Interfacial Fluorescence Research Articles

Glutaraldehyde-based desensitizers’ influence on bonding performances and dentin enzymatic activity of universal adhesives

To evaluate the influence of two glutaraldehyde-based desensitizers (L: GLUMA Desensitizer, Heraeus Kulzer and G: GLUMA Desensitizer PowerGel) prior to the adhesive procedures on microtensile bond strength (µTBS) to dentin and endogenous enzymatic activity. Noncarious human third molars (N=48) were cut to expose middle coronal dentin. Six experimental groups were formed according to the dentin pre-treatment (L or G) and the universal adhesives (IBU - iBond universal, Kulzer or AU - Adhese Universal, Ivoclar Vivadent) used in the self-etch mode (n=8): 1) L/IBU; 2) G/IBU; 3) IBU; 4) L/AU; 5) G/AU; 6) AU. Specimens were cut into sticks and stressed until failure after 24h (T0) or 1yr of aging (T12). Additional 4 teeth were used for in situ zymography evaluation and data were statistically analyzed (α=0.05). Dentin pre-treatment, adhesive and aging statistically influenced bond strength and enzymatic activity (P<0.001). AU demonstrated higher bond strength values than IBU (P<0.001). The L resulted in higher bond strength compared to the G and control groups (P<0.001). aging statistically influenced bonding performance, especially when no dentin pre-treatment was performed (P<0.001). In situ zymography revealed that at baseline the control groups exhibited lower interfacial fluorescence compared to the experimental groups, irrespective of the adhesive used (P<0,001). However, after 1yr of artificial storage, no differences were found among the groups (P>0.05). Glutharldeadeyde-based products increased bond strength and determined a stabilization of the adhesive interface over time apparently not related to the MMPs inhibition. The results of this in vitro study suggest that the application of glutaraldehyde-based desensitizers prior to the adhesive procedures when associated with universal adhesives could result in increased bond strength and stabilization of the adhesive interface over time.

Ion-modulated interfacial fluorescence in droplet microfluidics using an ionophore-doped oil.

Fluorescence at the oil-water interface is used for chemical sensing in droplet microfluidics. Potassium ions in aqueous droplets are extracted into oil segments doped with an ionophore, a cation exchanger, and a cationic dye to expel the dye. When a low concentration of dye with a balanced solubility is used, it actively accumulates at the thin interface between oil and water instead of getting dissolved in the aqueous phase. The interfacial fluorescence is monitored distinct from the fluorescence in the oil sensor and the aqueous sample, allowing for highly sensitive and selective turn-on fluorescence sensing of ions.

Feasible Modification of PEDOT:PSS by Poly(4-styrenesulfonic acid): A Universal Method to Double the Efficiencies for Solution-Processed Organic Light-Emitting Devices

A feasible, universal, and low-cost strategy for solution-processed organic light-emitting diodes (OLEDs) was provided to significantly enhance the electroluminescent performances. The commercially available poly(4-styrenesulfonic acid) (PSSA) aqueous solution was mixed into poly(styrene sulfonic acid)-doped poly(3,4-ethylenedioxythiphene) (PEDOT:PSS) to modify its chemical and physical properties. The corresponding work function can be easily elevated from 5.04 to 5.63 eV. The modification of PEDOT:PSS by PSSA is found to be a universal method to demonstrate highly efficient OLEDs with different solution-processed host/emitter combinations, covering phosphorescent and thermally activated delayed fluorescence devices. The benchmarking solution-processed OLEDs based on 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene and bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) achieved the maximum external quantum efficiencies of 26.6 and 22.4%, respectively, simply by modifying PEDOT:PSS with PSSA, corresponding to the improvement factors of 2.7 and 2.2. It is confirmed that such performances originate simultaneously from reduced interfacial fluorescence quenching, elevated work function, and reduced lateral conduction of the commonly used PEDOT:PSS (Clevios P VP Al 4083).

Amyloid-β Peptide-Lipid Bilayer Interaction Investigated by Supercritical Angle Fluorescence.

The understanding of the interaction between the membrane of neurons and amyloid-β peptides is of crucial importance to shed light on the mechanism of toxicity in Alzheimer's disease. This paper describes how supercritical angle fluorescence spectroscopy was applied to monitor in real-time the interaction between a supported lipid bilayer (SLB) and the peptide. Different forms of amyloid-β (40 and 42 amino acids composition) were tested, and the interfacial fluorescence was measured to get information about the lipid integrity and mobility. The results show a concentration-dependent damaging process of the lipid bilayer. Prolonged interaction with the peptide up to 48 h lead to an extraction and clustering of lipid molecules from the surface and a potential disruption of the bilayer, correlated with the formation of peptide aggregates. The natural diffusion of the lipid was slightly hindered by the interaction with amyloid-β(1-42) and closely related to the oligomerization of the peptide. The adsorption and desorption of Amyloid-β was also characterized in terms of affinity. Amyloid-β(1-42) exhibited a slightly higher affinity than amyloid-β(1-40). The former was also more prone to aggregate and to adsorb on the bilayer as oligomer.

Self-assembled aggregation-induced emission micelle (AIE micelle) as interfacial fluorescence probe for sequential recognition of Cu2+ and ATP in water

Abstract Cu2+ ions and adenosine-5′-triphosphate (ATP) play important roles in the process of cellular metabolism, building artificial chemosensor for detecting them are of great significance. In this work, on the basis of a tetraphenylethylene (TPE) amphiphile (1) which can generate the aggregation-induced emission (AIE) micelles through self-assembling in aqueous solution, we developed a new interfacial system for sequential recognitions of Cu2+ and ATP with high selectivity and sensitivity. Once Cu2+ was introduced into the 100% aqueous solution of probe 1, a complex composed by the probe and Cu2+ with a 1:2 stoichiometry was formed, leading to remarkable fluorescence quenching. Adding ATP to the solution of the in situ generated 1-Cu2+ ensemble can easily recover the fluorescence of the system. The limits of detection (LoD) for Cu2+ and ATP were calculated to be 1.0 × 10−7 and 1.5 × 10−6 M. Both 1 and the resultant 1-Cu2+ complex were demonstrated to have low cytotoxicity and good cell-membrane permeability, they were successfully applied to image Cu2+ ions and ATP in living HepG2 cells.

Distinct Interfacial Fluorescence in Oil‐in‐Water Emulsions via Exciton Migration of Conjugated Polymers

Commercial dyes are extensively utilized to stain specific phases for the visualization applications in emulsions and bioimaging. In general, dyes emit only one specific fluorescence signal and thus, in order to stain various phases and/or interfaces, one needs to incorporate multiple dyes and carefully consider their compatibility to avoid undesirable interactions with each other and with the components in the system. Herein, surfactant-type, perylene-endcapped fluorescent conjugated polymers that exhibit two different emissions are reported, which are cyan in water and red at oil-water interfaces. The interfacially distinct red emission results from enhanced exciton migration from the higher-bandgap polymer backbone to the lower-bandgap perylene endgroup. The confocal microscopy images exhibit the localized red emission exclusively from the circumference of oil droplets. This exciton migration and dual fluorescence of the polymers in different physical environments can provide a new concept of visualization methods in many amphiphilic colloidal systems and bioimaging.

Covalently Functionalized Graphene Composites: Mechanistic Study of Interfacial Fluorescence Quenching and Recovery Processes

Functionalized graphene oxide nanosheets (GONs) have received much attention in a broad range of applications from light harvesting devices to biological sensors. Owing to their implications in devices and sensors, the interactions between graphene and organic molecules, especially π–π interactions, have also been extensively investigated. Herein we present a mechanistic study of the interfacial fluorescence quenching and its recovery processes between a pyrene derivative, 1-(aminohexyl)-1-pyrenebutyricamide (4) as a fluorophore and nanometer-sized GO sheets. Owing to strong π–π interactions with 4, GON quenches the photoluminescence from pyrene in “folded” conformation of 4-GON. On the other hand, the treatment of 4-GON with sodium dodecyl sulfate (SDS) helps 4 overcome this strong pyrene/GON interactions and causes 4-GON to be in “unfolded” conformation where the fluorescence of pyrene is recovered. By time-resolved spectroscopy, the ultrafast energy and charge transfer behavior (<1 ps) is observed espe...

Quantum Dot and Gold Nanoparticle Immobilization for Biosensing Applications using Multidentate Imidazole Surface Ligands

A facile approach for modification of solid substrates with multidentate imidazole ligands was developed for immobilization of high densities of quantum dots (QDs) that were capped with hydrophilic thiol-based ligands, and for immobilization of noble metal nanoparticles. Imidazole polymer was synthesized using poly(acrylic acid) as a backbone, and grafted on amine functionalized substrate in a two-step approach. The polymer-modified surface was characterized using ellipsometry, water contact angle, and X-ray photoelectron spectroscopy. Fluorescence spectroscopy and scanning electron microscopy were used to evaluate nanoparticle immobilization. Homogeneous, high density (ca. 5 × 10(11) cm(-2)) QD films formed via self-assembly were obtained within 4-6 h. Similarly, the imidazole polymer was also shown to be effective for immobilization of gold nanoparticles as a uniform film. By making use of the pH-sensitive affinity of the imidazole rings to zinc on the surface of QDs, it was possible to achieve regeneration of functional ligands suitable for subsequent immobilization of new QDs. Immobilized QDs were used as a platform for bioconjugation with oligonucleotides and peptides. The transduction of nucleic acid hybridization and enzyme activity using QDs as energy donors in interfacial fluorescence resonance energy transfer (FRET) indicated that the immobilization strategy preserved the functional properties of the QDs. The multidentate imidazole ligands used for QD immobilization offer the highest denticity of binding in comparison to the currently available approaches without compromise in their optical properties and ability to interact with biomolecules in solution.

Rhodamine B aggregation in self-assembled multilayers induced by polyelectrolyte and interfacial fluorescence recognition for DNA

Photophysical properties of Rhodamine B bound to water-soluble polyanion sodium poly(4-styrenesulfonate) (PSS) in solution and Quartz/APES/PSS/RB SAMs were investigated. Experiments showed that Rhodamine B aggregated in Quartz/APES/PSS/RB SAMs and its fluorescence behavior was different from that in Quartz/APES/RB SAMs without PSS. The constructed Quartz/APES/PSS/RB SAMs were applied for label-free interfacial fluorescence sensing of DNA with extremely high sensitivity.

Highly sensitive interfacial fluorescence sensing of deoxyribonucleic acid based on self-assembled multilayers

Fluorescent dye Acridine Orange (AO) was indirectly assembled onto the surface of colloidal gold nanoparticles modified quartz and gold wafer, with cysteine as mediation. Strong fluorescence emission was observed from AO self-assembled multilayers. Formation of the self-assembled multilayers was confirmed and primarily characterized by electrochemical and fluorescence methods. The effect of assembling substrate on fluorescence intensity of the film was discussed. The self-assembled multilayers offer a high sensitive interfacial fluorescence sensing of deoxyribonucleic acid with the detection limit of 7.145 × 10 − 9 g L − 1 (3 S.D./K), which was five orders of magnitude lower than that of the bulk solution-phase. The self-assembled multilayers film has higher stability and good regeneration capacity.

Interaction and Stability of Mixed Micelle and Monolayer of Nonionic and Cationic Surfactant Mixtures

Interaction and stability of binary mixtures of cationic surfactants hexadecyltrimethylammonium bromide (HTAB) or hexadecylpyridinium bromide (HPyBr) with nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) have been studied at different mole fraction of cationic surfactants by using interfacial tension measurements and fluorescence probe techniques. From interfacial tension measurements, the critical micellar concentration and various interfacial thermodynamic parameters have been evaluated. The experimental cmc's were analyzed with the pseudophase separation model, the regular solution theory, and the Maeda's approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTAB + Mega-10 were obtained. It has been observed that the aggregation number of mixed micelles deviates negatively from the ideal behavior. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio and found to be increase with the increase of ionic content. The polarization of fluorescence probe Rhodamine B was monitored at different mole fraction of cationic surfactants.

Comparative Characterization of Lateral Organization and Packing Properties of Lipids in Pulmonary Surfactant Membranes and Interfacial Films

The main function of the lipid-protein complex pulmonary surfactant is to stabilize the respiratory surface by formation of a surface active interfacial film on top of the thin aqueous layer that covers the alveoli. From synthesis in the pulmonary epithelium, until formation of the functional film, surfactant complexes adopt different lamellar structures during its storage and secretion. The functional structure of surfactant makes Langmuir monolayers especially useful for the analysis of structure-function correlations in the pulmonary surfactant system, although they are also widely used as a model to obtain structural information about biological membranes. However, the exact correspondence between lateral organization and molecular packing in bilayers and monolayers is still a matter of controversy.The fluorescent probe laurdan (6-dodecanoyl-2-dimethylaminonaphthalene) is a lipophilic dye used to analyze the structure of membranes due to its spectral characteristics. Once inserted in membranes, the fluorescence emission of laurdan is very sensitive to the level of hydration of the phospholipid headgroups. Changes in packing or lateral organization of the membrane produce a shift of the emission maximum of the label from 440 nm in ordered membranes to 490 nm in disordered membrane phases. Taking advantage of the properties of this probe, films from pulmonary surfactant lipids containing laurdan were prepared and compressed to obtain surface pressure-area isotherms. Surface pressure and area occupied per molecule along compression were obtained in parallel with the generalized polarization function (GPF) of laurdan -as calculated from its interfacial fluorescence emission spectra- and compared with the fluorescence of laurdan in multilamellar suspensions of the same surfactant lipids at different temperatures.

Design of fluorescent self-assembled multilayers and interfacial sensing for organophosphorus pesticides

This paper details the fabrication of indole (ID) self-assembled multilayers (SAMs) and fluorescence interfacial sensing for organophosphorus (OP) pesticides. Quartz/APES/AuNP/L-Cys/ID film was constructed on L-cysteine modified Quartz/APES/AuNP surface via electrostatic attraction between ID and L-cysteine. Cyclic voltammetry indicates that ID is immobilized successfully on the gold surface. Fluorescence of the Quartz/APES/AuNP/L-Cys/ID film shows sensitive response toward OPs. The fluorescent sensing conditions of the SAMs are optimized that allow linear fluorescence response for methylparathion and monocrotophos over 5.97 x 10(-7) to 3.51 x 10(-6)gL(-1) and 3.98 x 10(-6) to 3.47 x 10(-5)gL(-1), with detection limit of 6.1 x 10(-8)gL(-1) and 3.28 x 10(-6)gL(-1), respectively. Compared to bulk phase detection, interfacial fluorescence sensing based on the SAMs technology shows higher sensitivity by at least 2 order of magnitude.

Fluorescence Spectral Properties of Rhodamine 6G at the Silica/Water Interface

In this work, total internal reflection synchronous fluorescence spectroscopy (TIRSF) is applied successfully to investigate rhodamine 6G (R6G) at the silica/water interface. In comparison with the bulk spectra, 5 nm red shift is observed in the interface spectra, which is mainly due to the limitation of freedom of rotational movement of R6G molecules at the interface. The increase of R6G concentration induces the self-quenching of adsorbate at the interface. The dependence of interfacial fluorescence on the acidity and ionic strength was studied. Both the acidity and ionic strength affect the adsorptive behaviors of R6G at the silica/water interface.

Total Internal Reflection Fluorescence Spectroscopy for Investigating the Adsorption of a Porphyrin at the Glass/Water Interface in the Presence of a Cationic Surfactant Below the Critical Micelle Concentration

Total internal reflection fluorescence (TIRF) spectroscopy was used to investigate the adsorption behavior of meso-tetrakis(p-sulfonatophenyl)porphyrin (TPPS) at the glass/water interface in the presence of a cationic surfactant (cetyltrimethylammonium bromide, CTAB) far below the critical micelle concentration. The adsorption model of TPPS at the glass/water interface in the presence of low concentration of CTAB was proposed, which was different from the adsorption of TPPS in the presence of micelles of CTAB at the glass/water interface. TPPS and CTAB did not form stable complex at the interface in dilute system. The interfacial species of TPPS were analyzed by comparing the spectra of TPPS at the glass/water interface and in the aqueous phase. The influences of the TPPS concentration, the CTAB concentration, and the pH values on the interfacial fluorescence spectra and intensities were studied. It was demonstrated that electrostatic interaction and hydrophobicity performed an important role on the adsorption of TPPS in the presence of CTAB. The different effects of TPPS concentration on the adsorption behaviour of TPPS at different pH were observed for the first time. It was found that the adsorption isotherms of TPPS at glass/water interface could fit Freundlich equation at pH 7.1.

Physicochemical Characterization of Phospholipid Solubilized Mixed Micelles and a Hydrodynamic Model of Interfacial Fluorescence Quenching

Mixed micelles of solubilized dimyristoyl phosphatidylcholine (DMPC) and the zwitterionic detergent dodecyldimethylammoniopropane sulfonate are characterized employing time-resolved fluorescence quenching (TRFQ), electron spin resonance (ESR), and surface tensiometry toward the goal of investigating interfacial reactions using these micelles as host reaction media. The properties measured are the micelle aggregation numbers, interfacial hydration index, microviscosity, and the critical micelle concentrations for various molar fractions, XDMPC, of DMPC, 0<or=XDMPC<0.35. A complementary interpretation of the experimental results from TRFQ and ESR within the framework of a polar shell model for the mixed micelle yields some microstructural features, including the micelle core radius, polar shell thickness, and the fraction of the total hydrocarbon that overlaps with the micelle-water interface. The results of the characterization are applied in investigating an interfacial reaction; namely, micellar fluorescence quenching. A bulk hydrodynamic model when modified appropriately so as to be applicable to reaction within the interface is shown to describe micellar fluorescence quenching kinetics and also provides some insight into the location of guest molecules in micelles.

STUDY OF MICELLAR EXTRACTION IN THE SYSTEM (2-ETHYLHEXYL) PHOSPHONIC ACID MONO-(2-ETHYLHEXYL) ESTER - Co (II) - SURFACTANT

ABSTRACT The equilibrium and kinetics of the extraction of cobalt (II) by P507 in Teric N9 micelles have been studied. The structure of the (2-ethylhexyl) phosphonic acid mono-(2-ethylhexyl) ester (known as P507), in Teric N9 micelles have been investigated using interfacial tension and fluorescence quenching measurements. It has been found that there is an interaction between these two components and mixed micelles are formed The complex of Co2+ with P507 in Teric N9 aqueous solution has been shown to have a 1:3 stoichiometry and the equilibrium constant has been obtained by slope analysis. The rate of complex formation in the micelle media is very fast with the reaction going to completion in less than 0.2 seconds.

Water-soluble polystyrene latexes as photoredox media. 1. Interfacial fluorescence quenching and triplet-state electron transfer from pyrene and 1-pyrenebutyric acid

Aromatic chromophores (pyrene and 1-pyrenebutyric acid) have been adsorbed on water-soluble polystyrene latex particles (commercially referred to as microspheres) from the aqueous phase. The fluorescence properties and quenching efficiencies of these chromophores have been measured using a zwitterionic viologen SPV (4,4'-bipyridino-1,1'-bis(propanesulfonate)). The quenching mechanism has been found to be diffusion controlled. The electron-transfer quenching of the triplet state by SPV was characterized. Triplet-state quenching does not occur for pyrene embedded in these polystyrene latexes in aqueous solution, which is attributed to the hydrophobic protection of the pyrene from the approach of water-soluble SPV

Characterization of an interfacial fluorescence technique using Langmuir-Blodgett deposited thin films

Characterization of an interfacial fluorescence technique using Langmuir-Blodgett deposited thin films

Fibronectin adsorption detected by interfacial fluorescence

An interface optical technique, total internal reflection fluorescence (TIRF), permits the intrinsic tryptophan fluorescence of adsorbed proteins to be monitored continuously, in situ . The protein fluorescence emission spectrum provides information on the local tryptophan microenvironment, which can be related to the orientation and conformation of the adsorbed macromolecule. This technique has been applied to the adsorption of human plasma fibronectin on hydrophilic and hydrophobic amorphous silica surfaces. Our experiments using the TIRF technique have shown increased fibronectin binding and more rapid adsorption kinetics on hydrophobic silanized-silica in contrast to hydrophilic silica. Adsorption was essentially irreversible on both the hydrophilic and the hydrophobic surface. A 5-nm red shift in the fluorescence emission maximum occurred on the hydrophobic surface suggesting a change in protein conformation and/or microenvironment. Such behavior may correlate with changes in biological function noted by other workers. We have demonstrated that the in situ TIRF technique, utilizing intrinsic tryptophan fluorescence, is useful for probing microenvironmental effects and possibly orientation or conformational changes in adsorbed proteins. This is the first report of intrinsic TIRF fluorescence spectral changes upon adsorption.