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Fluorescence quenching of molybdenum disulfide quantum dots for metal ion sensing
摘要： In the present work, we have used hydrothermally synthesized in situ functionalized MoS2-QDs for a sensitive (limit of detection ~ 2.06 μM) and selective detection of Fe3+ ions. A detailed study of fluorescence quenching behavior for MoS2-QDs in the presence of Fe3+ ions has been performed using the Stern–Volmer plot, modified Stern–Volmer plot, and time-resolved photoluminescence measurements. Absorption based titration spectra and time-resolved photoluminescence measurements confirmed the fluorescence quenching is static with three decay times originated from the three different fluorescing sites. Interestingly, it is found that emission spectra consist of three bands at positions ~ 450 nm (P1, ~ 2.76 eV), ~ 475 nm (P2, ~ 2.61 eV), and ~ 503 nm (P3, ~ 2.46 eV). These peaks show a systematic quenching with the increasing concentration of Fe3+ ions. Quenching constants corresponding to these emission bands are found of the order of ~ 103 M?1. Large values of bimolecular quenching constants (~ 1011 M?1 s?1) suggest a strong binding interaction between MoS2-QDs and Fe3+ ions. Furthermore, to understand the fluorescence quenching of MoS2-QDs in the presence of Fe3+ ions, a ground-state complex formation-based mechanism has been proposed and elucidated in detail.
关键词： Nanostructures,UV/Vis spectroscopy,Metal ion sensing,Time-resolved photoluminescence,Fluorescence spectroscopy
更新于2025-09-23 15:21:01
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[Methods in Enzymology] || Fluorescence Depolarization Kinetics to Study the Conformational Preference, Structural Plasticity, Binding, and Assembly of Intrinsically Disordered Proteins
摘要： Fluorescence depolarization kinetics measured by the time-resolved fluorescence anisotropy decay serves as a sensitive and powerful methodology to study the conformational dynamics of macromolecules. This methodology allows us to delineate the different modes of biomolecular motional dynamics including the local, segmental, and global rotational dynamics on the timescale ranging from picoseconds to nanoseconds. In this chapter, we describe the principles and applications of this methodology to obtain unique molecular insights into the intrinsically disordered proteins (IDPs). Fluorescence depolarization kinetics, when performed in a site-specific manner, can offer a reliable tool to monitor the intrinsic backbone torsional dynamics of expanded IDPs and is capable of discerning the conformational preference of IDPs. Additionally, the time-resolved fluorescence anisotropy measurements allow us to investigate the mechanism of binding and assembly of a wide range of IDPs that are involved in crucial function and disease.
关键词： Fluorescence depolarization kinetics,conformational dynamics,time-resolved fluorescence anisotropy decay,biomolecular interactions,intrinsically disordered proteins
更新于2025-09-23 15:21:01
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Determining Orientations of Optical Transition Dipole Moments Using Ultrafast X-ray Scattering
摘要： Identification of the initially prepared, optically active state remains a challenging problem in many studies of ultrafast photoinduced processes. We show that the initially excited electronic state can be determined using the anisotropic component of ultrafast time-resolved X-ray scattering signals. The concept is demonstrated using the time-dependent X-ray scattering of N-methyl morpholine in the gas phase upon excitation by a 200 nm linearly polarized optical pulse. Analysis of the angular dependence of the scattering signal near time zero renders the orientation of the transition dipole moment in the molecular frame and identifies the initially excited state as the 3pz Rydberg state, thus bypassing the need for further experimental studies to determine the starting point of the photoinduced dynamics and clarifying inconsistent computational results.
关键词： time-resolved experiments,ultrafast
更新于2025-09-23 15:21:01
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Complementary cathodoluminescence lifetime imaging configurations in a scanning electron microscope
摘要： Cathodoluminescence (CL) spectroscopy provides a powerful way to characterize optical properties of materials with deep-subwavelength spatial resolution. While CL imaging to obtain optical spectra is a well-developed technology, imaging CL lifetimes with nanoscale resolution has only been explored in a few studies. In this paper we compare three different time-resolved CL techniques and compare their characteristics. Two configurations are based on the acquisition of CL decay traces using a pulsed electron beam that is generated either with an ultra-fast beam blanker, which is placed in the electron column, or by photoemission from a laser-driven electron cathode. The third configuration uses measurements of the autocorrelation function g(2) of the CL signal using either a continuous or a pulsed electron beam. The three techniques are compared in terms of complexity of implementation, spatial and temporal resolution, and measurement accuracy as a function of electron dose. A single sample of InGaN/GaN quantum wells is investigated to enable a direct comparison of lifetime measurement characteristics of the three techniques. The g(2)-based method provides decay measurements at the best spatial resolution, as it leaves the electron column configuration unaffected. The pulsed-beam methods provide better detail on the temporal excitation and decay dynamics. The ultra-fast blanker configuration delivers electron pulses as short as 30 ps at 5 keV and 250 ps at 30 keV. The repetition rate can be chosen arbitrarily up to 80 MHz and requires a conjugate plane geometry in the electron column that reduces the spatial resolution in our microscope. The photoemission configuration, pumped with 250-fs 257-nm pulses at a repetition rate from 10 kHz to 25 MHz, allows creation of electron pulses down to a few ps, with some loss in spatial resolution.
关键词： Electron microscopy,Ultrafast,Cathodoluminescence,Time-resolved,Quantum wells
更新于2025-09-23 15:21:01
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Time-resolved fluorescence measurements on leaves: principles and recent developments
摘要： Photosynthesis starts when a pigment in the photosynthetic antennae absorbs a photon. The electronic excitation energy is then transferred through the network of light-harvesting pigments to special chlorophyll (Chl) molecules in the reaction centres, where electron transfer is initiated. Energy transfer and primary electron transfer processes take place on timescales ranging from femtoseconds to nanoseconds, and can be monitored in real time via time-resolved fluorescence spectroscopy. This method is widely used for measurements on unicellular photosynthetic organisms, isolated photosynthetic membranes, and individual complexes. Measurements on intact leaves remain a challenge due to their high structural heterogeneity, high scattering, and high optical density, which can lead to optical artefacts. However, detailed information on the dynamics of these early steps, and the underlying structure–function relationships, is highly informative and urgently required in order to get deeper insights into the physiological regulation mechanisms of primary photosynthesis. Here, we describe a current methodology of time-resolved fluorescence measurements on intact leaves in the picosecond to nanosecond time range. Principles of fluorescence measurements on intact leaves, possible sources of alterations of fluorescence kinetics and the ways to overcome them are addressed. We also describe how our understanding of the organisation and function of photosynthetic proteins and energy flow dynamics in intact leaves can be enriched through the application of time-resolved fluorescence spectroscopy on leaves. For that, an example of a measurement on Zea mays leaves is presented.
关键词： Leaf,Time-resolved spectroscopy,Fluorescence,Re-absorption
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Singapore (2018.7.16-2018.7.19)] 2018 IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits (IPFA) - Failure Analysis on Space Electronics: Best Practices, Challenges and Trends
摘要： Failure Analysis (FA) concerns all the industrial domains. Nevertheless, it is important to underline similarities and differences that are encountered in space related activities. Even if the process is the same, there are many differences related to space domain. They are due to the very high quality and reliability of satellites their cost, their mission duration and no reparability of satellites in orbit. Failure Analysis pays a key role in quality assessment to balance the lack of statistical approaches for the very low volume spacecraft market. Usually, we have only one failed part to analyze, sometime none (satellite in orbit issue) while the expertise output, including corrective actions, is mandatory to avoid repetition of similar issues. FA for space covers the full range of parts, including Mechanical, material and Electrical, Electronic and Electromechanical (EEE) parts. The failed EEE components from connectors to commercial VLSI, are analyzed in our CNES facilities. We will illustrate the wide range of targets, from components to system, through some case studies, including VLSI. Increasing number of commercial VLSI is a big trend and challenge, forcing us to develop new "CAD less" techniques to deal with the lack of netlist and layout for these critical complex devices.
关键词： Laser Stimulation,Satellite,Laucher,Expertise,Time Resolved Imaging,Laser Probing,VLSI,defect localization,Failure Analysis,Counterfeit,Integrated Circuits
更新于2025-09-23 15:21:01
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Time-resolved fluorescent immunochromatographic assay-based on three antibody labels for the simultaneous detection of aflatoxin B <sub/>1</sub> and zearalenone in Chinese herbal medicines
摘要： A time-resolved fluorescent immunochromatographic assay (TRFICA) was successfully developed for the sensitive, simultaneous, and quantitative detection of aflatoxin B1 (AFB1) and zearalenone (ZEN) in Chinese herbal medicines. Eu-nanospheres (EuNPs) with unique optical properties increased the stability and sensitivity of the immunochromatographic assay. To obtain stable quantitative results, we applied a three-label system in which monoclonal antibodies for AFB1 and ZEN were conjugated to the EuNPs as detection probes on the test line (T line), and EuNP-labelled chicken IgY conjugates acted as the reference on the control line (C line). The fluorescence intensities of the T and C lines were recorded, and the T/C ratio was employed as the quantitative signal for the elimination of strip variation and matrix effects. The parameters that affected the TRFICA were optimised. Under optimal conditions, the established TRFICA gave good linear ranges from 0.60 μg/kg to 3.92 μg/kg for AFB1 and from 0.40 μg/kg to 1.28 μg/kg for ZEN. The limits of detection for AFB1 and ZEN were as low as 0.60 and 0.40 μg/kg, respectively, in Chinese herbal medicines Semen coicis, Rhizoma dioscoreae, and Platycodon grandiflorus, respectively. The average recoveries of the spiked samples were 73%–95% for AFB1 and 75.83%–90% for ZEN, both with a relative standard deviation of < 9.08%. The results of 15 actual samples detected by the developed TRFICA showed a satisfactory correlation with those of ultra-performance liquid chromatography tandem mass spectrometry. Therefore, the TRFICA is a simple, rapid, and sensitive approach to quantitatively detect mycotoxins in Chinese herbal medicines.
关键词： aflatoxin B1,time-resolved fluorescent immunochromatographic assay,zearalenone,Three antibody labels,Chinese herbal medicines
更新于2025-09-23 15:21:01
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The Oscillatory Photoelectron Signal of <i>N</i> -Methylmorpholine as a Test Case for the Algebraic-Diagrammatic Construction Method of Second Order
摘要： Motivated by recent progress in the application of time-resolved photoelectron spectroscopy (TRPES) to molecular Rydberg states, we report herein a detailed assessment of the performance of the second-order algebraic diagrammatic construction (ADC(2)) method in the simulation of their TRPES spectra. As the test case, we employ the tertiary aliphatic amine N -methylmorpholine (NMM), which is notable for the fact that the signal of its 3s state exhibits long-lived oscillations along the electron binding energy axis. The relaxation process of photoexcited NMM is simulated via the Born-Oppenheimer molecular dynamics method, and the resulting TRPES spectrum is generated basing on ionization energies and approximate Dyson orbital norms calculated with the continuum orbital technique. On the whole, the simulated TRPES spectrum achieves satisfactory agreement with experiment, which suggests that the ADC(2) method provides a realistic description of the potential energy surfaces of the relevant excited and ionized states. In particular, the simulations reproduce the ?ne oscillatory structure of the signal of the 3s state, and provide evidence to the e?ect that it results from a coherent vibrational wavepacket evolving along the deformation modes of the six-membered ring. However, it is found that ADC(2) underestimates of electron binding energies by up to a few tenths of an electronvolt. The case of NMM demonstrates the usefulness of ADC(2) as a tool to aid the interpretation of the TRPES spectra of large organic molecules.
关键词： Dyson orbital,TRPES,ADC(2),time-resolved photoelectron spectroscopy,NMM,N-methylmorpholine,Rydberg states,Born-Oppenheimer molecular dynamics,continuum orbital technique,algebraic diagrammatic construction
更新于2025-09-23 15:21:01
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Correlation between Near-Field Enhancement and Dephasing Time in Plasmonic Dimers
摘要： Near-field enhancement and dephasing time play critical roles in several applications of localized surface plasmon resonance. Here, using an example gold dimer system, we reveal the correlation between the near-field enhancement and dephasing time via time-resolved photoemission electron microscopy. Compared with isolated particles, dimers with small gap sizes show stronger near-field enhancement and shorter dephasing times. These results are well reproduced by numerical simulations and further explained by a coupled dipole approximation model. The roles of near- and far-field coupling and plasmon localization in balancing near-field enhancement and dephasing time are also unveiled.
关键词： dephasing time,time-resolved photoemission electron microscopy,near-field enhancement,plasmonic dimers,coupled dipole approximation model
更新于2025-09-23 15:19:57
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Photo-induced meta-stable polar conformations in polystyrene microspheres revealed by time-resolved SHG microscopy
摘要： Photo-induced second harmonic generation (SHG) was observed in centrosymmetric polystyrene (PS) microspheres using 1064 nm, sub-nanosecond laser-pulse irradiation. The SHG signal gradually increased upon stationary laser-pulse irradiation. After stopping the irradiation, the increased SHG signal disappeared in approximately 30 min. When the PS bead was irradiated by laser pulses again, the SHG signal reappeared with similar temporal behavior, which was attributed to the probable growth and contraction of meta-stable polar conformations of PS chain segments under periodic photo-thermal stimuli.
关键词： second harmonic generation,photo-induced,polystyrene microspheres,time-resolved SHG microscopy
更新于2025-09-23 15:19:57