Increase In Fluorescence Lifetime Research Articles

Abstracts of the 17th International Symposium on Bioluminescence and Chemiluminescence ‐ (ISBC 2012)

WARNING : The light-emitting molecular structures responsible for the chemiluminescence and fluorescence phenomena are not necessarily the same!

Effect of dehydration techniques on the fluorescence spectral features and OH absorption of heavy metals containing fluoride tellurite glasses

Heavy metal containing fluoride tellurite glasses were prepared by different dehydration techniques and the effects of dehydration techniques on fluorescence spectral features, OH content and volatilization of the glass compositions were systematically studied by means of fluorescence spectral measurements FTIR and energy-dispersive X-ray spectrometer. Experimental results indicated that different dehydration induced difference in actual compositions of the glasses that resulted in the variation of their fluorescence spectral features, and melting the glass frits in close environment with mechanical stirring and simultaneous bubbling dry O2+CCl4 mixture in a O2-rich environment was much more effective to remove the OH groups in the glass matrix, through which an OH absorption coefficient and absorption concentration could be efficiently reduced to as low as 1.09cm−1 and 1.17×1019cm−3, respectively. The low OH content contributed to the increase in fluorescence lifetime, and resulted in the improvement of gain characteristic. The bubbling time of dry O2+CCl4 mixture was optimized via OH absorption concentration investigation.

The role of ligand coordination on the spectral features of Yb3+ ions in lead aluminum silicate glasses

Abstract The glasses of the composition (40 − x )PbO–(5 + x )Al 2 O 3 –54SiO 2 :1.0Yb 2 O 3 (in mol%) with x ranging from 5 to 10 have been synthesized. The IR spectral studies of these glasses have indicated that there is a gradual transformation of Al 3+ ions from tetrahedral to octahedral coordination with increase of Al 2 O 3 content in the glass network. The optical absorption and luminescence spectra have exhibited bands originating from 2 F 7/2 → 2 F 5/2 and 2 F 5/2 → 2 F 7/2 transitions, respectively. From these spectra, the absorption and emission cross-sections and fluorescence lifetime of Yb 3+ ions have been evaluated. Quantitative analysis of these data indicated a decreasing radiative trapping and increasing fluorescence lifetime of Yb 3+ ions with increasing Al 2 O 3 content. This may be explained by structural variations in the vicinity of Yb 3+ ions due to variation in the concentration of Al 2 O 3 in the glass network.

Correlation of optical properties and temperature-induced irreversible phase transitions in europium-doped yttrium carbonate nanoparticles

Nanophase europium-doped yttrium carbonate precursors are subjected to heat treatments, ranging from 300 °C to 1100 °C for dwell times of 5 min, 30 min, and 180 min. XRD, TEM, FT-IR, fluorescence, fluorescence excitation, and fluorescence lifetime measurements are used to characterize the materials. Upon heating, the material transitions through several amorphous stages until it reaches the crystalline cubic Y 2O 3 phase. DSC measurements show an exothermic transition at 665.7 °C, indicating the formation of crystalline Y 2O 3. The grain size development is fitted by the relaxation equation and yields an activation energy of 50.3 kJ/mol. The amorphous phases are characterized by inhomogenously broadened optical spectra. Heating up to 700 °C leads to an increased fluorescence lifetime (from about 1 ms to 2.4 ms). As the material is heated to higher temperatures and completes the formation of the crystalline cubic Y 2O 3 phase, the optical spectra become narrower and the fluorescence lifetime decreases to about 1.2 ms.

Inside Cover: Self‐Assembly Into Spheres of a Hybrid Diphenylalanine–Porphyrin: Increased Fluorescence Lifetime and Conserved Electronic Properties (Chem. Eur. J. 26/2011)

Inside Cover: Self‐Assembly Into Spheres of a Hybrid Diphenylalanine–Porphyrin: Increased Fluorescence Lifetime and Conserved Electronic Properties (Chem. Eur. J. 26/2011)

Self‐Assembly Into Spheres of a Hybrid Diphenylalanine–Porphyrin: Increased Fluorescence Lifetime and Conserved Electronic Properties

A series of protected phenylalanine and diphenylalanine derivatives have been coupled through a peptide bond to a monoaminoporphyrin to form new materials. A comparative study in solution and in the solid state has been performed and confirmed new and interesting properties for the self-assembled hybrid materials while conserving the electronic properties of the chromophore. Thus, they are powerful candidates for use in dye-sensitized solar cells.

Self-Assembly of an Optically Active Conjugated Oligoelectrolyte

Conjugated oligoelectrolytes are of emerging technological interest due to their recent function in the fabrication of optoelectronic devices, application in biosensors, and as species that facilitate transmembrane charge migration. Solubility in aqueous, or highly polar, solvents is important for many of these applications; however, there are few studies on how the self-assembly of conjugated oligoelectrolytes into multichromophore species influences linear and nonlinear optical properties. Here, we examine 1,4-bis(4'-(N,N-bis(6''-(N,N,N-trimethylammonium)hexyl)amino)-styryl)benzene tetraiodide (DSBNI) in water, a conjugated oligoelectrolyte based on the distyrylbenzene framework. We find that DSBNI aggregation leads to increased fluorescence lifetimes, coupled with hypsochromic shifts, and larger two-photon absorption cross sections. Liquid atomic force microscopy (AFM) and cryogenic transmission electron microscopy (cryo-TEM) were used to image DSBNI aggregates and to confirm that the planar molecules stack to form nanocylinders above a critical aggregation concentration. Finally, small-angle neutron scattering (SANS) was used to quantify the aggregate dimensions in situ. Comparison of the results highlights that the hydrophilic mica surface used to image via liquid AFM and the high concentrations required for cryo-TEM facilitate the propagation of the cylinders into long fibers. SANS experiments are consistent with equivalent molecular packing geometry but lower aspect ratios. It is therefore possible to understand the evolution of optical properties as a function of concentration and aggregation and the general geometric features of the resulting supramolecular structures.

Measuring Förster resonance energy transfer between fluorescent nanodiamonds and near-infrared dyes by acceptor photobleaching

Fluorescent nanodiamonds (FNDs) containing negatively charged nitrogen-vacancy centers as fluorophores are promising far-red biolables. The fluorophores are perfectly photostable, showing neither photobleaching nor photoblinking, and are useful as Förster resonance energy transfer (FRET) donors. This work demonstrates that it is possible to achieve an average FRET efficiency of up to 30% between a single 23-nm-sized FND (emission maximum ~ 685 nm) and multiple near-infrared dye molecules (absorption maximum ~ 774 nm) co-embedded in a poly-L-lysine matrix. The efficiency was determined by measuring the increases in both fluorescence intensity and lifetime of the FRET donor (i.e. FND) after photobleaching of the FRET acceptor (i.e. IRdye-800CW). Monte Carlo simulations indicate that on average, there are ~ 9 IRDye molecules located in close proximity to each FND particle.

Detection of enzyme activity in orthotopic murine breast cancer by fluorescence lifetime imaging using a fluorescence resonance energy transfer–based molecular probe

Cancer-related enzyme activity can be detected noninvasively using activatable fluorescent molecular probes. In contrast to "always-on" fluorescent molecular probes, activatable probes are relatively nonfluorescent at the time of administration due to intramolecular fluorescence resonance energy transfer (FRET). Enzyme-mediated hydrolysis of peptide linkers results in reduced FRET and increase of fluorescence yield. Separation of signal from active and inactive probe can be difficult with conventional intensity-based fluorescence imaging. Fluorescence lifetime (FLT) measurement is an alternative method to detect changes in FRET. Thus, we investigate FLT imaging for in vivo detection of FRET-based molecular probe activation in an orthotopic breast cancer model. Indeed, the measured FLT of the enzyme-activatable molecular probe increases from 0.62 ns just after injection to 0.78 ns in tumor tissue after 4 h. A significant increase in FLT is not observed for an always-on targeted molecular probe with the same fluorescent reporter. These results show that FLT contrast is a powerful addition to preclinical imaging because it can report molecular activity in vivo due to changes in FRET. Fluorescence lifetime imaging exploits unique characteristics of fluorescent molecular probes that can be further translated into clinical applications, including noninvasive detection of cancer-related enzyme activity.

Reduced nicotinamide adenine dinucleotide fluorescence lifetime detected poly(adenosine-5ʹ-diphosphate-ribose) polymerase-1-mediated cell death and therapeutic effect of pyruvate

Noninvasive detection of cell death has the potential for definitive diagnosis and monitoring treatment outcomes in real time. Reduced nicotinamide adenine dinucleotide (NADH) fluorescence intensity has long been used as a noninvasive optical probe of metabolic states. NADH fluorescence lifetime has recently been studied for its potential as an alternative optical probe of cellular metabolic states and cell death. In this study, we investigated the potential using NADH fluorescence intensity and/or lifetime to detect poly(adenosine-5'-diphosphate-ribose) polymerase-1 (PARP-1)-mediated cell death in HeLa cells. We also examined if NADH signals respond to treatment by pyruvate. The mechanism of PARP-1-mediated cell death has been well studied that extensive PARP-1 activation leads to cytosolic nicotinamide adenine dinucleotide depletion resulting in glycolytic inhibition, mitochondrial failure, and death. Pyruvate could restore electron transport chain to prevent energy failure and death. Our results show that NADH fluorescence lifetime, not intensity, responded to PARP-1-mediated cell death and the rescue effect of pyruvate. This lifetime change of NADH fluorescence happened before the collapse of mitochondrial membrane potential and mitochondrial uncoupling. Together with our previous findings in staurosporine-induced cell death, we suggest that NADH fluorescence lifetime increase during cell death is mainly due to increased protein-protein interactions but not the intracellular NADH content.

Synthesis and Aggregation Properties of Dansylated Glycerol‐Based Amphiphilic Polyether Dendrons

AbstractGlycerol‐based amphiphilic polyether mono azide third‐generation dendrons were synthesized through a divergent strategy. A repetitive synthetic sequence of O‐alkylation and isopropylidene deprotection reaction was adopted for the synthesis, pentamethylene was used as spacer. Dansyl chloride was attached to the focal point as a fluorophore. The photophysical property in aqueous solution of the protected dendrons showed self‐association behaviour from second generation onwards even at a very low concentration (1 × 10–8 M). A hypsochromic shift of around 60 nm in the emission maximum, significant increase in fluorescence intensity, almost ten‐fold increase in the fluorescence anisotropy and a fourfold increase in average fluorescence lifetime of dansyl moiety were observed on going from first generation dendron to higher generation dendrons in aqueous medium. The absence of such behavior in the corresponding unprotected, relatively hydrophilic dendritic units clearly indicated that the aggregation is due to the presence of hydrophobic isopropylidene end groups. Quenching studies of the dendrimersin aqueous solution using a hydrophilic quencher Ag+ revealed that the dansyl moiety in protected higher generations dendritic units is significantly shielded from the surroundings, which further rendered support to the fact that higher order dendrons undergo aggregation in aqueous medium.

Photobehavior of merocyanine 540 bound to human serum albumin

The photobehavior of merocyanine 540 (MC) was studied in homogeneous media (ethanol, buffer and glycerol), and in microheterogenous systems (Triton X-100 micelles and in the presence of human serum albumin) using stationary and time-resolved techniques. Merocyanine 540 in aqueous solution mostly forms aggregates, which in the presence of Triton X-100 or HSA are disaggregated. The extent of binding to HSA and its characteristics were estimated from dye absorption and fluorescence changes following protein addition; the Trp-214 fluorescence quenching was also employed to assess the extent of dye association, and physical separation was employed to evaluate the dye's apparent association constant. These results showed that dye adsorption on HSA takes place at both main protein-binding sites (I and II). This adsorption leads to dye monomerization, changing its photobehavior remarkably, with a noticeable increase in fluorescence and triplet lifetimes. These slower decays can be ascribed to a reduction of the dye photoisomerization rate. In addition, the adsorption of the dye partially protects it from the oxygen present in solution, thus reducing the apparent dye triplet-quenching rate constant. However, singlet oxygen and MC triplet quantum yields remain very low in all the systems tested. Finally, we found that the photoconsumption of merocyanine bound to HSA takes place predominantly by a type I mechanism, being more than seven times more efficient than that taking place in ethanol.

Confined Fast and Ultrafast Dynamics of a Photochromic Proton-Transfer Dye within a Zeolite Nanocage

We report on studies of salicylaldehyde azine (SAA) dissolved in dichloromethane solution and within the cages of the faujasite zeolite (NaX) using steady-state and femtosecond to nanosecond time-resolved spectroscopy. In solution, an excited-state intramolecular proton-transfer reaction takes place in less than 80 fs, leading to a keto-type tautomer. In contrast within NaX zeolite, a zwitterionic (Z) form is present both at S0 and S1 states, and a large hypsochromic shift of the stationary emission spectrum is observed. The increase in fluorescence lifetime upon encapsulation (from 54 ps to 0.2−2.8 ns) is mainly due to hindrance in twisting motion of the confined Z structure imposed by the nanocage. A significant dependence of the lifetimes on the guest concentration inside the zeolite indicates an interaction between neighboring guest molecules leading to a quenching of the fluorescence. The analysis of emission decays using stretched-exponential model suggests that the excited-state interactions between neighboring dyes play a key role in the deactivation of the trapped Z fluorophores. For the ultrafast relaxation dynamics of the SAA/NaX composite, intramolecular vibrational-energy redistribution and vibrational cooling process occur in longer times (up to 360 fs and 5 ps, respectively). Additionally, the presence of nonfluorescent twisted (n,π*) state is suggested to form in 6−10 ps. We believe that our results are important for a better understanding of the photocycle of azine-based photochromic material when interacting with nanomaterials.

Membrane interaction of the N-terminal domain of chemokine receptor CXCR1

The N-terminal domain of chemokine receptors constitutes one of the two critical ligand binding sites, and plays important roles by mediating binding affinity, receptor selectivity, and regulating function. In this work, we monitored the organization and dynamics of a 34-mer peptide of the CXC chemokine receptor 1 (CXCR1) N-terminal domain and its interaction with membranes by utilizing a combination of fluorescence-based approaches and surface pressure measurements. Our results show that the CXCR1 N-domain 34-mer peptide binds vesicles of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and upon binding, the tryptophan residues of the peptide experience motional restriction and exhibit red edge excitation shift (REES) of 19nm. These results are further supported by increase in fluorescence anisotropy and mean fluorescence lifetime upon membrane binding. These results constitute one of the first reports demonstrating membrane interaction of the N-terminal domain of CXCR1 and gain relevance in the context of the emerging role of cellular membranes in chemokine signaling.

Tuning the optical properties of flurophore-hexylcarbazole organic nanoribbons with dispersed inorganic nanocrystals (AgNCs)

A carbazole derivative (3-(2,2-dicyanovinyl)-9-hexylcarbazole, abbreviated as L) has been designed, synthesized and used to prepare a novel organic–inorganic nanohybrid consisting of silver nanocrystals (Ag NCs) uniformly dispersed on the surface of L nanoribbons. Detailed characterizations have been performed. The results reveal that L couples with Ag NCs through a π-conjugated unit, which results in a significant red-shift of the fluorescence (FL), an obvious increase of FL lifetime and enhanced Raman scattering.

Interactions of the β-blocker drug, propranolol, with detergents, β-cyclodextrin and living cells studied using fluorescence spectroscopy and imaging

Interactions of theβ-blocker drug, propranolol, with amphipathic systems have been studied using fluorescence spectroscopy. The results show a strong binding of propranolol with micelles of sodium dodecyl sulfate revealed through changes in the fluorescence spectrum and an increase in fluorescence lifetime. Quenching of propranolol fluorescence by iodide is used to demonstrate interaction withβ-cyclodextrin. At high concentrations, self-quenching of propranolol fluorescence was also observed withκq=2.5×109dm3mol–1s–1. Two-photon excited (630 nm) fluorescence lifetime imaging of propranolol in cells showed propranolol to be widely distributed in the cell cytoplasm, with fluorescence lifetimes shorter than in solution. The results suggest that intracellular propranolol is mainly confined within the aqueous cytoplasm and rather than membrane associated.

Solvation Effects on Isomeric Preferences of Curium(III) Complexes with Multidentate phosphonopropionic Acid Ligands: CmH2PPA2+ and CmHPPA+ Complexes

We have carried out both time-resolved laser fluorescence spectroscopic and computational studies on the complexes of curium(III) with multidentate Phosphonopropionic (PPA) acid ligands. A number of complexes of Cm(III) with these ligands, such as CmH(2)PPA(2+), CmHPPA(+), Cm[H(2)PPA](2)(+), and Cm[HPPA](2)(-) have been studied. Our computational studies focused on all possible isomers in the gas phase and aqueous solution so that the relative binding strengths of carboxylic versus phosphoric groups can be assessed in these multidentate systems. The solvation effects play an important role in the determination of the preferred configurations and binding propensities of carboxylate versus phosphate sites of the ligands. Our computations assess the relative strengths of single and multidentate complexes in solutions for these systems. The computed free energies of solvation explain the experimentally observed fluorescence spectra and the lifetimes of these complexes in that as more water molecules are displaced from the first hydration sphere by the ligands that bind to Cm(III), the fluorescence lifetime increases. We have found that the most stable complex for CmH(2)PPA(2+) in the aqueous phase exhibits a monodentate complex where the curium(III) is bound to the deprotonated phosphate oxygen atom. Our computations support the observed longer fluorescence lifetime of CmH(2)PPA(2+) (112 mus) compared to the free Cm(III) aquo ion (65 mus), suggesting a greater degree of H(2)O displacement from the hydration sphere. For the Cm-HPPA(+) complex, we find a tridentate form as the most stable structure which supports the observed fluorescence lifetime for the CmHPPA(+) complex (172 mus), confirming the removal of up to six water molecules from the inner hydration sphere. The relative stabilities of the complexes are found to vary substantially between the gas phase and solution, indicating a major role of solvation in the relative stabilities of these complexes.

RNA-Templated Fluorescent Zn/PbS (PbS + Zn2+) Supernanostructures

intensity of the 680 nm band. The nanofibers produced upon aging display a strong narrow emission band (fwhm e80 nm) at 680 nm having a quantum efficiency of 12 ( 0.2%. An increase in the fluorescence quantum efficiency with increasing Zn 2+ is also evidenced by a drastic increase in fluorescence lifetime from 0.06 µs in its absence to 0.23 µs for the colloids containing 2 × 10 -3 mol dm -3 Zn 2+ , which is further increased to 0.27 µs upon aging. These studies demonstrate a correlation between the morphology of nanostructures and their electronic properties.

Waveguiding and photoluminescence in Er 3+-doped Ta 2O 5 planar waveguides

The optimization of erbium-doped Ta 2O 5 thin film waveguides deposited by magnetron sputtering onto thermally oxidized silicon wafer is described. Optical constants of the film were determined by ellipsometry. For the slab waveguides, background losses below 0.4 dB/cm at 633 nm have been obtained before post-annealing. The samples, when pumped at 980 nm yielded a broad photoluminescence spectrum (FWHM∼50 nm) centred at 1534 nm, corresponding to 4I 13/2– 4I 15/2 transition of Er 3+ ion. The samples were annealed up to 600 °C and both photoluminescence power and fluorescence lifetime increase with post-annealing temperature and a fluorescence lifetime of 2.4 ms was achieved, yielding promising results for compact waveguide amplifiers.

Study of proteinous and micellar microenvironment using donor acceptor charge transfer fluorosensor N,N-dimethylaminonaphthyl-(acrylo)-nitrile

Interaction of charge transfer fluorophore N,N-dimethylaminonaphthyl-(acrylo)-nitrile (DMANAN) with globular proteins Human Serum Albumin (HSA) and Bovine Serum Albumin (BSA) brings forth a marked change in the position and intensity of band maxima both in case of absorption and fluorescence spectra. Spectroscopic approach has been elaborately implemented to explore the binding phenomena of the probe with HSA and BSA and it is found that the extent of binding of the probe to both serum albumins is similar in nature. Steady state fluorescence anisotropy values, fluorescence quenching study using acrylamide quencher and Red Edge Excitation Shift (REES) help in drawing reliable conclusions regarding the location of the probe molecule within the hydrophobic cavity of the proteins. An increase in fluorescence lifetime of the probe molecule solubilized in both the proteinous media also indicate that the probe is located at the motionally restricted environment inside the hydrophobic cavity of proteins and hence non-radiative channels are less operative than in the bulk water. Similarly, the variation of position and intensity of the emission maxima of DMANAN solubilized in micellar medium of Sodium Dodecyl Sulphate (SDS) also predicts well the critical micellar concentration (CMC) and polarity of micellar microenvironment.