The fluorescence enhancement effect of Tb-Gd-adenosine triphosphate-phen system and its analytical application

It is found that the fluorescence of Tb-adenosine triphosphate (ATP)-phenanthroline (phen) system can be enhanced by Gd³⁺. The fluorescence enhancement of the Tb-Gd-ATP-phen system is considered to originate from intramolecular and intermolecular energy transfers, and the energy-insulating sheath effect of Gd-ATP-phen complex. In addition, a new energy transfer pathway in Tb-ATP-phen system is proposed. As a mediator, phen can transfer the energy absorbed by ATP to Tb³⁺ through the stacking action between aromatic ring of phen and purine ring of ATP. The proposed method has been used to determine trace amount of ATP. The detection limit is 5.4 × 10⁻⁹ mol/l, which is about 40 times lower than that of the Tb-ATP-phen system. The proposed method is one of the most sensitive fluoremetries of ATP.     

Photochemical analysis studies-V Photochemical enhancement of the fluorescence signal of the antimalarial plasmocid in liquid solution and on silica-gel thin layers

Ultraviolet irradiation converts the antimalarial plasmocid into a highly fluorescent photoproduct. The effect of pH, solvent composition and irradiation time on the photochemical enhancement of the fluorescence signal of plasmocid has been investigated in solution and on silica-gell thin layers. A significant increase in the fluorescence intensity in very acidic medium is explained by the formation of a triprotonated plasmocid species. The photochemical-fluorescence enhancement factors are particularly large, ranging between about 10 and 20 on silica-gel thin layers. Linear calibration plots are obtained over a concentration range of nearly three orders of magnitude. The photochemical-fluorimetric detection limit of plasmocid on thin layers is 10 ng. The results presented demonstrate the potential of thin-layer phototochemical fluorimetry as a sensitive analytical method.     

Significant fluorescence enhancement by supramolecular complex formation between berberine chloride and cucurbit(n=7)uril and its analytical application

The supramolecular interaction of cucurbit(n = 7)uril (Q[7]) with berberine chloride (BER) has been studied in aqueous solution at pH 2.0 and room temperature by spectro-fluorimetry. The association constant of the complex was 2.07 × 10⁶ L mol⁻¹ calculated by using a nonlinear least squares method. ¹H NMR spectra confirmed that a 1:1 stable complex is formed between Q[7] and BER. This work proposes a possible interaction mode, in which the guest BER is incorporated inside the hydrophobic cavity of the host Q[7] via the isoquinoline ring part of the guest molecule. Based on a significant enhancement of the fluorescence intensity of this supramolecular complex, a spectrofluorimetric method with high sensitivity and selectivity has been developed for the determination of BER in aqueous solution in the presence of Q[7]. The linear range of the method was from 7.43 to 11.2 × 10³ ng mL⁻¹with the detection limit 4.2 ng mL⁻¹. There was no interference from the compounds normally used in tablets, serum or urine constituents. The proposed method was applied to the determination of BER in tablets, serum and urine samples with satisfactory results and good consistency with those obtained by the pharmacopoeia method. This shows that it has promising potential for therapeutic drug monitoring and pharmokinetics and for clinical application.     

Enoxacin-Tb complex as an environmentally friendly fluorescence probe for DNA and its application

The fluorescence intensity of the enoxacin (ENX)-Tb³⁺ complex enhanced by DNA was studied. On the basis of this study, an environmentally friendly fluorescence probe of enoxacin-Tb³⁺ for the determination of single-stranded and double-stranded DNA was developed. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 2.0 × 10⁻⁸ to 2.0 × 10⁻⁶ g mL⁻¹ for hsDNA, 1.0 × 10⁻⁸ to 1.0 × 10⁻⁶ g mL⁻¹ for ctDNA and 5.0 × 10⁻⁹ to 1.0 × 10⁻⁶ g mL⁻¹ for thermally denatured ctDNA. The detection limits (S/N = 3) were 5.0, 9.0 and 3.0 ng mL⁻¹, respectively. The interaction modes between ENX-Tb³⁺ and DNA and the mechanism of the fluorescence enhancement were also discussed in details. The experimental results from UV absorption spectra, fluorescence spectra and the competing combination tests between the ENX-Tb³⁺ complex and EB probe indicated that the possible interaction modes between enoxacin-Tb³⁺ complex and DNA had at least two different binding modes: the electrostatic binding and the intercalation binding. Additionally, this fluorescence probe was used to study the interaction between heavy metals and DNA.     

Study on the fluorescence enhancement in Lanthanum(III)-carminic acid-cetyltrimethylammonium bromide system and its analytical application

A fluorescent enhancement system carminic acid (CA)-La3+-CTAB is found and based on this finding a new fluorimetric method for the determination of CA is developed. Under optimized conditions, the enhanced intensities of fluorescence are quantitatively in proportion to the concentrations of CA in the range of 0.01231-12.31 μg mL(-1). The detection limit is 10.92 ng mL(-1). Compared with other methods that have been reported to determine CA, this method has high sensitivity, stability and wide linear range. In addition, the luminescence mechanism indicates that the complex of La3+-CA (1:2) forms and solubilizes in CTAB micelle.     

Preparation of a new core-shell Ag@SiO2 nanocomposite and its application for fluorescence enhancement

Ag@SiO₂ nanoparticles with different shell thicknesses were synthesized via modified Stöber method. Rhodamine B isothiocyanate was covalently bound onto the surface of Ag@SiO₂ nanoparticles to form fluorescent core-shell Ag@SiO₂ nanocomposites. Effects of shell thickness on the fluorescence enhancement were examined using the corresponding nanobubbles prepared by cyanide etching as a control. The result showed that the fluorescence enhanced as the shell thickness increased till the distance between fluorophore and metal core reached about 75 nm with the optimal enhancement factor of ∼5-folds. Further increasing of fluorophore-metal distance caused a decrease in the enhancement factor.     

Gelation-induced fluorescence enhancement of benzoxazole-based organogel and its naked-eye fluoride detection

The benzoxazole derivative gelator forms a stable DMF/toluene cosolvent gel with dramatically enhanced fluorescence emission compared to its mother solution. The translucent colorless gel was changed to a solution with strong greenish fluorescence in the presence of fluoride anion with disruption of the gel structure.     

Peroxidase-dependent fluorescence decrease of carboxyfluorescein and its enhancement by liposome encapsulation

The fluorescence intensity of 5(6)-carboxyfluorescein (CF) was decreased by addition of horseradish peroxidase (HRP) and hydrogen peroxide (H₂O₂). The reaction inside a liposome containing CF and HRP on addition of H₂O₂ was measured fluorometrically after destruction of the liposome with Triton X-100. The reaction efficiency was higher than that without liposome because CF and HRP were concentrated inside the latter. The determination of H₂O₂ can be performed with a smaller amount of HRP by liposome encapsulation.     

The fluorescence of ellagic acid and its borax complex

The absorption and fluorescence properties of the plant phenol ellagic acid have been studied in alcohol and aqueous solutions. Fluorescence is weak in all kinds of solvents, but is greatly enhanced by addition of borax. The resulting complex emits much more intensely in methanol than in water solution. UV and fluorescence data reveal that the complex formed in methanol is different from the complex formed in aqueous solution. The enormous fluorescence enhancement of ellagic acid by borax offers a simple method for the visualization and quantification of the potent anti-mutagen ellagic acid as well as a fluorimetric method for the determination of boron.The IUPAC name for ellagic acid is 2,3,7,8-tetra-hydroxy[1]benzopyrano[5,4,3—c,d,e][1]-benzopyran-5,10-dione.     

The new fluorescence enhancement system Tb-N-(2-pyridinyl) ketoacetamide-Et(3)N-Zn and its application

A sensitive fluorescence enhancement system was developed for the determination of terbium. The fluorescence intensity of the Tb-N-(2-pyridinyl) ketoacetamide (PKAA) system was greatly enhanced by the addition of triethylamine (Et(3)N) and zinc nitrate in the methanol solution. The excitation and emission wavelengths were 329 and 546 nm, respectively. Under optimal conditions, the fluorescence intensities varied linearly with the concentration of Tb(3+) in the range of 7.5 x 10(-8)-8.2 x 10(-6)M with a detection limit of 6.4 x 10(-8)M. The interferences of some rare earth ions were described. This method was applied to the determination of trace amounts of terbium (III) in a synthetic rare earth oxide and a high purity Y(2)O(3) matrix. The mechanism of fluorescence enhancement was also studied.     

Biotin induced fluorescence enhancement in resonance energy transfer and application for bioassay

A novel method to significantly enhance fluorescence resonance energy transfer (FRET) signal which occurred from fluoresceine isothiocyanate (FITC) to Dylight 549 was studied in this paper. Streptavidin was labeled with the donor fluorophore FITC and biotinamide was conjugated to the acceptor Dylight 549. When biotinamide bound to streptavidin, FRET would occur from FITC to Dylight 549 while a remarkable fluorescence enhancement of streptavidin-FITC was observed. The fluorescence enhancement of streptavidin-FITC in the presence of biotin was utilized in the FRET system to obtain higher fluorescence signal. Increase of fluorescence intensity of FITC and decrease of Dylight 549 depended on the concentration of competitive biotin. A homogeneous analysis method was established based on the fluorescence recovery of FITC in the FRET system with fluorescence enhancement. This method is highly sensitive and simple to determine the concentration of biotin. The detection limit for biotin was 0.5 nM and the linear range of the assay was 0.8-9.8 nM. The response time is no more than 15 min during the one-step assay due to the high affinity between streptavidin and biotin.     

A new mechanism of Raman enhancement and its application

Strong electronic Raman bands corresponding to the transition between 4I9/2 and 4I11/2 manifolds of Nd3+, caused by a Raman-enhancement effect, are observed in the FT-Raman spectrum of Nd2O3. Neither resonance enhancement (RR) nor surface enhancement (SERS) accounts for the Raman enhancement observed here. We propose a new mechanism of Raman enhancement called the "feed-back" mechanism. A YAG laser excites the final state of the Raman transition (4I11/2 of Nd3+) to the 4F3/2 state and causes a significant decrease in the population of Nd3+ at the 4I11/2 state. This causes the population ratio of Nd3+ at 4I9/2 and 4I11/2 to deviate from the value required by Boltzmann's law. To restore equilibrium, Raman scattering is enhanced so that more Nd3+ ions are brought from the 4I9/2 state to the 4I11/2 state. This hypothesis gets support from the temperature-variable FT-Raman spectroscopic results. Additionally, obvious differences between the Stokes and anti-Stokes Raman spectrum of Nd3+ provide further evidence to support the feed-back mechanism. The Raman-enhancement effect confers on the electronic Raman bands a special ability to reflect the variation of coordinated structure around metal ions. The structural variations in polymer-metal ion composites and biomineralization systems have been investigated by using the electronic Raman bands.     

Selective recognition of monohydrogen phosphate by fluorescence enhancement of a new cerium complex

Bis(8-hydroxy quinoline-5-solphonate) cerium(III) chloride (Ce(QS)(2)Cl) (L) was synthesized and then used as a novel fluorescent sensor for anion recognition. Preliminarily study showed that fluorescence of L enhanced selectively in the presence of HPO(4)(2-) ion. This enhancement is attributed to a 1:1 complex formation between L and HPO(4)(2-) anion. The association constant of 1:1 complex of L-HPO(4)(2-) was calculated as 3.0×10(6). Thus, L was utilized as a basis for a selective detection of HPO(4)(2-) anion in solution. The linear response range of the proposed fluorescent chemo-sensor covers a concentration range of HPO(4)(2-) from 3.3×10(-7) to 5.0×10(-6) mol L(-1) with a detection limit of 2.5×10(-8) mol L(-1). L showed selective and sensitive fluorescence enhancement response toward HPO(4)(2-) ion in comparison with I(3)(-), NO(3)(-), CN(-), CO(3)(2-), Br(-), Cl(-), F(-), H(2)PO(4)(-) and SO(4)(2-) ions. It was probably attributed to the higher stability of the inorganic complex between HPO(4)(2-) ion and L. The method was successfully applied for analysis of phosphate ions in some fertilizers samples.     

Study on the new fluorescence enhancement system of Zn-bis-(trimethylolaminomethane)-4-tert-butyl-disalicylicimine in the presence of beta-cyclodextrin and its analytical application

A new bis-Schiff base ligand, bis-(trimethylolaminomethane)-4-tert-butyl-disalicylicimine (HL), was synthesized. The fluorescence intensity of HL-Zn²⁺ complex was increased by about 8-fold upon addition of β-cyclodextrin (β-CD). The spectrofluorimetric determination of trace amounts of Zn²⁺ based on the phenomenon was carried out. The excitation and emission wavelengths are 405 and 465 nm, respectively. Under optimal conditions, the fluorescence intensities vary linearly with the concentration of Zn²⁺ in the range 0-317 μg l⁻¹ with a detection limit of 1.0 μg l⁻¹. The interferences of some inorganic ions were described. The method is a selective, sensitive, rapid, and simple analytical procedure for the determination of Zn²⁺ in crops. The mechanism for the fluorescence enhancement was also discussed.     

Micellar enhancement of benzodiazepine fluorescence

The interactions that exist between benzodiazepines and surfactants provide micellar enhancement factors for their fluorimetric determination in the range 1.2-6.5, depending on the nature of both the benzodiazepine and the surfactant. A series of benzodiazepines and anionic surfactants were treated topologically to determine the influence of each benzodiazepine substituent on the basic benzodiazepine structure and the influence of both the hydrophobic moiety of the surfactant and its counter ion on the sensitisation process. Sensitisation parameters were used to quantify the effect of the chemical structures of both surfactants and drugs on their interaction.     

铜纳米簇的制备、聚集诱导荧光增强性能及应用研究进展

铜纳米簇不仅具有金属纳米簇的特异性,还有前驱体价格便宜等优点,因此有广泛的应用前景。从配体辅助法、模板法、微波法、电化学法和刻蚀法等综述了铜纳米簇的制备方法。从离子诱导聚集、pH诱导聚集、组装诱导聚集和溶剂诱导聚集增强发射等方面综述了铜纳米簇聚集诱导荧光发射增强性能。从离子检测、小分子检测、酶活性检测、生物大分子检测和生物成像等方面综述了铜纳米簇的应用,并对铜纳米簇的制备、性能优化和应用等方面作了展望。     

Synthesis of a quinone-functionalized macrocyclic ligand and the intense fluorescence of its zinc complex

The redox-active quinone-functionalized macrocyclic ligand 1,4,14,17-tetrahydroxyhemiporphyrazine, H2hp(OH)4, has been synthesized and its zinc complex, [Zn(hp(OH)4)(py)], found to exhibit intense fluorescence.     

Mechanism of polarization-induced single-photon fluorescence enhancement

The single-photon fluorescence (SPF) of IR125 can be enhanced when the laser polarization changes from linear through elliptical to circular [A. Nag and D. Goswami, J. Chem. Phys. 132, 154508 (2010)]. In this paper, we further explain and discuss the physical control mechanism. Our theoretical and experimental results demonstrate that the SPF enhancement can be attributed to the nonresonant two-photon absorption of a higher excited state. We conclude that the SPF intensity involving the nonresonant multiphoton absorption of the higher excited state can be controlled by varying the laser polarization.     

Terbium-sensitized fluorescence method for the determination of pazufloxacin mesilate and its application.

A simple, rapid and highly sensitive fluorometric method for the determination of pazufloxacin mesilate (PZFX) is described. It is based on the formation of the complex [Tb(PZFX)2](3+), which shows the intensive characteristic bands of Tb3+. Optimum conditions for the determination were investigated. Under the optimum experimental condition, the fluorescence intensity responds linearly to the PZFX concentration in the range of 2.0 x 10(-8) - 5.0 x 10(-6) mol/l with a detection limit of 6.2 x 10(-9) mol/l. The method has been successfully applied to the determination of PZFX in urine and serum samples.     

钼(Ⅵ)-水杨基荧光酮络合物吸附波的研究与应用

在邻苯二甲酸氢钾 HCl 乙醇 水溶液中,钼(Ⅵ) 水杨基荧光酮体系在滴汞电极上,于-1.10V(vs.SCE)处有一良好的极谱波,其二阶导数峰电流与钼(Ⅵ)在8×10-10～6×10-8mol L范围内有良好的线性关系,检出限为5×10-10mol L。研究了极谱波的性质和电极反应机理。该方法已用于水及生物样品的测定。