Optosensing of hydrochloric acid based on the fluorescence quenching of a flavone copolymer

An optical fiber sensor for the continuous determination of hydrochloric acid is presented. It is based on the fluorescence quenching of a flavone containing copolymer membrane by hydrochloric acid. The quenching efficiency is greatly enhanced in the presence of Fe(III). This enhancement is attributed to the primary inner filter effect, as well as the formation of a complex between the 4′-N,N-dimethylaminoflavone group in the copolymer and the Fe(III) species extracted from hydrochloric acid solution. The optical response is linear and reversible for 0.10–6.00 mol L^–1 HCl with a response time of the order of a second. The standard deviations for repeated alternative measurements of 0.20 and 2.00 mol L^–1 hydrochloric acid are 0.32% and 0.46% (n = 10), respectively, indicating a good reproducibility. Because of the covalently bonding of the dye to polymer, the sensor exhibits also a good stability. Selectivity has also been evaluated for some potential interferents. The sensor in conjunction with a flow-injection system can be used for on-line determination of hydrochloric acid. Received: 15 January 1998 / Revised: 14 April 1998 / Accepted: 18 April 1998     

基于荧蒽荧光熄灭的苦味酸荧光敏感膜的研究

本文基于苦味酸水溶液对固定于增塑的PVC膜中荧蒽的可逆荧光熄灭作用,研制了测定苦味酸浓度的荧光敏感膜.该膜的最佳组成为1～6mg荧蒽,50mgPVC粉, 100mg邻苯二甲酸二异辛酯.在1.50mol·L^-^1硫酸测试底液中,此膜测定苦味酸的浓度范围为1.78×10^-^6～1.28×10^-^3mol·L^-^1,重现性良好,响应时间小于30s.该法选择性好,许多常见亲脂阴离子不干扰测定.将该法用于药物辛可宁的间接测定, 结果令人满意     

A reversible optode membrane for picric acid based on the fluorescence quenching of pyrene

Pyrene immobilized in plasticized poly(vinyl chloride) (PVC) membrane is able to extract selectively picric acid from the sample solution into the organic membrane phase. Since this extraction equilibrium is accompanied by a change in the fluorescence spectrum of pyrene, the chemical recognition process can be directly translated into an optical signal. With the optode membrane described, picric acid in sample solutions from 8.7 x 10(-6) to 4.3 x 10(-3)M can be determined. The calibration curve of the optode membrane for picric acid shows a good correlation with the mathematically derived formalism and thus confirms the theoretically expected behaviour. Besides a high reproducibility of the optical signals, the very short response times less than 35 sec are realized. The optode membrane presented exhibits good selectivity for picric acid over many other usual hydrophobic anions.     

Probing solubilization sites in block copolymer micelles using fluorescence quenching

The solubilization sites provided by micelles formed by a diblock copolymer with one neutral hydrophobic block, polystyrene, and one charged hydrophilic block, poly(acrylic acid) or poly(methacrylic acid), have been studied by fluorescence quenching of pyrene by polar and nonpolar quenchers. Pyrene solubilized into these micelles is distributed between the inner corona and the micelle core. The fraction of pyrene residing in the inner corona is almost unity for star micelles, where the corona-forming blocks are larger than the core-forming blocks, and around 0.5 for crew-cut micelles where the opposite situation prevails. The kinetics of the quenching process depends on the pyrene location, i.e. is static in the micelle core, and largely dynamic in the inner corona at low quencher concentration. The rate constants for fluorescence quenching by nitromethane are shown to increase with increasing pH.     

Uranyl ion assessment based on the fluorescence quenching of Norfloxacin

Journal of Radioanalytical and Nuclear Chemistry - A new turn-off fluorescent sensor for trace analysis of uranyl ion (UO22+) in aqueous samples has been introduced in this study. Norfloxacin...     

动力学荧光猝灭法测定柠檬酸的研究

在稀H2SO4介质中,柠檬酸活化钒(Ⅴ)催化溴酸钾氧化吡口罗红Y的褪色反应,使其荧光猝灭,建立了动力学荧光猝灭法测定柠檬酸的新方法。反应在沸水浴中进行10min,测定柠檬酸的线性范围为0.1～4.0μg/mL,检出限为6.0×10-8g/L。本法用于饮料中柠檬酸的测定,并进行了加标回收试验,回收率在96%～103%之间。     

A reversible chemosensor for nitrite based on the fluorescence quenching of a carbazole derivative

The carbazole derivative, with an amino group in 9-position (9-methylacryloylamino carbazole (MAC), has been utilized to prepare a fluorescent sensor and used for the determination of NO₂⁻ based on the reaction between nitrite (NO₂⁻) and excess I⁻ to form I₃⁻, which can quench the fluorescence of carbazole derivative. MAC, as a fluorescent carrier, has a terminal double bond and is covalently immobilized on a quartz glass plate surface by photo-polymerization to prevent the leakage of the dye. The sensor shows sufficient repeatability, selectivity, operational lifetime of 8 weeks, and a fast response of less then 30 s. NO₂⁻ can be determined in the range between 1.0×10⁻⁶ and 1.0×10⁻⁴ mol l⁻¹ with a detection limit of 8.0×10⁻⁷ mol l⁻¹ at pH of 2.0. The quenching mechanism is discussed. Most commonly coexisting ions do not interfer with the NO₂⁻ assay.     

Immunosensor based on fluorescence quenching matrix of the conducting polymer polypyrrole

In this study, the combination of autofluorescent proteins and fluorescence quenching polymers was shown to be a design which can increase the selectivity and sensitivity of immunosensors. With this objective, the conducting polymer polypyrrole (Ppy) was used as a matrix for immobilization of proteins, which enables biological recognition of the analyte, and as a fluorescence quencher, which increases the selectivity of fluorescence-based detection. In this study, bovine leukemia virus proteins gp51 were immobilized within the Ppy matrix and formed a polymeric layer with affinity for antibodies against protein gp51 (anti-gp51). The anti-gp51 antibodies are present at high levels in the blood serum of cattle infected by bovine leukemia virus. Secondary antibodies labeled with horseradish peroxidase (HRP) were used as specific fluorescent probes for detection of a particular target, because the fluorescence of HRP was readily detectable at the required sensitivity. The Ppy was used as fluorescent background, because its fluorescence was almost undetectable when excited by near UV light at 325 nm. Moreover the Ppy quenched the fluorescence of some fluorescent agents including fluorescein-5(6)-isothiocyanate (fluorescein), rhodamine B, and HRP by almost 100% when these fluorescent agents were adsorbed on the surface of Ppy. It is predicted that Ppy-induced fluorescence quenching could be used in the design of immunosensors to increase selectivity and sensitivity.     

Antigen detection based on background fluorescence quenching immunochromatographic assay

Gold immunochromatographic assay (GICA) has been around for quite a while, but it is qualitative in the vast majority of applications. A fast, simple and quantitative GICA is in call for better medicine. In the current study, we have established a novel, quantitative GICA based on fluorescence quenching and nitrocellulose membrane background signals, called background fluorescence quenching immunochromatographic assay (bFQICA). Using model analyte alpha-fetoprotein (AFP), the present study assessed the performance of bFQICA in numerous assay aspects. With serial dilutions of the international AFP standard, standard curves for the calculation of AFP concentration were successfully established. At 10 and 100 ng mL⁻¹ of the international AFP standard, the assay variability was defined with a coefficient of variance at 10.4% and 15.2%, respectively. For samples with extended range of AFP levels, bFQICA was able to detect AFP at as low as 1 ng mL⁻¹. Fluorescence in bFQICA strips stayed constant over months. A good correlation between the results from bFQICA and from a well-established Roche electrochemiluminescence immunoassay was observed in 27 serum samples (r = 0.98, p < 0.001). In conclusion, our study has demonstrated distinctive features of bFQICA over conventional GICA, including utilization of a unique fluorescence ratio between nitrocellulose membrane background and specific signals (F1/F2) to ensure accurate measurements, combined qualitative and quantitative capabilities, and exceptionally high sensitivity for detection of very low levels of antigens. All of these features could make bFQICA attractive as a model for antigen-antibody complex based GICA, and could promote bFQICA to a broad range of applications for investigation of a variety of diseases.     

Optical sensor for sulfur dioxide based on fluorescence quenching

A series of potential indicator dyes is evaluated for use in the development of optical sensors for measuring sulfur dioxide in gaseous samples. Rhodamine B isothiocyanate is selected on the basis of relative sensitivity to dynamic quenching by sulfur dioxide and oxygen. A solid-state fluorometer is described for monitoring the sulfur dioxide induced fluorescence quenching of sensing membranes composed of silicone and rhodamine B isothiocyanate. A modulated blue LED is coupled with the lock-in detection of a photodiode detector to provide high signal-to-noise ratios. The limit of detection is 0.114+/-0.009% for sulfur dioxide in a carrier stream of nitrogen gas. Selectivity measurements indicate no interference from several common gases (HCl, NH(3), NO, and CO(2)). Oxygen alters the sensor response when comparing signals for sulfur dioxide in 0, 20 and 100% oxygen environments.     

Sensitive iodate sensor based on fluorescence quenching of gold nanocluster

In this report we described a highly selective and sensitive iodate sensor. Due to its interaction with fluorescent gold nanoclusters, iodate was capable of oxidizing and etching gold core of the nanoclusters, resulting in fluorescence quenching. Furthermore, it was found that extra iodide ion could enhance this etching process, and even a small amount of iodate could lead to significant quenching. Under an optimized condition, linear relationship between the iodate concentration and the fluorescence quenching was obtained in the range 10 nM–1 μM. The developed iodate sensor was found selective and capable of detecting iodate as low as 2.8 nM. The sensor was then applied for the analysis of iodate in real sample and satisfactory recoveries were obtained.     

Gas-diffusion flow injection assay for the selective determination of chlorine dioxide based on the fluorescence quenching of chromotropic acid

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λ_ex. = 347 nm, λ_em. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l^− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (s_r = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l^− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to c_L = 0.03 mg l^− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1-105.9%.     

荧光反猝灭法测定药剂中卡托普利

建立荧光反猝灭法测定卡托普利(CAT)的体系.碘(I-3)与罗丹明B(RhB)缔合作用使罗丹明B荧光信号强度减弱直至荧光猝灭,而卡托普利可将I-3还原为I-,使体系荧光信号再现.在2～20μmol·L-1范围内荧光强度再现值ΔF与卡托普利浓度有线性关系:ΔF=-8.438+10.774c(r=0.9986),检出限为3...     

牛血红蛋白催化荧光猝灭法测定痕量甲巯咪唑

在NH3·H2O-NH4Cl缓冲溶液中,牛血红蛋白催化H202氧化L-酪氨酸产生荧光,甲巯咪唑对该荧光体系具有较强的猝灭作用.据此建立了酶催化荧光猝灭法测定痕量甲巯咪唑的方法.结果表明,甲巯咪唑含量在0.986～14.8 μg/L范围内与荧光强度变化值呈线性关系,其线性回归方程为△F405nm=50.923p+191....     

Steric effect on fluorescence quenching

In this communication we have reported the steric effect on the fluorescence quenching rate constants of the electron transfer (ET) process. We have done a comparative study using donor (D)-acceptor (A) systems with different exergonicity (-deltaG(f)). Different carbazole derivatives (CZ): 1,4-dicyanobenzene (DCB) systems (-deltaG(f) = 0.7-0.8 eV) were found to be among those limiting systems that show a clear-cut steric dominance in the process of fluorescence quenching. It is known that with increasing exergonicity the ET distance increases and hence steric dependence becomes insignificant. On the other hand, with decreasing exergonicity the ET distance decreases and a pronounced steric dominance should be observed. However, in the D-A systems having lower exergonicity compared to CZ-DCB systems, this steric dominance is observed only in polar medium. In non-polar medium due to exciplex formation the D-A distance effectively becomes much longer and therefore no steric dominance is observed.     

基于荧光猝灭的铜传感器研究

研究了过渡金属离子对荧光分子 1 萘胺二乙酸钠 (NADA)的荧光猝灭现象及其猝灭机理 ,并基于此建立铜离子传感体系。该铜离子传感器的检测限为8.2 7× 1 0 - 6mol/L ,定量检测范围为 2 .6 9× 1 0 - 5～ 1 .2 0× 1 0 - 4 mol/L。     

Flow-injection determination of hydrogen peroxide based on fluorescence quenching of chromotropic acid catalyzed with Fe(II)

Flow-injection analysis system (FIA system), which was based on Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide, was developed for the determination of hydrogen peroxide. The chromotropic acid has a fluorescence measured at λ_em = 440 nm (emission wavelength) with λ_ex = 235 nm (excitation wavelength), and the fluorescence intensity at λ_em = 440 nm quietly decreased in the presence of hydrogen peroxide and Fe(II), which was caused by Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide. By measuring the difference of fluorescence intensity, hydrogen peroxide (1.0 × 10⁻⁸-1.0 × 10⁻³ mol L⁻¹) could be determined by the proposed FIA system, whose analytical throughput was 40 samples h⁻¹. The relative standard deviation (RSD) was 1.03% (n = 10) for 4.0 × 10⁻⁸ mol L⁻¹ hydrogen peroxide. The proposed FIA technique could be applied to the determination of hydrogen peroxide in rain water samples.     

Stimulated fluorescence and fluorescence quenching in chlorophyll a and bacteriochlorophyll a

This communication deals with the photophysical processes that take place in chlorophyll solutions under intense nitrogen laser irradiation. The effect of the pump photon density on the fluorescence yield depends strongly on the geometry of the irradiation and the sampling set-up. If the fluorescence cell and sampling probe are placed close to the transverse arrangement used for obtaining laser output, line narrowing and gain, which are processes associated with high population inversions and stimulated fluorescence, are observed. A normal fluorescence spectrum and a decrease in fluorescence quantum yield with increasing pump power are observed in the fluorescence cells in oriented at an angle of 20–40° with respect to the transverse axis of the exciting beam. The decrease in quantum yield appears to result from absorption of the pump photons by the excited singlet of the chlorophylls, and it is suggested that an analogous mechanism may be responsible for the anomalous fluorescence quantum yield reported for in in vivo Chlorella vulgaris algae.     

Magnetic quenching of fluorescence

The direct and indirect mechanisms for the magnetic enhancement of radiationless decay processes are described, and used to account for the experimental observations of the magnetic quenching of fluorescence from carbon disulphide, glyoxal, and nitrogen dioxide.     

Determination of DNA based on fluorescence quenching of terbium doped carbon dots

This work describes the preparation of carbon dots doped with terbium(III) (Tb-CDs) via a hydrothermal method, starting from terbium ion and ethylenediamine. The size, composition and spectral properties of the Tb-CDs were characterized by transmission electron microscopy, infrared spectra, and fluorescence spectra. The results show that doping of the CDs with Tb(III) reduces the particle size and results in more uniform particles, while fluorescence (at excitation/emission peaks of 380/475 nm) is strongly enhanced. The interaction between Tb-CDs and ct-DNA results in fluorescence quenching of Tb-CDs. The findings were exploited to design a quenchometric method for the determination of ct-DNA. The signal drops linearly in the 80 ng·mL^?1 to 50 μg·mL^?1 ct-DNA concentration range, and the detection limit is 53 ng·mL^?1. The method was applied to the determination of ct-DNA in spiked samples and gave satisfactory results. The possible fluorescence quenching mechanism (which is mainly static) was investigated using the Stern–Volmer equation and thermodynamic equations.

Open image in new window

Graphical abstract A kind of carbon dots doped with terbium(III) (Tb-CDs) were prepared via a hydrothermal method, using terbium ion and ethylenediamine as precursor. Doping with Tb(III) reduced the particle size of CDs and results in uniform particle size and stronger fluorescence. The interaction between the Tb-CDs and dsDNA results in quenching of the fluorescence of Tb-CDs and can be applied to determination of dsDNA.