Time-resolved Fluorescence Technique Research Articles

Experimental Branching Fractions, Transition Probabilities, and Oscillator Strengths in Sm ii

Branching fractions (BFs) of Sm ii for 71 lines from 12 excited levels ranging from 31,638.79 to 35,463.91 cm−1 were determined for the first time based on the Fourier transform spectra available from the National Solar Observatory database. New transition probabilities and oscillator strengths for these lines were derived by combining the determined BFs with reliable lifetimes measured using a time-resolved laser-induced fluorescence technique. Furthermore, BFs for 38 lines from five levels included in earlier studies were also determined for comparisons. The new results reported in this work will be useful in many fields, especially for astrophysics.

Binding Study of Antibacterial Drug Ciprofloxacin with Imidazolium-Based Ionic Liquids Having Different Halide Anions: A Spectroscopic and Density Functional Theory Analysis.

Herein, we have shown the interaction of an antibiotic drug ciprofloxacin (CIP) with three surface-active ionic liquids (ILs), having the same cation and different anions, namely, 1-decyl-3-methylimidazoliumtetrafluoroborate [C10mim][BF4], 1-decyl-3-methylimidazolium bromide [C10mim][Br], and 1-decyl-3-methylimidazolium chloride [C10mim][Cl]. This study has been performed by exploiting various spectroscopic techniques such as steady-state fluorescence, time-resolved fluorescence, and UV-visible spectroscopy. The fluorescence emission study of CIP with ILs was performed at various concentrations of all the three ILs. The emission spectra of CIP decreased in the presence of ILs, suggesting complex formation between CIP-IL. The effect of different concentrations of ILs on the emission spectra of CIP was exploited in terms of quenching and binding parameters. Further, fluorescence emission study was validated by the time-resolved fluorescence technique by measuring the average lifetime (τavg) of CIP in the presence of all the three ILs. The τavg value of the drug changed with the addition of ILs, which suggests complex formation between the drug and ILs. This complex formation was also confirmed by UV-visible spectroscopy results of CIP with all the three ILs. Further, for evaluating the thermodynamic parameters of the CIP-IL interactions, isothermal titration calorimetry (ITC) was performed. The ITC experiment yielded the thermodynamic parameters, ΔH (change in the enthalpy of association), ΔG (Gibbs free energy change), ΔS (entropy change), and binding constant (Ka). The binding parameters driven by ITC revealed that CIP-IL interactions are spontaneous in nature and enthalpy-driven, involving hydrophobic forces. Further, the classical density functional theory (DFT) calculations were performed, which provided deep insight for CIP-IL complex formation.

Time-resolved Fluorescence DNA-based Sensors for Reducing Background Fluorescence of Environment

The fluorescence assay is one of the popular methods that is applied for detection of different targets. However, this method may show low sensitivity and high background in biological samples due to the natural fluorescence of different compounds in complicated samples. In addition, it inevitably affects the detection results accuracy. A fundamental solution to this problem is the use of the time-resolved fluorescence technique (TRF). The main component of this technique is the use of long fluorescence lifetime reagents. In this review, various time-resolved fluorescent reagents such as complexes of lanthanide ions, lanthanide-doped inorganic nanoparticles; Mn-doped ZnS quantum dots (QDs) and pyrene excimer are introduced. Moreover, TRF sensors, especially TRF aptasensors (DNA-based sensors) are discussed. This review will give new ideas for researchers to develop novel high-sensitive TRF sensors that can remove or decrease background fluorescence and use them for the detection of various targets in complicated samples without treatment.

Direct Tracking of Charge Carrier Drift and Extraction from Perovskite Solar Cells by Means of Transient Electroabsorption Spectroscopy.

The best perovskite solar cells currently demonstrate more than 25% efficiencies, yet many fundamental processes that determine the operation of these devices are still not fully understood. In particular, even though the device performance strongly depends on charge carrier transport across the perovskite layer to selective electrodes, information about this process is still very controversial. Here, we investigate charge carrier motion and extraction from an archetypical CH3NH3PbI3 (MAPI) perovskite solar cell. We use the ultrafast electric-field-modulated transient absorption technique, which allows us to evaluate the electric field dynamics from the time-resolved electroabsorption spectra and to visualize the motion of charge carriers with subpicosecond time resolution. We demonstrate that photogenerated holes drift across the mesoporous TiO2/perovskite layer during hundreds of picoseconds. On the other hand, their extraction into the spiro-OMeTAD hole transporting layer lasts for more than 1 nanosecond, suggesting that the hole extraction is limited by the perovskite/spiro-OMeTAD interface rather than by the hole transport through the perovskite layer. Additionally, we use the ultrafast time-resolved fluorescence technique that reveals fluorescence decay during tens of picoseconds, which we attribute to the spatial separation of electrons and holes.

Relationship between Changes in the Protein Folding Pathway and the Process of Amyloid Formation: The Case of Bovine Carbonic Anhydrase II

Many proteins form amyloid fibrils only under conditions when the probability of transition from a native (structured, densely packed) to an intermediate (labile, destabilized) state is increased. It implies the assumption that some structural intermediates are more convenient for amyloid formation than the others. Hence, if a mutation affects the protein folding pathway, one should expect that this mutation could affect the rate of amyloid formation as well. In the current work, we have compared the effects of amino acid substitutions of bovine carbonic anhydrase II on its unfolding pathway and on its ability to form amyloids at acidic pH and an elevated temperature. Wild-type protein and four mutant forms (L78A, L139A, I208A, and M239A) were studied. We analyzed the change of the protein unfolding pathway by the time-resolved fluorescence technique and the process of amyloid formation by thioflavin T fluorescence assay and electron microscopy. It was revealed that I208A substitution accelerates amyloid formation and affects the structure of the late (molten globule-like)-intermediate state of carbonic anhydrase, whereas the other mutations slow down the growth of amyloids and have either no effect on the unfolding pathway (L78A, L139A) or alter the conformational states arising at the early unfolding stage (M239A).

Experimental and Theoretical Radiative Parameters of Highly Excited Odd-parity Levels in Ir ii

Using the time-resolved laser-induced fluorescence technique, the radiative lifetimes for 15 odd-parity levels from 47,003 to 61,475 cm−1 in Ir ii were measured. To the best of our knowledge, 11 lifetime results among these levels are reported for the first time, and hence they should be a good complement to the measured lifetime data of 10 levels previously published in the literature. The pseudorelativistic Hartree–Fock including core-polarization corrections method was used to calculate the lifetimes and branching fractions (BFs) of the investigated energy levels. Combining the experimental lifetime with the theoretical BFs, the transition probabilities and oscillator strengths for 124 transitions were determined.

Investigation of the Photoluminescence and Nonlinear Optical Properties of Ce₂O₃-TiO₂ Nanocomposites.

This paper reports the photoluminescence and nonlinear optical (NLO) properties of Ce₂O₃-TiO₂ nanocomposites synthesized via sol-gel process with different concentrations of cerium. The physical characterization studies by means of XRD indicated for the successful incorporation of Ce into the lattice of TiO₂, while the UV-visible spectra for an absorption edge shift of TiO₂ to the higher wavelength side following the Ce addition, and FESEM analysis for the morphology and particles sizes of the synthesized materials. On testing of the photoluminescence properties recorded through time-resolved fluorescence (TCSPC) technique, a decrease in the intensity of TiO₂ with that of increased Ce concentration was observed and is due to an escalation in the number of oxygen vacancies. Further, the observation NLO properties for Ce₂O₃-TiO₂ was done by a Z-scan technique of 5ns continuous wave (cw) laser at 532 nm, where the involvement of active mechanisms in the nonlinear refraction and nonlinear absorption are due to the saturable absorption (SA) and nonlinear thermal effects.

Bacterial Luciferases from Vibrio harveyi and Photobacterium leiognathi Demonstrate Different Conformational Stability as Detected by Time-Resolved Fluorescence Spectroscopy.

Detecting the folding/unfolding pathways of biological macromolecules is one of the urgent problems of molecular biophysics. The unfolding of bacterial luciferase from Vibrio harveyi is well-studied, unlike that of Photobacterium leiognathi, despite the fact that both of them are actively used as a reporter system. The aim of this study was to compare the conformational transitions of these luciferases from two different protein subfamilies during equilibrium unfolding with urea. Intrinsic steady-state and time-resolved fluorescence spectra and circular dichroism spectra were used to determine the stages of the protein unfolding. Molecular dynamics methods were applied to find the differences in the surroundings of tryptophans in both luciferases. We found that the unfolding pathway is the same for the studied luciferases. However, the results obtained indicate more stable tertiary and secondary structures of P. leiognathi luciferase as compared to enzyme from V. harveyi during the last stage of denaturation, including the unfolding of individual subunits. The distinctions in fluorescence of the two proteins are associated with differences in the structure of the C-terminal domain of α-subunits, which causes different quenching of tryptophan emissions. The time-resolved fluorescence technique proved to be a more effective method for studying protein unfolding than steady-state methods.

Immersion solvent dependent photophysical and photovoltaic properties of Porphyrin/TiO2 interface

In this work, the role of immersion solvents on light harvesting efficiency, photoinduced electron injection and photovoltaic properties of porphyrin/TiO2 have been investigated. Time resolved fluorescence technique was used to characterize the kinetics of electron injection at the porphyrin/TiO2 interface. The results show that electron injection from photoexcited porphyrin to the conduction band of TiO2 is highly sensitive to the nature of the solvent used during self-assembly of the TiO2-porphyrin interface. Based on the findings, the t-BuOH:ACN solvent is suitable for achieving long lived electrons in a H2MP/TiO2 device.

Radiative parameters of high-lying levels in neutral rhodium

ABSTRACT Radiative lifetimes of 20 high-lying excited levels in neutral rhodium (Rh i) were measured using time-resolved laser-induced fluorescence technique, 17 of which are reported for the first time to our knowledge. These lifetimes were combined with theoretical branching fractions obtained from pseudo-relativistic Hartree–Fock calculations to deduce semi-empirical transition probabilities and oscillator strengths for 63 Rh i spectral lines.

Bovine serum albumin/chitosan-nanoparticle bio-complex; spectroscopic study and in vivo toxicological – Hypersensitivity evaluation

This study, investigates the interaction of bovine serum albumin (BSA) with synthesized chitosan nanoparticles (CSNPs) using steady-state fluorescence and UV–vis absorbance spectroscopy as well as picosecond time-resolved fluorescence technique. The fluorescence quenching mechanism of BSA by CSNPs indicates the presence of both static and dynamic mechanism. The loading efficiency of BSA-CSNPs exhibited a decrease by about 6% in neutral pH under physiological temperature. Transmission electron microcopy (TEM) images revealed the Synthesized CSNPs were irregular in shape with size of ~42 nm. The safety and biocompatibility of BSA-CSNPs inside the body was investigated after intraperitoneal (IP) injection of male mice for nine days, analysis of in vivo results, revealed no toxicity with a hypocholesterolemic effect and a predicted mild activation of WBCs due to CSNPs adjuvant and immunogenic peptides in BSA. Accordingly, no signs of hypersensitivity were observed due to the administration of such formulations. The results can be used for a better understanding the interaction of CSNPs within biological protein environment.

Facile synthesis of carbon nanocubes and its applications for sensing antibiotics

Conversion of natural resources into value added products has attracted fabulous concern owing to their exceptional properties such as stability, biocompatibility, tunable emission and low toxicity. Herein, an inexpensive, environmentally benign and green method was adapted to synthesis of carbonaceous nanomaterials via hydrothermal process of mahua flowers without any additives. Cubical shape and average particle size of 4–5 nm was revealed from electron microscopic measurements. The prepared carbon nanocubes (CNCs) are rich in carbon and oxygenous functionality and the various chemical compositions was confirmed by spectroscopic measurements. CNCs are excitation dependent fluorescent in nature and exhibits the quantum yield of 7%. Under optimized conditions, the prepared CNCs were used to modify the glassy carbon electrode for the sensitive detection of antibiotics such as nitrofurazone and sulfamethoxazole via electrochemical method and LOD was calculated as 80 μM and 13 μM respectively. Additionally, fluorescence based sensing of nitrofurazone with a limit of detection as low as 0.7 μM has been discriminated. Inner filter effect (IFE) based quenching mechanism is proven via time resolved fluorescence technique. Moreover, this method was successfully applied to nitrofurazone discrimination in commercial milk sample. Therefore, the practicability of CNCs obtained from mahua flowers has also been validated.

Current Status and Developments of the Atomic Database on Rare-Earths at Mons University (DREAM)

The main purpose of the Database on Rare Earths At Mons University (DREAM) is to provide the scientific community with updated spectroscopic parameters related to lanthanide atoms (Z = 57–71) in their lowest ionization stages. The radiative parameters (oscillator strengths and transitions probabilities) listed in the database have been obtained over the past 20 years by the Atomic Physics and Astrophysics group of Mons University, Belgium, thanks to a systematic and extensive use of the pseudo-relativistic Hartree-Fock (HFR) method modified for taking core-polarization and core-penetration effects into account. Most of these theoretical results have been validated by the good agreement obtained when comparing computed radiative lifetimes and accurate experimental values measured by the time-resolved laser-induced fluorescence technique. In the present paper, we report on the current status and developments of the database that gathers radiative parameters for more than 72,000 spectral lines in neutral, singly-, doubly-, and triply-ionized lanthanides.

Experimental and Theoretical Radiative Lifetimes, Branching Fractions, Transition Probabilities, and Oscillator Strengths of Nb i Levels

Abstract Radiative lifetimes for 60 odd-parity levels of Nb i belonging to the 4d35s5p and 4d45p configurations, except for two levels with unknown configuration, which are in the energy range between 23,910.90 and 37,188.28 cm−1, are measured by the time-resolved laser-induced fluorescence technique. The lifetime values range from 7.1 to 118.7 ns with uncertainties less than 10%. To our knowledge, 45 lifetime values determined in this paper are reported for the first time. By combining the experimental lifetimes with measured or computed branching fractions, we obtain transition probabilities and oscillator strengths for the individual channels depopulating the investigated levels.

Inhibitory effect of endophytic fungi from Dysosma versipellis on HIV-1 IN-LEDGF/p75 interaction

To determine the inhibitory effect of endophytic fungi from Dysosma versipellis on HIV-1 IN-LEDGF/p75 interaction,the protein-protein interaction between human immunodeficiency virus type 1( HIV-1) integrase and lens epithelial growth factor p75 protein( LEDGF/p75) was used as a target. The homogeneous time-resolved fluorescence( HTRF) technique was used in the inhibitory activity assay. The results showed that eight endophytic fungi with anti-IN-LEDGF/p75 interaction activity were screened out from fifty-three strains with different morphological characteristic. Among them,106 strain showed strong inhibitory activity against HIV-1 IN-LEDGF/p75 interaction with IC50 value of 5. 23 mg·L-1,and was identified as a potential novel species of Magnaporthaceae family by the analyses of ITS-rDNA,LSU and RPB2 sequences data. This study demonstrated that potential natural active ingredients against the HIV-1 IN-LEDGF/p75 interaction exist in the endophytic fungi of D. versipellis. These results may provide available candidate strain resources for the research and development of new anti-acquired immunodeficiency syndrome drugs.

Experimental radiative lifetimes, branching fractions, and oscillator strengths of Ta I levels

Radiative lifetimes for 20 levels of Ta I in the energy range of 30 664.66–43 550.78 cm−1 were measured by the time-resolved laser-induced fluorescence technique. Among the results, to our knowledge, 17 lifetimes are reported for the first time. These lifetime values are in the range from 8.5–97 ns. A good agreement is achieved between the present and previously reported results. Branching fractions (BFs) of 97 transitions related to 13 of these levels were determined from the emission spectra of hollow cathode lamps recorded by the Fourier transform spectrometer at the National Solar Observatory on Kitt Peak, USA, available from digital library (http://diglib.nso.edu/ftp.html). By combining these BFs with our lifetime results, absolute transition probabilities and oscillator strengths for these lines were obtained.

Radiative lifetime measurements and semi-empirical transition parameter calculations for high-lying levels in Ba I

Radiative lifetimes for 18 highly excited levels belonging to 5d4f, 5d6p, and 6snp (n = 10, 12, 14–19) configurations of barium were measured by time-resolved laser-induced fluorescence (TR-LIF) technique. The uncertainties of the results are less than 10%. To our best knowledge, there are 16 lifetimes of Ba I reported for the first time. Two lifetimes were measured to compare with the previous results, and good agreements were achieved. From the combination of these experimental lifetimes and theoretical branching fractions calculated using a pseudo-relativistic Hartree–Fock model including core-polarization effects, a set of semi-empirical transition probabilities and oscillator strengths was derived for 46 Ba I spectral lines in the wavelength region from 240 to 3765 nm. For about half of these transitions, the uncertainties affecting the new decay parameters were found to be equal or better than 50%.

The determination of radiative lifetime for some Eu I levels by time-resolved laser-induced fluorescence spectroscopy

Natural radiative lifetimes for 15 excited levels of Eu I were measured using time-resolved laser-induced fluorescence (TR-LIF) technique in a laser-induced europium plasma. The levels are in the energy range from 35612.47 to 50040 cm−1. The lifetimes range from 9.4 to 436 ns with the uncertainties within ten percent. To our best knowledge, 11 lifetimes of Eu I are reported for the first time.

NIR-Light-Active ZnO-Based Nanohybrids for Bacterial Biofilm Treatment.

Nanomaterials with antimicrobial properties triggered by external stimuli appear to be a promising and innovative substitute for the destruction of antibiotic-resistant superbugs as they can induce multiple disruptions in the cellular mechanism. This study demonstrates the use of squaraine (SQ) dye as the photosensitive material, activated in the near-infrared tissue-transparent therapeutic window. The dye has been covalently attached to the ZnO nanoparticle surface, forming ZnO-SQ nanohybrids. The formation of the nanohybrids is confirmed using Fourier transform infrared and other optical spectroscopic methods. The photoinduced interfacial electron transfer process (as confirmed using the time-resolved fluorescence technique) from the excited state of SQ to the conduction band of ZnO is responsible for the greater reactive oxygen species (ROS) generation ability of the nanohybrid. The production of photoactivated ROS (especially singlet oxygen species) by ZnO-SQ provides remarkable antimicrobial action against clinically significant Staphylococcus aureus. Detailed investigations suggest synergistic involvement of cell membrane disruption and nanoparticle internalization followed by photoinduced intracellular ROS generation, which result in an unprecedented 95% bacterial killing activity by the nanohybrid. Moreover, the efficacy of the nanohybrid for disruption of bacterial biofilms has been examined. The electron microscopic images suggest significant bacterial cell death following structural alteration and reduced adherence property of the biofilms. Nanodimension-driven greater internalization of ZnO-SQ followed by an improved dissolution of ZnO in an acidic environment of the biofilm as well as red-light-driven interfacial charge separation and ROS generation improves the efficacy of the material for biofilm destruction. An artificial medical implant mimicking titanium sheets coated with ZnO-SQ depicts light-triggered disruption in the adherence property of matured biofilms. The cytotoxicity and hemolysis assays show inherent biocompatibility of the photoactive nanohybrid. This study is notably promising for the treatment of life-threatening drug-resistant infections and eradication of biofilms formed within artificial implants.

Experimental and Theoretical Radiative Lifetimes, Branching Fractions, Transition Probabilities, and Oscillator Strengths of Some Highly Excited Odd-parity Levels in Ir i

Abstract Radiative lifetimes of 62 odd-parity levels of Ir i in the energy range between 32513.43 and 58625.10 cm−1 were measured using the time-resolved laser-induced fluorescence technique. The lifetime values obtained are in the range from 3.2 to 345 ns. To our best knowledge, 59 results are reported for the first time. These are compared to computed data deduced from a pseudo-relativistic Hartree–Fock model including core-polarization contributions. From the combination of the experimental lifetime measurements and branching fraction calculations, a new set of transition probabilities and oscillator strengths is derived for 134 Ir i spectral lines of astrophysical interest in the wavelength region from 205 to 418 nm.