Highly sensitive fluorescence detection of glycoprotein based on energy transfer between CuInS2 QDs and rhodamine B

A highly sensitive fluorescence method for glycoprotein detection has been established based on fluorescence resonance energy transfer (FRET) between CuInS₂ quantum dots (QDs) and rhodamine B (RB). Lectins comprise a group of proteins with unique affinities toward carbohydrate structures, so the process of FRET can occur between lectin‐coated QDs (CuInS₂ QDs–Con A conjugates, acceptors) and carbohydrate‐coated RB (RB–NH₂‐glu conjugates, donors). The fluorescence of lectin‐coated QDs was recovered in the presence of a glycoprotein such as glucose oxidase (GOx) and transferrin (TRF), which significantly reduced the FRET efficiency between the donor and the acceptor. Under optimal conditions, a linear correlation was established between the fluorescence intensity ratio I₆₅₄/I₅₇₇ and the TRF concentration over the range of 6.90 × 10^‐10 to 3.45 × 10^‐8 mol/L, with a detection limit of 2.5 × 10^‐10 mol/L. The linear range for GOx is 3.35 × 10^‐10 to 6.70 × 10^‐8 mol/L, with a detection limit of 1.5 × 10^‐10 mol/L. The proposed method was applied to the determination of glycoprotein in human serum and cell‐extract samples with satisfactory results. Furthermore, CuInS₂ QDs–Con A conjugates are used as safe and efficient optical nanoprobes in HepG2 cell imaging. Copyright © 2015 John Wiley & Sons, Ltd.     

Rapid determination of gatifloxacin in biological samples and pharmaceutical products using europium‐sensitized fluorescence spectrophotometry

A europium‐sensitized fluorescence spectrophotometry method using an anionic surfactant, sodium dodecyl benzene sulphonate (SDBS), was developed for the determination of gatifloxacin (GFLX). The GFLX–Eu³⁺–SDBS system was studied and it was found that SDBS significantly enhanced the fluorescence intensity of the GFLX–Eu³⁺ complex (about 25‐fold). The optimal experimental conditions were determined as follows: excitation and emission wavelengths of 338 and 617 nm, pH 7.5, 3.0 × 10^–6 mol/L europium(III), and 5.0 × 10^–5 mol/L SDBS. The enhanced fluorescence intensity of the system (ΔI_f) showed a good linear relationship with the concentration of GFLX over the range 1.0 × 10^–8–8.0 × 10^–7 mol/L with a correlation coefficient of 0.9990. The detection limit (S:N = 3) was determined as 1.0 × 10^–9 mol/L. This method has been successfully applied for the determination of GFLX in pharmaceuticals and human urine/serum samples. Compared with most other methods reported, the rapid and simple procedure proposed here offered higher sensitivity, wider linear range and good stability. The luminescence mechanism of the system is also discussed in detail. Copyright © 2008 John Wiley & Sons, Ltd.     

Utility of gold nanoparticles in luminescence determination of trovafloxacin: comparison of chemiluminescence and fluorescence detection

Two novel sensitive sequential injection chemiluminescence analysis and fluorescence methods for trovafloxacin mesylate detection have been developed. The methods were based on the enhancement effect of gold nanoparticles on luminol–ferricyanide–trovafloxacin and europium(III)–trovafloxacin complex systems. The optimum conditions for both detection methods were investigated. The chemiluminescence signal was emitted due to the enhanced effect of gold nanoparticles on the reaction of luminol–ferricyanide–trovafloxacin in an alkaline medium. The response was linear over a concentration range of 1.0 × 10^–9 to 1.0 × 10^–2 mol/L (%RSD = 1.3), (n = 9, r = 0.9991) with a detection limit of 1.7 × 10^–10 mol/L (S/N = 3). The weak fluorescence intensity signal of the oxidation complex of europium(III)–trovafloxacin was strongly enhanced by gold nanoparticles and detected at λ_ex = 330 and λ_em = 540 nm. Fluorescence detection enabled the determination of trovafloxacin mesylate over a linear range of 1.0 × 10^–8 to 1.0 × 10^–3 mol/L (%RSD = 1.2), (n = 6, r = 0.9993) with a detection limit of 3.3 × 10^–9 mol/L. The proposed methods were successfully applied to the determination of the studied drug in its bulk form and in pharmaceutical preparations. The results were treated statistically and compared with those obtained from other reported methods. Copyright © 2015 John Wiley & Sons, Ltd.     

A highly selective fluorescent probe for pyrophosphate detection in aqueous solutions

A novel and simple fluorescence enhancement method is introduced for selective pyrophosphate (PPi) sensing in an aqueous solution. The method is based on a 1:1 metal complex formation between tris(8‐hydroxyquinoline‐5‐sulphonate) thulium(III) [Tm(QS)₃] and PPi ion. The linear response covers a concentration range of 1.6 × 10^?7–1.0 × 10^?5 mol/L PPi and the detection limit is 2.3 × 10^?8 mol/L. The association constant of Tm(QS)₃–PPi complex was calculated as 2.6 × 10⁵ mol/L. Tm(QS)₃ shows a selective and sensitive fluorescence enhancement toward PPi ion in comparion with I₃^?, NO₃^?, CN^?, CO₃^2?, Br^?, Cl^?, F^?, H₂PO₄^? and SO₄^2?, which is attributed to higher stability of the inorganic complex between pyrophosphate ion and Tm(QS)₃. Copyright © 2011 John Wiley & Sons, Ltd.     

Selective recognition of acetate ion based on fluorescence enhancement chemosensor

Fluorescence study of the complexation between uranyl salophen (L) and some common anions in acetonitrile–water (90:10, v/v) solution showed a tendency of L toward acetate ion (AcO^?). The fluorescence enhancement of L is attributed to a 1:1 complex formation between L and acetate ion which was utilized as the basis for the selective detection of AcO^?. The association constant of the 1:1 complex formation of L–AcO^? was calculated as 6.60 × 10⁶. The linear response range of the fluorescent chemosensor covers a AcO^? concentration range of 1.6 × 10^?7 to 2.5 × 10^?5 mol/L, with a detection limit of 2.5 × 10^?8 mol/L. L showed a selective and sensitive fluorescence enhancement response toward acetate ion over I₃^?, NO₃^?, CN^?, CO₃^2?, Br^?, Cl^?, F^?, H₂PO4^? and SO₄^2?, which was attributed to the higher stability of inorganic complex between acetate and L. Copyright © 2012 John Wiley & Sons, Ltd.     

Highly sensitive spectrofluorimetic determination of rutin based on its activated effect on a multi‐enzyme redox system

A highly sensitive and simple spectrofluorimetric method for the determination of rutin, based on its activated effect on a haemoglobin‐catalysed reaction, was developed. Under optimum conditions, the concentration of rutin was linear, with decreased fluorescence (ΔF) of the system under optimal experimental conditions. The calibration graph was linear in the range 1.0 × 10^–7–3.0 × 10^–5 mol/L, with a detection limit of 7.0 × 10^–8 mol/L. The relative standard deviation (RSD) was 3.26% for 11 determinations of 1.0 × 10^–5 mol/L. This method was used for the determination of rutin in pharmaceuticals with satisfactory results. Copyright © 2011 John Wiley & Sons, Ltd.     

Gold nanoparticles‐based fluorescence enhancement of the terbium–levofloxacin system and its application in pharmaceutical preparations

A sensitive fluorescence (FL) technique is proposed for the determination of levofloxacin (LVX). The method is based on the fact that the weak FL signal of the Tb(III)–LVX system is strongly enhanced in the presence of gold nanoparticles. Gold nanoparticles were prepared by the citrate reduction of HAuCl₄ and characterized by transmission electron microscopy (TEM). Levofloxacin and Tb(III) ion form a fluorescence complex in aqueous solution, and its maximum emission wavelength was found at 545 nm. Optimal conditions for the formation of the levofloxacin–Tb(III) complexes were studied. Levofloxacin was detected by measuring the FL intensity, which increases linearly with the concentration of LVX in the range 6.2 × 10⁻¹⁰–2.6 × 10⁻⁸ mol/L. Recovery of the target analytes was > 96% with good quality parameters: linearity (r² > 0.996), limit of detection (LOD) and limit of quantification (LOQ) values 2.1 × 10⁻¹⁰ mol/L and 7.2 × 10⁻¹⁰ mol/L, and run‐to‐run and day‐to‐day precisions with relative standard deviations (RSDs) around 3%. Thus, the proposed method can be successfully applied to the routine determination of levofloxacin in pharmaceutical preparations. Copyright © 2011 John Wiley & Sons, Ltd.     

Fluorescence quenching studies on the interaction of riboflavin with tryptophan and its analytical application

The ineraction between riboflavin (RBF) and tryptophan (Trp) was investigated using fluorescence spectroscopy and UV–vis absorption spectroscopy under physiological conditions. The fluorescence of Trp was quenched by RBF via dynamic quenching, which was analyzed using the Stern–Volmer relation. The value of the Forster distance R₀ (2.31 nm) was obtained according to the Forster's theory of nonradiative energy transfer. Under physiological conditions, a linear relationship could be established between the quenched fluorescence intensity of Trp and the concentration of RBF in the range of 5.8 × 10^‐7–2.0 × 10^‐5 mol/L. The detection limit was 1.8 × 10^‐7 mol/L. The method was successfully applied to determine riboflavin concentrations in pharmaceutical samples. Copyright © 2012 John Wiley & Sons, Ltd.     

Highly sensitive spectrofluorimetric determination of trace amounts of prulifloxacin using the aluminium(III)–prulifloxacin system

The fluorescence of the prulifloxacin (PUFX)–Al(III) system was investigated . Experiments indicated that the fluorescence intensity of prulifloxacin could be greatly enhanced by Al(III) and sensitized by sodium dodecylbenzene sulphonate (SDBS). Accordingly, a sensitive spectrofluorimetric method for the determination of prulifloxacin was established. While excited at 275 nm, the enhanced fluorescence intensity at 412 nm of the system (ΔF) showed a good linear relationship with the concentration of prulifloxacin within the range 4.0 × 10^–8–3.0 × 10^–6 mol/L. The regression equation was ΔF = 9.83 + 10.8 × 10⁷c (mol/L); the correlation coefficient and detection limit (3σ/k) were 0.99901 and 2.0 × 10^–8 mol/L, respectively. The proposed method has been successfully applied to determine prulifloxacin in real pharmaceutical samples. The luminescence mechanism of the system is also discussed in detail. Copyright © 2008 John Wiley & Sons, Ltd.     

Fluorescence sensing of nitric oxide in aqueous solution by triethanolamine‐modified CdSe quantum dots

The water‐soluble luminescent CdSe quantum dots were prepared by ligand exchange with triethanolamine (TEA). Oxygen can reversibly enhance the fluorescence of the synthesized quantum dots (TEA‐CdSe‐QDs) in aqueous solution. Nitric oxide radical (NO) can react easily with dissolved oxygen in water and was found to have a significant quenching effect on the fluorescence of the TEA‐CdSe‐QDs. The fluorescence responses were concentration‐dependent and can be well described by the typical Stern–Volmer equation. A good linear relationship (R² = 0.9963) was observed over the range 5.92 × 10^?7 to 1.85 × 10^?5 mol/L nitric oxide. Above this concentration was a second linear region ranging from 2.12 × 10^?5 to 1.12 × 10^?4 mol/L NO with a gentler slope. The detection limit, calculated following the 3σ IUPAC criteria, was 3.02 × 10^?7 mol/L. The interference effect of some common interferents such as nitrite (NO₂^?), nitrate (NO₃^?), glucose and l ‐ascorbic acid on the detection of NO was negligible for the proposed system, demonstrating the potential utility of this probe for the detection of NO in biological systems. The possible mechanism was also discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Fluorescent bovine serum albumin interacting with the antitussive quencher dextromethorphan: a spectroscopic insight

The interaction of dextromethorphan hydrobromide (DXM) with bovine serum albumin (BSA) is studied by using fluorescence spectra, UV–vis absorption, synchronous fluorescence spectra (SFS), 3D fluorescence spectra, Fourier transform infrared (FTIR) spectroscopy and circular dichroism under simulated physiological conditions. DXM effectively quenched the intrinsic fluorescence of BSA. Values of the binding constant, K_A, are 7.159 × 10³, 9.398 × 10³ and 16.101 × 10³ L/mol; the number of binding sites, n, and the corresponding thermodynamic parameters ΔG°, ΔH° and ΔS° between DXM and BSA were calculated at different temperatures. The interaction between DXM and BSA occurs through dynamic quenching and the effect of DXM on the conformation of BSA was analyzed using SFS. The average binding distance, r, between the donor (BSA) and acceptor (DXM) was determined based on Förster's theory. The results of fluorescence spectra, UV–vis absorption spectra and SFS show that the secondary structure of the protein has been changed in the presence of DXM. Copyright © 2015 John Wiley & Sons, Ltd.     

Flow‐injection chemiluminescence determination of haemoglobin in the blood

In this study, a sensitive and simple flow‐injection chemiluminescence (CL) method was developed for the quantitative analysis of haemoglobin. The method is based on the ability of haemoglobin to enhance the CL signal generated by a H₂O₂–K₄Fe(CN)₆–fluorescein alkaline system enhanced by CdTe quantum dots. Under the optimized conditions, haemoglobin can be detected in concentration range 7.35 × 10^–9–2.5 × 10^–6 mol/L, with a detection limit (3σ) of 1.8 × 10^–9 mol/L and a relative standard deviation (RSD; for 5 × 10^–7 mol/L haemoglobin) of 2.06% (n = 11). The present CL method was successfully applied for the determination of haemoglobin in three kinds of blood samples taken from an infant, an adult man, an adult woman and two reference samples. Compared with previous reports, the CL method described in this work is simple and rapid, with high sensitivity. Copyright © 2012 John Wiley & Sons, Ltd.     

BSA‐conjugated zinc oxide nanoparticles as luminescent probes for the determination of histidine

Zinc oxide nanoparticles doped with bovine serum albumin were used to determine histidine in aqueous solutions using a fluorescence spectroscopic technique. The results showed that histidine effectively quenched the fluorescence of the modified ZnO nanoparticles, whereas other amino acids did not significantly affect the light emission, thereby allowing selective and sensitive histidine detection in amino acid mixtures. Under optimal conditions (pH 7.0, 25 °C, 10 min preincubation), the detection limit for histidine was ~ 9.87 × 10^–7 mol/L. The high value of the determined quenching rate constant K_q (3.30 × 10¹³ L/mol/s) was consistent with a static quenching mechanism. Copyright © 2015 John Wiley & Sons, Ltd.     

Ozone exposure results in various carry-over effects and prolonged reduction in biomass in birch (Betula pendula Roth)

In the first experiment, saplings of ozone-sensitive and a more tolerant clone of Betula pendula Roth were exposed to ambient ozone (control treatment, accumulated exposure over a threshold 40 nmol mol ^{? 1} (AOT40) exposure of 1·0 μmol mol ^{? 1} h) and 1·5 × ambient ozone (elevated-ozone treatment, AOT40 of 17·3 μmol mol ^{? 1} h) over one growing season, 1996. After over-wintering, the dormant elevated-ozone saplings were transferred to the control blocks and assessed for short-term carry-over effects during the following growing season. In the second experiment, three sensitive, four intermediate and three tolerant clones were grown under ambient ozone (control treatment, AOT40 of 0·5–0·8 μmol mol ^{? 1} h per growing season) and 1·6–1·7 × ambient ozone (elevated-ozone treatment, AOT40 of 18·3–18·6 μmol mol ^{? 1} h per growing season) from May 1994 until May 1996, and were assessed for long-term carry-over effects during growing season 1997, after a 12–16 months recovery period. Deleterious short-term carry-over effects of ozone exposure included reduced contents of Rubisco, chlorophyll, carotenoids, starch and nutrients in leaves, lower stomatal conductance, and decreased new shoot growth and net assimilation rate, followed by a 7·5% (shoot dry weight (DW)), 15·2% (root DW) and 23·2% (foliage area) decreased biomass accumulation and yield over the long term, including a reduced root : shoot ratio. However, a slow recovery of relative growth rates during the following two seasons without elevated ozone was apparent. Several long-lasting structural, biochemical and stomatal acclimation, stress-defence and compensation reactions were observed in the ozone-tolerant clone, whereas in the sensitive clone allocation shifted from growth towards defensive phenolics such as chlorogenic acid. The results provide evidence of persistent deleterious effects of ozone which remain long after the ozone episode.     

Synthesis of a novel fluorescent probe based on 7‐nitrobenzo‐2‐oxa‐1,3‐diazole skeleton for the rapid determination of vitamin B12 in pharmaceuticals

A new fluorescent probe, 4‐N,N‐di(2‐hydroxyethyl)imino‐7‐nitrobenzo‐2‐oxa‐1,3‐diazole (HINBD) was synthesized in a single step with reasonably good yield. The water‐soluble HINBD emits strongly in the visible region (λ_ex = 479 nm, λ_em = 545 nm) and is stable over a wide range of pH values. It was found that vitamin B₁₂ (VB₁₂) had the ability to quench the fluorescence of HINBD, and the quenched fluorescence intensity was proportional to the concentration of VB₁₂. A method for VB₁₂ determination based on the quenching fluorescence of HINBD was thus established. Interference effects of various substances, including sugars, vitamins, amino acids, inorganic cations and some organic substances have been studied. Under optimal conditions, the linear range is 0.0–2.4 × 10^–5 mol/L. The determination limit is 8.3 × 10^–8 mol/L. The method was applied to measure VB₁₂ in pharmaceutical preparations with satisfactory results. Copyright © 2013 John Wiley & Sons, Ltd.     

Cupric oxide nanoparticles‐enhanced chemiluminescence method for measurement of β‐lactam antibiotics

A simple, sensitive cupric oxide nanoparticles (CuO NPs) enhanced chemiluminescence (CL) method was developed for the measurement of β‐lactam antibiotics, including amoxicillin and cefazolin sodium. The method was based on suppression of the CuO NPs–luminol–H₂O₂ CL reaction by β‐lactam antibiotics. Experimental parameters that influenced the inhibitory effect of the antibiotic drugs on the CL system, such as NaOH (mol/L), luminol (µmol/L), H₂O₂ (mol/L) and CuO NPs (mg/L) concentrations, were optimized. Calibration graphs were linear and had dynamic ranges of 1.0 × 10^–6 to 8.0 × 10^–6 mol/L and 3.0 × 10^–5 to 5.0 × 10^–3 mol/L for amoxicillin and cefazolin sodium, respectively, with corresponding detection limits of 7.9 × 10^–7 mol/L and 1.8 × 10^–5 mol/L. The relative standard deviations of five replicate measurements of 5.0 × 10^–6 amoxicillin and 5 × 10^–4 cefazolin sodium were 5.43 and 5.01%, respectively. The synthesized CuO NPs were characterized by X‐ray diffraction (XRD) and transmission electronmicroscopy (TEM). The developed approach was exploited successfully to measure antibiotics in pharmaceutical preparations. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of colloidal β-cyclodextrins-Fe(3) O(4) magnetic nanoparticles on the chemiluminescence enhancement of luminol-Ag(III) complex for rapid and sensitive determination of cysteine in human serum

Colloidals solution of Fe₃O₄ magnetic nanoparticles (MNPs), capped with β‐cyclodextrins (β‐CD) as inclusion complexes, were found to enhance the chemiluminescence (CL) intensity of the luminol–diperiodatoargentate(III) (DPA) system. On injection of cysteine into the luminol–DPA–β‐CD–Fe₃O₄ MNPs inclusion complexes system, the CL intensity is strongly enhanced. The enhanced CL signal is ascribed to the catalytic effect of Fe₃O₄ MNPs capped with β‐CD, which is assumed to stabilize the CL intermediate. Based on these findings, a rapid and sensitive assay was developed for the determination of cysteine in human serum. The effects of analytical variables on the CL signal were studied and optimized. Under the optimum conditions, the CL intensity was directly proportional to the concentration of cysteine in the range 8.0 × 10^–9–1.0 × 10^–6 mol/L. The detection limit was 2.8 × 10^–9 mol/L (3 S_b/m) and the relative standard deviation (RSD) for 10 replicate determinations of 1.0 × 10^–7 mol/L cysteine was 3.5%. The proposed method was applied to the sensitive determination of cysteine in human serum samples, and compared with the Ellman method with satisfactory results. Copyright © 2011 John Wiley & Sons, Ltd.     

Thermodynamics of mucopolysaccharide–dye binding. II. Binding constant and cooperativity parameters of acridine orange–dermatan sulfate system

In the acridine orange–dermatan sulfate system, free and bound dye can be distinguished from each other spectroscopically. This permits the use of fluorometric methods to study the binding of acridine orange to the acid mucopolysaccharide dermatan sulfate. Experiments were conducted at 24°C in 10^?3 M citrate/phosphate buffer at pH = 7.0. The binding of the dye is highly cooperative, as evidenced by considerable interaction between adjacent bound dye molecules. Analysis of the data indicates that dermatan sulfate binds 2.3 ± 0.3 mol of acridine orange per dermatan sulfate uronic acid residue with a cooperative binding constant, K_q ranging from 4.9 to 6.0 × 10⁵ M^?1 which corresponds to a free energy of 7.74 ? ΔG° ? 7.86. The cooperativity parameter q apparently increases with increasing polymer-to-dye ratio.     

Capillary electrophoresis coupled with end‐column electrochemiluminescence for the determination of ephedrine in human urine,and a study of its interactions with three proteins

A tris(2,2‐bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺)‐based electrochemiluminescence (ECL) detection coupled with capillary electrophoresis (CE) method has been established for the sensitive determination of ephedrine for the first time. Under the optimized conditions [ECL detection at 1.15 V, 25 mmol/L phosphate buffer solution (PBS), pH 8.0, as running buffer, separation voltage 12.5 kV, 5 mmol/L Ru(bpy)₃²⁺ with 60 mmol/L PBS, pH 8.5, in the detection cell] linear correlation (r = 0.9987) between ECL intensity and ephedrine concentration was obtained in the range 6.0 × 10^–8–6.0 × 10^–6 g/mL. The detection limit was 4.5 × 10^–9 g/mL (S:N = 3). The developed method was successfully applied to the analysis of ephedrine in human urine and the investigation of its interactions with three proteins, including bovine serum albumin (BSA), cytochrome C (Cyt‐C) and myoglobin (Mb). The number of binding sites and the binding constants between ephedrine and BSA, Cyt‐C and Mb were 8.52, 12.60, 10.66 and 1.55 × 10⁴ mol/L, 6.58 × 10³ mol/L and 1.59 × 10⁴ mol/L, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of free cholesterol based on a novel flow‐injection chemiluminescence method by immobilizing enzyme

A novel flow injection chemiluminescence method is proposed for determination of cholesterol in this paper. The cholesterol oxidase was immobilized onto sol–gel and prepared as an enzymatic reaction column. The determination of cholesterol was performed by quantitative determination of hydrogen peroxide produced from an enzymatic reaction. The luminol–H₂O₂–metal chelate diperiodatocuprate(III) system ensured that the method was highly sensitive and selective. Free cholesterol was determined over the range 5.0 × 10^–8 mol/L–5.0 × 10^–7 mol/L, with a limit of detection (3σ) of 1.9 × 10^–8 mol/L. The relative standard deviation (RSD) for 2.5 × 10^–7 mol/L was 2.7% (n = 7). The proposed method offered the advantages of sensitivity, selectivity, simplicity and rapidity for free cholesterol determination, and was successfully applied to the direct determination of free cholesterol in serum. Copyright © 2008 John Wiley & Sons, Ltd.