Changes In Lifetime Research Articles

Anharmonic lattice dynamics and thermal transport of monolayer InSe under equibiaxial tensile strains

Two-dimensional (2D) InSe, which exhibits high electron mobility and a wide band gap has emerged as a promising material for photoelectric and thermoelectric applications. The inadequate understanding of the lattice thermal conductivity (κ), however, hampers the advancement of 2D InSe. Herein, by taking into account anharmonicity up to the fourth order and introducing the equibiaxial tensile strain (ϵ), we have performed an in-depth study on the lattice dynamics of 2D InSe. Interestingly, the κ exhibits a non-monotonic behaviour as a function of equibiaxial tensile strain, which can be attributed to the changes in acoustic phonon lifetimes. At the Γ point, a blue-shift of the lowest optical mode and a red-shift of the uppermost optical mode are reported for the first time. More strikingly, the blue-shift can be largely suppressed by equibiaxial tensile strain. Further study indicates that the unique transition of the potential energy surface is responsible for the disappearance of the blue-shift. Our work may enlighten the future research on phonon engineering and management of the lattice thermal conductivity of 2D InSe.

Impact of electron injection on carrier transport and recombination in unintentionally doped GaN

The impact of electron injection on minority carrier (hole) diffusion length and lifetime at variable temperatures was studied using electron beam-induced current, continuous, and time-resolved cathodoluminescence techniques. The hole diffusion length increased from 306 nm to 347 nm with an electron injection charge density up to 117.5 nC/μm3, corresponding to the lifetime changing from 77 ps to 101 ps. Elongation of the diffusion length was attributed to the increase in the non-equilibrium carrier lifetime, which was determined using ultrafast time-resolved cathodoluminescence and related to non-equilibrium carrier trapping on gallium vacancy levels in the GaN forbidden gap.

Measuring Changes in Keap1-Nrf2 Protein Complex Conformation in Individual Cells by FLIM-FRET.

The nuclear factor-erythroid 2 p45-related factor 2 (Nrf2)-mediated stress response is a major cellular defense mechanism against endogenous and exogenous oxidants, electrophiles, and pro-inflammatory agents. A number of Nrf2 inducers are being developed to therapeutically stimulate this pathway. Inducers are typically sensed by Kelch-like ECH-associated protein 1 (Keap1), a negative regulator and a binding partner of Nrf2. Modifications of Keap1 by oxidants or electrophiles, or its targeting by compounds that disrupt its interaction with Nrf2, alter the conformation of the Keap1-Nrf2 protein complex, which initiates the accumulation of Nrf2 required for mounting a stress response. To detect conformational changes in the Keap1-Nrf2 complex in live cells, we have developed a procedure based on Fluorescence Lifetime Imaging-Förster Resonance Energy Transfer (FLIM-FRET). The procedure includes a FLIM time course in cells expressing fluorescently-tagged Nrf2 and Keap1, followed by an extended analysis pipeline that quantifies changes in fluorescence lifetime of labeled Nrf2. The analysis visualizes and removes intensity-dependent bias in fluorescence lifetime measured with the Time-Correlated Single Photon Counting (TCSPC) approach, thereby improving the accuracy of quantification. The throughput is increased by the whole-experiment analysis within the newly developed FLIM dataset tool (FLIMDAST) and by the time-lapse FLIM described here. This pipeline is also suitable for applications beyond the Nrf2 field that assess small changes in fluorescence lifetime of objects with variable fluorescence intensities measured using TCSPC-based FLIM. © 2020 The Authors. Basic Protocol 1: Lipofectamine 2000 transfection Alternate Protocol 1: Calcium phosphate transfection Basic Protocol 2: Time course with individual FLIM Alternate Protocol 2: Time course with time-lapse FLIM Support Protocol: Measuring Instrument Response Function (IRF) Basic Protocol 3: Data analysis in SPCImage Basic Protocol 4: Data processing in ImageJ/FIJI Basic Protocol 5: Experiment analysis in FLIMDAST.

Microglia activation visualization via fluorescence lifetime imaging microscopy of intrinsically fluorescent metabolic cofactors.

Significance: A major obstacle to studying resident microglia has been their similarity to infiltrating immune cell types and the lack of unique protein markers for identifying the functional state. Given the role of microglia in all neural diseases and insults, accurate tools for detecting their function beyond morphologic alterations are necessary.Aims: We hypothesized that microglia would have unique metabolic fluxes in reduced nicotinamide adenine dinucleotide (NADH) that would be detectable by relative changes in fluorescence lifetime imaging microscopy (FLIM) parameters, allowing for identification of their activation status. Fluorescence lifetime of NADH has been previously demonstrated to show differences in metabolic fluxes.Approach: Here, we investigate the use of the label-free method of FLIM-based detection of the endogenous metabolic cofactor NADH to identify microglia and characterize their activation status. To test whether microglial activation would also confer a unique NADH lifetime signature, murine primary microglial cultures and adult mice were treated with lipopolysaccharide (LPS).Results: We found that LPS-induced microglia activation correlates with detected changes in NADH lifetime and its free-bound ratio. This indicates that NADH lifetime can be used to monitor microglia activation in a label-free fashion. Moreover, we found that there is an LPS dose-dependent change associated with reactive microglia lifetime fluxes, which is also replicated over time after LPS treatment.Conclusion: We have demonstrated a label-free way of monitoring microglia activation via quantifying lifetime of endogenous metabolic coenzyme NADH. Upon LPS-induced activation, there is a significant change in the fluorescence lifetime following activation. Together, these results indicate that NADH FLIM approaches can be used as a method to characterize microglia activation state, both in vitro and ex vivo.

Diversification of petal monoterpene profiles during floral development and senescence in wild roses: relationships among geraniol content, petal colour, and floral lifespan

Wild roses store and emit a large array of fragrant monoterpenes from their petals. Maximisation of fragrance coincides with floral maturation in many angiosperms, which enhances pollination efficiency, reduces floral predation, and improves plant fitness. We hypothesized that petal monoterpenes serve additional lifelong functions such as limiting metabolic damage from reactive oxygen species (ROS), and altering isoprenoid hormonal abundance to increase floral lifespan. Petal monoterpenes were quantified at three floral life-stages (unopened bud, open mature, and senescent) in 57 rose species and 16 subspecies originating from Asia, America, and Europe, and relationships among monoterpene richness, petal colour, ROS, hormones, and floral lifespan were analysed within a phylogenetic context. Three distinct types of petal monoterpene profiles, revealing significant developmental and functional differences, were identified: Type A, species where monoterpene abundance peaked in open mature flowers depleting thereafter; Type B, where monoterpenes peaked in senescing flowers increasing from bud stage, and a rare Type C (8 species) where monoterpenes depleted from bud stage to senescence. Cyclic monoterpenes peaked during early floral development, whereas acyclic monoterpenes (dominated by geraniol and its derivatives, often 100-fold more abundant than other monoterpenes) peaked during floral maturation in Type A and B roses. Early-diverging roses were geraniol-poor (often Type C) and white-petalled. Lifetime changes in hydrogen peroxide (H2O2) revealed a significant negative regression with the levels of petal geraniol at all floral life-stages. Geraniol-poor Type C roses also showed higher cytokinins (in buds) and abscisic acid (in mature petals), and significantly shorter floral lifespan compared with geraniol-rich Type A and B roses. We conclude that geraniol enrichment, intensification of petal colour, and lower potential for H2O2-related oxidative damage characterise and likely contribute to longer floral lifespan in monoterpene-rich wild roses.

Dogs race through development

Aging To get a better understanding of epigenetic changes that occur during development and aging, Wang et al. compared lifetime changes in the DNA methylomes of dogs and humans. Changes in methylation of cytosine-guanine dinucleotides in DNA provide an epigenetic clock that corresponds to age in humans and other animals. The authors alleviated some technical difficulties to allow comparison of data from 104 Labrador retrievers with data from humans and mice. The dog methylomes remodeled quickly in early life, reflecting not just life span but also timing of developmental changes. The authors found a strong association of methylation changes in genes that control developmental pathways, indicating that aging is, in some respects, a continuation of development. Cell Syst. 11 , 1 (2020).

Investigating Origins of FLIm Contrast in Atherosclerotic Lesions Using Combined FLIm-Raman Spectroscopy.

Background: Fluorescence lifetime imaging (FLIm) is a spectroscopic imaging technique able to characterize the composition of luminal surface of arterial vessels. Studies of human coronary samples demonstrated that distinct atherosclerotic lesion types are characterized by FLIm features associate with distinct tissue molecular makeup. While conventional histology has provided indications about potential sources of molecular contrast, specific information about the origin of FLIm signals is lacking. Here we investigate whether Raman spectroscopy, a technique able to evaluate chemical content of biological samples, can provide additional insight into the origin of FLIm contrast.Methods: Six human coronary artery samples were imaged using FLIm (355 nm excitation)-Raman spectroscopy (785 nm excitation) via a multimodal fiber optic probe. The spatial distribution of molecular contrast in FLIm images was analyzed in relationship with histological findings. Raman data was investigated using an endmember technique and compared with histological findings. A descriptive modeling approach based on multivariate regression was used to identify Raman bands related with changes in lifetime in four spectral channels (violet: 387/35 nm, blue: 443/29 nm, green: 546/38 nm, and red: 628/53 nm).Results: Fluorescence lifetime variations in the violet, blue and green spectral bands were observed for distinct areas of each tissue sample associated with distinct pathologies. Analysis of Raman signals from areas associated with normal, pathological intimal thickening, and fibrocalcific regions demonstrated the presence of hydroxyapatite, collagenous proteins, carotene, cholesterol, and triglycerides. The FLIm and Raman descriptive modeling analysis indicated that lifetime increase in the violet spectral band was associated with increased presence of cholesterol and carotenes, a new finding consistent with LDL accumulation in atherosclerotic lesions, and not with collagen proteins, as expected from earlier studies.Conclusions: The systematic, quantitative analysis of the multimodal FLIm-Raman dataset using a descriptive modeling approach led to the identification of LDL accumulation as the primary source of lifetime contrast in atherosclerotic lesions in the violet spectral range. Earlier FLIm validation studies relying on histopathological findings had associated this contrast to increased collagen content, also present in advanced lesions, thus demonstrating the benefits of alternative validation methods.

Exploring the chemistry behind protein-glycosaminoglycan conjugate: A steady-state and kinetic spectroscopy based approach.

The impact of glycosaminoglycan (chondroitin sulphate, CS) on bone morphogenetic protein - 2 (BMP - 2) structure, stability (thermal and chemical), association kinetics and conformation was monitored by multiple spectroscopic techniques (UV-Visible, fluorescence and circular dichroism). The absorbance in peptide region and fluorescence intensity of BMP - 2 was quenched in presence of CS; thus, confirming the formation of a ground-state complex. As there was an increase in Stern-Volmer constant observed as a function of temperature, idea of dynamic quenching was established. However, the negligible changes in lifetime indicated static quenching; thus, making the process a combination of static-dynamic quenching. Basically, the protein - glycan interaction was driven by entropy of the system and mediated by hydrophobic interactions. Secondary structure (CD spectroscopy) of native protein was significantly affected (intensity became more negative) in presence of CS, thus, introducing more compactness in the protein. CS infused thermal and chemical stability into BMP - 2 via alteration in its conformation. The rate of association was inversely proportional to concentration of quencher (CS), which confirmed the correlation between large size (~ 5 times the size of protein) and structural complexity of CS with fewer binding sites present in BMP - 2. The rate of association in presence of urea, suggested a decrease in association rate as a function of urea concentration for 15μM CS. Experimental evidences suggested an interaction between protein and glycan mediated by hydrophobic interactions, which deciphers structural, thermal and chemical stability into protein.

Satellite evidence for changes in the NO2 weekly cycle over large cities

Anthropogenic activities, by far the largest source of NOx into the atmosphere, induce a weekly cycle of NO2 abundances in cities. Comprehensive analysis of the 2005–2017 OMI NO2 dataset reveals significant weekly cycles in 115 of the 274 cities considered. These results are corroborated by a full year of high-resolution TROPOMI NO2 observations. The OMI dataset permits us to identify trends in the weekly cycle resulting from NOx emissions changes. The data show a clear weakening of the weekly cycle over European and U.S. cities, an evolution attributed to the decline in anthropogenic emissions and the resulting growing importance of background NO2, whereas NO2 lifetime changes also play a minor role. In particular, the Sunday NO2 columns averaged over all U.S. cities are found to increase, relative to the weekly average, from 0.72 during 2005–2007 to 0.88 in 2015–2017. The opposite tendency is recorded in regions undergoing rapid emission growth. Multiyear simulations over the U.S. and the Middle East using the chemistry-transport model MAGRITTEv1.1 succeed in capturing the observed weekly cycles over the largest cities, as well as the observed long-term trends in the weekly cycle.

Correlated Exciton Fluctuations in a Two-Dimensional Semiconductor on a Metal.

Excitons in nanoscale materials can exhibit fluorescence fluctuations. Intermittency is pervasive in zero-dimensional emitters such as single molecules and quantum dots. In contrast, two-dimensional semiconductors are generally regarded as stable light sources. Noise contains, however, valuable information about a material. Here, we demonstrate fluorescence fluctuations in a monolayer semiconductor due to sensitivity to its nanoscopic environment focusing on the case of a metal film. The fluctuations are spatially correlated over tens of micrometers and follow power-law statistics, with simultaneous changes in emission intensity and lifetime. At low temperatures, an additional spectral contribution from interface trap states emerges with fluctuations that are correlated with neutral excitons and anticorrelated with trions. Mastering exciton fluctuations has implications for light-emitting devices such as single-photon sources and could lead to novel excitonic sensors. The quantification of fluorescence fluctuations, including imaging, unlocks a set of promising tools to characterize and exploit two-dimensional semiconductors and their interfaces.

Characterization of planar phosphorescence based oxygen sensors on a TCSPC-PLIM macro-imager

A set of phosphorescent materials were evaluated using a new macro-imager based on fast time-stamping Tpx3Cam camera with phosphorescent lifetime imaging (PLIM) capabilities. The near-infrared emitting O2-sensitive dye PtBP was embedded in several polymers having different permeability for O2 and applied as solid-state coatings on polyester film support. These sensor materials were placed on a temperature-controlled stage of the imager and imaged under pulsed excitation with a 627 nm LED. The resulting PLIM images showed good uniformity, accuracy and contrast of measured lifetime values for the different phosphorescent materials, and the anticipated lifetime changes with altered temperature or oxygenation conditions, proving the dynamic mechanism of quenching by O2. By imaging the coatings with decreasing dye concentration, stability and limits of sensitivity of the PLIM mode were determined and compared with intensity-based imaging. Several commercial O2 sensors were also imaged and compared with the hand-made sensors, while lifetime measurements on the new imager were compared with those performed on the confocal TCSPC-PLIM microscope.

9-Acridinemethanamine and Acridine-9-Carboxaldehyde as Potential Fluorescence Lifetime pH Indicators

A significant challenge concerning the development of fluorescence lifetime (FL) based pH sensors is the paucity of fluorophores with sufficiently large FL variation with pH. Acridine is amongst the indicators with highest fluoresce lifetime responses to pH, with a change in lifetime of about 13 ns within a pH range of 5–8. Here we examine the two acridine derivatives, 9-acridinemethanamine (9-AMA) and acridine-9-carbaldehyde (9-ACA) in terms of their FL pH sensitivity and pH sensing range. Both indicators are characterized when dissolved in buffer solutions, as well as when immobilized in support materials. 9-AMA has a change in FL of 11 ns between pH 2–5, both when dissolved in solution and when immobilized in surfactant-filled mesoporous silica. The FL of 9-ACA is not sensitive to pH when dissolved in buffer solutions; however, when covalently bound to amine-modified silica, its FL changes 15 ns between pH 3–6. 9-AMA and 9-ACA represent promising FL in the pH range of pH 2–6, and could potentially form the basis of new FL pH sensors.Graphical

Surgical correction of hydrothorax complicating pediatric peritoneal dialysis.

Hydrothorax complicating continuous cycling peritoneal dialysis (CCPD) is an uncommon event. Its presentation may occur shortly after or years after initiation of dialysis. Surgical intervention offers the advantage of direct visualization and repair of the diaphragmatic defect. Video assisted thoracoscopy surgery (VATS) has been increasingly used in identifying these defects to facilitate this repair. We present 2 pediatric cases who underwent successful direct surgical repair of diaphragmatic defects using VATS with return to CCPD. Initial approach with VATS should be strongly considered in patients in whom a lifetime change in modality has significant repercussions.

Structure properties of warm dense hydrogen

The warm dense hydrogen is studied by the ab initio molecular dynamics in the region of the fluid–fluid phase transition. A method for calculating the properties such as concentration and lifetime of H2 molecules is developed. As warm dense hydrogen passes the transition, the concentration of H2 molecules decreases smoothly, while the lifetime changes abruptly by several orders.

Kinetics of Phosphorescence Decay of the New Paramagnetic Osmium(IV) Tetra-Crown Porphyrinate in Polystyrene at Temperatures of 77 and 298 K

The reaction of osmium(II) tetra-15-crown-5-porphyrin (Os(II)TCP) with molecular iodine in high yield yielded the corresponding osmium(IV) porphyrin containing iodide ions in the axial positions of the osmium(IV) atom and possessing paramagnetic properties according to 1H NMR. The iodine anions in the complex create an additional heavy atom effect in addition to such an effect from the osmium(IV) cation, which is of certain interest from the point of view of increasing the probability of phosphorescence transitions in osmium(IV) crown porphyrin molecules. The paramagnetism of osmium(IV) crown porphyrin also affects the probability of phosphorescence transitions, and this effect depends on temperature. These two effects (paramagnetism and the heavy atom effect) create some interest in terms of the possibility of creating a phosphorescent temperature sensor based on the new osmium(IV) crown porphyrin. A comparative analysis of the kinetics of phosphorescence decay of osmium(IV), osmium(VI) and osmium(II) porphyrins in the polystyrene matrix at temperatures of 298 and 77 K. It was found that the new osmium(IV) crown porphyrin has the highest phosphorescence lifetime with temperature in this series and can be considered as a luminescent temperature sensor for changes in phosphorescence lifetime.

Responsive Fluorophore Aggregation Provides Spectral Contrast for Fluorescence Lifetime Imaging.

Fluorophores experience altered emission lifetimes when incorporated into and liberated from macromolecules or molecular aggregates; this trend suggests the potential for a fluorescent, responsive probe capable of undergoing self-assembly and aggregation and consequently altering the lifetime of its fluorescent moiety to provide contrast between the active and inactive probes. We developed a cyanobenzothioazole-fluorescein conjugate (1), and spectroscopically examined the lifetime changes caused by its reduction-induced aggregation in vitro. A decrease in lifetime was observed for compound 1 in a buffered system activated by the biological reducing agent glutathione, thus suggesting a possible approach for designing responsive self-aggregating lifetime imaging probes.

Optical properties and zeta potential of carbon quantum dots (CQDs) dispersed nematic liquid crystal 4′- heptyl-4-biphenylcarbonitrile (7CB)

In this work, carbon quantum dots (CQDS) of three concentrations 0.1, 0.2 and 0.5 wt% have been dispersed in nematic liquid crystal 4′-Heptyl-4-biphenylcarbonitrile (7 CB). The results on the optical properties and zeta potential of pure and CQDs dispersed nematic 7CB have been reported. It has been observed that the dispersion of CQDs in host nematic matrix induces quenching of photoluminescence and reduces the Ultra-Violet-Visible (UV–Vis) absorbance of pure nematic at a lower wavelength. From the result of fluorescence decay profile, the fluorescence life time of pristine and dispersed nematic systems have been obtained. No remarkable changes in nematic lifetime in the presence of CQDs have been observed, which confirm that no energy is transferred from nematic to CQDs. Further, it has been found that due to dispersion of CQDs the numerical values of zeta potential are increased for the dispersed systems with 0.1 and 0.2 wt% concentrations of CQDs as compared to pure 7 CB. This result demonstrates that the study of zeta potential provides useful information on the stability and aggregation of the CQDs dispersed nematic systems.

Radiation hardness and post irradiation regeneration behavior of GaInAsP solar cells

Recent developments have renewed the demand for solar cells with increased tolerance to radiation damage. To investigate the specific irradiation damage of 1 MeV electron irradiation in GaInAsP lattice matched to InP for varying In and P contents, a simulation based analysis is employed: by fitting the quantum efficiency and open-circuit voltage simultaneously before and after irradiation, the induced changes in lifetime are detected. Furthermore, the reduction of irradiation damage during regeneration under typical satellite operating conditions for GEO missions (60 °C and AM0 illumination) is investigated. A clear decrease of the radiation damage is observed after post irradiation regeneration. This regeneration effect is stronger for increasing InP-fraction. It is demonstrated that the irradiation induced defect recombination coefficient for irradiation with 1 MeV electrons after regeneration for 216 h can be described with a linear function of InP-fraction between 1⋅10 −5 cm2/s for GaAs and 7⋅10−7 cm2/s for InP. The results show that GaInAsP is a promising material for radiation hard space solar cells.

Direct-indirect GeSn band structure formation by laser Radiation: The enhancement of Sn solubility in Ge

Low equilibrium solid solubility of Sn atoms in Ge (less than 1%) leads to limitations in application of this material for IR detectors and emitters. Providing of non-equilibrium conditions by powerful pulsed laser radiation can be successfully applied for enhancement of solubility of impurity atoms in the host material. Here we present laser-induced monotonous redistribution of Sn atoms in Ge, based on the thermogradient effect aiming overcoming equilibrium limitations in the solubility. We applied pulsed nanosecond laser radiation to epitaxial Ge0.96Sn0.04 layer grown on Si substrate to increase Sn atomic concentration up to 14% at the surface layer. As a result, indirect-direct graded bandgap GeSn structure was formed. The TEM/EDS cross-section analysis, X-ray photoelectron spectroscopy, Raman and UV reflection spectra confirmed the increase of Sn atomic content at the surface by order of magnitude. SEM and AFM imaging provided evident microstructure changes, while carrier lifetime changes, determined by differential transmittivity, were not observed, indicating that laser irradiation does not generate defects which reduce electronic quality of the material.

Zn(II) Schiff Bases: Bright TADF Emitters for Self-referenced Decay Time-Based Optical Temperature Sensing.

Thermally activated delayed fluorescence (TADF) is a highly temperature-dependent process and can be used in optical thermometry. TADF-based optical thermometers reported so far show fairly high-temperature sensitivity but have poor brightness and significant oxygen cross-talk. A new class of TADF emitters, Zn(II) Schiff base complexes, possess excellent brightness and high temperature sensitivity of the decay time at ambient temperature (4.1%/K change of TADF lifetime at 25 °C), enabling a resolution better than 0.03 °C. Oxygen cross-sensitivity is eliminated by covering the sensing layer (luminophore in polystyrene) with an off-stoichiometry thiol–ene polymer as an oxygen-consuming layer, and a poly(vinylidene chloride-co-acrylonitrile) layer as an oxygen barrier. The material is stable after more than 2 months of storage at ambient air, which enables long-term temperature monitoring.