A terbium‐sensitized spectrofluorimetric method for determination of catecholamines in a serum sample with micelle medium

A terbium‐sensitized spectrofluorimetric method has been developed for determination of catecholamines such as norepinephrine (NE), epinephrine (EP) and dopamine (DA), using sodium dodecyl benzene sulphonate (SDBS). Fluorescence sensitization of terbium ions (Tb³⁺) by complexation with catecholamines in the presence of SDBS was observed. The fluorescence intensities of the Tb³⁺–catecholamine complexes were highly enhanced by introducing SDBS with an emission maximum at 545 nm after excitation at 290 nm. The conditions for the complex formation of Tb³⁺–catecholamine were investigated systematically and optimized to determine catecholamines in a serum sample. Under the optimum conditions, the fluorescence intensities of the Tb³⁺–catecholamine complexes were increased linearly with the concentration of NE, EP and DA over the ranges 2.5 × 10^–10–1.0 × 10^–8, 2.5 × 10^–10–1.0 × 10^–8 and 2.5 × 10^–9–1.0 × 10^–7 g/mL with correlation coefficients of 0.999, 0.999 and 0.9996, respectively. The limits of detection (3δ) of NE, EP and DA were found to be 4.6 × 10^–11, 7.8 × 10^–11 and 8.38 × 10^–10 g/mL, respectively. Precision of the method was tested at the concentration level of 1.2 × 10^?7 g/mL for five replicate measurements of NE, EP and DA, giving relative standard deviations (RSDs) of 1.41%, 1.23% and 1.89%, respectively. The interaction mechanism of the Tb³⁺–catecholamine complexes system was investigated and presented with ultraviolet absorption spectra. The proposed method has been applied for the quantitative determination of NE, EP and DA in a spiked serum sample and a pharmaceutical preparation sample. Copyright © 2011 John Wiley & Sons, Ltd.     

Sensitive determination of protein based on the fluorescence enhancement effect of terbium (III)–epinephrine–protein–sodium dodecylsulfate system

It was found that the fluorescence of Tb³⁺–epinephrine (E) complex can be enhanced by both bovine serum albumin (BSA) and sodium dodecylsulfate (SDS), and stabilized by ascorbic acid (AA). It is considered that the fluorescence enhancement of the Tb³⁺–E–BSA–AA–SDS system originates not only from the hydrophobic microenvironment provided by BSA–SDS, but also from the energy transfer from BSA to Tb³⁺ in this system. Therefore, a new fluorescence method for the determination of protein concentrations as low as 1.3 × 10^?9 g mL^?1 BSA is established using Tb³⁺–epinephrine complex as probe. The method has been applied for the determination of BSA and human serum albumin in actual samples, and the results obtained are satisfactory. Compared with other fluorescence methods, this method is simpler and more sensitive for the determination of protein. The mechanism of the fluorescence enhancement of the system is studied in detail. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of nucleic acid by [tetra‐(3‐methoxy‐4‐hydroxyphenyl)]–Tb3+ porphyrin as the fluorescence spectral probe in bis(2‐ethylhexyl)sulfosuccinate sodium salt micelle system

A new system for the determination of nucleic acid by rare earth metallic porphyrin of [tetra‐(3‐methoxy‐4‐hydroxyphenyl)]–Tb³⁺ [T(3‐MO‐4HP)–Tb³⁺] porphyrin as fluorescence spectral probe has been developed in this paper. Nucleic acid can enhance the fluorescence intensity of the T(3‐MO‐4HP)–Tb³⁺ porphyrin in the presence of bis(2‐ethylhexyl)sulfosuccinate sodium salt(AOT) micelle. In pH 8.00 Tris–HCl buffer solution, under optimum conditions, the enhanced fluorescence intensity is in proportion to the concentration of nucleic acids in the range of 0.05–3.00 µg mL^?1 for calf thymus DNA (ct DNA) and 0.03–4.80 µg mL^?1 for fish sperm DNA(fs DNA). Their detection limits are 0.03 and 0.01 µg mL^?1, respectively. In addition, the binding interaction mechanism between T(3‐MO‐4HP)–Tb³⁺ porphyrin and ct DNA is also investigated by resonance scattering and fluorescence spectra. The maximum binding number is calculated by molar ratio method. The new system can be used for the determination of nucleic acid in pig liver, yielding satisfactory results. Copyright © 2009 John Wiley & Sons, Ltd.     

Luminescent and hydrophilic LaF3–polymer nanocomposite for DNA detection

Luminescent LaF₃–Ce³⁺/Tb³⁺ nanocrystals have been successfully prepared via a simple wet chemical technique. For the next bioapplication, these nanoparticles dispersed in cyclohexane have also been functionalized with poly(St‐co‐MAA), based on a designed oil‐in‐water microemulsion system. These polymer‐coated nanospheres are water‐soluble and bioconjugable. Unlike semiconductor quantum dots, the as‐prepared lanthanum fluoride nanocrystals possess non‐size‐dependent emissions and completely stable photocycles. With functionalized LaF₃ nanospheres as fluorescence probes, a fluorescence method was developed for the rapid quantitative analysis of DNA, due to the quenching effect of fluorescence by the DNA. Under optimum conditions, the fluorescence intensity was proportional to the concentration of the introduced DNA over the range 2.5–35 µg/mL for calf thymus DNA (ctDNA) and 2.5–30 µg/mL for fish sperm DNA (fsDNA), respectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Luminescent complexes of terbium ion for molecular recognition of ibuprofen

The complexation behavior and luminescent properties of terbium (Tb³⁺) complexes containing bi‐dental ligands were studied: nitrogen – 1,10‐phenanthroline, and oxygen – trifluoroacetylacetone as well as acetylacetone ligands with ibuprofen (Ibu; a non‐steroidal anti‐inflammatory drug). Aqueous and aqueous alcohol microheterogeneous solutions were used as media. The effects of solubilization by various micellar solutions, pH and ligand type on luminescent properties of Tb³⁺ complexes were investigated. Sensitized luminescence of mixed ligand complex Tb(1,10‐phenanthroline)‐Ibu and dynamic quenching effect in complex Tb(trifluoroacetylacetone)₃‐Ibu allow Ibu determination with the limit of detection 5.3 × 10^–8 mol/L and 1.26 × 10^–6 mol/L, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

The fluorescence enhancement of quercetin–nucleic acid system and the analytical application

Nucleic acid can greatly enhance the fluorescence intensity of quercetin in HMTA‐HCl (pH 5.5) buffer. The enhanced intensity is in proportion to the concentration of nucleic acids in the range 5.0 × 10^?9 to 1.0 × 10^?6 g/mL for fsDNA, 5.0 × 10^?9 to 7.0 × 10^?7 g/mL for ctDNA and 5.0 × 10^?9 to 1.0 × 10^?6 g/mL for yRNA, and their detection limits (S/N = 3) are 3.5 × 10^?9, 7.8 × 10^?10 and 2.6 × 10^?9 g/mL, respectively. In comparison with most reported fluorescent probes for the determination of nucleic acids, the proposed probe has higher sensitivity and lower toxicity. The interaction investigation indicates that quercetin binds with double‐strand DNA in groove binding mode, resulting in fluorescence enhancement of this system. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of amlodipine using terbium‐sensitized luminescence in the presence of europium(III) as a co‐luminescence reagent

A sensitive time‐resolved luminescence method for the determination of amlodipine (AM) in methanol and in aqueous solution is described. The method is based on the luminescence sensitization of terbium (Tb³⁺) by formation of a ternary complex with AM in the presence of tri‐n‐octylphosphine oxide (TOPO) as co‐ligand, dodecylbenzenesulfate as surfactant and europium ion as a co‐luminescence reagent. The signal for Tb–AM–TOPO is monitored at λ_ex = 242 nm and λ_em = 550 nm. Optimum conditions for the formation of the complex in aqueous system were 0.015 m Tris (hydroxylmethyl) amino methane buffer, pH 9.0, TOPO (1.0 × 10^–4 m ), Eu³⁺ (2.0 × 10^–7 m ), dodecylbenzenesulfate (0.14%) and 6.0 × 10^–5 m of Tb³⁺, which allows the determination of 10–50 ppb of AM with a limit of detection of 1.2 ppb. The relative standard deviations of the method range between 0.1 and 0.2% indicated excellent reproducibility of the method. The proposed method was successfully applied for the assay of AM in pharmaceutical formulations and in plasma samples. Average recoveries of 98.5 ± 0.2% and 95.2 ± 0.2% were obtained for AM in tablet and plasma samples respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectrofluorimetric determination of folic acid in tablets and urine samples using 1,10‐phenanthroline‐terbium probe

A new spectrofluorimetric method was reported for the determination of folic acid (FA), based on its quenching effect on the fluorescence intensity of Tb³⁺–1,10‐phenanthroline complex as a fluorescent probe. The quenched fluorescence intensity at an emission wavelength of 545 nm was proportional to the concentration of FA in Tris–HCl buffer solution of pH 6.2. The effects of pH, time, order of addition of reagents, temperature and concentrations of Tb³⁺, buffer and 1,10‐phenanthroline were investigated and optimized. The linear range for the determination of FA was 0.01–1.1 mg/L. The detection limit was 0.003 mg/L and the relative standard deviation for replicated determination of 1 mg/L of folic acid was 1.2%. This method was simple, practical and relatively free from interference effects. It was successfully applied to assess FA in pharmaceutical tablets and urine samples. Copyright © 2010 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.     

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.     

Synthesis,crystal structure and fluorescence properties of terbium complexes with phenoxyacetic acid and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine

Two complexes of Tb³⁺, Gd³⁺/Tb³⁺ and one heteronuclear crystal Gd³⁺/Tb³⁺ with phenoxyacetic acid (HPOA) and 2,4,6‐tris‐(2‐pyridyl)‐s–triazine (TPTZ) have been synthesized. Elemental analysis, rare earth coordination titration, inductively coupled plasma atomic emission spectrometry (ICP‐AES) and thermogravimetric analysis‐differential scanning calorimetry (TG‐DSC) analysis show that the two complexes are Tb₂(POA)₆(TPTZ)₂·6H₂O and TbGd(POA)₆(TPTZ)₂·6H₂O, respectively. The crystal structure of TbGd(POA)₆(TPTZ)₂·2CH₃OH was determined using single‐crystal X‐ray diffraction. The monocrystal belongs to the triclinic system with the P‐1 space group. In particular, each metal ion is coordinately bonded to three nitrogen atoms of one TPTZ and seven oxygen atoms of three phenoxyacetic ions. Furthermore, there exist two coordinate forms between C₆H₅OCH₂COO^– and the metal ions in the crystal. One is a chelating bidentate, the other is chelating and bridge coordinating. Fluorescence determination shows that the two complexes possess strong fluorescence emissions. Furthermore, the fluorescence intensity of the Gd³⁺/Tb³⁺ complex is much stronger than that of the undoped complex, which may result from a decrease in the concentration quench of Tb³⁺ ions, and intramolecular energy transfer from the ligands coordinated with Gd³⁺ ions to Tb³⁺ ions. Copyright © 2015 John Wiley & Sons, Ltd.     

Determination of fluoxetine in pharmaceutical and biological samples based on the silver nanoparticle enhanced fluorescence of fluoxetine–terbium complex

In this study, a simple and sensitive spectrofluorimetric method is presented for the determination of fluoxetine based on the enhancing effect of silver nanoparticles (AgNPs) on the terbium–fluoxetine fluorescence emission. The AgNPs were prepared by a simple reduction method and characterized by UV–Vis spectroscopy and transmission electron microscopy. It was indicated that these AgNPs have a remarkable amplifying effect on the terbium‐sensitized fluorescence of fluoxetine. The effects of various parameters such as AgNP and Tb³⁺ concentration and the pH of the media were investigated. Under obtained optimal conditions, the fluorescence intensity of the terbium–fluoxetine–AgNP system was enhanced linearly by increasing the concentration of fluoxetine in the range of 0.008 to 19 mg/L. The limit of detection (b + 3s) was 8.3 × 10^‐4 mg/L. The interference effects of common species found in real samples were also studied. The method had good linearity, recovery, reproducibility and sensitivity, and was satisfactorily applied for the determination of fluoxetine in tablet formulations, human urine and plasma samples. Copyright © 2016 John Wiley & Sons, Ltd.     

Spectrofluorimetric determination of bilirubin in serum samples

A new spectrofluorimetric method was developed for determination of trace amount of bilirubin. Using oxytetracycline–Eu³⁺ as a fluorescent probe, in the buffer solution of pH = 7.3, bilirubin can reduce remarkably the fluorescence intensity of the oxytetracycline–Eu³⁺ complex at λ = 612 nm and the reduced fluorescence intensity was in proportion to the concentration of bilirubin. Optimum conditions for the determination of bilirubin were also investigated. The linear range and limit of detection for the determination of bilirubin were 5.0 × 10^?7, 3.0 × 10^?5 and 7.7 × 10^?8 mol L^?1, respectively. This method is simple, practical and relatively free of interference from coexisting substances and can be successfully applied to assess bilirubin in serum samples and compared with the modified Jendrassik–Grof method in clinical analysis. The quenching mechanism of the fluorescence intensity in the system is also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

A new quaternary photoluminescence enhancement system of Eu−N‐(o‐vanillin)‐1,8‐diaminonaphthalene−1,10‐phenanthroline−Zn and its application in determining trace amounts of europium and zinc

A new sensitive quaternary photoluminescence enhancement system has been successfully developed to determine trace amounts of Eu³⁺ and Zn²⁺. The photoluminescence intensity of Eu ? N‐(o‐vanilin)‐1,8‐diaminonaphthalene systems was greatly increased by the addition of specific concentrations of 1, 10‐phenanthroline and Zn²⁺. The excitation and emission wavelengths were 274 and 617 nm, respectively. Under optimal system conditions, the photoluminescence intensity showed a linear response toward Eu³⁺ in the range of 5.0 × 10^–6 ~ 2.0 × 10^–5 M with a limit of detection (= 2.2 × 10^–9 M) and the photoluminescence intensity of the system decreased linearly by increasing the Zn²⁺ concentration in the range of 5.0 × 10^–8 ~ 1.0 × 10^–6 M with a limit of detection (= 8.8 × 10^–11 M). This system was successfully applied for the determination of trace amounts of Eu³⁺ in a high purity La₂O₃ matrix and in the synthetic rare earth oxide mixture, and of Zn²⁺ in a high purity Mg(NO₃)₂ · 6H₂O matrix and in synthetic coexisting ionic matrixes. The energy transfer mechanism, photoluminescence enhancement of the system and interference of other lanthanide ions and common coexisting ions were also studied in detail. Copyright © 2013 John Wiley & Sons, Ltd.     

Flow‐injection chemiluminescence of the luminol–potassium periodate system enhanced by TGA–capped CdTe quantum dots for the determination of theophylline

The chemiluminescence (CL) behaviour of the luminol–potassium periodate system enhanced by CdTe quantum dots capped with thioglycolic acid (TGA–CdTe QDs) was studied using kinetic experiments, CL spectra, UV–vis absorption spectra and fluorescence spectra. The production of oxygen‐containing reactant intermediates (O₂^?? and OH^?) in the present CL system was verified by CL. The possible CL mechanism was discussed in detail. Furthermore, theophylline (THP) was determined based on its enhancement of the CL intensity of the CdTe QDs–luminol–potassium periodate system coupled with a flow‐injection technique. Under these optimized conditions, the linear range was found to be from 1.0 × 10^?8 to 1.0 × 10^?5 g/mL with a detection limit of 2.8 × 10^?9 g/mL (3σ). The recoveries for the determination of THP in tablets were from 98.2 to 99.6%.     

Determination of ferulic acid by flow injection chemiluminescence analysis based on enhancement of the N‐bromobutanimide–eosin–CrCl3 system in alkaline solution

A simple and sensitive flow injection chemiluminescence method has been developed for the determination of ferulic acid (FA) based on the significant enhancement effect of FA on the CL signal of the N‐bromobutanimide (NBS)–eosin–CrCl₃ system in alkaline solution. Under optimum conditions, the enhanced CL intensity is linearly related to the concentration of FA in its pharmaceutical preparations and human plasma samples. The corresponding linear regression equations were established over the 4.0 × 10^–10–1.0 × 10^–7 g/mL for FA tablets and 2.0 × 10^–10–1.0 × 10^–7 g/mL for plasma samples. The limit of detection for FA tablets and limit of quantification for plasma samples were 2.8 × 10^–10 g/mL (3 σ) and 3.04 × 10^–10 g/mL (10 σ), respectively. A complete analysis could be performed within 40 s, including washing and sampling, giving a throughput of ≈90/h. The proposed method was successfully applied to the determination of FA in pharmaceutical preparations and human plasma samples with satisfactory results. The recoveries of pharmaceutical preparations and human plasma samples at three different concentrations were 97.8–102.6% and 96.7–104.0%, respectively. Furthermore, the possible mechanism of CL reactions was also discussed briefly. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and fluorescence properties of 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazol derivatives and their terbium complexes

Eight novel 1,2,4‐triazolo[3,4‐b]‐1,3,4‐thiadiazol derivatives have been designed and synthesized, and their corresponding Tb³⁺ complexes were also prepared successfully. The fluorescence properties and fluorescence quantum yields of the target complexes were investigated, the results showed that the ligands were an efficient sensitizer for Tb³⁺ luminescence, and the target complexes exhibited characteristic fluorescence emissions of Tb³⁺ ion. The fluorescence intensity of the complex substituted by chlorine was stronger than that of other complexes. The substituents' nature has a great effect upon the electrochemical properties of the target complexes. The results showed that the introduction of the electron‐withdrawing groups tended to decrease the oxidation potential and highest occupied molecular orbital energy levels of the target Tb³⁺ complexes; however, introduction of the electron‐donating groups can increase the corresponding complexes' oxidation potential and highest occupied molecular orbital energy levels. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of the binding of paylean and DNA by fluorescence,UV spectroscopy and molecular docking techniques

The interaction of paylean (PL) with calf thymus DNA (ctDNA) was investigated using fluorescence spectroscopy, UV absorption, melting studies, ionic strength, viscosity experiments and molecular docking under simulated physiological conditions. Values for the binding constant K_a between PL and DNA were 5.11 × 10³, 2.74 × 10³ and 1.74 × 10³ L mol^–1 at 19, 29 and 39°C respectively. DNA quenched the intrinsic fluorescence of PL via a static quenching procedure as shown from Stern–Volmer plots. The relative viscosity and the melting temperature of DNA were basically unchanged in the presence of PL. The fluorescence intensity of PL–DNA decreased with increasing ionic strength. The value of K_a for PL with double‐stranded DNA (dsDNA) was larger than that for PL with single‐stranded DNA (ssDNA). All the results revealed that the binding mode was groove binding, and molecular docking further indicated that PL was preferentially bonded to A–T‐rich regions of DNA. The values for ΔH, ΔS and ΔG suggested that van der Waals forces or hydrogen bonding might be the main acting forces between PL and DNA. The binding distance was determined to be 3.37 nm based on the theory of Förster energy transference, which indicated that a non‐radiation energy transfer process occurred. Copyright © 2015 John Wiley & Sons, Ltd.     

Resonance light‐scattering enhancement effect of the protein–Y3+–TTA–SLS system and its analytical application

In this paper, a sensitive resonance light scattering (RLS) method for the determination of protein is reported. In the Tris–HCl (pH 7.50) buffer, protein enhanced the RLS intensity of the Y³⁺–2‐thenoyltrifluoroacetone (TTA)–sodium dodecyl sulphate (SLS) system. The enhanced RLS intensities were in proportion to the concentrations of proteins in the range 8.0 × 10^?9–1.0 × 10^?5 g/mL for BSA, 1.0 × 10^–8–1.0 × 10^?5 g/mL for HSA and 1.0 × 10^–8–1.0 × 10^?6 g/mL for EA, and their detection limits were 5.0, 5.4 and 6.7 ng/mL, respectively. Actual samples were satisfactorily determined. The interaction mechanism was also studied. Copyright © 2008 John Wiley & Sons, Ltd.     

A highly efficient and selective turn‐on fluorescent sensor for Hg2+, Ag+ and Ag nanoparticles based on a coumarin dithioate derivative

Based on chelation‐enhanced fluorescence, a new fluorescent coumarin derivative probe 3(1‐(7‐hydroxy‐4‐methylcoumarin)ethylidene)hydrazinecarbodithioate for Hg²⁺, Ag⁺ and Ag nanoparticles is reported. Fluorescent probe acts as a rapid and highly selective “off–on” fluorescent probe and fluorescence enhancement by factors 5 to12 times was observed upon selective complexation with Hg²⁺, Ag⁺ and Ag nanoparticles. The molar ratio plots indicated the formation of 1:1 complexes between Hg²⁺ and Ag⁺ with the probe. The linear response range covers a concentration range 0.1 × 10^–5–1.9 × 10^–5 mol/L, 0.1 × 10^–5–2.3 × 10^–5 mol/L and 0.146 × 10^–12–2.63 × 10^–12 mol/L for Hg²⁺, Ag⁺ and Ag nanoparticles, respectively. The interference effect of some anions and cations was also tested. Copyright © 2013 John Wiley & Sons, Ltd.