Graphene oxide wrapped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@Au nanostructures as substrates for aptamer-based detection of <Emphasis Type="Italic">Vibrio parahaemolyticus</Emphasis> by surface-enhanced Raman spectroscopy

The authors describe a sensitive surface-enhanced Raman scattering (SERS)-based aptasensor for the detection of the food pathogen Vibrio parahaemolyticus. Nanostructures consisting of Fe₃O₄@Au particles wrapped with graphene oxide (GO) were used both as SERS substrates and separation tools. A first aptamer (apt 1) was immobilized on the Fe₃O₄@Au/GO nanostructures to act as a capture probe via the affinity binding of aptamer and V. parahaemolyticus. A second aptamer (apt-2) was modified with the Raman reporter molecule TAMRA to act as a SERS sensing probes that binds to the target the same way as the Fe₃O₄@Au/GO-apt 1. The sandwich formed between Fe₃O₄@Au/GO-apt 1/V. parahaemolyticus and apt 2-TAMRA can be separated with the aid of a magnet. The concentration of V. parahaemolyticus can be quantified by measurement of the SERS intensity of TAMRA. Under optimal conditions, the signal is linearly related to the V. parahaemolyticus concentration in the range between 1.4 × 10² to 1.4 × 10⁶ cfu·mL^?1, with a detection limit of 14 cfu·mL^?1. Recoveries ranging from 98.5% to 105% are found when analyzing spiked salmon samples. In our perception, the assay described here is a useful tool for quantitation of V. parahaemolyticus in real samples.

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Graphical abstract GO wrapped Fe₃O₄@Au nanostructures were synthesized as the substrate and modified with with a first aptamer (apt 1) to capture V. parahaemolyticus. TAMRA labelled aptamer 2 was then used as signal probe. The V. parahaemolyticus concentrations are closely related to the Raman intensity of TAMRA.

     

On the weak solutions to a shallow water equation

We obtain the existence of global‐in‐time weak solutions to the Cauchy problem for a one‐dimensional shallow‐water equation that is formally integrable and can be obtained by approximating directly the Hamiltonian for Euler's equation in the shallow‐water regime. The solution is obtained as a limit of viscous approximation. The key elements in our analysis are some new a priori one‐sided supernorm and space‐time higher‐norm estimates on the first‐order derivatives. © 2000 John Wiley & Sons, Inc.     

窄线宽、高光束质量的外腔双反馈激光二极管阵列

设计了一种离轴双反馈外腔能够有效地改善激光二极管阵列的线宽和光束质量。闪耀光栅和高反镜之间形成了一个共振腔。通过调整光栅和高反镜之间的倾角可以选定一个空间模在共振腔中放大。将一个半波片插入外腔中的光栅反馈支路,来控制反馈光的数量,激光从光栅反馈支路输出。运用这项技术,在工作电流16 A,可以把激光二极管阵列的输出线宽压缩到0.15 nm,光束束宽积减小到283 mm·mrad。由于光栅的锁定作用,中心波长几乎不随温度的变化而改变。在工作电流17 A时,输出激光的功率为2.44 W,斜率效率为0.5 W/A。     

A Dual-Mode Method Based on Aptamer Recognition and Time-Resolved Fluorescence Resonance Energy Transfer for Histamine Detection in Fish

Histamine produced via the secretion of histidine decarboxylase by the bacteria in fish muscles is a toxic biogenic amine and of significant concern in food hygiene, since a high intake can cause poisoning in humans. This study proposed a fluorometric and colorimetric dual-mode specific method for the detection of histamine in fish, based on the fluorescence labeling of a histamine specific aptamer via the quenching and optical properties of gold nanoparticles (AuNPs). Due to the fluorescence resonance energy transfer phenomenon caused by the proximity of AuNPs and NaYF4:Ce/Tb, resulting in the quenching of the fluorescence signal in the detection system, the presence of histamine will compete with AuNPs to capture the aptamer and release it from the AuNP surface, inducing fluorescence recovery. Meanwhile, the combined detection of the two modes showed good linearity with histamine concentration, the linear detection range of the dual-mode synthesis was 0.2–1.0 μmol/L, with a detection limit of 4.57 nmol/L. Thus, this method has good selectivity and was successfully applied to the detection of histamine in fish foodstuffs with the recoveries of 83.39~102.027% and 82.19~105.94% for Trichiurus haumela and Thamnaconus septentrionalis, respectively. In addition, this method was shown to be simple, rapid, and easy to conduct. Through the mutual verification and combined use of the two modes, a highly sensitive, rapid, and accurate dual-mode detection method for the analysis of histamine content in food was established, thereby providing a reference for the monitoring of food freshness.     

Divergent Construction of Diverse Scaffolds through Catalyst-Controlled C−H Activation Cascades of Quinazolinones and Cyclopropenones

A transition-metal-catalyzed C−H activation cascade strategy to rapidly construct diverse quinazolinone derivatives in a one-pot manner is reported. The catalysts play an important role in the different transformations. Additionally, the procedure is scalable, proceeds with high efficiency and good chemo-/regio-selectivity, and tolerates a range of functional groups.     

Empirical likelihood method for intermediate quantiles

Intermediate quantiles play an important role in the statistics of extremes with particular applications in risk management. For interval estimation of quantiles, Chen and Hall (1993) proposed the so-called smoothed empirical likelihood method. In this paper, we apply the method in Chen and Hall (1993) to construct confidence intervals for an intermediate quantile by deriving the corresponding Wilks Theorem.     

A highly sensitive fluorescence resonance energy transfer aptasensor for staphylococcal enterotoxin B detection based on exonuclease-catalyzed target recycling strategy

An ultrasensitive fluorescence resonance energy transfer (FRET) bioassay was developed to detect staphylococcal enterotoxin B (SEB), a low molecular exotoxin, using an aptamer-affinity method coupled with upconversion nanoparticles (UCNPs)-sensing, and the fluorescence intensity was prominently enhanced using an exonuclease-catalyzed target recycling strategy. To construct this aptasensor, both fluorescence donor probes (complementary DNA₁–UCNPs) and fluorescence quencher probes (complementary DNA₂–Black Hole Quencher₃ (BHQ₃)) were hybridized to an SEB aptamer, and double-strand oligonucleotides were fabricated, which quenched the fluorescence of the UCNPs via FRET. The formation of an aptamer–SEB complex in the presence of the SEB analyte resulted in not only the dissociation of aptamer from the double-strand DNA but also both the disruption of the FRET system and the restoration of the UCNPs fluorescence. In addition, the SEB was liberated from the aptamer–SEB complex using exonuclease I, an exonuclease specific to single-stranded DNA, for analyte recycling by selectively digesting a particular DNA (SEB aptamer). Based on this exonuclease-catalyzed target recycling strategy, an amplified fluorescence intensity could be produced using different SEB concentrations. Using optimized experimental conditions produced an ultrasensitive aptasensor for the detection of SEB, with a wide linear range of 0.001–1 ng mL⁻¹ and a lower detection limit (LOD) of 0.3 pg mL⁻¹ SEB (at 3σ). The fabricated aptasensor was used to measure SEB in a real milk samples and validated using the ELISA method. Furthermore, a novel aptasensor FRET assay was established for the first time using 30 mol% Mn²⁺ ions doped NaYF₄:Yb/Er (20/2 mol%) UCNPs as the donor probes, which suggests that UCNPs are superior fluorescence labeling materials for food safety analysis.     

On scaling invariance and type-I singularities for the compressible Navier-Stokes equations

Science China Mathematics - We find a new scaling invariance of the barotropic compressible Navier-Stokes equations. Then it is shown that type-I singularities of solutions with $$\mathop {\lim...