Screening of fluoroquinolones in environmental waters using disk-based solid-phase extraction combined to microplate fluorimetric determination and LC-MS/MS

Fluoroquinolones are in the order of the day concerning environmental contamination through anthropogenic activities, resulting in increased risk for antibiotic resistance dissemination. In this context, accessible, low-cost analytical methods are required for implementation of comprehensive surveillance and screening schemes. In this work, we propose a down-scaled disk-based solid-phase extraction system from which the eluate can be first screened by miniaturized fluorimetric reading, followed by individual determination of target fluoroquinolones (ciprofloxacin, norfloxacin, and enrofloxacin) by liquid chromatography combined to tandem mass spectrometry. The fluorimetric measurement is based on the intrinsic fluorescence of fluoroquinolones. Disk-based retention was performed after sample acidification (pH 4.0) by mixed-mode cation exchange using polystyrene divinylbenzene sulphonated sorbent. Sample loading was precisely controlled in a dedicated flow system operating at 4.0 mL min^?1. Different eluent compositions were tested, with elution performed by 1.00 mL of methanol-ammonium hydroxide (98:2, v/v), with subsequent reading of eluate in both detectors. Quantification was attained for 2–25 µg L^?1 range, with LOD values at 1 µg L^?1. The proposed approach was successfully applied to estuarine waters from the Douro River, with comparable results to a conventional SPE-LC-MS/MS procedure.     

高通量微孔板DAMBO-P~H荧光检测一氧化氮

一氧化氮(NO)是生物体内的一种重要生物信号传导分子,广泛参与生物体内多种生理及病理过程.为建立快速高效、准确检测生物体释放NO的分析方法,本文选用高灵敏度、高选择性的NO特异性荧光探针8-(3,4-diaminophenyl)-2,6-bis(2-carboxyethyl)-4,4-difluoro-1,3,5,7-tetramethyl-4- bora-3a,4a-diaza-s-indacene (DAMBO-P~H),激发波长和发射波长分别为520 nm和535 nm,以高通量微孔板(384孔)作为实验工具载体.该方法荧光强度与NO浓度在8.0×10~(-10)～8.0×10~(-7) mol·~(-1)范围内呈良好线性关系,R=0.9989,检出限为0.18 nmol·~(-1),回收率为98%～102%.该方法应用于多种生物样品中释放NO的分析检测,结果令人满意.     

硬盘驱动器巨磁电阻(GMR)磁头:从微米到纳米

近年来电脑硬盘存储密度的飞速增长(年增长100％)已超出摩尔定律的预言．这种惊人的高速增长中，最关键的因素是自旋阀纳米多层膜结构，即巨磁电阻(GMR)读传感器磁头的应用．事实上，巨磁电阻磁头读传感器(reader sensor)已经实现由微电子器件向纳米电子器件转化，并且形成大规模产业．这一过程包含了自旋电子学、材料科学、微电子工程学、化学、微机械力学和工程学等诸学科和相关微加工技术综合性挑战极限，进入纳米科技领域实质性进步．     

Aberration-corrected catadioptric magnifiers useful for simple microfiche readers

The present paper considers the magnifying power and aberration properties of three different catadioptric magnifying systems useful for application as simple hand-held microfiche readers. These are in the form of a plano-convex lens, a meniscus lens and an achromatic doublet lens and all their outer surfaces have been coated with a semi-reflecting film so that they behave like catadioptric elements. These can be designed to give magnification in the range of 15 × to 25 × with sufficient eye relief. Using such magnifiers, it is possible to read microfiche having frame sizes of 16 × 12 mm and 12 × 9 mm. The cemented achromatic doublet coated on the outer surfaces seems to give a very good image for use in microfiche reader.     

Chemiluminescent and Colorimetric Aptamer-Based Assays of Human α-Thrombin

Abstract

A microplate-based sandwich assay for the determination of α-human thrombin (HTb) was developed. Fluorescein-modified 29-mer thrombin binding aptamer (FAM-TBA29) and biotinylated 15-mer thrombin binding aptamer (Bio-TBA15) reacting with different exosites of HTb were used as the biorecognition components in the assay. FAM-TBA29 (capture aptamer) was immobilized using its interaction with anti-fluorescein antibody adsorbed on the microplate surface. As a sensitive signaling system, a combination of Bio-TBA15 and streptavidin-polyHRP conjugate was used. Under the optimized conditions, the detection limit for HTb was 1.4?nM; this value was the same in both the colorimetric and the chemiluminescent assays. The replacement of colorimetry for HRP measurement with chemiluminescence increased the assay sensitivity from 0.06 to 1.7?×?10⁶?nM^?1 that clearly demonstrated advantage of the latter approach.     

A new method for determination of antithrombotic activity of egg white protein hydrolysate by microplate reader

A new method for the determination of antithrombotic activity of egg white protein hydrolysate(EWPH)was developed using amicroplate reader.Reaction was carried out at 37℃ and pH 7.2 with fibrinogen concentration 0.1%.Microplate reading wasconducted at 405 nm.Inhibition rate of EWPH on thrombin activity showed linearity(R~2=0.9971),when the inhibition rate was inthe range of 10-90%.The lower limit of detection(LLD,at 99.7%probability)and the biological limit of detection(BLD,at 99.7%probability)of the method were 10.643 and 40 mg/mL,respectively.The repeatability standard deviation(R.S.D.)was 1.08%.Thestandard deviation of the method was 0.027 AT-U.     

Evaluation of the applicability of backscattered light measurements to the determination of microbial cell densities in microtiter plates

The turbidity of a microbial suspension sample is routinely determined by measuring the optical density (often referred to as the “absorbance”). This method requires a dilution step at moderate and high cell densities in order to ensure that measurements fall within the region where biomass concentration is linearly correlated to optical density. The measurement of backscattered light (often referred to as the “reflectance”), which has so far been mainly applied to large-scale stirred tanks, should also be applicable on the microscale. To evaluate the validity of this assumption, a standard fluorescence microplate reader was adapted to measure backscattered light. Backscattered light readings from undiluted microbial fermentation samples determined using this modified reader gave similar growth curves to optical density measurements from diluted samples determined in a standard cell photometer. Indeed, the fact that the dilution procedure is not necessary for backscattered light measurements gives them an important advantage over optical density measurements. Such an apparatus is not only suitable for manual operation, but also shows the potential for integration into fully automated robotic systems used for high-throughput experimentation.     

Well-posedness of two-phase local/nonlocal integral polar models for consistent axisymmetric bending of circular microplates

Previous studies have shown that Eringen's differential nonlocal model would lead to the ill-posed mathematical formulation for axisymmetric bending of circular microplates. Based on the nonlocal integral models along the radial and circumferential directions, we propose nonlocal integral polar models in this work. The proposed strainand stress-driven two-phase nonlocal integral polar models are applied to model the axisymmetric bending of circular microplates. The governing differential equations and boundary conditions (BCs) as well as constitutive constraints are deduced. It is found that the purely strain-driven nonlocal integral polar model turns to a traditional nonlocal differential polar model if the constitutive constraints are neglected. Meanwhile, the purely strain-and stress-driven nonlocal integral polar models are ill-posed, because the total number of the differential orders of the governing equations is less than that of the BCs plus constitutive constraints. Several nominal variables are introduced to simplify the mathematical expression, and the general differential quadrature method (GDQM) is applied to obtain the numerical solutions. The results from the current models (CMs) are compared with the data in the literature. It is clearly established that the consistent softening and toughening effects can be obtained for the strain-and stress-driven local/nonlocal integral polar models, respectively. The proposed two-phase local/nonlocal integral polar models (TPNIPMs) may provide an e-cient method to design and optimize the plate-like structures for microelectro-mechanical systems.     

单晶金微米片的电磁场增强及伴随的SERS效应

我们通过SERS的方法研究了单个金微米片表面不同区域的电磁场增强。首次对单个金属粒子采用拉曼区域成像的方法为电磁场增强提供了直接的实验证据。用结晶紫作为探针分子,通过对金微米六边形及截断的金微米三角形的SERS研究,直接证明金属粒子的边和角比面的电磁场增强更强。排除分子吸附、杂质干扰、晶体缺陷、表面活性剂等因素的影响,最后得出金微米片上电磁场增强的强弱顺序是角#边#面。     

生物炭施用对土壤磷及磷酸酶活性影响的可见和荧光光谱法研究

含碳丰富的秸秆在无氧或限氧的条件下低温热解后得到生物炭可施入土壤,有利于缓解秸秆处理压力、减少污染、减少温室气体排放,并改良土壤。在重要的农粮基地辽宁潮棕壤上布置了生物炭还田试验。玉米田施用不同量的生物炭(0,360,1 800和3 600 kg·ha-1)一个生长季后,研究土壤有效磷(P)、有机P和全P含量的变化,并采用荧光共轭物质作为测定底物,通过酶解产生荧光物质研究土壤磷酸酶活性的响应。结果表明,生物炭添加到土壤后,土壤有效P含量随生物炭施用量增加而显著升高、有机P和全P的含量没有显著的变化。其原因是生物炭携带有效P而引起的。碱性磷酸单酯酶和磷酸二酯酶活性随生物炭添加量的增加而增大,适量生物炭处理(1 800 kg·ha-1)可显著增加酸性磷酸酶,而高量生物炭处理(3 600 kg·ha-1)对酸性磷酸酶略有抑制,可能是生物炭自身的偏碱性使土壤pH值增大所致。生物炭的添加对土壤磷素和磷酸酶活性的影响是土壤物理性质、化学性质及土壤微生物群落结构和代谢能力的综合体现,需要进一步深入研究。