Simultaneous two color image capture for sub-diffraction localization fluorescence microscopy

A sub-diffraction limit fluorescence localization microscope was constructed using a standard cooled 1.4 mega-pixel fluorescence charge-coupled device (CCD) camera to simultaneously resolve closely adjacent paired quantum dots on a flat surface with emissions of 540 and 630 nm. The images of the overlapping Airy discs were analyzed to determine the center of the point spread function after noise reduction using Fourier transformation analysis. The Cartesian coordinates of the centers of the point spread functions were compared in serial images. Histograms constructed from serial images fit well to Gaussian functions for resolving two quantum dots separated by as little as 10 nm in the x–y coordinates. Statistical analysis of multiple pairs validated discrimination of inter-fluorophore distances that vary by 10 nm. The method is simple and developed for x–y resolution of dilute fluorophores on a flat surface, not serial z sectioning.     

Speciation analysis of arsenic in Mya arenaria Linnaeus and Shrimp with capillary electrophoresis-inductively coupled plasma mass spectrometry

An improved sheath-flow interface used to couple capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS) and a microwave-assisted extraction used to extract each arsenic species in seafood were developed in this work. The improved sheath-flow interface completely avoids laminar flow in CE capillary caused by the suction from ICP-MS, makes electric supply more stable in CE, and transports analyte solution to ICP-MS easily and more efficiently. CE-ICP-MS coupled with our interface have two quantitative analysis modes: continuous sample-introduction mode and collective sample-introduction mode. The collective sample-introduction technique greatly reduced the dead volume of interface to approximately zero, obviously avoided the excessive dilution of analyte, and eventually led to a much lower detection limit and a much better electrophoretic resolution. This was demonstrated by the better symmetry and narrow peak widths (10-12 s) and much lower detection limits (0.030-0.042 μg/L) of four species of arsenic determined with collective sample-introduction mode.With the help of this improved sheath-flow interface and the microwave-assisted extraction, we have successfully separated and determined four arsenic species, As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in dried Mya arenaria Linnaeus and Shrimp samples using CE-ICP-MS within 10 min with a relative standard deviation of 2-4% (peak areas, n = 6) and a recovery of 96-105%.     

Effect of Constant Glucose Feeding on the Production of Exopolysaccharides by <Emphasis Type="Italic">Tremella fuciformis</Emphasis> Spores

A fed-batch culture system with constant feeding (glucose 80 g L⁻¹, 0.25 ml min⁻¹) was used to study the influence of glucose on cell dry weight and exopolysaccharides production from submerged Tremella fuciformis spores in a 5-L stirred-tank bioreactor. The results showed that high levels of cell mass (9.80 g L⁻¹) and exopolysaccharides production (3.12 g L⁻¹) in fed-batch fermentation were obtained after 1 h of feeding, where the specific growth rate (μ) and exopolysaccharides yield on substrate consumed (YP/S) were 0.267 d⁻¹ and 0.14 g g⁻¹. Unlike batch fermentation, maximal cell mass and exopolysaccharides production merely reached 7.11 and 2.08 g L⁻¹; the specific growth rate (μ) and exopolysaccharides yield on substrate consumed (YP/S) were 0.194 d⁻¹ and 0.093 g g⁻¹, respectively. It is concluded that the synthesis of exopolysaccharides can be promoted effectively when feeding glucose at a late exponential phase.     

Synthesis and Crystal Structure of 3-（4-Chlorophenyl）-8-cyano-2-（di-isopropylamino）-5-methyl-7-（methylthio）-pyrido[4,3-d]pyrimidine-4（3H）-one

The crystal structure of the new title compound 3-(4-chlorophenyl)-8-cyano-2-(di-iso-propylamino)-5-methyl-7-(methylthio)-pyrido[4,3-d]pyrimidine-4(3H)-one(C22H24ClN5OS,Mr = 441.97)has been determined by single-crystal X-ray diffraction. The crystal is of orthorhombic,space group Pna21 with a = 7.6721(5),b = 18.9370(11),c = 15.6260(9),V = 2270.2(2)3,Z = 4,Dc = 1.293 g/cm3,F(000)= 928,μ = 0.283 mm-1,MoKa radiation(λ = 0.71073 ),R = 0.0494 and wR = 0.1062 for 3278 observed reflections with I > 2σ(I). X-ray diffraction analysis reveals that all ring atoms in the py-ridopyrimidinone moiety are almost coplanar. Intramolecular C(20)-H(20)···N(4),C(19)-H(19A)···N(3),C(18)-H(18C)···N(3)and C(16)-H(16B)···O(5)hydrogen bonds together with weak C···π interactions are found in the structure.     

Speciation analysis of selenium in rice samples by using capillary electrophoresis-inductively coupled plasma mass spectrometry

An enzyme-assisted extraction used to extract all species of selenium in rice sample and a sensitive analytical method for the determination of ultratrace Se(VI), Se(IV), SeCys₂ (selenocystine) and SeMet (selenomethionine) with capillary electrophoresis-inductively coupled plasma mass spectrometry were firstly described in this study. The extraction method is simple, effective and can be used to extract trace selenium compounds in rice with high extraction efficiency and no altering its species. The analytical method has a detection limit of 0.1-0.9 ng Se/mL, and can be used to determine trace Se(VI), Se(IV), SeCys₂ and SeMet in rice directly without any derivatization and pre-concentration. With the help of above methods, we have successfully determined Se(VI), Se(IV), SeCys₂ and SeMet in selenium-enriched rice within 18 min with a recovery of 90-103% and a RSD (relative standard deviation, n = 6) of 3-7%. Our results indicated that selenium-enriched rice contained only one species of selenium, SeMet, and its concentration is in range of 0.136-0.143 μg Se/g dried weight. The proposed method providing a realistic approach for the nutritional and toxical evaluation of different selenium compounds in nutritional supplements.     

Lateral flow test for visual detection of silver(I) based on cytosine-Ag(I)-cytosine interaction in C-rich oligonucleotides

The authors describe an oligonucleotide-based lateral flow test for visual detection of Ag(I). The assay is based on cytosine-Ag(I)-cytosine [C-Ag(I)-C] coordination chemistry to capture gold nanoparticle (AuNP) tags in the test zone. A thiolated C-rich oligonucleotide probe was immobilized on the AuNPs via gold-thiol chemistry, and a biotinylated C-rich oligonucleotide probe was immobilized on the test zone. The AuNPs labelled with C-rich oligonucleotides are captured by Ag(I) ions in the test zone through the C-Ag(I)-C coordination. The resulting accumulation of AuNPs produces a readily visible red band in the test zone. Under optimized conditions, the test is capable of visually detecting 1.0 ppb of Ag(I) which is 50 times lower than the maximum allowable concentration as defined by the US Environmental Protection Agency for drinking water. Hence, the test is inexpensive and highly sensitive. It was applied to the detection of Ag(I) in spiked samples of tap water and river water. In our perception, the test is a particularly valuable tool in limited resource settings.

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