool, interface and bulk solvent. Furthermore, RB was used as a probe to develop a method for determining the critical micelle concentration (CMC) in CTAC solutions. Abrupt variations in the intensities and wavelengths of the absorption and emission maxima of RB were observed at the CMC. The standard free energy of micellization was also evaluated from the CMC data.
We have developed an analytical system capable of detecting point mutations in a higher copy number of wild-type DNA based on an allele-specific ligase detection reaction (LDR) in conjunction with fluorescence resonance energy transfer (FRET). Streptavidin-functionalized quantum dots (QDs) used as FRET donors effectively captured biotinylated LDR products (target DNA strands) labeled with fluorophores as a FRET acceptor, enabling the formation of a sensitive energy transfer pair and direct detection of the targets without any post-LDR separation process, which is generally required for the LDR-based mutation analysis. Our experiments indicated that the present system had an ability to detect one mutant sequence in 10 normal sequences at a signal-to-background ratio of ca. 3.9.
A simple and homogeneous method based on aptamer and pyrene moieties for the detection of K+ was developed. The aptamer was labeled by pyrene moiety at 3′ end as the molecular recognition element. In the presence of K+, the complementary oligonucleotide labeled by pyrene moiety at 5′ end was displaced from the aptamer, which was accompanied by a dramatic decrease of the excimer fluorescence of pyrene. However, the excimer fluorescence remains in the absence of the target. With optimum conditions, relative changes of the pyrene excimer fluorescence intensity were proportional to the concentrations of K+ in the range of 6.3 × 10−4 to 1.0 × 10−2 M with a detection limit of 5.0 × 10−4 M. Importantly, in the presence of Na+, NH4+, Mg2+ and Ca2+ cations of biological fluids, this method was able to detect K+ with high selectivity. In a word, the assay seems to have great potential applications, especially in biological fluids due to its simplicity, specificity and homogeneous detection.
A novel label-free electrochemical nucleic acid aptasensor for the determination of cocaine by the immobilization of thiolated self-assembled DNA sequences on a gold nanoparticles-modified electrode is presented. When cocaine was complexed specifically to the aptamer, the configuration of the nucleic acid aptamer switched to a locked structure and the interface of the biosensor changed, resulting in a variation of the corresponding peak current of an electrochemical probe ([Fe(CN)6]3−/4−). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to characterize modifications of the electrode surface. The peak current was detected by differential pulse voltammetry (DPV). Under the optimized experimental conditions, the presented sensor exhibits a nice specificity towards cocaine. The decrease of the peak current response of the aptasensor has a linear relationship with the concentration of cocaine ranging from 1.0 × 10−6 to 1.5 × 10−4 mol L−1 with a detection limit of 3 × 10−7 mol L−1 at 3σ. The proposed aptasensor can be easily regenerated by the denaturalization of aptamer-target complexes in a heated water bath at 80 – 90°C. Besides, this biosensor has a high reproducibility and selectivity, which can be a promising method to detect cocaine in real samples.
Excitation-emission matrix fluorescence (EEM) was proposed to quantify three polycyclic aromatic hydrocarbons of anthracene (AN), phenanthrene (PHE) and pyrene (PY) in this paper. Direct analysis through selecting the appropriate areas from the data of EEMs and another approach using all data of EEM combined with the Parallel Factor (PARAFAC) were discussed respectively. The results showed that the predicted concentrations of PHE and PY approached the actual one for both methodologies, and that the room-mean-square errors of the prediction were no more than 0.5 μg L−1. In addition, a new quantificational method was suggested, in which the sum intensity around the peak value replaced the maximum intensity in the selected regions. The sensitivity can be improved ten times compared with the conventional analysis.
Diabetes mellitus is a complex metabolic disorder characterized by chronic hyperglycemia, hypoinsulinemia, and ketosis. To access the biochemical process of diabetes, we applied quantitative 1H NMR-based metabonomics to analyze urine, serum, and liver extracts from streptozotocin-induced diabetic rats. Principle component analysis (PCA) of 1H NMR spectra disclosed metabolic pattern differences between diabetic and control rats, and identified the related metabolic changes. The PCA scores plot demonstrated that the diabetic group could be distinguished from the control group, indicating that the metabolic characteristics of the two groups were markedly different. Our work reveals the accumulation of triglycerides, fatty acids and acetoacetate in diabetic rats, and may provide an efficient, convenient way for evaluating the pathological state and biochemical process of diabetes mellitus.
A new polystyrene divinylbenzene-based chelating resin was synthesized by functionalizing Amberlite XAD-4 with N,N′-bis(o-vanillinidene)ethylenediamine. This resin was capable of preconcentrating Cu(II), Cd(II) and Pb(II) in water samples prior to FAAS determination. Various parameters, such as the pH, eluent type and concentration, volume of the eluent and the sample, and diverse ion effects have been studied. The recoveries for the analytes under the optimum working conditions were higher than 95%. The accuracy of the method was tested with standard reference materials (MBH-C31XB20, GBW-02703 and CRM BCR-32) and Cd(II), Cu(II) and Pb(II) standard solutions. The method was successfully applied to water samples.
A sensitive HPLC method combined with a column-switching system and tris(bipyridine)ruthenium(III) electrogenerated chemiluminescence (ECL) detection has been developed for the quantitative determination of mexiletine (MEX). MEX was derivatized by divinylsulfone (DVS) and then measured. The optimum conditions for the derivatization reaction were 10 μL of sample solutions, 40 mM DVS (pH 8.0), a reaction temperature of 50°C, and a reaction time of 15 min. The derivatized samples were cleaned up by an on-line pretreatment column. Also, after column-switching to the analytical column, the derivatized MEX was separated and detected. The calibration curves of MEX in human control serum showed good linear regression (r = 0.9996) from 0.008 to 6.56 μg ml−1. The detection limit of MEX was 0.008 μg ml−1 (S/N = 3). At a concentration of 2.0 μg ml−1 MEX, the relative standard deviation (n = 5) was 0.98%. In this method the concentration of MEX in human control serum was readily measured, and this method was successfully applied to the time courses of the concentration of MEX in rabbit plasma after intravenous administration. The proposed method involved a simple and minimum sample-preparation procedure and a short run time (<20 min). Therefore it can be applied to routine therapeutic monitoring and pharmacokinetic studies of MEX.
X-ray powder diffractometry/Rietveld refinement was employed to estimate the purity of several chrysotile powders for calibrating standards. α-Corundum powder was mixed into each chrysotile sample as an internal standard. X-ray diffractometry was performed on these mixtures, and the mass fractions of amorphous and impurity phase content were calculated using Rietveld refinement. The chrysotile samples had 56.7 – 92.0% crystalline purity. X-ray diffraction intensities of chrysotile (002) from the samples showed good correlation with the crystalline purity data. In differential thermal analysis results, the exothermal peak intensities were found to be directly proportional to crystalline contents for crystalline purity lower than 80%. Any chrysotile sample can be used as a standard material for quantitative determination upon correction of the crystalline purity, which can be estimated using the proposed method.
The gas temperature of atomospheric gas in a graphite atomizer was measured during an atomization stage in graphite furnace atomic absorption spectrometry (GF-AAS), by using a two-line method under the assumption of Boltzmann distribution. Iron and nickel were chosen as the probe elements to compare the gas temperatures obtained with different pairs of spectral lines. The atomic absorptions of two iron atomic lines and those of two nickel atomic lines were simultaneously monitored to obtain their absorbances for the temperature determination. Their gas temperatures were lower than the wall temperature which was monitored by the conventional temperature control for GF-AAS. Furthermore, the temporal variations at the atomizing stage were different between the iron lines and the nickel lines: the maximum peak of the nickel gas temperature appeared to be more delayed and broadly than that of the iron gas temperature. This result could be attributed to the fact that nickel species began to be atomized a little behind iron species, probably because it was more difficult to reduce nickel oxide with graphite carbon than an iron oxide when these oxide species would be formed at the charring stage. A graphite furnace varies the temperature during the atomizing-duration time and also the distribution becomes inhomogeneous at different portions; therefore, the gas temperature would provide overall information along the optical path of incident radiation, when the probe elements diffuse in the furnace. The two-line method enables variations not only in the gas temperature but in the atomizing of probe elements to be directly determined, due to the ability of remote sensing and rapid response.
An anion-exchange chromatographic method has been developed for simultaneous analysis of cyanuric acid (CA) and five inorganic anions (F−, Cl−, NO3−, HPO42− and SO42−) in milk powder. The separation was achieved within 15 min on an anion-exchange column with simple elution of Na2CO3/NaHCO3 buffer as mobile phase. Furthermore, the effect of the total concentration of Na2CO3/NaHCO3 buffer on the retention of five inorganic anions was more obvious than that on CA retention, which indicated that CA retention on anion-exchange column depends not only on anion-exchange interaction but also on hydrophobic interactions between CA and anion-exchange column. The linear range of the calibration curve for CA was 0.1 – 100 mg L−1. The detection limit calculated at S/N = 3 was 0.083 mg L−1. The method was successfully applied to the analysis of CA in milk powder.
An analytical method has been described for the determination of mercury using a carbon paste electrode. Conditions for the preparation of the carbon paste electrode were optimized for low background current in order to use it for the determination of ultra trace levels of mercury. The carbon paste electrode was found to be a good electrode material for the determination of mercury. The optimized pH for the determination was in the range of 2.5 to 3.5. The three sigma detection limit of mercury was obtained as 0.095 μg L−1. Method has been modified for determination of mercury in cobalt sulfate samples.