A rapid and universal bacteria-counting approach using CdSe/ZnS/SiO2 composite nanoparticles as fluorescence probe

In this paper, a rapid, simple, and sensitive method was described for detection of the total bacterial count using SiO₂-coated CdSe/ZnS quantum dots (QDs) as a fluorescence marker that covalently coupled with bacteria using glutaraldehyde as the crosslinker. Highly luminescent CdSe/ZnS were prepared by applying cadmium oxide and zinc stearate as precursors instead of pyrophoric organometallic precursors. A reverse-microemulsion technique was used to synthesize CdSe/ZnS/SiO₂ composite nanoparticles with a SiO₂ surface coating. Our results showed that CdSe/ZnS/SiO₂ composite nanoparticles prepared with this method possessed highly luminescent, biologically functional, and monodispersive characteristics, and could successfully be covalently conjugated with the bacteria. As a demonstration, it was found that the method had higher sensitivity and could count bacteria in 3 × 10² CFU/mL, lower than the conventional plate counting and organic dye-based method. A linear relationship of the fluorescence peak intensity (Y) and the total bacterial count (X) was established in the range of 3 × 10²–10⁷ CFU/mL using the equation Y = 374.82X − 938.27 (R = 0.99574). The results of the determination for the total count of bacteria in seven real samples were identical with the conventional plate count method, and the standard deviation was satisfactory.     

2-(5-Benzoacridine)ethyl-p-toluenesulfonate as sensitive reagent for the determination of bile acids by HPLC with fluorescence detection and online atmospheric chemical ionization-mass spectrometric identification

2-(5-Benzoacridine)ethyl-p-toluenesulfonate (BAETS), a dual-sensitive probe, was reacted with bile acids in the presence of K₂CO₃ catalyst in dimethyl sulfoxide (DMSO) solvent to give BAETS–bile acid derivatives. Derivatives exhibited intense fluorescence (FL) with an excitation maximum at λ _ex 270 nm and an emission maximum at λ _em 510 nm. MS analysis using APCI-MS indicated that derivatives had excellent APCI-MS ionizability with percentage ionization δ values changing from 0 to 88.83% in aqueous acetonitrile and from 0 to 89.15% in aqueous methanol. The collision induced dissociation spectra of m/z [M + H]⁺ contained specific fragment ions at m/z [M + H−H₂O]⁺, [M + H−2H₂O]⁺, [M + H−3H₂O]⁺, 347.3, and 290.1. Repeatability was good for LC separation of BAETS–bile acid derivatives with aqueous acetonitrile as mobile phase. The relative standard deviations (RSDs) of retention time and peak area at 6.6 nmol mL⁻¹ levels with fluorescence detection (FL) were from 0.045 to 0.072% and from 2.16 to 2.73%, respectively. Excellent linear responses were observed, with regression coefficients >0.9995. The FL detection limits (S/N = 3) were in the range of 18.0–36.1 fmol. The online APCI-MS detection limits are in the range of 500–790 fmol (at a signal-to-noise ratio of 3).     

Patterned growth of vertically aligned silicon nanowire arrays for label-free DNA detection using surface-enhanced Raman spectroscopy

Patterning is of paramount importance in many areas of modern science and technology. As a good candidate for novel nanoscale optoelectronics and miniaturized molecule sensors, vertically aligned silicon nanowire (SiNW) with controllable location and orientation is highly desirable. In this study, we developed an effective procedure for the fabrication of vertically aligned SiNW arrays with micro-sized features by using single-step photolithography and silver nanoparticle-induced chemical etching at room temperature. We demonstrated that the vertically aligned SiNW arrays can be used as a platform for label-free DNA detection using surface-enhanced Raman spectroscopy (SERS), where the inherent “fingerprint” SERS spectra allows for the differentiation of closely related biospecies. Since the SiNW array patterns could be modified by simply varying the mask used in the photolithographic processing, it is expected that the methodology can be used to fabricate label-free DNA microarrays and may be applicable to tissue engineering, which aims to create living tissue substitutes from cells seeded onto 3D scaffolds.

Synthesis, Crystal Structure, Photophysical Properties, and DFT Calculations of a Bis(tetrathia-calix[4]arene) Tetracadmium Complex

Abstract  

Thiacalix[4]arenes are a unique family of polydentate ligands that offer a combination of four soft sulfur atoms together with four hard phenol oxygen atoms for binding to metal ions. In this study, the tetranuclear cadmium (II) complex Cd₄^II(tca)₂·1.5CH₂Cl₂ (tca⁴⁻ = tetra-anionic p-tert-butylthiacalix[4]arene) (1) was synthesized by reaction of a deprotonated p-tert-butylthiacalix[4]arene and various Cd^II salts. The structure of 1 was established by single crystal X-ray diffraction analysis. The neutral complex 1 contains a square arrangement of four cadmium (II) ions sandwiched between two tca⁴⁻ ligands that have a ‘cone’ conformation similar to that of the free ligand. The absorption and emission properties of the free ligand H₄tca and complex 1 have been recorded and explained by DFT calculations of the molecular orbitals and electronic transitions between them.     

Structures and properties of metal-free and magnesium tetrathieno[2,3-b]porphyrazine investigated using density functional theory

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculation were adopted to study the structures and properties of metal-free and magnesium tetrathieno[2,3-b]porphyrazine (TTPPzH₂ and TTPPzMg) using B3LYP method with the 6–31G(d) basis set. A comparison of the geometrical structures, atomic charges, molecular orbitals, UV-vis spectra and infrared (IR) spectra among tetrathieno[2,3-b]porphyrazine (TTPPzH₂), phthalocyanine (H₂Pc) and porphyrazine (H₂Pz) compounds was performed. The substituent effect of the thiophene heterocycle for electron-donating on the structures and properties of these compounds has been discussed. Compared with other atoms, the charge distribution of C_β atoms adjacent to the sulfur atom is significantly influenced by the thiophene heterocycle substituents. The enlargement of the HOMO-LUMO gaps from H₂Pc and MgPc to TTPPzH₂ and TTPPzMg is at the origin of the observed blue shift of the Q band when moving from H₂Pc to TTPPzH₂ compounds. Special emphasis has been devoted to the strongest B bands for TTPPzH₂ compounds which show red shift due to the large destabilization of the lower lying occupied orbitals compared with the corresponding B bands of H₂Pc compounds. With the assistance of animated pictures produced on the basis of the normal coordinates, the significant peaks and vibration modes in the IR spectra of all the compounds were assigned and analyzed.     

2-甲氨基-5-(2-芳氧吡啶-3-基)-1,3,4-噻二唑类化合物的合成与荧光性质研究

设计合成了一系列未见文献报道的2-甲氨基-5-(2-芳氧吡啶-3-基)-1,3,4-噻二唑衍生物,其结构均经过1HNMR,IR和元素分析表征.测定了其荧光性能,结果显示此类化合物具有较好的荧光性,其荧光发射波长在384～390nm范围,最大荧光量子产率为0.12.     

Highly sensitive trivalent copper chelate-H2O2 system for CE-chemiluminescent detection of luminol-type compounds

Luminol-type compounds can be used as chemiluminescent (CL) derivatization reagents for amines, carboxylic acids and protein. Copper chelate diperiodatocuprate(III) (K5[Cu(HIO6)2], DPC) was synthesized by complexation of copper at trivalent oxidation state and periodate in a strong basic medium. It was found that DPC can greatly enhance the reaction between luminol-type compounds and H2O2 to produce very strong CL emission. Based on this fact, a rapid CE method combined with high-sensitive end-column CL detection was established to simultaneously analyze luminol and N-(4-aminobutyl)-N-ethylisoluminol (ABEI) with wide concentration range of 3.0-300 nmol/L in 5 min. The RSDs of the signal intensity and the migration time were less than 3.9 and 7.0% for a standard sample containing 100 nmol/L luminol and ABEI (n=5), respectively. The investigation implies that DPC is a promising sensitizer for CE-CL detection of a great variety of biomolecules and drugs in biological samples after derivatization using luminol derivatives.     

Determination of Fatty Acids (C1 – C10) from Bryophytes and Pteridophytes

A simple and mild method for the determination of fatty acids (C₁ – C₁₀) based on a condensation reaction using 7-aminonaphthalene-1,3-disulfonic acid (ANDSA) as labeling reagent with capillary zone electrophoresis has been developed. The detection was performed with a diode array detector at 254 nm. A 58.5 cm × 50 μm i.d. (50 cm effective length) untreated fused-silica capillary was used. To optimize the separation conditions, the background electrolyte concentration, column temperature, voltage and other factors were evaluated. The optimal separation conditions were as follows: 30 mmol L⁻¹ borate buffer (pH 9.5), 15 mmol L⁻¹ β-CD, temperature at 20 °C, pressure 50 mbar and injection time 8 s. Under the established conditions, 10 fatty acid derivatives could be well-separated within 17 min. The linearity was in the range of 0.07–5.0 μmol L⁻¹. Detection limits (at a signal-to-noise ratio of 3) were in the range of 0.027–0.042 μmol L⁻¹. The fatty acids from the extracted Funaria Hedw. and Selaginella samples were determined with satisfactory results.

     

Determination and quantification of active phenolic compounds in pigeon pea leaves and its medicinal product using liquid chromatography–tandem mass spectrometry

A novel method using liquid chromatography coupled to electrospray ionization mass spectrometry (LC-ESI-MS) has been optimized and established for the qualitative and quantitative analysis of ten active phenolic compounds originating from the pigeon pea leaves and a medicinal product thereof (Tongluo Shenggu capsules). In the present study, the chromatographic separation was achieved by means of a HiQ Sil C18V reversed-phase column with a mobile phase consisting of methanol and 0.1% formic acid aqueous solution. Low-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS) using the selected reaction monitoring (SRM) analysis was employed for the detection of ten analytes which included six flavonoids, two isoflavonoids and two stilbenes. All calibration curves showed excellent coefficients of determination (r(2) ≥ 0.9937) within the range of tested concentrations. The intra- and inter-day variations were below 5.36% in terms of relative standard deviation (RSD). The recoveries were 95.08-104.98% with RSDs of 2.06-4.26% for spiked samples of pigeon pea leaves. The method developed was a rapid, efficient and accurate LC-MS/MS method for the detection of phenolic compounds, which can be applied for quality control of pigeon pea leaves and related medicinal products.     

Partial melting and recrystallization of isotactic polypropylene

<正>A relatively high predetermined crystallization temperature(135℃) was chosen to grow well developed iPP spherulites,then the partial melting was carried out at a temperature of 165℃,where the preformed spherulites were seen to only decrease their size but not completely melted.The crystallization behavior of partially melted isotactic polypropylene (iPP) has been carefully examined by different scanning calorimetry(DSC) and polarized light microscopy(PLM).The experimental results show that at a special annealing temperature(165℃) the melting behavior of iPP includes two parts with different mechanism,one part is the melting of iPP spherulite outside,another is the partial lamellae perfection during longer annealing time in the unmelted spherulite.The conformational orders of the iPP melt decrease with the increase of the annealing temperature.