A square optical loop used to observe the Sagnac effect was constructed by using a 632.8-nm He–Ne laser, a polarizing beam splitter and three mirrors, combined with a detection system. When a magnetic field was applied from the transversal direction to the beam of the loop, which passed through the sample cell containing magnetic nanoparticles (MNPs) in water, Sagnac interference was observed depending on the concentration of MNPs, indicating evolution of the magnetic birefringence. A possible analytical use of the magnetic Sagnac effect has been suggested.
Organophosphorus pesticides (OPs) represent a very important class of pesticides that are widely used in agriculture because of their relatively high-performance and moderate environmental persistence, hence the sensitive and specific detection of OPs is highly significant. Based on the inhibitory effect of acetylcholinesterase (AChE) induced by inhibitors, including OPs and carbamates, a colorimetric analysis was used for detection of OPs with computer image analysis of color density in CMYK (cyan, magenta, yellow and black) color space and non-linear modeling. The results showed that there was a gradually weakened trend of yellow intensity with the increase of the concentration of dichlorvos. The quantitative analysis of dichlorvos was achieved by Artificial Neural Network (ANN) modeling, and the results showed that the established model had a good predictive ability between training sets and predictive sets. Real cabbage samples containing dichlorvos were detected by colorimetry and gas chromatography (GC), respectively. The results showed that there was no significant difference between colorimetry and GC (P > 0.05). The experiments of accuracy, precision and repeatability revealed good performance for detection of OPs. AChE can also be inhibited by carbamates, and therefore this method has potential applications in real samples for OPs and carbamates because of high selectivity and sensitivity.
A simple and sensitive surface-enhanced Raman scattering (SERS) method for the detection of ethyl carbamate (EC) is reported in this work. Star-shaped silver nanostars (Ag NSs) were used as a novel SERS substrate. In comparison to other plasmonic nanoparticles (NPs), including Au NPs, Au NSs and Ag NPs, Ag NSs exhibit best SERS activity. Raman signal of EC at a trace level can be enhanced by several orders of magnitude with the help of Ag NSs. The Raman intensity of EC increased linearly with an increase of the EC concentration in the range from 5 × 10−9 mol L−1 to 1.0 × 10−4 mol L−1 with detection limit (LOD) of 1.37 × 10−9 mol L−1 (S/N = 3). The developed SERS approach also has the advantages of being simple, fast and requiring less amount of the sample. It could serve as a useful technology for the rapid determination of EC in both alcoholic beverages and fermented food.
Okadaic acid (OA), a lipophilic shellfish toxin, was accurately quantified using quantitative nuclear magnetic resonance with internal standards for the development of an authentic reference standard. Pyridine and the residual proton in methanol-d4 were used as removable internal standards to limit any contamination. They were calibrated based on a maleic acid certified reference material. Thus, the concentration of OA was traceable to the SI units through accurate quantitative NMR with an internal reference substance. Signals from the protons on the oxygenated and unsaturated carbons of OA were used for quantification. A reasonable accuracy was obtained by integrating between the lower and upper 13C satellite signal range when more than 4 mg of OA was used. The best-determined purity was 97.4% (0.16% RSD) when 20 mg of OA was used. Dinophysistoxin-1, a methylated analog of OA having an almost identical spectrum, was also quantified by using the same methodology.
Proteinaceous materials, such as ovabumin and collagen, were commonly used as binding media, and as adhesives and protective coatings. However, the identification of ancient proteinaceous binders is a great challenge for archaeologists, due to their limited sample size, complex combinations of various ingredients and reduced availability of the binder during the process of protein degradation. In this paper, an enzyme-linked immunosorbent assay (ELISA) provides to be a particularly promising method for the detection of proteinaceous binding materials in ancient relics. The present work focused on the specific identification of proteins in archaeological binders, which was brushed on the Tripitaka. Two samples, the adhesion area (S1) and the ink area (S2), were tested by ELISA. The results showed that both S1 and S2 reacted positively when treated with an anti-collagen-I antibody. It proved the existence of proteinaceous binders in Ancient Tripitaka, and the percentage of collagen in S1 and S2 was 61.44 and 15.4%, respectively. Compared with other conventional techniques, ELISA has advantages of high specificity, sensitivity, rapidity and low cost, making it especially suitable for the protein detection in the archaeological field.
A thiourea-based receptor has been extensively studied for selective anion recognition for reasons of its strong hydrogen bond donor ability. In the present study, the thermodynamics of complexation between a thiourea-based receptor and acetate was examined in a water/acetonitrile mixture. The receptor used in this study was N,N′-bis(p-nitrophenyl)thiourea (BNPTU). UV/vis spectroscopic titration and isothermal titration calorimetry (ITC) experiments clearly revealed endothermic and entropy-driven complexation of BNPTU with acetate in water/acetonitrile mixtures. Since the endothermic peaks found in water/acetonitrile mixtures were about three times greater than those in acetonitrile, it appears that preferential hydration of both receptor and acetate was responsible for the endothermic and entropy-driven complexation reaction. The thermodynamic properties found in this study have the potential to contribute to the design of a thiourea-based anion receptor.
A unique water-soluble porphyrin [5,10,15,20-tetra(3-ethoxy-4-hydroxy-5-sulfonate)phenyl porphyrin, H2TEHPPS] was designed and synthesized, which could be used as a potential sensor for the determination of Cu2+. Studies were performed in the solution. The concentration of H2TEHPPS was 5 μmol L−1. The optical properties of H2TEHPPS were investigated based on the absorption spectra. The results show that the absorbance of H2TEHPPS at 417 nm is directly proportional to the concentration of Cu2+ in the range of 0 – 2.5 μmol L−1. H2TEHPPS can thus be used as a novel class of Cu2+ sensors.
The common drawbacks of the current colorimetric sensing platform using gold nanoparticles (AuNP) as an indictor is its relatively low sensitivity, which restrict their analytical application for low-level analytes, such as the detection of the microRNA (miRNA). In the present work, we developed a novel strategy to construct a colorimetric sensing platform for miRNA based on target catalyzed hairpin DNA assembling. Unlike a single-stranded DNA probe or a single-arm hairpin structure DNA probe, in our strategy the double-arm hairpin structure DNA probe was first designed, and was further demonstrated to work well in catalysis the of hairpin DNA assembly reaction, which significantly enhanced the sensitivity of the AuNP based colorimetric sensing platform. In addition, compared to other miRNA detection schemes reported previously, the proposed strategy is not only enzyme-free, label-free, immobilization-free, but also eliminates the need for any sophisticated instrumentation. The proposed strategy may open a new way to allow miRNAs expression to be profiled in a decentralized setting, such as at point-of-care.
In this work, an aptasensor-based resonance light-scattering (RLS) method was developed for the sensitive and selective detection of acetamiprid. The ABA (acetamiprid binding aptamer)-stabilized gold nanoparticles (ABA-AuNPs) were used as a probe. Highly specific single-strand DNA (ssDNA, i.e, aptamers) that bind to acetamiprid with high affinity were employed to discriminate other pesticides, such as edifenphos, kanamycin, metribuzin et. al. The sensing approach is based on a specific interaction between acetamiprid and ABA. Aggregation of AuNPs was specifically induced by the desorption of the ABA from the surface of AuNPs, which caused the RLS signal intensity to be enhanced at 700 nm. The alteration of AuNPs’ aggregation has been successfully optimized by controlling several conditions. Under the optimal conditions, the RLS intensity changes (I/I0) of AuNPs were linearly correlated with the acetamiprid concentration in the range of 0 – 100 nM. The detection limit is 1.2 nM (3σ). This method had also been used for acetamiprid detection in lake water samples.
Polymeric ionic liquid-coated magnetic nanoparticles have been successfully prepared as adsorbents for the magnetic solid-phase extraction of four drugs, namely alfuzosin, doxazosin, terazosin and prazosin, from pharmaceutical preparations, urine samples and plasma samples. The four drugs were detected by fluorescence spectrophotometer. Several extraction parameters, including the pH of the solution; the type, ratio and volume of the desorbing reagent; the amount of adsorbent; the time of the extraction and desorption processes; and the addition of NaCl, were investigated and optimized. Linear responses were determined for the four drugs in the concentration range of 0.5 – 45 ng mL−1. The limit of detection values for alfuzosin, doxazosin, terazosin and prazosin, which were defined as three times the standard deviation of a blank sample, were determined to be 0.035, 0.034, 0.027 and 0.028 ng mL−1 (n = 11), respectively. Furthermore, this new method gave preconcentration factors of 114.5, 111.3, 111.1 and 108.5 for these four drugs.
A simple and rapid method was developed for the detection of poly(diallyldimethylammonium chloride) (PDADMAC) using citrate-capped silver nanoparticles (AgNPs). Detection was based on anti-aggregation of AgNPs in phosphate buffer caused by PDADMAC. Due to its positive charges, PDADMAC was adsorbed onto AgNPs via electrostatic interaction with citrate, which resulted in the charges at the particle surfaces to become positive and caused repulsion among particles. Furthermore, long-chain PDADMAC provided steric hindrance. These two effects promoted the dispersion of AgNPs in the phosphate buffer. A change in the state of dispersion influenced the surface plasmon resonance (SPR) of AgNPs. Therefore, in this work, the concentration of PDADMAC was determined by monitoring changes in absorbance (at 396 nm) caused by SPR of AgNPs. Under optimal conditions, the calibration was linear over the range of 1 to 100 mg L−1 with a detection limit of 0.7 mg L−1. Satisfactory precision was obtained (RSD = 2.8%). This method was successfully applied to the determination of PDADMAC in tap water samples. The recoveries ranged from 86.0 – 107.5%.
A promising strategy for trace analysis of hydrogen peroxide (H2O2) in natural water was established based on solid substrate room temperature phosphorimetry. The use of TiO2/SiO2 composite material as a phosphor for H2O2 detection was investigated. TiO2/SiO2 nanoparticle material was manufactured into a test kit for synchronous multilevel sampling test in the water sample reservoir. The proposed TiO2/SiO2 test kit displayed a wide linear response to H2O2 concentrations ranging from 1.0 × 10−6 to 1.0 × 10−1 M with a detection limit of 4.6 × 10−7 M. When the concentration of other species was 100 times of 1.0 × 10−4 M H2O2, the proposed test kit exhibited good selectivity toward the coexistence of 20 foreign ions. Satisfactory agreement between the proposed kit and spectrophotometric method was obtained, which demonstrated the possibility of its further development into a promising commercial phosphorescence sensor.
The strontium (Sr) isotope ratio (87Sr/86Sr) and Sr content were used to trace the geographical origin of onions from Japan and other countries, including China, the United States of America, New Zealand, Australia, and Thailand. The mean 87Sr/86Sr ratio and Sr content (dry weight basis) for onions from Japan were 0.70751 and 4.6 mg kg−1, respectively, and the values for onions from the other countries were 0.71199 and 12.4 mg kg−1, respectively. Linear discriminant analysis was performed to classify onions produced in Japan from those produced in the other countries based on the Sr data. The discriminant equation derived from linear discriminant analysis was evaluated by 10-fold cross validation. As a result, the origins of 92% of onions were correctly classified between Japan and the other countries.
Resonance-enhanced multiphoton ionization time-of-flight mass spectrometry was applied to measurements of multiple emulsions with no pretreatment; a method for the quantitative evaluation of aging was proposed. We prepared water-in-oil-in-water (W/O/W) multiple emulsions containing toluene and m-phenylenediamine. The samples were measured immediately following both preparation and after having been stirred for 24 h. Time profiles of the peak areas for each analyte species were obtained, and several intense spikes for toluene could be detected from each sample after stirring, which suggests that the concentration of toluene in the middle phase had increased during stirring. On the other hand, in the case of a W/O/W multiple emulsion containing phenol and m-phenylenediamine, spikes for m-phenylenediamine, rather than phenol, were detected after stirring. In the present study, the time-profile data were converted into a scatter plot in order to quantitatively evaluate the aging. As a result, the ratio of the plots where strong signal intensities of toluene were detected increased from 8.4% before stirring to 33.2% after stirring for 24 h. The present method could be a powerful tool for evaluating multiple emulsions, such as studies on the kinetics of the encapsulation and release of active ingredients.
Simultaneous electrochemical determination of nicotinamide adenine dinucleotide (NADH) and ascorbic acid (AA) at a carbon nanotube electrode is presented. The discrimination of NADH and AA is conducted with the difference of peak potential by differential pulse voltammetry. Two well-distinguished anodic peaks, +0.56 and +0.26 V, due to NADH and AA are observed. The characteristics of those peaks were independent from each other. The attained characteristics for simultaneous determination of NADH and AA are (i) NADH measurement at the concentration range of 0.030 – 2.0 mM in the presence of 1.2 mM AA, and (ii) AA measurement at the concentration range of 0.030 – 2.0 mM in the presence of 2.0 mM NADH.
The molar extinction coefficients of light-harvesting complex 2 (LH2) have been ambiguous in spite of its fame and wide utilization. Herein we determine the molar extinction coefficients of the LH2 proteins derived from the three purple photosynthetic bacteria Rhodoblastus acidophilus, Rhodobacter sphaeroides and Phaeospirillum molischianum at 298 K by direct extraction of bacteriochlorophyll (BChl) a from the lyophilized proteins, followed by estimation of BChl a amounts from their electronic absorption spectra.
Although ice chromatography is a useful probe of ice interfaces, its low separation efficiency has often made difficult to access the ice/water interface. Coupling of this method with shear-driven flow chromatography, which has high separation potential, solves the problems involved in ice chromatography. This paper reports on shear-driven flow ice chromatographic instrumentation, and discusses the separation performance. Electrostatic separation of positively and negatively charged dyes is demonstrated with an OH−-doped ice plate as a stationary phase.