Quencher Concentration Research Articles

Simultaneous one-dimensional fluorescence lifetime measurements of OH and CO in premixed flames

A method for simultaneous measurements of fluorescence lifetimes of two species along a line is described. The experimental setup is based on picosecond laser pulses from two tunable optical parametric generator/optical parametric amplifier systems together with a streak camera. With an appropriate optical time delay between the two laser pulses, whose wavelengths are tuned to excite two different species, laser-induced fluorescence can be both detected temporally and spatially resolved by the streak camera. Hence, our method enables one-dimensional imaging of fluorescence lifetimes of two species in the same streak camera recording. The concept is demonstrated for fluorescence lifetime measurements of CO and OH in a laminar methane/air flame on a Bunsen-type burner. Measurements were taken in flames with four different equivalence ratios, namely I center dot = 0.9, 1.0, 1.15, and 1.25. The measured one-dimensional lifetime profiles generally agree well with lifetimes calculated from quenching cross sections found in the literature and quencher concentrations predicted by the GRI 3.0 mechanism. For OH, there is a systematic deviation of approximately 30 % between calculated and measured lifetimes. It is found that this is mainly due to the adiabatic assumption regarding the flame and uncertainty in H2O quenching cross section. This emphasizes the strength of measuring the quenching rates rather than relying on models. The measurement concept might be useful for single-shot measurements of fluorescence lifetimes of several species pairs of vital importance in combustion processes, hence allowing fluorescence signals to be corrected for quenching and ultimately yield quantitative concentration profiles. (Less)

Interface Study on Zinc Oxide Quantum Dots Using Fluorometric and Regression Analysis in View of Optical Sensing

A study has been performed to investigate the interface property of zinc oxide quantum dots (ZnO-Qdots) for optical sensing ability. Bare and L-cysteine capped ZnO-Qdots were prepared using simple sol-gel hydrolysis method at ambient conditions and the surface property was evaluated using a fluorometric technique. Data were interpreted and modeled using regression analysis, taking into account the effect of temperature and quencher concentration. The capping of L-cysteine caused the fluorescent yield to decrease up to 16-fold as compared to the bare ZnO-Qdots. Upon addition of an external quencher, emission of both bare and capped samples was quenched accordingly and dependent upon the concentration of the quencher. Regression analysis has confirmed with a significant low p-value (<0.05) that bare ZnO-Qdots obtained a dynamic quenching mechanism in the presence of copper (II) ion. Conversely, the capped ZnO-Qdots had a static quenching mechanism. Based on the interface mechanism understanding, it was found that capping effort reduced the sensing sensitivity while the bare one portrayed good sensing potential with a detection limit down to 41.30 ± 0.05 nM. A multi-variable model was constructed for the bare ZnO-Qdots and successfully predicted the concentration of copper (II) ion accurately even at different temperature conditions.

Dynamics of intermolecular electron transfer from amines to the excited states of 9-fluorenone

Abstract Dynamics of photoinduced electron transfer (PET) reactions between the singlet (S 1 ) and the triplet (T 1 ) excited states of 9-fluorenone or simply fluorenone and a few aromatic and aliphatic amines have been investigated under both diffusive and non-diffusive conditions. Formation of the fluorenone anion radical confirms the electron transfer (ET) from the amines to the excited states of fluorenone. Rate constants for both the forward ET process, k CS , and the charge recombination (CR) process, k CR , have been determined in acetonitrile and benzene solutions. Sub-picosecond time-resolved transient absorption study reveals that quenching of the S 1 state in acetonitrile is biexponential. Lifetime of one of these two components is independent of quencher concentration and its values determined for aniline (7.1 ps), dimethylaniline (8.5 ps) and diethylaniline (6.8 ps) are very similar. It represents the non-diffusive component of the PET reaction. But the lifetime of the other component decreases with increasing quencher concentration and the rate of this diffusive component of the PET reaction nearly agrees with the value determined using steady state fluorescence quenching method. To determine the intrinsic values of the rates of the PET reactions involving the S 1 state of fluorenone, the PET dynamics have been studied in these three neat donor solvents. The forward ET process is biexponential and the lifetimes of these two components are very similar in these solvents and vary in the range 0.3–0.5 ps and 6–8 ps. Nonexponential dynamics of the PET reactions conducted in neat donor–solvents have been discussed using a simple solvent reorientational model.

Critical dimension uniformity and contact edge roughness in extreme ultraviolet lithography: effect of photoacid generator, sensitizer and quencher

One of the main challenges for developing extreme ultraviolet resists is to satisfy critical dimension uniformity (CDU) and sidewall roughness of contacts to the allowable limit. To this end, further understanding of the effects of resist ingredients on CDU and contact edge roughness (CER) is required. We investigate the effects of a photoacid generator (PAG), sensitizer and quencher concentrations on the CDU and CER. We find that the dependencies of CDU on sensitizer and quencher are dominated by photon shot noise (PSN) effects whereas a more complicated interplay between PSN and PAG distribution statistics should be considered in the dependence of CDU on PAG concentration. The estimated CER parameters [root mean square (RMS) value and correlation length ξ ] exhibit a merging trend when plotted against the final critical dimension (CD). In addition, RMS value increases with exposure dose and PAG loading contrary to shot noise expectations. Power spectrum analysis reveals the dominant contribution of low-frequency undulations to CER, which is attributed to the enhanced interaction along specific directions between the aerial image and/or acid kinetics of nearby contacts. This inter-contact effect is further intensified with CD for fixed pitch and may explain the observed CER behavior.

Effect of Number and Location of Amine Groups on the Thermodynamic Parameters on the Acridine Derivatives to DNA

The thermodynamic parameters for the intercalative interaction of structurally related well known intercalators, 9-aminoacridine (9AA) and proflavine (PF) were determined by means of fluorescence quenching study. The fluorescence intensity of 9AA decreased upon intercalation to DNA, poly[d(A-T)2] and poly[d(G-C)2]. A van’t Hoff plot was constructed from the temperature-dependence of slope of the ratio of the fluorophore in the absence and presence of a quencher molecule with respect to the quencher concentration, which is known as a Stern-Volmer plot. Consequently, the thermodynamic parameters, enthalpy and entropy change, for complex formation was calculated from the slope and y-intercept of the van’t Hoff plot. The detailed thermodynamic profile has been elucidated the exothermic nature of complex formation. The complex formation of 9AA with DNA, poly[d(A-T)2] and poly[d(G-C)2] was energetically favorable with a similar negative Gibb’s free energy. On the other hand, the entropy change appeared to be unfavorable for 9AA-poly[d(G-C)2] complex formation, which was in contrast to that observed with native DNA and poly[d(A-T)2] cases. The equilibrium constant for the intercalation of PF to poly[d(G-C)2] was larger than that to DNA, and was the largest among sets tested despite the most unfavorable entropy change, which was compensated for by the largest favorable enthalpy. The favorable hydrogen bond contribution to the formation of the complexes was revealed from the analyzed thermodynamic data.

Quenching effect of l-tyrosine on peroxyoxalate chemiluminescence of berberine as the fluorophore

The present work deals with the first attempt to study the effect of L-tyrosine on the characteristics of the peroxyoxalate chemiluminescence. Berberine was applied as an efficient fluorophore. The investigated parameters include rise and fall rate constant for the chemilumines- cence burst, theoretical and experimental maximum intensity, the time needed to reach maximum intensity and the total light yield emission, which is theoretically eval- uated using the pooled intermediate model by a comput- erized non-linear least-squares curve fitting program (KINFIT). Furthermore, based on the observed quenching effect of tyrosine, the Stern-Volmer plot with KQ value of 7.7 9 10 4 M -1 in the quencher concentration range 4 9 10 -6 -5 9 10 -5 M. Moreover, this method is applied

Secondary avalanches in gas mixtures

Avalanche development in gas-based detectors relies not only on direct ionisation but also on excitation of noble gas atoms. Some quencher molecules can be ionised when they collide with excited atoms, a process on which we reported earlier [1]. Alternatively, excited atoms can decay by photon emission. If these photons are insufficiently absorbed by the quencher, yet capable of ionising, then they may escape from the avalanche region and start secondary avalanches. This process, called photon feedback, leads to an over-exponential increase of the gas gain which limits the working range. In this paper, we derive photon feedback parameters from published gain measurements for several gas mixtures and fit these parameters in a model which describes their dependence on the quencher concentration and the pressure.

Effect of fsDNA on chemiluminescence characteristics of luminol–H2O2 system catalyzed by Mn(III)–Tetrakis (4-sulfonatophenyl)-porphyrin

In the present work, the effect of fsDNA (fish sperm DNA) on kinetic parameters of chemiluminescence (CL) of the luminol–hydrogen peroxide system catalyzed by Mn(III)–Tetrakis (4-sulfonatophenyl)-porphyrin was investigated. These parameters including pseudo first-order rise and fall rate constant for the chemiluminescence burst, maximum level intensity, time to reach maximum intensity, total light yield, and values of the intensity at maximum CL were evaluated by computer fitting of the resulted intensity–time plots. Results reveal that CL parameters are dramatically affected due to interaction of metalloporphyrin with DNA. In order to observe quenching effect of DNA on CL intensity, Stern–Volmer plot with kQ value of 1.18 × 105 M−1 was calculated in the quencher concentration range of 4 × 10−6–8.5 × 10−5 M.

Critical material properties for pattern collapse mitigation

Modern high-resolution lithography, which employs a chemically amplified resist (CAR) at either 193 or 13.5 nm wavelength, is often limited by pattern collapse. While the general concepts of how CAR platforms work are widely understood, the influence of composition on pattern collapse has been studied to a lesser extent. In addition, the subject is often further complicated by non-disclosure of the resist chemistry used in the lithographic evaluation. Open-source photoresist platforms can be beneficial for fundamental studies on how individual components influence pattern collapse. Such platforms should mimic a typical CAR, containing-apart from the polymer-additional components such as photo acid generators (PAGs) and base quenchers. Here, 193 nm and extreme ultraviolet lithography open-source platforms are presented wherein the chemistry, composition, and concentration are all disclosed. With the aim of fundamentally understand how resist composition and behavior influences pattern collapse, the molecular weight of the polymer backbone and the concentration of both PAG and base quencher were varied. These sets of resists were exposed using high-end optical lithography scanners. The results are presented such that the probability of pattern collapse is derived as a function of the exposure wavelength, chemistry, and component concentrations.

Bimolecular Photoinduced Electron Transfer in Imidazolium-Based Room-Temperature Ionic Liquids Is Not Faster than in Conventional Solvents

The fluorescence quenching of 3-cyanoperylene upon electron transfer from N,N-dimethylaniline in three room-temperature ionic liquids (RTILs) and in binary solvent mixtures of identical viscosity has been investigated using steady-state and time-resolved fluorescence spectroscopy. This study was stimulated by previous reports of bimolecular electron transfer reactions faster by one or several orders of magnitude in RTILs than in conventional polar solvents. These conclusions were usually based on a comparison with data obtained in low-viscous organic solvents and extrapolated to higher viscosities and not by performing experiments at similar viscosities as those of the RTILs, which we show to be essential. Our results reveal that (i) the diffusive motion of solutes in both types of solvents is comparable, (ii) the intrinsic electron transfer step is controlled by the solvent dynamics in both cases, being slower in the RTILs than in the conventional organic solvent of similar viscosity, and (iii) the previously reported reaction rates much larger than the diffusion limit at low quencher concentration in RTILs originate from a neglect of the static and transient stages of the quenching, which are dominant in solvents as viscous as RTILs.

Interaction of an Antituberculosis Drug with Nano‐sized Cationic Micelle: Förster Resonance Energy Transfer from Dansyl to Rifampicin in the Microenvironment

In this contribution, we report studies on the interaction of an antituberculosis drug rifampicin (RF) in a macromolecular assembly of CTAB with an extrinsic fluorescent probe, dansyl chloride (DC). The absorption spectrum of the drug RF has been employed to study Förster resonance energy transfer (FRET) from DC, bound to the CTAB micelle using picosecond resolved fluorescence spectroscopy. We have applied a kinetic model developed by Tachiya to understand the kinetics of energy transfer and the distribution of acceptor (RF) molecules around the donor (DC) molecules in the micellar surface with increasing quencher concentration. The mean number of RF molecules associated with the micelle increases from 0.24 at 20 μm RF concentration to 1.5 at 190 μm RF concentration and consequently the quenching rate constant (k(q)) due to the acceptor (RF) molecules increases from 0.23 to 0.75 ns(-1) at 20 and 190 μm RF concentration, respectively. However, the mean number of the quencher molecule and the quenching rate constant does not change significantly beyond a certain RF concentration (150 μm), which is consistent with the results obtained from time resolved FRET analysis. Moreover, we have explored the diffusion controlled FRET between DC and RF, using microfluidics setup, which reveals that the reaction pathway follows one-step process.

Effect of Human and Bovine Serum Albumin on kinetic Chemiluminescence of Mn (III)-Tetrakis (4-Sulfonatophenyl) Porphyrin-Luminol-Hydrogen Peroxide System

The present work deals with an attempt to study the effect of human and bovine serum albumin on kinetic parameters of chemiluminescence of luminol-hydrogen peroxide system catalyzed by manganese tetrasulfonatophenyl porphyrin (MnTSPP). The investigated parameters involved pseudo-first-order rise and fall rate constant for the chemiluminescence burst, maximum level intensity, time to reach maximum intensity, total light yield, and values of the intensity at maximum CL which were evaluated by nonlinear least square program KINFIT. Because of interaction of metalloporphyrin with proteins, the CL parameters are drastically affected. The systems resulted in Stern-Volmer plots with k Q values of 3.17 × 105 and 3.7 × 105 M−1 in the quencher concentration range of 1.5 × 10−6 to 1.5 × 10−5 M for human serum albumin (HSA) and bovine serum albumin (BSA), respectively.

Fluorescence quenching of laser grade dye coumarin 440 in presence of hydrogen peroxide

Fluorescence quenching of coumarine 440 in ethanol due to the presence in aqueous solution of hydrogen peroxide is reported here. The Stern-Volmer plot is very much linear and quencher concentration could easily be estimated. An optical sensor for the detection of aqueous hydrogen peroxide could thus be easily constructed using the dye solution.

Analysis of Dose-Pitch Matrices of Line Width and Edge Roughness of Chemically Amplified Fullerene Resist

The resist materials are evaluated using their resolution, line edge roughness (LER), and sensitivity. However, the evaluation of chemically amplified resists is tricky because of the trade-off relationships between resolution, LER, and sensitivity. In this study, we investigated a chemically amplified resist with a fullerene matrix by analyzing the dose-pitch matrices of line width and LER. The effective quencher concentration of the fullerene resist obtained by the analysis was higher than those of typical polymer-type resists. This suggests that the quantum efficiency of acid generation in the fullerene matrix is slightly lower than those of polymer-type resists. The effective reaction radius was 0.06 nm, which was smaller than those of polymer-type resists. The proportionality constant between LER and the chemical gradient of the fullerene resist was smaller than those of polymer-type resists, probably owing to its molecular size.

Quenching of the Luminescence of Upconverting Luminescent Nanoparticles by Heavy Metal Ions

We report that the luminescence of upconverting luminescent nanoparticles (UCLNPs) is quenched by heavy metal ions and halide ions in aqueous solution. The UCLNPs consist of hexagonal NaYF(4) nanocrystals doped with trivalent rare earth ions and were synthesized by both the oleic acid (solvothermal) method and the ethylenediaminetetraacetic acid (co-precipitation) method. Quenching was studied for the Cu(II), Hg(II), Pb(II), Cd(II), Co(II), Ag(I), Fe(III), Zn(II), bromide, and iodide ions and is found to be particularly strong for Hg(II). Stern-Volmer plots are virtually linear up to quencher concentrations of 10-25 mM, but deviate from linearity at higher quencher concentrations, because static quenching causes an additional effect. The UCLNPs display two main emission bands (blue, green, red or near-infrared), and the quenching efficiencies for these are found to be different. The effect seems to be generally associated with UCLNPs because it was observed for all UCLNPs doped with trivalent lanthanide ions including Yb(III), Er(III), Ho(III), and Tm(III). The results are discussed in terms of quenching mechanisms and with respect to potential applications such as optical sensing.

Analysis of Dose-Pitch Matrices of Line Width and Edge Roughness of Chemically Amplified Fullerene Resist

The resist materials are evaluated using their resolution, line edge roughness (LER), and sensitivity. However, the evaluation of chemically amplified resists is tricky because of the trade-off relationships between resolution, LER, and sensitivity. In this study, we investigated a chemically amplified resist with a fullerene matrix by analyzing the dose-pitch matrices of line width and LER. The effective quencher concentration of the fullerene resist obtained by the analysis was higher than those of typical polymer-type resists. This suggests that the quantum efficiency of acid generation in the fullerene matrix is slightly lower than those of polymer-type resists. The effective reaction radius was 0.06 nm, which was smaller than those of polymer-type resists. The proportionality constant between LER and the chemical gradient of the fullerene resist was smaller than those of polymer-type resists, probably owing to its molecular size.

Substituted p-phenylene ethynylene trimers as fluorescent sensors for nitroaromatic explosives

New sensory materials based on p-phenylene ethynylene trimers integrating calix[4]arene receptors ( CALIX-PET) and tert-butylphenol ( TBP-PET) moieties have been synthesized and their sensitivity and selectivity for the detection of nitroaromatic compounds (NACs) such as nitrobenzene (NB), 2,4-dinitrotoluene (2,4-DNT), 2,4,6-trinitrotoluene (TNT) and picric acid (PA) investigated in fluid phase and solid-state. It was found that both fluorophores displayed high sensitivities toward NACs detection in solution as evaluated by the Stern–Volmer formalism. For all the tested explosives, the ratio of fluorescence intensities ( F 0/ F) is a linear function of the quencher concentration only after appropriate correction of fluorescence quenching data for inner-filter effects. The quenching efficiencies for CALIX-PET and TBP-PET follow the order PA ≫ TNT > DNT > NB, which correlate well with the quenchers electron affinities as evaluated from their LUMOs energies thereby suggesting a photoinduced electron transfer as the dominant mechanism of fluorescence quenching. The selectivity of these sensors was checked against exemplar interferents possessing differentiated electronic properties (benzoic acid, 2,4-dichlorophenol and benzoquinone) and reduced quenching activity was detected. The quenching efficiencies and response times of the two fluorophores in the solid-state toward NB, 2,4-DNT and TNT vapors were evaluated through steady-state fluorescence quenching experiments with the materials dispersed in polymeric matrices or as neat films. The most significant fluorescence quenching responses were achieved for drop-casted films of TBP-PET upon exposure to nitroaromatics.

Three-dimensional Fluorescence Lifetime Imaging with a Single Plane Illumination Microscope provides an improved Signal to Noise Ratio

We designed a widefield frequency domain Fluorescence Lifetime Imaging Microscopy (FLIM)setup, which is based on a Single Plane Illumination Microscope (SPIM). A SPIM provides an inherent optical sectioning capability and reduces photobleaching compared to conventional widefield and confocal fluorescence microscopes. The lifetime precision of the FLIM was characterized with Rhodamine 6G solutions of different quencher concentrations [KI]. We demonstrate the high spatial resolution of the SPIM-FLIM combination in the intensity domain as well as in the lifetime domain with latex bead samples and multiple recordings of three-dimensional live Madine-Darby Canine Kidney (MDCK) cysts. We estimate that the bleaching rate after 600 images have been recorded is below 5%.

Theoretical Study of Exposure Latitude of Chemically Amplified Resists Used for Extreme Ultraviolet Lithography

The trade-off relationships between resolution, line edge roughness (LER), and sensitivity are well known and the most serious problem in the development of chemically amplified resists used for extreme ultraviolet (EUV) lithography. Also, the exposure latitude (EL) is an important factor from the viewpoint of the productivity of production lines of semiconductor devices. However, the relationships of EL with resolution, LER, and sensitivity remain unclear. In this study, the EL of chemically amplified EUV resists was investigated using simulation based on reaction mechanisms. The relationship between EL and LER depended on dissolution point and quencher concentration. EL and resolution had a trade-off relationship. The relationship between EL and sensitivity was also a trade-off one with a weak dependence under the simulation conditions used in this study.

Study on the interaction of CdTe quantum dots with coumaric acid and caffeic acid based on fluorescence reversible tune

This paper describes the synthesis of CdTe quantum dots (QDs) together capped by glutathione and thioglycolic acid (GSH and TGA) in aqueous solution. The narrow photoluminescence (fwhm ≤ 40 nm) CdTe QDs, whose emission spans most of the visible spectrum from green through red, has a quantum yield (QY) of 68% at room temperature. GSH/TGA-CdTe QDs are characterized by various experimental techniques such as optical absorption, photoluminescence and AFM measurements. Coumaric acid and caffeic acid is able to quench the fluorescence of GSH/TGA-CdTe QDs, and the fluorescence intensity is linearly proportional to the concentration of quenchers. The addition of bovine serum albumin (BSA) restores the fluorescence intensity of GSH/TGA-CdTe QDs-coumaric acid system and GSH/TGA-CdTe QDs-caffeic acid system. The fluorescence recovery was due to the interaction of BSA with coumaric acid and caffeic acid, leading to the freeing of the GSH/TGA-CdTe QDs. The fluorescence quenching mechanism of GSH/TGA-CdTe QDs was discussed. The binding constant and thermodynamics parameters of BSA-coumaric acid and BSA-caffeic acid during the binding process were calculated in the paper.