Comparison of μm and mm sized disk electrodes for end-column electrochemical detection in capillary electrophoresis

End-column electrochemical detection based on either the use of a 25 μm microdisk electrode or a 0.5 mm macrodisk electrode has been compared with respect to performance and influence on non-aqueous capillary electrophoretic separations. Despite the much higher coulometric efficiency obtained with the larger disk electrode, the microdisk electrode configuration offers comparable limits of detection (LOD) for the neutral and positively charged ferrocene compounds employed in conjunction with a non-aqueous acetonitrile-based buffer. The LODs for ferrocene were found to be 4.0 × 10^–8 M and 6.7 × 10^–8 M for the microdisk and macrodisk detector, respectively. In addition, both detector arrangements showed different relative responses for neutral and positively charged analytes. The macroelectrode-based detector introduced additional zone broadening while this was not found to be the case with the microelectrode arrangement. Using the microelectrode detector, the band broadening in an electro-osmotically driven flow system was compared to that in a gravity flow-based system. It was demonstrated that the zone broadening under gravity flow conditions was approximately twice as large as under electro-osmotic flow conditions for a typical set of experimental parameters.     

Comparison of μm and mm sized disk electrodes for end-column electrochemical detection in capillary electrophoresis

End-column electrochemical detection based on either the use of a 25 μm microdisk electrode or a 0.5 mm macrodisk electrode has been compared with respect to performance and influence on non-aqueous capillary electrophoretic separations. Despite the much higher coulometric efficiency obtained with the larger disk electrode, the microdisk electrode configuration offers comparable limits of detection (LOD) for the neutral and positively charged ferrocene compounds employed in conjunction with a non-aqueous acetonitrile-based buffer. The LODs for ferrocene were found to be 4.0 × 10^–8 M and 6.7 × 10^–8 M for the microdisk and macrodisk detector, respectively. In addition, both detector arrangements showed different relative responses for neutral and positively charged analytes. The macroelectrode-based detector introduced additional zone broadening while this was not found to be the case with the microelectrode arrangement. Using the microelectrode detector, the band broadening in an electro-osmotically driven flow system was compared to that in a gravity flow-based system. It was demonstrated that the zone broadening under gravity flow conditions was approximately twice as large as under electro-osmotic flow conditions for a typical set of experimental parameters. Received: 1 June 1998 / Revised: 20 August 1998 / Accepted: 24 August 1998     

Histamine determination in human urine using sub-2 μm C18 column with fluorescence and mass spectrometric detection

A fast, sensitive, and selective method for the determination of histamine in human urine samples by ultrahigh pressure liquid chromatography (LC) with fluorescence and mass spectrometry (MS) detection is investigated. A fluorescent reagent, 4-(1-pyrene) butyric acid N-hydroxysuccinimide ester was conjugated to the primary and secondary amino moieties of histamine. The structure of dipyrene-labeled histamine in human urine was determined by quadrupole time-of-flight MS with electospray ionization interface. The determination of the dipyrene derivative of histamine in urine samples was achieved within 3.9 min on an ultrahigh pressure LC Eclipse Zorbax XDB-C(18) column with 1.8 μm particle diameter. In this work, histamine separation was achieved significantly faster (3.9 min) with improved detection limit (signal-to-noise = 3) of 0.04 nM than 19.5 min with a detection limit of 0.183 nM as reported in a previous method.     

A fluorescence enhanced probe for sulfur dioxide detection and fluorescence imaging in living cellsEI北大核心CSCD

基于香豆素和苯并吡啶基团,构建了用于二氧化硫(SO_(2))高效检测的荧光探针P1,其化学结构通过核磁氢谱(^(1)H NMR)、碳谱(^(13)C NMR)和高分辨质谱(HR-MS)确证。在缓冲溶液体系中,单独的探针P1具有微弱的荧光,识别SO_(2)后荧光发射强度明显增强,能够实现对SO_(2)的专一性裸眼识别,检出限为126 nmol/L。生物应用实验结果表明,该探针具有较低的细胞毒性,可用于生物活细胞中外源性SO_(2)的荧光成像。     

Simultaneous laser-induced fluorescence and contactless-conductivity detection for microfluidic chip

A combined detection system involving simultaneous LIF and contacfless-conductometric measurements at the same place of the microfluidic chip was described. The LIF measurement was designed according to the confocal principle and a moveable contactless-conduetivity detector was used in C^4D. Both measurements were mutually independent and advantageous in analyses of mixtures. Various experimental parameters affecting the response were examined and optimized. The performances were demonstrated by simultaneous detection of Rhodamine B. And the results showed that the combined detection system could be used sensitively and reliably.     

A fluorescence “on–off” sensor for the highly selective and sensitive detection of Cu2+ ion

In an attempt to obtain a model of copper(II) ion-selective sensors, a new 1,8-naphthalimide-based fluorescence chemosensor, N-allylamine-4-[(E)-4-(([2-aminoethyl]imino)methyl) benzene-1,3-diol]-1,8-naphthalimide (NABN), was designed and synthesized. The sensor NABN is fully characterized by melting point analysis, fourier transform infrared spectra, Ultraviolet–visible (UV–vis) spectra, fluorescence spectra, ¹H NMR and ¹³C NMR spectroscopy, and mass spectrometry. NABN showed an unrivaled sensing behavior and an ardent selectivity toward copper(II) ion over other competitive metal ions tested in solution (N,N-Dimethylformamide (DMF)/Tris–HCl buffer, 1:1, v/v, pH = 7.2). The sensor showed a linear fluorescence quenching toward copper(II) ion in the range 0–50 μM, with a detection limit of 1.92 × 10⁻⁷ M estimated. Job's method indicated the formation of a 2:1 coordinative mode of the sensor with copper(II) ion with a high threshold of binding constant of 4 × 10¹² M⁻¹. Combining the above results, the quenching response of NABN toward Cu(II) ions could be ascribed to the strong, intrinsic paramagnetic behavior of Cu(II).     

A serial of 2D Co-Zn isomorphous metal–organic frameworks for photodegradation and luminescent detection properties

A series of 2D isomorphous MOFs [M (HBTC)(BMIOPE)·DMF·H₂O]_n (M = Zn ( 1 ), Zn_0.7Co_0.3 ( 2 ), Zn_0.5Co_0.5 ( 3 ), Zn_0.3Co_0.7 ( 4 ), Co ( 5 ), H₃BTC = 1,3,5-benzenetricarboxylic acid, BMIOPE = 4,4′-bis(2-methylimidazol-1-yl)diphenyl ether) were synthesized to investigate the correction between the center metal ions and the photocatalytic behaviors. The photocatalytic results show that with the increase of Co²⁺ content, the photodegradation properties are continuously improved from 1 to 5 , which fully indicate that only changing metal ions could regulate the photodegradation properties. In detail, 1 is an inactive photocatalyst to degrade methylene blue (MB), while 5 exhibits preeminent photocatalytic properties under visible light irradiation. Moreover, 1 shows good selective sensing toward Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution. To the best of our knowledge, 1 is the first MOF example for the optical detection of Fe³⁺, Cr³⁺, UO₂²⁺, CrO₄²⁻ and Cr₂O₇²⁻ ions in aqueous solution.     

A biacylhydrazone-based chemosensor for fluorescence ‘turn-on’ detection of Al3+ with high selectivity and sensitivity

A simple Al³⁺ fluorescent chemosensor (1) based on diacylhydrazone has been designed and synthesized by the condensation reaction of 2-hydroxy naphthaldehyde and metaphthalic hydrazide. The chemosensor 1 displays a specific and sensitive response to Al³⁺ over other cations in DMSO solution. Upon the addition of DMSO solution of Al³⁺, the sensor 1 shows an immediate fluorescence ‘turn-on’ response and emitting strong blue emission with visible color change from colorless to green. The fluorescence quantum yield enhanced from 7.24% to 48.68%. Meanwhile, the fluorescence and UV absorption spectra detection limits of the chemosensor 1 for Al³⁺ were 2.0 × 10^?7 M and 5.6 × 10^?7 M respectively, indicating the high sensitivity of 1 to Al³⁺. Furthermore, test strips based on 1 were fabricated, which could be used as a convenient test kit for the detection of Al³⁺ and an efficient Al³⁺ controlled fluorescent security display materials.     

Liquid chromatography–fluorescence detection for simultaneous analysis of sulfonamide residues in honey

A rapid, accurate LC analytical method has been developed for determination of eight sulfonamides (sulfacetamide, sulfapyridine, sulfamerazine, sulfamethoxypyridazine, sulfameter, sulfachloropyridazine, sulfamethoxazole and sulfadimethoxine) in honey. The sample was dissolved in phosphoric acid solution (pH 2). After filtration, the sample solution was cleaned by use of two solid-phase extraction (SPE) cartridges-an aromatic sulfonic cation-exchange cartridge and an Oasis HLB cartridge. The eight sulfonamides were then derivatized with fluorescamine and the derivatives were determined by LC with fluorescence detection at excitation and emission wavelengths of 405 and 495 nm, respectively. Average recoveries at three fortification levels in the range 0.02-0.50 mg kg(-1) in twelve different kinds of honey were 73.5-94.1% with coefficients of variation of 4.35-16.60%. The limit of detection (LOD) was 0.002 mg kg(-1) for sulfacetamide, sulfapyridine, sulfamerazine, and sulfamethoxypyridazine; that for sulfameter, sulfachloropyridazine, sulfamethoxazole and sulfadimethoxine was 0.005 mg kg(-1). The limit of quantitation (LOQ) was 0.005 mg kg(-1) for sulfacetamide, sulfapyridine, sulfamerazine, and sulfamethoxypyridazine; that for sulfameter, sulfachloropyridazine, sulfamethoxazole, and sulfadimethoxine was 0.010 mg kg(-1). The method is suitable for determination of multiresidue sulfonamides in the various kinds of honey.     

A one-step selective fluorescence turn-on detection of cysteine and homocysteine based on a facile CdTe/CdS quantum dots–phenanthroline system

In this paper, we report a simple, selective, sensitive and low-cost turn-on photoluminescent sensor for cysteine and homocysteine based on the fluorescence recovery of the CdTe/CdS quantum dots (QDs)–phenanthroline (Phen) system. In the presence of Phen, the fluorescence of QDs could be quenched effectively due to the formation of the non-fluorescent complexes between water-soluble thioglycolic acid (TGA)-capped QDs and Phen. Subsequently, upon addition of cysteine and homocysteine, the strong affinity of cysteine and homocysteine to QDs enables Phen to be dissociated from the surface of QDs and to form stable and luminescent complexes with cysteine and homocysteine in solution. Thus, the fluorescence of CdTe/CdS QDs was recovered gradually. A good linear relationship was obtained from 1.0 to 70.0 μM for cysteine and from 1.0 to 90.0 μM for homocysteine, respectively. The detection limits of cysteine and homocysteine were 0.78 and 0.67 μM, respectively. In addition, the method exhibited a high selectivity for cysteine and homocysteine over the other substances, such as amino acids, thiols, proteins, carbohydrates, etc. More importantly, the sensing system can not only achieve quantitative detection of cysteine and homocysteine but also could be applied in semiquantitative cysteine and homocysteine determination by digital visualization. Therefore, as a proof-of-concept, the proposed method has potential application for the selective detection of cysteine and homocysteine in biological fluids.     

2-Aminopyridine derivative as fluorescence ‘On–Off’ molecular switch for selective detection of Fe3+/Hg2+

2-Amino-6-methyl-4-phenyl-nicotinonitrile 1, a 2-aminopyridine-based fluorescent compound, was found to be a fluorescent chemosensor for the detection of Fe³⁺ and Hg²⁺ ions over a number of other metal ions. Compound 1 was synthesized in one step using a multicomponent reaction, and characterized using common spectroscopic tools. During Fe³⁺/Hg²⁺ sensing the compound 1 followed a ‘switch-off’ mechanism. Further, compound 1 could sense Fe³⁺ over Hg²⁺ by its distinct absorption and fluorescence quenching behaviors. 1:1 complex formation of 1 with Fe³⁺ and Hg²⁺ was clearly understood from Job’s plot. The present work brings additional evidence on the importance of multicomponent reactions which could lead to the development of fluorescence chemosensor in one step for the selective detection of biologically important metal ions.     

A library for X-ray–matter interaction cross sections for X-ray fluorescence applications

Quantitative estimate of elemental composition by spectroscopic and imaging techniques using X-ray fluorescence requires the availability of accurate data of X-ray interaction with matter. Although a wide number of computer codes and data sets are reported in literature, none of them is presented in the form of freely available library functions which can be easily included in software applications for X-ray fluorescence. This work presents a compilation of data sets from different published works and an xraylib interface in the form of callable functions. Although the target applications are on X-ray fluorescence, cross sections of interactions like photoionization, coherent scattering and Compton scattering, as well as form factors and anomalous scattering functions, are also available.     

A simple molecular mechanics potential for μm scale graphene simulations from the adaptive force matching method

A simple molecular mechanics force field for graphene (PPBE-G) was created by force matching the density functional theory Perdew-Burke-Ernzerhof forces using the adaptive force matching method recently developed in our group. The PPBE-G potential was found to provide significantly more accurate forces than other existing force fields. Several properties of graphene, such as Young's modulus, bending rigidity, and thermal conductivity, have been studied with our potential. The calculated properties are in good agreement with corresponding density functional theory and experimental values. The thermal conductivity calculated with reverse non-equilibrium molecular dynamics depends sensitively on graphene size thus requiring the simulation of large sheets for convergence. Since the PPBE-G potential only contains simple additive energy expressions, it is very computationally efficient and is capable of modeling large graphene sheets in the μm length scale.     

Photocurable Sol-Gel Coatings: Channel Waveguides for Use at 1.55 μm

The development and characterization of channel waveguides using wet-process, low temperature sol-gel chemistry is described. Two structures have been developed. The first one is a one-layer structure, composed of a sol-gel solution which is a mixture of photopolymerizable organosilicate and organozirconate precursors. The other is a multilayer structure with a buffer under the guide and a protective coating. The layers are deposited by the dipping technique. The devices are obtained by UV light exposure of the coating through a predefined mask (channel waveguides). The refractive index increase is sufficient enough to allow the use of waveguides in the 1.55 m telecommunication window.These waveguides are thick enough to reduce the coupling losses with an optical fiber below 0.5 dB. Also, because of our sandwich structure, the propagation losses are less than 0.1 dB.     

A switch-on fluorescence assay for bacterial β-lactamases with amyloid fibrils as fluorescence enhancer and visual tool

Herein is described the development of a novel switch-on fluorescence assay for detecting β-lactamases. The fluorescence assay comprises two components: solid beads coated with a β-lactam antibiotic, which is linked to an environment-sensitive fluorophore (dansylaminothiophenol, DTA), and amyloid fibrils of hen lysozyme (acting as fluorescence enhancer and visual tool). In the presence of the clinically significant TEM-1 β-lactamase, the DTA-antibiotic complex on the solid beads is hydrolyzed, thus releasing the DTA dye into solution. The DTA dye is only weakly fluorescent in solution but gives strong green fluorescence upon binding to lysozyme fibrils. These strongly fluorescent DTA-bound fibrils can be easily visualized by the naked eye upon illumination of the sample with a simple UV lamp. The fluorescence assay can detect TEM-1 at low concentration (0.01 nM). In contrast, no observable fluorescence appears when the fluorescence assay is performed on samples without the TEM-1 β-lactamase.     

Integrated sorption–energy-dispersive X-ray fluorescence detection for automatic determination of lead and cadmium in low-concentration solutions

Sorbent material packed in a PTFE laboratory-made flow cell located in the specimen holder of an energy-dispersive X-ray fluorescence (EDXRF) detector has been used for in situ solid-phase extraction (SPE) preconcentration–detection of metals. The flow cell was connected to a single-channel flow-injection (FI) manifold (for full automation of the steps and proper development of the method) by two PTFE tubes of 0.5-mm inner diameter introduced into the spectrometer specimen holder by a small orifice without distortion or modification of the instrument. The optical window open in the PTFE flow cell was adjusted to the X-ray irradiation zone of the spectrometer and fixed to it. The approach was tested by using both Pb and Cd aqueous solutions and a Dowex 50 cation-exchange resin as a sorbent, and flushing the sample through the flow cell for EDXRF measurements after removal of the sample matrix. The limits of detection and the limits of quantification (LOQs) thus obtained were 0.15 and 0.5 μg for Pb and 0.3 and 0.8 μg for Cd, respectively, values that allow the approach to be used for the analysis of drinking water by injecting a 100-mL sample into the FI manifold, taking into account the EC drinking water directives. The linear dynamic ranges are between the LOQ and 600 μg for both analytes. The method was validated by the standard addition method using tap-water samples. In addition, the integrated SPE–EDXRF approach enables the study of the variables influencing the sorption step–namely the effects of the volume of sample flushed through the column, concentrations of the analytes in the sample, breakthrough volume of the resin, elution profiles, sample pH and retention and elution flow rates–in an automatic, cheap, fast and precise way.     

Heavy fullerenes for semiconducting photodiodes operating at 1.5–5.0 μm wavelengths

A new method for the passivation of the surface of infrared photodiodes operating at room temperature, spectral range 1.5–5.0 μm, by a mixture of higher fullerenes (h-f-mix) C₇₆ + C₇₈ + C₈₄ + C₉0 + … was suggested. The main service characteristics of photodiodes were studied. The passivation of photodiodes decreased their dark current by 14%. The Peltier effect was observed for the A³B⁵ semiconductor/h-f-mix heterojunction.     

Contaminant detection in treated water using Optiqua’s MiniLab™ biosensing system: a case study for Bisphenol A

An inhibition assay for detection of Bisphenol A (BPA) in treated water has been developed and validated for the MiniLab? system from Optiqua Technologies. This biosensor-based analytical system can be used for detection of specific contaminants in solution. The system uses an integrated optic Mach-Zehnder interferometer chip that is functionalised with a biochemical interface layer. The sensor chip surface was first coated with aminodextran which formed a hydrophilic layer suitable for further modification. 4,4-bis(4-hydroxyphenyl) valeric acid (BVA), which is a structural analogue of BPA, was then successfully coupled to the aminodextran layer. This surface chemistry was used in a qualitative inhibition assay format for the selective detection of the presence of BPA. The assay was developed and optimised using a polyclonal anti-BPA antibody. Samples from 12 different water matrices of Singapore were spiked with known amounts of BPA and tested with the MiniLab? system. The working range of the BPA inhibition assay is from 0.5 to 5 µg/L. Intra- and inter-assay variations were measured, with calculated relative standard deviation averaging of about 15%. BPA concentrations of the spiked samples were also verified and confirmed with LC-MS. Such functionalised biosensor chip can be reused for more than 200 sample injections over a period longer than 6 months. Developed as a robust, user-friendly and cost-effective system that can be field deployed, the MiniLab? system enables target-specific assays currently only available in the lab to become available in the field.