Continuous glucose detection using boronic acid-substituted viologens in fluorescent hydrogels: linker effects and extension to fiber optics

A fluorescent anionic dye and a viologen appended with boronic acids, which serve as glucose receptors, have been synthesized and immobilized into a poly(2-hydroxyethyl methacrylate) hydrogel for use as a continuous glucose monitor. The fluorescence of the dye is modulated by the quenching efficiency of the viologen-based receptor, which in turn is dependent on the glucose concentration. Two monomeric versions of the quencher/receptor unit were prepared and their performance within the hydrogel evaluated. By tethering the quencher/receptor to the hydrogel matrix using a single-point attachment, slightly improved glucose sensing was observed. The hydrogels were tested for their ability to continuously and reversibly detect glucose over the course of several hours. The tests were carried out using a cuvette-based system, as well as a fiber-optic-based configuration. Under physiological conditions (0.1 M phosphate buffer, pH 7.4, 37 degrees C), the fluorescent hydrogels display an excellent dynamic response to glucose concentrations within the biologically significant range (2.5-20 mM).     

Effects of polymer aggregation and quencher size on amplified fluorescence quenching of conjugated polyelectrolytes

The fluorescence of conjugated polyelectrolytes (CPEs) is efficiently quenched by low concentrations of quenchers with opposite charges. We have reported the close correlation between this amplified quenching phenomenon and CPE chain aggregation. In this paper, we further demonstrate the profound correlation between the fluorescence quenching efficiency, CPE chain aggregation, and quencher molecular size. Aggregation of a poly(phenylene ethynylene)-type CPE (PPE-CO2-) is induced by the addition of either water or Ca2+ to methanol solution, as indicated by absorption, fluorescence, dynamic light scattering, and fluorescence microscope measurements. For quencher ions with a small molecular size, such as methyl viologen (MV2+), either the loose (induced by the addition of Ca2+) or the compact (induced by the addition of water) CPE chain aggregates are beneficial to the fluorescence quenching. For quencher ions with large molecular size, such as tris(4,7-diphenyl-1,10-phenanthroline)ruthenium (Ru(dpp)32+), however, the loose chain aggregates are found to be favorable for quenching, while the quenching efficiency is lower for the compact polymer aggregates present in aqueous solution.     

Dependence of fluorescence quenching of a poly(p-phenyleneethynylene) polyelectrolyte on the electrostatic and hydrophobic properties of the quencher

This study investigates the fluorescence quenching of a poly(p-phenyleneethynylene) (1) based polyelectrolyte by positively charged and neutral macromolecules. This work shows that the change in the fluorescence yield of 1 depends on a number of factors, including electrostatic, hydrophobic, and energy transfer interactions with the quencher and also changes in the solution conditions such as concentration and ionic strength. The fluorescence quenching is attributed to the formation of aggregates that form upon addition of different quenchers to a solution of 1 and/or the solution conditions. The extent of 1's aggregation is shown to depend on the type of interaction between the polymer and the quencher, the concentration of the polymer, and the ionic strength of the solution.     

Probing the interaction between fluorophores and DNA nucleotides by fluorescence correlation spectroscopy and fluorescence quenching

We have investigated the association interactions between the fluorescent dyes TAMRA, Cy3B and Alexa-546 and the DNA deoxynucleoside monophosphates by means of fluorescence quenching and fluorescence correlation spectroscopy (FCS). The interactions of Cy3B and TAMRA with the nucleotides produce a decrease in the apparent diffusion coefficient of the dyes, which result in a shift toward longer times in the FCS autocorrelation decays. Our results with Cy3B demonstrate the existence of Cy3B-nucleotide interactions that do not affect the fluorescence intensity or lifetime of the dye significantly. The same is true for TAMRA in the presence of dAMP, dCMP and dTMP. In contrast, the diffusion coefficient of Alexa 546 remains practically unchanged even at high concentrations of nucleotide. These results demonstrate that interactions between this dye and the four dNMPs are not significant. The presence of the negatively charged sulfonates and the bulky chlorine atoms in the phenyl group of Alexa 546 possibly prevent strong interactions that are otherwise possible for TAMRA. The characterization of dye-DNA interactions is important in biophysical research because they play an important role in the interpretation of energy transfer experiments, and because they can potentially affect the structure and dynamics of the DNA.     

荧光猝灭法研究胆红素与牛血清白蛋白的相互作用

在模拟生理条件下,利用荧光猝灭法研究了胆红素(BR)和牛血清白蛋白(BSA) 的相互作用.结果表明胆红素对BSA有较强的荧光猝灭作用,两者形成了新的复合物,属于静态荧光猝灭,发生了分子内的非辐射能量转移.计算了不同温度下的结合位点数n,结合常数KA,以及对应的热力学参数ΔG,ΔH和ΔS.根据Foster非辐射能量转移理论确定了胆红素和BSA间的结合距离r.此外,利用同步荧光光谱,分析了胆红素对牛血清白蛋白构象的影响.     

Water-soluble fluorescent boronic acid compounds for saccharide sensing: substituent effects on their fluorescence properties

Four new naphthalene-based boronic acid compounds (1-4) were synthesized. The effect of various carbohydrates on their fluorescence properties has been studied in aqueous phosphate buffer at pH 7.4. Different substitutions on the aniline group of the naphthalene ring resulted in significant differences in fluorescence properties for these four compounds. Compound 1 shows ratiometric fluorescence changes upon addition of a sugar. Compounds 2 and 3 do not show ratiometric fluorescence changes but show very large fluorescence intensity changes (about 70-fold fluorescence intensity increase). In addition to the quantifiable fluorescence property changes upon sugar addition, the fluorescence color changes of 1-3 are also visible to the naked eye. However, amidation of the aniline nitrogen atom significantly diminishes the fluorescence intensity of compound 4. The crystal structure of one boronic acid provided some insight into the structural features that are important for the fluorescence properties of these compounds.     

Study of the interaction of carbamazepine with bovine serum albumin by fluorescence quenching method.

The interaction between carbamazepine (CBZ) and bovine serum albumin (BSA) was studied using fluorescence spectroscopy (FS) and ultraviolet spectroscopy (UV). The experimental results showed that the CBZ could insert into the BSA and quench the inner fluorescence of BSA by forming the CBZ-BSA complex. It was found that both static quenching and non-radiation energy transfer were the main reasons leading to the fluorescence quenching. The apparent binding constants (K) between CBZ and BSA were found to be 1.8 x 10(4) (27 degrees C) and 2.8 x 10(4) (37 degrees C) and the binding site values (n) were 0.97 (27 degrees C) and 1.01 (37 degrees C), respectively. According to the Forster theory of non-radiation energy transfer, the binding distances (r) between CBZ and BSA were 3.6 nm and 3.4 nm at 27 degrees C and 37 degrees C, respectively. The process of the binding was a spontaneous molecular interaction in which entropy increased and Gibbs free energy decreased, indicating that the interaction between CBZ and BSA was mainly driven by the hydrophobic force.     

A simple chip free‐flow electrophoresis for monosaccharide sensing via supermolecule interaction of boronic acid functionalized quencher and fluorescent dye

Here, a simple micro free‐flow electrophoresis (μFFE) was developed for fluorescence sensing of monosaccharide via supermolecule interaction of synthesized boronic acid functionalized benzyl viologen (ο‐BBV) and fluorescent dye. The μFFE contained two open electrode cavities and an ion‐exchange membrane was sandwiched between two polymethylmethacrylate plates. The experiments demonstrated the following merits of developed μFFE: (i) up to 90.5% of voltage efficiency due to high conductivity of ion‐exchange membrane; (ii) a strong ability against influence of bubble produced in two electrodes due to open design of electrode cavities; and (iii) reusable and washable separation chamber (45 mm × 17 mm × 100 μm, 77 μL) avoiding the discard of μFFE due to blockage of solute precipitation in chamber. Remarkably, the μFFE was first designed for the sensing of monosaccharide via the supermolecule interaction of synthesized ο‐BBV, fluorescent dye, and monosaccharide. Under the optimized conditions, the minimum concentration of monosaccharide that could be detected was 1 × 10^?11 M. Finally, the developed device was used for the detection of 0.3 mM glucose spiked in human urine. All of the results demonstrated the feasibility of monosaccharide detection via the μFFE.     

Ligand exchange and fluorescence quenching studies of the fulvic acid-iron interaction: Effects of ph and light

The effects of pH and light on the interaction between fulvic acid and iron have been investigated through studies of the kinetics of exchange of iron between fulvic acid and 1,10-pehnanthroline(a strong iron(II) complexing agent), and of the quenching of intrinsic fulvic acid fluorescence by iron in solutions of pH 4.0 and 6.5 containing an excess of fulvic acid. The results enable the iron-fulvic acid interaction to be described in terms of operationally defined iron-fulvic acid groupings, the proportions of which are markedly dependent on pH and light conditions. At pH 4.0 fulvic acid exhibits considerable reducing ability with the result that a substantial portion of iron is present in reduced, unbound form. Irradiation of fulvic acids at this pH markedly increases their reducing ability. Iron that is not reduced is present as small (ultrafilterable), strongly bound iron(III) complexes. Iron bound in this form is an effective quencher of intrinsic fulvic acid fluorescence. At higher pH, essentially all of the iron is relatively strongly bound, with most being in the form of large (non-ultrafilterable) iron(III)—fulvic acid groupings. These groupings are not altered significantly by irradiation and iron bound in this form is not a very effective quencher of intrinsic fulvic acid fluorescence.     

Synthesis of new azaphthalocyanine dark quencher and evaluation of its quenching efficiency with different fluorophores

New unsymmetrical zinc azaphthalocyanine (AzaPc) was synthesized using statistical condensation of two precursors. Postsynthetic modifications led to incorporation of azide group that efficiently underwent Cu(I)-catalyzed azide/alkyne 1,3-dipolar cycloaddition with terminal alkyne on a solid phase. The modified solid phase was then used for synthesis of oligodeoxyribonucletides labeled with AzaPc. DNA hybridization assays confirmed high quenching efficiency (QE>96%) of zinc AzaPc quencher with six different fluorophores ranging in emission maxima from 517 nm to 701 nm (FAM, HEX, Cy3, Cy3.5, Cy5, and Cy5.5).     

Effect of salts on the excited state of pyranine as determined by steady-state fluorescence

Pyranine is a pH-sensitive fluorescent probe useful in the pH range of 4.5–8, and it has been extensively employed to determine pH inside cells, membranes and membrane models. The fluorescent properties of pyranine are a consequence of the excited states ROH^* and RO^−*. The prototropic equilibrium of these excited species has a much lower than that of the ground state. In this paper we determined the (1.42 ± 0.06) and the relative quantum yield of pyranine in the pH range of 1–8 by analyzing the component peaks of the steady-state of the dye's emission spectrum. As pyranine is very sensitive to the medium we studied the influence of salts formed by mono-, di-, and trivalent ions on the apparent . In all cases, the presence of salts reduced the apparent to varying degrees depending on the valence of the cations. The strategy used to obtain this information was a dual emission ratiometric method at 441 and 511 nm after excitation at 350 nm. The results obtained demonstrate that pyranine is suitable to determine the pH of aqueous solutions in the range of 1–3.5.     

Fluorescence quenching by charge transfer interaction. Exciplexes of fluorene and hetero-analogues with electron donors and acceptors

The fluorescence quenching of fluorene, dibenzofuran and dibenzothiophen by aliphatic amines (electron donors) and aromatic nitriles (electron acceptors) has been studied in different solvents. Emission spectra, solvent effects and the observed relationship between the quenching rate constants and ionization potentials of the donors or reduction potentials of the acceptors support an electron-transfer mechanism with exciplex formation. Carbazole does not enter in this scheme and is probably quenched via a different mechanism.     

Siloxanes with pendent naphthalene diimides: synthesis and fluorescence quenching

Cyclic siloxanes with pendent naphthalene diimide groups were synthesized via hydrosilylation to form amorphous electron-accepting compounds. Photophysical measurements and >99.9% fluorescence quenching of well-known p-type polymers by the siloxanes demonstrate that these siloxanes form a new class of highly efficient n-type materials that provide some control over intermolecular interactions.     

Studies of dynamic interactions between a pyrene-labeled polyelectrolyte and an oppositely charged rodlike micelle by a fluorescence quenching technique with use of a hydrophobic quencher

Electrostatic interactions of poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) (PyPAMPS) labeled with pyrene and a rodlike micelle of dimethyloleylamine oxide (DMOAO), an amine oxide type surfactant, mixed with varying mole fractions (Y) of hexadecyltrimethylammonium chloride (CTAC), a cationic surfactant, were investigated by a fluorescence quenching technique using 3,4'-dimethylbenzophenone (DBP), a hydrophobic quencher, that can only reside in the micellar phase. Fluorescence measurements were performed under homogeneous conditions in the region 0Yc, the fluorescence was efficiently quenched by DBP-carrying DMOAO/CTAC mixed micelles, both steady-state and time-dependent fluorescence data indicating that the degree of the quenching and hence the extent of the complex formation increased significantly with increasing Y. Applying a kinetic model to the steady-state and time-dependent fluorescence data, the residence time for PyPAMPS in the polymer-micelle complex was calculated. The residence time was found to depend on both Y and mu, e.g., when Y was increased from 0.01 to 0.03, the residence time increased from 4 to 80 mus at mu=0.05 whereas little or no increase in the residence time was observed in this range of Y at mu=0.20. At this higher ionic strength, the residence time increased only moderately from 3 to 10 mus when Y was increased from 0.01 to 0.09.     

Substituent effects on the intramolecular charge transfer and fluorescence of bimetallic platinum complexes

An investigation of a series of platinum-containing organometallic complexes for the study of fluorescence phenomena in organometallic chromophores controlled by the intramolecular charge transfer (ICT) is presented in this work. We report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the substituent effects on the ICT and fluorescence emission. We demonstrate that the fluorescence maximum and lifetimes greatly depend on different substituents and the presence of bimetallic platinum donor. This work paves the way for an understanding of the fluorescence phenomena controlled by molecular ICT characters of these kinds of platinum-containing organometallic complexes.     

The dependence of quinine fluorescence quenching on ionic strength

The Stern-Volmer constant for the quenching of quinine fluorescence by chloride ions has been found to be markedly dependent on acid concentration. Steady-state and time-resolved fluorescence measurements under different acid and salt concentrations have further shown that the decrease in quenching arises from the influence of increasing ionic strength on the diffusion-controlled rate constant for the bimolecular quenching process. Two possible mechanisms for this dependence are discussed: a decrease in the intrinsic rate constant for the reaction due to the kinetic salt effect, and a decrease in the effective encounter distance due to screening of the charges on the reactants. © 1996 John Wiley & Sons, Inc.     

桔皮苷与牛血清白蛋白相互作用的研究

运用荧光光谱、紫外光谱法研究了桔皮苷与牛血清白蛋白(BSA)的相互作用。桔皮苷分子与BSA作用导致BSA内源荧光猝灭,猝灭机理主要为静态猝灭,并存在非辐射能量转移。测定了不同温度下该反应的结合常数、结合位点数及结合热力学参数。结果表明:桔皮苷与BSA之间主要为氢键或范德华作用力,作用过程是一个熵增加、自由能降低的自发分子间作用过程;测得了供体与受体间结合距离r和能量转移效率E;并用同步荧光技术考察了桔皮苷对BSA构象的影响。     

Studies of interaction between colchicine and bovine serum albumin by fluorescence quenching method

We investigated the interaction between colchicine and bovine serum albumin (BSA) by fluorescence and UV–Vis absorption spectroscopy. In the mechanism discussion, it was proved that the fluorescence quenching of BSA by colchicine is a result of the formation of colchicine–BSA complex; van der Waals interactions and hydrogen bonds play a major role in stabilizing the complex. The modified Stern–Volmer quenching constant K_a and corresponding thermodynamic parameters ΔH, ΔG, ΔS at different temperatures were calculated. The distance r between donor (BSA) and acceptor (colchicine) was obtained according to fluorescence resonance energy transfer (FRET).     

The quenching of the fluorescence of carbon dots: A review on mechanisms and applications

Carbon dots (CDs) possess unique optical properties such as tunable photoluminescence (PL) and excitation dependent multicolor emission. The quenching and recovery of the fluorescence of CDs can be utilized for detecting analytes. The PL mechanisms of CDs have been discussed in previous articles, but the quenching mechanisms of CDs have not been summarized so far. Quenching mechanisms include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). Following an introduction, the review (with 88 refs.) first summarizes the various kinds of quenching mechanisms of CDs (including static quenching, dynamic quenching, FRET, PET and IFE), the principles of these quenching mechanisms, and the methods of distinguishing these quenching mechanisms. This is followed by an overview on applications of the various quenching mechanisms in detection and imaging.

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Graphical abstract Schematic representation of the quenching mechanisms of carbon dots (CDs) which include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer(PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). All these effects can be used to detect and image analytes.