Fluorescence Decay Time Research Articles

A spectroscopic study on stability of curcumin as a function of pH in silica nanoformulations, liposome and serum protein

The effect of pH on the stability of curcumin formulated with different carriers has been studied spectroscopically. This was investigated by monitoring the absorption and emission kinetics and fluorescence decay time of four different curcumin formulations suspended in buffer with pH varying from 5 to 8.5. The carriers were organically modified silica NP (SiNP) having 3-amino propyl and/or vinyl groups, liposome and serum protein. The results reveal that stability of curcumin formulated with SiNP functionalized with 3-amino propyl group (SiNP-VA) is significantly higher as compared to SiNP with only vinyl group (SiNP-V) and buffer but lower as compared to serum protein and liposome. However, fluorescence quantum yield (QY) is highest in SiNP-VA among all the nano formulations at pH 7.4 and below, which is attributed to the excited state interaction of curcumin with the amino groups of SiNP-VA. Results suggest that SiNP-VA could be an effective carrier for curcumin, which may have applications for imaging and drug delivery.

Acetylsalicylic acid sensitized lasing luminescence of terbium complex in PVA: A case of energy avalanche via 1, 10-Phenanthroline

Abstract Ternary complexes of Terbium with acetylsalicylic acid (ASA) and 1, 10 Phenanthroline (Phen) were synthesized in PVA polymer film. The structural properties of the complex were evaluated using XRD and formation of complex was verified by FT-IR technique. The absorption, excitation and photoluminescence properties of the Tb3+ ion get improved when complexed with ASA and Phen ligands. Selective excitations of Tb3+, ASA and Phen revealed an efficient energy transfer enhancing green luminescence of Tb3+ ion on excitation with 355, 335 and 306 nm radiations respectively. The emission intensity arising from Tb(ASA)3Phen complex in PVA has been observed to be much more as compared to the one with Tb3+ ions only. The fluorescence decay time for Tb3+ (5D4 → 7F5 transition) is seen to increase from 557 μs in Tb3+ to 628 μs in presence of Tb(ASA)3Phen complex. The fluorescence decay time for Phen and ASA is seen to decrease from 4.43 ns to 1.64 ns and from 5.75 ns to 1.58 ns respectively in Tb(ASA)3Phen complex. This reflects an energy transfer from excited Phen to ASA and finally to Tb3+ is proposed as the cause of the above observations and thus an energy avalanche. The intense green luminescence on 266 nm excitation in Tb(ASA)3Phen complex in PVA with quantum yield of 0.32 shows a tendency towards lasing.

Red‐ to NIR‐Emitting, BODIPY‐Based, K+‐Selective Fluoroionophores and Sensing Materials

Optical sensing materials for the selective measurement of potassium ions (K+) in water are presented. The indicator dyes are based on an aza‐crown ether as a receptor and borondipyrromethenes (BODIPY) dyes as fluorophores. Fluorescence enhancement is caused by the reduction of photoinduced electron transfer (PET) upon complexation with K+ ions. The family of new indicators possesses tuneable optical properties (green to red excitation, red to NIR emission) and PET efficiencies. They exhibit high brightness with quantum yields between 0.20 and 0.47 in the “on” state and a molar absorption coefficient between 30 000 and 290 000 m−1 cm−1. The new indicator dyes are immobilized in biocompatible hydrogel matrices to obtain stable nonleaching and fast responding (t90 ≈ 10 s) sensing materials for continuous measurements of potassium. They are realized in various formats such as planar optodes, fiber‐optic sensors, and water‐dispersible polymer‐based nanoparticles. Apart from fluorescence intensity measurements, self‐referenced read‐out of fluorescence decay time is demonstrated. All sensor materials display a high K+/Na+ selectivity and are not influenced by pH within the physiologically relevant range. Practical applicability of the materials is emphasized by application of a fiber‐optic sensor to quantification of K+ in serum, which shows excellent correlation with the reference measurements.

Europium–enabled luminescent single crystal and bulk YAG and YGG for optical imaging

Europium doped small particles presently receive great attention due to their excellent photoluminescent (PL) intensity, (photo)chemical stability, and linearity in the orange-red spectral region and find challenging biomedical application. Europium doped compounds are extremely good candidates for optical imaging due to stable luminescence, long fluorescence decay time, sharp emission peaks, i.e. narrow band width, in the red to near-infrared (NIR) region. Moreover, lasers based on red emission of europium also could be an attractive choice for medical application since NIR radiation can penetrate biological tissues such as human skin. This study allows to discuss luminescent properties of europium (5 at-% or 30 at-%) doped Y3Al5O12 and Y3Ga5O12 garnets in single crystals and powders. Europium enabled luminescent properties are discussed based on the concentration of europium and dopant local environment. All these compounds possess dominant 5D0 → 7F4 emission in the NIR region and are thus potential candidates for optical imaging.

Detection of Sugars via Chirality Induced in Europium(III) Compounds.

Detection and resolution of simple monosaccharides are difficult tasks because their structure is quite similar. The present study shows that circularly polarized luminescence (CPL) induced in europium complexes provides very specific spectral patterns for fructose, mannose, glucose, and galactose. Differences were also observed between bare Eu(3+) ion and its complexes, when interacting with these sugars. The CPL spectra were measured on a Raman optical activity (ROA) spectrometer, which ensured high fluorescence intensity owing to the strong 532 nm laser excitation. The induced fluorescence was recorded in the same spectrum as the vibrational Raman bands. On the basis of the ligand field theory, most fluorescence spectral peaks could be assigned to f-shell europium transitions. Additional information on the interaction of the lanthanide with the sugar component was provided by measurement of time-dependent fluorescence, as formation of different complexes led to variations in fluorescence decay times. In nuclear magnetic resonance (NMR), the paramagnetic metal ion interacting with the sugars caused specific changes in (13)C chemical shifts. The spectroscopic data and molecular dynamics modeling showed that the interaction between the monosaccharides and Eu ion is rather weak due to the competition of the OH sugar groups with water molecules. However, multiple binding modes are possible, which contributes to the complexity and specificity of the spectra. The induced chirality and fluorescence spectra thus appear to be convenient means for monosaccharide detection and identification.

Spectral and kinetic effects accompanying the assembly of core complexes of Rhodobacter sphaeroides

In the present work, spectral and kinetic changes accompanying the assembly of the light-harvesting 1 (LH1) complex with the reaction center (RC) complex into monomeric RC-LH1 and dimeric RC-LH1-PufX core complexes of the photosynthetic purple bacterium Rhodobacter sphaeroides are systematically studied over the temperature range of 4.5–300K. The samples were interrogated with a combination of optical absorption, hole burning, fluorescence excitation, steady state and picosecond time resolved fluorescence spectroscopy. Fair additivity of the LH1 and RC absorption spectra suggests rather weak electronic coupling between them. A low-energy tail revealed at cryogenic temperatures in the absorption spectra of both monomeric and dimeric core complexes is proved to be due to the special pair of the RC. At selected excitation intensity and temperature, the fluorescence decay time of core complexes is shown to be a function of multiple factors, most importantly of the presence/absence of RCs, the supramolecular architecture (monomeric or dimeric) of the complexes, and whether the complexes were studied in a native membrane environment or in a detergent - purified state.

Direct Observation of Excimer-Mediated Intramolecular Electron Transfer in a Cofacially-Stacked Perylene Bisimide Pair.

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.

Insight into the Modification of Polymeric Micellar and Liposomal Nanocarriers by Fluorescein-Labeled Lipids and Uptake-Mediating Lipopeptides.

Encapsulation of diagnostic and therapeutic compounds in transporters improves their delivery to the point of need. An even more efficient treatment of diseases can be achieved using carriers with targeting or protecting moieties. In the present work, we investigated micellar and liposomal nanocarriers modified with fluorescein, peptides, and polymers that are covalently bound to fatty acids or phospholipids to ensure a self-driven incorporation into the micelles or liposomes. First, we characterized the photophysics of the fluorescent probes in the absence and in the presence of nanocarriers. Changes in the fluorescence decay time, quantum yield, and intensity of a fluorescein-labeled fatty acid (fluorescein-labeled palmitic acid [fPA]) and a fluorescein-labeled lipopeptide (P2fA2) were found. By exploiting these changes, we investigated a lipopeptide (P2A2 as an uptake-mediating unit) in combination with different nanocarriers (micelles and liposomes) and determined the corresponding association constant Kass values, which were found to be very high. In addition, the mobility of fPA was exploited using fluorescence correlation spectroscopy (FCS) and fluorescence depolarization (FD) experiments to characterize the nanocarriers. Cellular uptake experiments with mouse brain endothelial cells provided information on the uptake behavior of liposomes modified by uptake-mediating P2A2 and revealed differences in the uptake behavior between pH-sensitive and pH-insensitive liposomes.

Luminescence and Scintillation Properties of Czochralski Grown LYGBO Crystals

Mixed crystals Li6YxGd1–x(BO3)3:Ce3+ (LYGBO) (where, x = 0.0, 0.2, 0.5, 0.8, 1.0) are grown by using Czochralski method with different proportions of Li6Y(BO3)3 and Li6Gd(BO3)3. All crystals are doped with 3 mole% optimized concentrations of Ce3+ ions. The grown crystals are 20–70 mm in length and 5–10 mm in diameter. Detailed sintering and crystal growth procedure is presented in this study. The required phase of the grown crystals is confirmed by powder X-ray diffraction (XRD) analysis. Ultraviolet (UV) photoluminescence and X-ray induced luminescence of the grown crystals at room temperature are measured. Various scintillation properties such as energy resolution, light yield, $\alpha /\beta $ ratio and fluorescence decay time under the excitation by $^{137}\mathrm {Cs}~\gamma $ -ray and 241Am particles are also presented.

Monitoring the Collapse of pH-Sensitive Liposomal Nanocarriers and Environmental pH Simultaneously: A Fluorescence-Based Approach.

Nowadays, the encapsulation of therapeutic compounds in so-called carrier systems is a very smart method to achieve protection as well as an improvement of their temporal and spatial distribution. After the successful transport to the point of care, the delivery has to be released under controlled conditions. To monitor the triggered release from the carrier, we investigated different fluorescent probes regarding their response to the pH-induced collapse of pH-sensitive liposomes (pHSLip), which occurs when the environmental pH falls below a critical value. Depending on the probe, the fluorescence decay time as well as fluorescence anisotropy can be used equally as key parameters for monitoring the collapse. Especially the application of a fluorescein labeled fatty acid (fPA) enabled the monitoring of the pHSLips collapse and the pH of its microenvironment simultaneously without interference. Varying the pH in the range of 3 < pH < 9, anisotropy data revealed the critical pH value at which the collapse of the pHSLips occurs. Complementary methods, e.g., fluorescence correlation spectroscopy and dynamic light scattering, supported the analysis based on the decay time and anisotropy. Additional experiments with varying incubation times yielded information on the kinetics of the liposomal collapse.

Phosphate content influence on structural, spectroscopic, and lasing properties of Er,Yb-doped potassium-lanthanum phosphate glasses

The influence of the phosphorus pentoxide (P2O5) content on the material properties of Er,Yb-doped potassium-lanthanum phosphate glass was studied. Glass samples of the following nominal composition 35.0K2O-6.8Yb2O3-8.0La2O3-0.2Er2O3-50.0P2O5 (in mol%) were prepared from starting materials mixed with five additional amounts of P2O5 (0, 7.5, 15.0, 30.0, and 45.0 mol% related to the nominal glass composition). The P2O5 addition influence on properties of prepared glasses was studied using Raman, absorption, and fluorescence spectroscopy. The glass residual IR absorption and Judd–Ofelt intensity parameters together with absorption and emission cross sections were estimated. The results showed the increasing polymerization of glass and the P─O bond shortening with P2O5 content increase. The spectroscopy of Er3+ and Yb3+ ions was affected only marginally by the glass composition. It was found that fluorescence decay time corresponding to upper-laser-level I413/2 increased with the decrease of P2O5 content in the glasses, which was related to increasing OH− contamination of the glass. The laser action at 1.53 μm under 975-nm pulsed laser diode pumping was successfully demonstrated. Low threshold and laser slope efficiency up to 21% in respect to absorbed pumping power were obtained.

Trigonal Pyramidal {AsO2(OH)} Bridging Tetranuclear Rare-Earth Encapsulated Polyoxotungstate Aggregates.

The one-pot assembly reaction of Na2WO4·2H2O, RE(NO3)3·6H2O, and NaAsO2 in the participation of dimethylamine hydrochloride as an organic solubilizing agent in the acidic aqueous solution led to a class of trigonal pyramidal {AsO2(OH)} bridging rare-earth substituted arsenotungstate (AT) aggregates [H2N(CH3)2]8Na8{[W3RE2(H2O)8AsO8(OH)][B-α-AsW9O33]2}2·65H2O [RE = Eu(III) (1), Gd(III) (2), Tb(III) (3), Dy(III) (4), Ho(III) (5), Y(III) (6)], which were structurally characterized by elemental analyses, IR spectra, single-crystal X-ray diffraction, and thermogravimetric (TG) analyses. The common structural feature of 1-6 is that their polyoxoanions consist of a novel tetrameric unit [(W3RE2(H2O)8AsO8(OH))(B-α-AsW9O33)2]2(16-) constituted by four trivacant Keggin [α-AsW9O33](9-) fragments linked through an unseen elliptical [W6RE4(H2O)16As2O16(OH)2](20+) moiety. Their polyoxoanionic infrastructures can also be described as a fusion of two equivalent dimeric subunits [(W3RE2(H2O)8O7)(B-α-AsW9O33)2](8-) bridged via two μ2-{AsO2(OH)} linkers. To the best of our knowledge, such a linking mode with trigonal pyramidal {AsO2(OH)} groups as linkers connecting adjacent RE containing polyoxometalate moieties together is very rare. The thermal stability of 1-6 was also investigated on the crystalline samples, and the thermal decomposition processes of 1, 4, and 6 were comparatively deeply studied. The fluorescent properties and decay times of 1, 3, and 4 were measured, and they exhibit the characteristic emissions of RE centers. The lifetimes of 1 and 3 mainly originate from the contribution of RE ions whereas the overall lifetime of 4 is contributed by the synergistic interactions of AT fragments and Dy(3+) ions.

Disturbance of serum albumin conformation in patients with melancholic depression

IntroductionThe last years it is became clear that disturbances in molecular processes in pathological conditions can be connected with conformational changes in protein structure.AimInvestigation of blood albumin conformation in patients with melancholic depression.Material and methodsThere were investigated 19 patients with melancholic depression (12 women and 7 men) and 25 health volunteers. Patient's state according to ICD-10 criteria was defined as a depressive episode in the frame of bipolar depressive disorder (type 2) (F32) and in the structure of recurrent depressive disorder (F33). Subnanosecond laser time resolved fluorescence spectroscopy (SLTRFS) (subnanosecond diapason) with K-35 fluorescent probe was used for the investigation of albumin conformation.Results and discussionThere were revealed 3 binding sites in albumin molecule with fluorescent decay time of 1, 3 and 9 nanoseconds (A1, A3 and A9 sites, respectively) in healthy volunteers using SLTRFS approach. There were found significant differences between albumin binding sites of volunteers and patients with melancholic depression, respectively, А1–117 ± 7 и 142 ± 10; А3–358 ± 14 и 420 ± 26; А9–371 ± 16 и 433 ± 29.ConclusionThese findings point out that melancholic depression is followed by conformational changes of albumin molecule that can affect its functional properties. We can hypothesized that albumin binding properties can serve as a biomarker of the efficacy of psychopharmacotherapy.Disclosure of interestThe authors have not supplied their declaration of competing interest.

Fluorescence characteristics of the fuel tracers triethylamine and trimethylamine for the investigation of fuel distribution in internal combustion engines.

Laser-induced fluorescence based on fuel tracers like amines is a suitable measurement technique for mixing studies in internal combustion (IC) engines. Triethylamine has often been used in gasoline IC engines; however, no detailed fluorescence characterization for excitation at 263 or 266 nm is available. Trimethylamine (TMA) exhibits high potential as a gaseous fuel tracer but little information about TMA fluorescence is currently available. A picosecond laser source combined with a streak camera equipped with a spectrograph was used to determine the spectral fluorescence emission and fluorescence decay time of both tracers. The tracers were investigated at various temperatures and pressures in a calibration cell with nitrogen as bath gas. The results provide an in-depth understanding of the fluorescence characteristics of both tracers and allow assessment of their application to the investigation of fuel distribution in IC engines.

Spectroscopic and magnetic properties of neodymium doped in GdPO4 sub-micron-stars prepared by solvothermal method

Neodymium-doped gadolinium orthophosphate (GdPO4:Nd3+) luminomagnetic sub-micron-stars were prepared by solvothermal method using metal nitrates and phosphoric acid. Monoclinic star shaped in six lobed sub-micron-stars with 600 nm length is obtained with uniform particle size distribution. After heat-treatment at 800 °C for 1 h in air, the stars separate into isolated petal shaped particles and show characteristic emission bands of Nd3+ with the strongest emission at 1064 nm. The emission intensities and fluorescence decay times are dependent on the Nd3+ concentration with the highest emission intensity and longest fluorescence decay time of 311 μs at 1064 nm with 0.5 mol% Nd3+. Under 808 nm excitation with 12 W/cm2 power density a quantum yield of 9% was obtained for the 1.0 mol% Nd3+. The presence of paramagnetic Gd3+ gives magnetic properties to the phosphor with a calculated magnetic moment of 1510 and 107,965 Bohr magneton at 300 and 5 K, respectively.

Quantitative sampling of conformational heterogeneity of a DNA hairpin using molecular dynamics simulations and ultrafast fluorescence spectroscopy.

Molecular dynamics (MD) simulations and time resolved fluorescence (TRF) spectroscopy were combined to quantitatively describe the conformational landscape of the DNA primary binding sequence (PBS) of the HIV-1 genome, a short hairpin targeted by retroviral nucleocapsid proteins implicated in the viral reverse transcription. Three 2-aminopurine (2AP) labeled PBS constructs were studied. For each variant, the complete distribution of fluorescence lifetimes covering 5 orders of magnitude in timescale was measured and the populations of conformers experimentally observed to undergo static quenching were quantified. A binary quantification permitted the comparison of populations from experimental lifetime amplitudes to populations of aromatically stacked 2AP conformers obtained from simulation. Both populations agreed well, supporting the general assumption that quenching of 2AP fluorescence results from pi-stacking interactions with neighboring nucleobases and demonstrating the success of the proposed methodology for the combined analysis of TRF and MD data. Cluster analysis of the latter further identified predominant conformations that were consistent with the fluorescence decay times and amplitudes, providing a structure-based rationalization for the wide range of fluorescence lifetimes. Finally, the simulations provided evidence of local structural perturbations induced by 2AP. The approach presented is a general tool to investigate fine structural heterogeneity in nucleic acid and nucleoprotein assemblies.

Synthesis, Ensemble, and Single Molecule Characterization of a Diphenyl-Acetylene Linked Terrylenediimide Dimer.

The synthesis and the photophysical characterization at the ensemble and single molecule level of a terrylenediimide (TDI) dimer are reported. The spectroscopic experimental data are compared with those obtained for the corresponding model compound TDI. Steady-state and ps time-correlated single photon counting have shown that both chromophores in the TDI dimer are in the weak coupling regime allowing their interaction by Förster resonance energy transfer. Femtosecond transient absorption experiments showed an excitation power dependence of the fluorescence decay, which could indicate the occurrence of singlet-singlet annihilation. Single molecule intensity traces were investigated for the TDI dimer and suggested two intensity levels. For both intensity levels several parameters among which emission maximum, fluorescence decay times, antibunching, blinking off-times and rate of dark state formation were compared. The blinking analysis revealed that the yield of dark state formation is an order of magnitude higher when the two chromophores are still active compared to the case where one is photobleached. The off-times remain however similar.

Localized surface plasmon-influenced fluorescence decay in dye-doped metallo-dielectric opals

Well-ordered opaline photonic crystals are grown by inward growing self-assembly method from Rhodamine B dye-doped polystyrene colloids. Subsequent to self-assembly, the crystals are infiltrated with gold nanoparticles of 40 nm diameter. Measurements of the stopband features and photoluminescence intensity from these crystals are supplemented by fluorescence decay time analysis. The fluorescence decay times from the dye-doped photonic crystals before and after the infiltration are dramatically different from each other. A lowered fluorescence decay time was observed for the case of gold infiltrated crystal along with an enhanced emission intensity. Double-exponential decay nature of the fluorescence from the dye-doped crystal gets converted into single-exponential decay upon the infiltration of gold nanoparticles due to the resonant radiative process resulting from the overlap of the surface plasmon resonance with the emission spectrum. The influence of localized surface plasmon due to gold nanoparticles on the increase in emission intensity and decrease in decay time of the emitters is established.

Interaction of 6-methoxyquinoline with anionic sodium dodecylsulfate micelles: Photophysics and rotational relaxation dynamics at different pH

Interactions of different species of 6-methoxyquinoline (6MQ) with anionic micelles have been studied at different pre-micellar, micellar and post-micellar concentrations using steady state, time resolved fluorescence and fluorescence anisotropy techniques. The sensitivity of fluorescence of 6MQ to change in its local environment was used to probe sodium dodecylsulfate (SDS) micelles. At post-micellar concentrations of SDS, the observed blue shift in the fluorescence spectrum and increase in quantum yield are attributed to the incorporation of solute molecule to micelles. 6MQ has been found to bind to the surface of the anionic micelles instead of penetrating inside the core of micelles. The binding constant (Kb) calculated for 6MQ revealed that the electrostatic forces mediate charged probe–micelle association, whereas, hydrophobic interaction allowed neutral 6MQ to associate with SDS micelles. The charged 6MQ gets inserted deeper into the micelle surface than its neutral form. The fluorescence anisotropy decay of 6MQ in SDS micelles studied at different pH allowed determination of restriction of motion of the fluorophore. The location of the probe molecule in micellar systems is justified by a variety of spectral parameters such as refractive index, dielectric constant, ET(30), average fluorescence decay time, radiative and non-radiative rate constants, and rotational relaxation time. The micro-environment around the fluorophore reveals that the photophysics of 6MQ is very sensitive to the microenvironment of SDS and probe molecules reside at the water–micelle interface.

Controlled synthesis and luminescence properties of Ca0.5Y1-x(MoO4)2:xRE3+ (RE = Eu, Pr, Sm, Tb, Dy, Yb/Er, Yb/Tm, and Yb/Ho) phosphors by hydrothermal method versus pulsed laser deposition

Herein, we report on rare-earth (RE) activated Ca0.5Y1-x(MoO4)2:xRE3+ (RE = Eu, Pr, Sm, Tb, Dy, Yb/Er, Yb/Ho, and Yb/Tm) phosphors synthesized using a surfactant-mediated hydrothermal route. Timedependent experiments were performed, and the morphological evolution of the phosphors was studied. From prepared powder samples of Ca0.5Y1-x(MoO4)2:xRE3+ (RE = Eu and Yb/Er), nano-sized thin phosphor films were grown using pulsed laser deposition (PLD). The surface topography of the as-grown thin phosphor films was analyzed. The asprepared phosphors were characterized by structural and optical studies. The powder phosphor exhibited bi pyramid-like micro-architectures. Structural studies indicated that Ca0.5Y1-x(MoO4)2 possesses the scheelite tetragonal crystal structure. The down-conversion luminescence of Ca0.5Y1-x(MoO4)2:xRE3+ (RE = Eu, Pr, Sm, Tb, and Dy) as powder phosphors and Eu3+ doped Ca0.5Y1-x(MoO4)2 thin phosphor film were studied. Upon irradiation with a 980 nm laser, the Ca0.5Y1-x(MoO4)2: xRE3+ (RE = Yb/Er, Yb/Ho, and Yb/Tm) powder phosphors and Ca0.5Y1-x(MoO4)2:xRE3+ (RE = Yb/Er) thin phosphor film showed intense up-converted visible emissions in green, yellow, and blue regions. The fluorescence decay time and color co-ordinates were determined for all synthesized phosphors. From the obtained results, the prepared powder and thin film phosphors are suggested to be suitable candidates for display and electro-luminescence applications.