Increase In Fluorescence Emission Intensity Research Articles

Photo-Controlled Nano-Supramolecular Size and Reversible Luminescent Behaviors Based on Cucurbit[7]uril Cascaded Assembly.

Supramolecular luminescent material with switchable behavior and photo-induced aggregation with emission enhancement is a current research hot spot. Herein, a size-tunable nano-supramolecular assembly with reversible photoluminescent behavior was constructed by noncovalent polymerization of diarylethene-bridged bis(coumarin) derivative (DAE-CO), cucurbit[7]uril (CB[7]), and β-cyclodextrin-grafted hyaluronic acid (HACD). Benefiting from the macrocyclic confinement effect, the guest molecule DAE-CO was included into the cavity of CB[7] to give enhanced fluorescence emission of the resulting DAE-CO⊂CB[7]2 with longer lifetime at 432 nm to 1.43 ns, thereby further enhancing fluorescence output and lifetime (1.46 ns) when further assembled with HACD, compared with the free DAE-CO (0.95 ns). In addition, DAE-CO, DAE-CO⊂CB[7]2, and DAE-CO⊂CB[7]2&HACD all possessed characteristics of aggregation-induced emission and reversible photo-switched structural interconversion, exhibiting an obvious photophysical activation phenomenon of self-aggregation into larger nanoparticles with increase in fluorescence emission intensity, lifetime, and size after irradiation, which could be increased step by step with the alternating irradiation of 254 nm (5 min) or >600 nm (30 s) repeated 7 times. These supramolecular assemblies were successfully used in the tumor cells' targeted imaging and anti-counterfeiting because of the capability of HACD for recognizing specific receptors overexpressed on the surface of tumor cells and the excellent photo-regulated switch ability of DAE-CO, providing an approach of constructing photo-induced emission-enhanced luminescent materials.

Oxali(IV)Fluors: Fluorescence Responsive Oxaliplatin(IV) Complexes Identify a Hypoxia-Dependent Reduction in Cancer Cells.

Platinum(IV) anticancer agents have demonstrated the potential to overcome the limitations associated with the widely used Pt(II) chemotherapeutics, cisplatin, carboplatin, and oxaliplatin. In order to identify therapeutic scenarios where this type of chemotherapy can be applied, an improved understanding on the intracellular reduction of Pt(IV) complexes is needed. Here, we report the synthesis of two fluorescence responsive oxaliplatin(IV)(OxPt) complexes, OxaliRes and OxaliNap. Sodium ascorbate (NaAsc) was shown to reduce each OxPt(IV) complex resulting in increases in their respective fluorescence emission intensities at 585 and 545 nm. The incubation of each OxPt(IV) complex with a colorectal cancer cell line resulted in minimal changes to the respective fluorescence emission intensities. In contrast, the treatment of these cells with NaAsc showed a dose-dependent increase in fluorescence emission intensity. With this knowledge in hand, we tested the reducing potential of tumor hypoxia, where an oxygen-dependent bioreduction was observed for each OxPt(IV) complex with <0.1% O2 providing the greatest fluorescence signal. Clonogenic cell survival assays correlated with these observations demonstrating significant differences in toxicity between hypoxia (<0.1% O2) and normoxia (21% O2). To the best of our knowledge, this is the first report showing carbamate-functionalized OxPt(IV) complexes as potential hypoxia-activated prodrugs.

PHENYLETHYLAMINE DERIVATIVE OF CALIX[4]ARENE SCHIFF BASE FOR FLUOROMETRIC DETECTION OF ZINC ION

As a Zn2+ fluorescent probe, we have designed and synthesized a new type of calixarene Schiff-base ligand (L) possessing a 1-phenylethylamine group as the fluorophore and the receptor. As only Zn2+ caused a significant increase in fluorescence emission intensity at 480 nm and the limit of detection (LOD) reached 4.8 x 10-7 M, the synthesized fluorescent probe L demonstrated high selectivity and sensitivity towards Zn2+ compared to other metal ions. In addition, the formation of a 1:1 complex between probe L and Zn2+ was determined. As a consequence, it was determined that probe L can be utilized for the detection and monitoring of Zn2+ in the environment.

Triazine based fluorescent sensor for sequential detection of Hg2+ and L-Cysteine in real samples and application in logic Gate: A combination of Extensive experimental and theoretical analysis

Triazine based fluorescent sensor TBT was rationally designed and synthesized to achieve sequential detection of Hg2+ and L-cysteine based on the presence of sulfur moiety and suitable cavity in the molecule. Sensor TBT exhibited excellent sensing potential for the selective detection of Hg2+ ions and L-cysteine (Cys) in real samples. Upon addition of Hg2+ to sensor TBT, enhancement in emission intensity of sensor TBT was observed which was accredited to the presence of sulfur moiety and size of cavity in the sensor. Upon interaction with Hg2+ blockage of intramolecular charge transfer (ICT) along with chelation-enhanced fluorescence (CHEF) resulted in the increase in fluorescence emission intensity of sensor TBT. Further, TBT-Hg2+ complex was employed for the selective detection of Cys through fluorescence quenching mechanism. This was attributed to the significantly stronger interaction of Cys with Hg2+, which resulted in the formation of Cys-Hg2+ complex and subsequently sensor TBT was released from TBT-Hg2+ complex. The nature of interaction between TBT-Hg2+ and Cys-Hg2+ complex was evaluated through 1H NMR titration experimentations. Extensive DFT studies were also carried out which include thermodynamic stability, frontier molecular orbitals (FMO), density of states (DOS), non-covalent interaction (NCI), quantum theory of atom in molecule (QTAIM), electron density differences (EDD) and natural bond orbital (NBO) analyses. All the studies supported the non-covalent type of interaction between analytes and sensor TBT. The limit of detection for Hg2+ ions was found to be as low as 61.9 nM. Sensor TBT was also employed for the quantitative detection of Hg2+ and Cys in real samples. Additionally, logic gate was fabricated by using sequential detection strategy.

Construction of Mechanically Interlocked Fluorescence Photoswitchable [2]Rotaxane with Aggregation-Induced Emission and Molecular Shuttling Behaviors

Here, we report the design, synthesis, and optical behaviors of a multistimuli responsive [2]rotaxane system constructed from noncovalent interactions between diarylethene (DAE)-based axle and a tetraphenylethene (TPE)-based macrocycle using a snapping supramolecular assembly approach. The shuttling behavior of the macrocycle (Ring-TPE) between dialkylammonium and urea stations could be realized by the influence of acid-base stimuli using 1H NMR spectroscopy. Switching between the open-form (OF) [2]rotaxanes (DAE-R1-OF and DAE-R2-OF) is highly reversible using external chemical stimuli. These rotaxane systems exhibit enhanced blue fluorescence in their aggregation states despite being weak or nonemissive in solution. A significant increase in fluorescence emission intensity of typical TPE in DAE-R1-OF and DAE-R2-OF at ca. 467 nm was observed as the water content was increased to ≥70% in CH3CN/H2O solvent mixtures. However, the fluorescence emission of TPE at its maximum aggregation state (95% fw) could be rapidly quenched upon UV light irradiation due to a very efficient energy transfer from the excited TPE (donor) to the closed form of DAE (acceptor). In contrast, OF DAE does not affect the fluorescence of the TPE unit, which remains at high level. Furthermore, the [2]rotaxanes showed excellent photochromic and fluorescent properties in solution, making them suitable for information storage and reversible photo-patterning applications.

Fluorescence-based chemical tools for monitoring ultrasound-induced hydroxyl radical production in aqueous solution and in cells.

We report the synthesis of hydroxyl-radical (˙OH) responsive fluorescent probes that utilise the 3,5-dihydroxybenzyl (DHB) functionality. 4-Methylumbeliferone-DHB (Umb-DHB) and resorufin-DHB (Res-DHB) in the presence of ˙OH radicals resulted in significant increases in their respective fluorescent emission intensities at 460 nm and 585 nm. The incubation of Res-DHB in HeLa cells followed by therapeutic ultrasound (1 MHz) resulted in a significant increase in fluorescence emission intensity thus permitting the ability to monitor ultrasound-induced ˙OH production in live cells.

Fluorophores “Turned-On” by Corrosion Reactions Can Be Detected at the Single-Molecule Level

We demonstrate that fluorogenic molecules that "turn-on" upon redox reactions can sense the corrosion of iron at the single-molecule scale. We first observe the cathodic reduction of nonfluorescent resazurin to fluorescent resorufin in the presence of iron in bulk solution. The progression of corrosion is seen as a color change that is quantified as an increase in fluorescence emission intensity. We show that the fluorescence signal is directly related to the amount of electrons that are available due to corrosion progression and can be used to quantify the catalyzed increase in the rate of corrosion by NaCl. By using modern fluorescence microscopy instrumentation we detect real-time, single-molecule "turn-on" of resazurin by corrosion, overcoming the previous limitations of microscopic fluorescence corrosion detection. Analysis of the total number of individual resorufin molecules shows heterogeneities during the progression of corrosion that are not observed in ensemble measurements. Finally, we discuss the potential for single-molecule kinetic and super-resolution localization analysis of corrosion based on our findings. Single-molecule florescence microscopy opens up a new spatiotemporal regime to study corrosion at the molecular level.

Carbazole-based fluorescent probes for G-quadruplex DNA targeting with superior selectivity and low cytotoxicity

G-quadruplex DNA plays a very important role in clinical diagnosis and fluorescence analysis has attracted extensive attention. A class of carbazole-based fluorescent probes for the detection of G-quadruplex DNA was established in this work. In this system, the installation of an oligo(ethylene glycol) chain on the scaffold will improve the water-solubility and biocompatibility. The presence of styrene-like different side groups could tune the selectivity toward G-quadruplex DNA binding. Results revealed that the substitution pattern and position gave a great influence on the ability for the discrimination of the G-quadruplex from other DNA structures. Especially, probe E1 bound to G-quadruplex DNA with superior selectivity, which exhibiting almost no fluorescence response in the presence of non-G-quadruplex DNA structures. Comprehensive analyses revealed that E1 could bind both ends of the G-quadruplex, resulting in a significant increase of fluorescence emission intensity. Cellular uptake assay suggested that E1 could pass through membrane and enter living cells with low cytotoxicity.

A fluorescein-carbazole-based fluorescent probe for imaging of endogenous hypochlorite in living cells and zebrafish

In this article, a fluorescent probe FCZ with fluorescein-carbazole as the basic skeleton was designed and synthesized. In contrast to the presences of other coexisting anions, active oxygen and organic thiols, the probe could be "turn-on", exhibiting specific fluorescence performance towards hypochlorite (ClO-). Comprehensive analyses by electrospray ionization mass spectrometry (ESI-MS), thin-layer chromatography (TLC), nuclear magnetic resonance (NMR), and density functional theory/time-dependent density functional theory (DFT/TDDFT) revealed that ClO- could react with the imine bond of the probe, forming fluorescein, resulting in a significant increase of fluorescence emission intensity. The probe has a detection limit for ClO- in water of 0.056 μmol/L. In addition, the probe was successfully applied to detect ClO- in water samples, as well as in the imaging of ClO- in RAW264.7 cells and zebrafish.

Inclusion of dihydroxyaromatics by a lanthanum(III) 2,6-dipicolinate complex

Lanthanum complexes possessing dihydroxyaromatic guests namely, (H2bpy)1.5[La(26pdc)3]·2(cat)·4H2O, (H2bpy)3[La(26pdc)3]2·3(23dhn)·19H2O, (H2bpy)1.5 [La(26pdc)3]·3(27dhn)·10H2O [26pdc=2,6-pyridinedicarboxylate, bpy=4,4′-bipyridine, cat=1,2-dihydroxybenzene, 23dhn=2,3-dihydroxynaphthalene, 27dhn=2,7-dihydroxynaphthalene] are synthesized from 4,4′-bipyridinium lanthanum(III) tris-pyridinedicarboxylate and structurally characterized. Two different types of templates to accommodate hosts are found in these host–guest complexes. 1,2-Dihydroxybenzene molecules are held by template formed by interactions of a [tris-2,6-dipicolinate lanthanum(III)] anion with a 4,4′-bipyridinium cation; whereas dihydroxynaphthalene molecules are held by templates formed between two complex anions interacting with one 4,4′-bipyridinium cation. Complexes 1 and 2 without guest molecules are fluorescent in solid state; whereas dihydroxyaromatic guest included complexes 3–5 are non-fluorescent in solid state. However, in solution, complex 1 causes increase in fluorescence emission intensity of 1,2-hydroxyaromatic compounds and recognition of 1,2-dihydroxybenzene by complex 1 is significant.

A reusable thioether-rich crown-based fluorescent sensor for the detection and removal of mercuric ions

Based on the thioether-rich crown receptor, we describe a naphthalimide based bifunctional fluorescent sensor (FS-G) for simultaneous detection and separation of trace Hg2+ in water. FS-G exhibited excellent selectivity toward Hg2+ in aqueous environment and showed 5-fold increase in fluorescence emission intensity upon the addition of Hg2+. A good linearity was observed between the fluorescence enhancement and the dose of Hg2+ with a lower detection limit of 33.4ppb. Additionally, adsorption capacity of FS-G is 7.4mgg−1. FS-G can be easily regenerated when treated with dimercaptosuccinic acid. These results indicate that FS-G has potential applications for detection and removal of trace Hg2+ in water.

Enzyme-sensing chitosan hydrogels.

We report on a chitosan hydrogel-based platform for the detection of enzymes, which is compatible with the implementation in infection-sensing wound dressings. Thin films of the established wound dressing biopolymer chitosan were functionalized with a fluorogenic substrate, which is released upon enzymatic degradation, resulting in a pronounced increase in fluorescence emission intensity. In this first model study, the fluorogenic substrate alanyl-alanyl-phenylalanine-7-amido-4-methylcoumarin (AAP-AMC) was covalently conjugated via amide bond formation to chitosan and was shown to facilitate the detection of the serine protease α-chymotrypsin. Systematic investigations established the dependence of hydrogel thickness and substrate loading on the hydrogel preparation conditions, as well as the dependence of the rate of the reaction on the initial enzyme concentration and the loading of AAP-AMC in the hydrogel. The initial release rate of the fluorophore 7-AMC was found to be linear with enzyme concentration and substrate loading and was independent of hydrogel thickness. Under optimized conditions the hydrogel reports the presence of α-chymotrypsin in <5 min with a limit of detection of ≤10 nM. This generic approach, which can be adapted to detect different kinds of enzymes by using appropriate fluorogenic or chromogenic substrates, is highly interesting for targeting the detection of specific pathogenic bacteria, e.g., in wound dressings.

A highly selective fluorescent probe for Cu2+ based on rhodamine B derivative

A new fluorescent probe 1 for Cu2+ based on a rhodamine B derivative was designed and synthesized. Probe 1 displays high sensitivity toward Cu2+ and about a 37-fold increase in fluorescence emission intensity is observed upon the addition of 10 equiv. Cu2+ in 50% water/ethanol buffered at pH 7.10. Besides, upon binding Cu2+ a remarkable color change from colorless to pink was easily observed by the naked eyes. The reversible dual chromo- and fluorogenic response toward Cu2+ is likely due to the chelation-induced ring-opening of rhodamine spirolactam. The linear response range covers a concentration range of Cu2+ from 8.0×10−7 to 1.0×10−4mol/L and the detection limit is 3.0×10−7mol/L. Except Co2+, the probe exhibits high selectivity for Cu2+ over a large number of cations such as alkaline, alkaline earth and transitional metal ions. The accuracy and precision of the method were evaluated by the analysis of the standard reference material, copper in water (1.0mol/L HNO3). The proposed probe has been used for direct measurement of Cu2+ content in river water samples and imaging of Cu2+ in living cells with satisfying results, which further demonstrates its value of practical applications in environmental and biological systems.

A new turn-on fluorescent sensor based on NBD for highly selective detection of Hg2+ in aqueous media and imaging in live cells

A new and simple fluorescent probe bearing 7-nitrobenz-2-oxa-1,3-diazole and N,N-bis(thiophen-2-ylmethyl)ethane-1,2-diamine was developed as a fluorescent chemosensor with high selectivity and sensitivity toward Hg2+ over other cations tested. The signaling is due to the coordination of S and N atoms of N,N-bis(thiophen-2-ylmethyl)ethane-1,2-diamine to Hg2+. Upon addition of 30 equivalents of Hg2+, a 45-fold increase in fluorescence emission intensity was observed. Moreover, the probe is further successfully used to image Hg2+ in MCF-7 cells.

A highly selective fluorescent chemosensor for Hg2+ based on rhodamine B and its application as a molecular logic gate

A novel and simple fluorescent chemosensor based on rhodamine (R-2) is designed and synthesized to detect Hg2+. Probe R-2 exhibits high selectivity and sensitivity for sensing Hg2+ with a detection limit at 10(-8) M level, and displays a significant color change from colorless to pink color in the presence of Hg2+. About a 400-fold increase in fluorescence emission intensity is observed upon binding excess Hg2+ in 50% H2O/CH3CN HEPES buffer at pH 7.00. The titration results show a 1:1 complex formation between R-2 and Hg2+. The reversibility of chemosensor R-2 is verified through its spectral response toward Hg2+ and I- titration experiments. Using Hg2+ and I- as chemical inputs and the fluorescence intensity signal as outputs, R-2 can be utilized as an INHIBIT logic gate at molecular level. (C) 2013 Elsevier Ltd. All rights reserved.

Fluorescence spectroscopy measures yeast PAH1-encoded phosphatidate phosphatase interaction with liposome membranes

Phosphatidate (PA) phosphatase, the enzyme that catalyzes the penultimate step in triacylglycerol synthesis, is a cytosolic enzyme that must associate with the membrane where its substrate PA resides. Fluorescence spectroscopy was used to measure the interaction of yeast PAH1-encoded PA phosphatase with model liposome membranes. PA phosphatase contains five tryptophan residues and exhibited inherit fluorescence that increased upon interaction with phosphatidylcholine liposomes. The interaction was enhanced by inclusion of other phospholipids and especially the substrate PA. Interaction was dependent on both the concentration of phosphatidylcholine-PA liposomes as well as the surface concentration of PA in liposomes. Mg(2+) ions, which were required for catalysis, did not affect PA phosphatase interaction with phosphatidylcholine-PA liposomes. PA phosphatase was a substrate for protein kinase A, protein kinase C, and casein kinase II, and these phosphorylations decreased PA phosphatase interaction with phosphatidylcholine-PA liposome membranes.

A new photoinduced fluorescent switch based on a photochromic diarylethene with a rhodamine fluorophore

A new photoinduced fluorescent switch based on a photochromic diarylethene with a rhodamine fluorophore has been successfully explored. The target compound exhibits excellent photochromism with good fatigue-resistance upon photo-irradiation. Upon addition of Cr(III), the color of the diarylethene turns from colorless to pink accompanied with a 300-fold increase in fluorescence emission intensity in methanol. In the presence of Cr(III), an efficient FRET process from the rhodamine moiety (FRET donor) to the closed-ring diarylethene moiety (FRET acceptor) occurs upon UV light stimuli, and its emission intensity can be recovered upon irradiation with visible light. Also, the ability of the compound to detect metal ions has been evaluated by monitoring the changes of emission intensity in methanol. Amongst the tested metal ions, only Cr(III), Al(III) and Fe(III) are efficiently detected. The result indicates that the diarylethene can selectively recognize Cr(III) with significant color and fluorescence changes.

Measuring Fast Calcium Fluxes in Cardiomyocytes

Cardiomyocytes have multiple Ca(2+) fluxes of varying duration that work together to optimize function (1,2). Changes in Ca(2+) activity in response to extracellular agents is predominantly regulated by the phospholipase Cβ- Gα(q;) pathway localized on the plasma membrane which is stimulated by agents such as acetylcholine (3,4). We have recently found that plasma membrane protein domains called caveolae(5,6) can entrap activated Gα(q;)(7). This entrapment has the effect of stabilizing the activated state of Gα(q;) and resulting in prolonged Ca(2+) signals in cardiomyocytes and other cell types(8). We uncovered this surprising result by measuring dynamic calcium responses on a fast scale in living cardiomyocytes. Briefly, cells are loaded with a fluorescent Ca(2+) indicator. In our studies, we used Ca(2+) Green (Invitrogen, Inc.) which exhibits an increase in fluorescence emission intensity upon binding of calcium ions. The fluorescence intensity is then recorded for using a line-scan mode of a laser scanning confocal microscope. This method allows rapid acquisition of the time course of fluorescence intensity in pixels along a selected line, producing several hundreds of time traces on the microsecond time scale. These very fast traces are transferred into excel and then into Sigmaplot for analysis, and are compared to traces obtained for electronic noise, free dye, and other controls. To dissect Ca(2+) responses of different flux rates, we performed a histogram analysis that binned pixel intensities with time. Binning allows us to group over 500 traces of scans and visualize the compiled results spatially and temporally on a single plot. Thus, the slow Ca(2+) waves that are difficult to discern when the scans are overlaid due to different peak placement and noise, can be readily seen in the binned histograms. Very fast fluxes in the time scale of the measurement show a narrow distribution of intensities in the very short time bins whereas longer Ca(2+) waves show binned data with a broad distribution over longer time bins. These different time distributions allow us to dissect the timing of Ca(2+)fluxes in the cells, and to determine their impact on various cellular events.

Photophysics, Photochemistry and Energetics of UV Light Induced Disulphide Bridge Disruption in apo-α-Lactalbumin

Continuous 295 nm excitation of whey protein bovine apo-α-lactalbumin (apo-bLA) results in an increase of tryptophan fluorescence emission intensity, in a progressive red-shift of tryptophan fluorescence emission, and breakage of disulphide bridges (SS), yielding free thiol groups. The increase in fluorescence emission intensity upon continuous UV-excitation is correlated with the increase in concentration of free thiol groups in apo-bLA. UV-excitation and consequent SS breakage induce conformational changes on apo-bLA molecules, which after prolonged illumination display molten globule spectral features. The rate of tryptophan fluorescence emission intensity increase at 340 nm with excitation time increases with temperature in the interval 9.3-29.9°C. The temperature-dependent 340 nm emission kinetic traces were fitted by a 1st order reaction model. Native apo-bLA molecules with intact SS bonds and low tryptophan emission intensity are gradually converted upon excitation into apo-bLA molecules with disrupted SS, molten-globule-like conformation, high tryptophan emission intensity and red-shifted tryptophan emission. Experimental Ahrrenius activation energy was 21.8 ± 2.3 kJ x mol(-1). Data suggests that tryptophan photoionization from the S(1) state is the likely pathway leading to photolysis of SS in apo-bLA. Photoionization mechanism(s) of tryptophan in proteins and in solution and the activation energy of tryptophan photoionization from S(1) leading to SS disruption in proteins are discussed. The observations present in this paper raise concern regarding UV-light pasteurization of milk products. Though UV-light pasteurization is a faster and cheaper method than traditional thermal denaturation, it may also lead to loss of structure and functionality of milk proteins.

Broadband luminescence and emission enhancement

Three novel quinoline– and fluorene–coumarin hybrids were prepared and characterised by Fourier Transform–infrared spectroscopy, proton and carbon nuclear magnetic resonance spectroscopy, mass spectrometry, elemental analysis and ultraviolet–visible spectrophotometry. Their photoluminescence properties were investigated. All of these hybrid molecules exhibited a broadband emission from ca. 450 to 800 nm when excited by a 325 nm helium–cadmium laser at room temperature. Importantly, the fluorene–coumarin hybrid shows a very bright red emission at ca. 650 nm and displays up to a 10-fold increase in fluorescence emission intensity, as compared with the other samples. The experimental results confirm that remarkable enhancements in the fluorescence emission intensity can be obtained by introducing a fluorene group into the azo-bridged coumarin-based π-conjugated framework. The geometry structures and frontier orbitals are calculated by the ab initio Hartree–Fock method.