Sensitivity, precision, and accuracy of fs-LIBS for heavy metal detection in flowing aqueous solutions.

This investigation employs femtosecond laser-induced breakdown spectroscopy (fs-LIBS) to measure the concentrations of chromium (Cr), lead (Pb), and copper (Cu) in flowing aqueous solutions. The fs pulsed laser excites the water, generating plasma in a dynamic setting that prevents liquid splashing-a notable advantage over static methods. The flowing water column maintains a stable liquid level, circumventing the laser focus irregularities due to liquid-level fluctuations. Calibration curves, based on a linear function, reveal limits of detection (LODs) as low as 0.0179 µg/mL for Cr, 0.1301 µg/mL for Pb, and 0.0120 µg/mL for Cu. The reliability of the experiment is confirmed by R2 values exceeding 0.99. These findings offer valuable insights for the analysis of trace heavy metals in flowing aqueous solutions using fs-LIBS, demonstrating the technique's potential for environmental monitoring.

Exploring the Femtosecond Filamentation Threshold in Liquid Media Using a Mach-Zehnder Interferometer.

We experimentally studied the supercontinuum induced by femtosecond filamentation in different liquid media. Using a Mach-Zehnder interferometer, we determined the relative filamentation thresholds (Pth) of these media. Research has shown that the value of the filamentation threshold is greater than that of Pcr (critical power for self-focusing), which can mainly be attributed to the strong dispersion effect. Changing the focal length of the focusing lens affects filamentation dynamics, thereby affecting the measured results regarding the filamentation threshold. With shorter focal lengths, the linear focusing (i.e., geometrical focusing) regime dominates, and the measured values of Pth for different liquid media are almost the same; as the focal length becomes larger, self-focusing starts to play a role, making the values of Pth for different media different from each other. This study presents an efficient method for investigating the femtosecond filamentation phenomenon in liquid media, helpful to provide further insights into the physical mechanism of supercontinuum generation via femtosecond filamentation in liquid media.

Turn-on stimuli-responsive switch: strategies for activating a new fluorescence channel by pressure.

The stimulus-responsive smart switching of aggregation-induced emission (AIE) features has attracted considerable attention in 4D information encryption, optical sensors and biological imaging. Nevertheless, for some AIE-inactive triphenylamine (TPA) derivatives, activating the fluorescence channel of TPA remains a challenge based on their intrinsic molecular configuration. Here, we took a new design strategy for opening a new fluorescence channel and enhancing AIE efficiency for (E)-1-(((4-(diphenylamino)phenyl)imino)methyl)naphthalen-2-ol. The turn-on methodology employed is based on pressure induction. Combining ultrafast and Raman spectra with high-pressure in situ showed that activating the new fluorescence channel stemmed from restraining intramolecular twist rotation. Twisted intramolecular charge transfer (TICT) and intramolecular vibration were restricted, which induced an increase in AIE efficiency. This approach provides a new strategy for the development of stimulus-responsive smart-switch materials.

Metal micro/nanostructure enhanced laser-induced breakdown spectroscopy.

This study used a femtosecond laser to ablate a Cu sample, forming a micro/nanostructural layer on the surface. And the effect of this structural layer on nanosecond laser-induced breakdown spectroscopy (LIBS) was discussed. Firstly, the effect of the micro/nanostructural layer on the intensity of laser-induced Cu plasma spectra was investigated. The micro/nanostructure could significantly enhance the spectral intensity of the Cu plasma by 82.5 times at 13.3 mJ laser energy. Secondly, the Cu plasma temperature and electron density were calculated. The micro/nanostructures could significantly increase Cu plasma temperature and electron density. Finally, the effect of micro/nanostructure surface on the spectral intensities of Pb and Cr elements in water was investigated for LIBS analysis. It was found that the detection limit of Pb and Cr trace metal elements in water was 1.85 ng/mL and 0.51 ng/mL at a lower laser energy (13.3 mJ), which was significantly better than other LIBS methods reported so far. The results show that the micro/nanostructure enhanced LIBS is a more sensitive method for detecting trace metal elements in the water.

Propagation distance-resolved characteristics of copper plasma emission induced by axicon-focused femtosecond laser filamentation in air.

It is well known that Bessel beams have non-diffractive characteristics, which can be generated by Gaussian beams focused by an ideal axicon. In general, the length of filament generated by Bessel beams is longer than that by Gaussian beams and the electron density in the filament generated by Bessel beams is more uniform. This paper experimentally studied the propagation distance-resolved characteristics of copper plasma emission induced by axicon-focused femtosecond laser filamentation in the air. The evolution of the spectral intensity, plasma temperature, and electron density with the filament propagation path was obtained. The experiment results showed that when the base angle of the axicon was 5.0°, the spectral intensity along with the filament propagation path was more stable than that the base angle of the axicon was 0.5°. The changes in the plasma temperature and electron density along the filament propagation path were consistent with the change in the spectral intensity. This work provides a demonstration for the applications of filament-induced breakdown spectroscopy (FIBS), such as long-distance detection.

Physical Insights on the Thermoelectric Performance of Cs2SnBr6 with Ultralow Lattice Thermal Conductivity.

This study has investigated the microscopic mechanisms of ultralow lattice thermal conductivity by the first-principles density functional theory. By solving the phonon Boltzmann equation iteratively, we find that the thermal conductivity of the lattice is abnormally low and that glass like heat transfer behavior occurs. Therefore, in addition to the contribution about the particle-like propagation to heat transport, the off-diagonal elements of the heat-flux operator through wave-like interbranch tunneling of phonon modes are also considered. The results provided new insights into the minimum thermal conductivity (κL) for Cs2SnBr6 (0.17 W m-1 K-1 at 450 K). It was also found that polar optical phonon scattering severely affects carrier lifetime. In addition, an impressive thermoelectric figure of merit of 0.55 at 450 K for Cs2SnBr6 was obtained in the case of doping p-type carriers. The study helps us understand the ultralow κL in complex crystals with strong anharmonicity and find that Cs2SnBr6 is a new and promising thermoelectric material.

ARF1 with Sec7 Domain-Dependent GBF1 Activates Coatomer Protein I To Support Classical Swine Fever Virus Entry.

Classical swine fever virus (CSFV), a positive-sense, enveloped RNA virus that belongs to the Flaviviridae family, hijacks cell host proteins for its own replication. We previously demonstrated that Golgi-specific brefeldin A (BFA) resistance factor 1 (GBF1), a regulator of intracellular transport, mediates CSFV infection. However, the molecular mechanism by which this protein regulates CSFV proliferation remains unelucidated. In this study, we constructed a series of plasmids expressing GBF1 truncation mutants to investigate their behavior during CSFV infection and found that GBF1 truncation mutants containing the Sec7 domain could rescue CSFV replication in BFA- and GCA (golgicide A)-treated swine umbilical vein endothelial cells (SUVECs), demonstrating that the effect of GBF1 on CSFV infection depended on the activity of guanine nucleotide exchange factor (GEF). Additionally, it was found that ADP ribosylation factors (ARFs), which are known to be activated by the Sec7 domain of GBF1, also regulated CSFV proliferation. Furthermore, we demonstrated that ARF1 is more important for CSFV infection than other ARF members with Sec7 domain dependence. Subsequent experiments established the function of coatomer protein I (COP I), a downstream effector of ARF1 which is also required for CSFV infection by mediating CSFV invasion. Mechanistically, inhibition of COP I function impaired CSFV invasion by inhibiting cholesterol transport to the plasma membrane and regulating virion transport from early to late endosomes. Collectively, our results suggest that ARF1, with domain-dependent GBF1 Sec7, activates COP I to facilitate CSFV entry into SUVECs. IMPORTANCE Classical swine fever (CSF), a highly contact-infectious disease caused by classical swine fever virus (CSFV) infecting domestic pigs or wild boars, has caused huge economic losses to the pig industry. Our previous studies have revealed that GBF1 and class I and II ARFs are required for CSFV proliferation. However, a direct functional link between GBF1, ARF1, and COP I and the mechanism of the GBF1-ARF1-COP I complex in CSFV infection are still poorly understood. Here, our data support a model in which COP I supports CSFV entry into SUVECs in two different ways, depending on the GBF1-ARF1 function. On the one hand, the GBF1-ARF1-COP I complex mediates cholesterol trafficking to the plasma membrane to support CSFV entry. On the other hand, the GBF1-ARF1-COP I complex mediates CSFV transport from early to late endosomes during the entry steps.

Ultrahigh Aggregation Induced Emission Efficiency in Multitwist-Based Luminogens under High Pressure.

Increasing aggregation induced emission (AIE) efficiency is of fundamental interest as it directly reflects performance of multitwist-based luminogens in bioimaging and in the photoelectric device field. However, an effective and convenient methodology to increase AIE efficiency significantly remains a challenge. Here, we present a general strategy to increase AIE efficiency of multitwist-based luminogens by pressure, resulting in a 120.1-fold enhancement of the AIE intensity of tris[4-(diethylamino)phenyl]amine (TDAPA) under high pressure compared to that of the traditional method. AIE efficiency of TDAPA increases from 0.5% to 46.1% during compression. Experimental and theoretical investigations reveal that the AIE efficiency enhancement originates from intramolecular vibration and the twisted intramolecular charge transfer are suppressed under high pressure. High AIE efficiency under high pressure provides an important inspiration for improving performance of multitwist-based luminogens in the lighting and biomedical fields.

Förster resonance energy transfer outpaces Auger recombination in CdTe/CdS quantum dots-rhodamine101 molecules system upon compression.

Förster resonance energy transfer (FRET) and Auger recombination in quantum dots (QDs)-molecules system are important mechanisms for affecting performance of their optoelectronic and photosynthesis devices. However, exploring an effective strategy to promote FRET and suppress Auger recombination simultaneously remains a daunting challenge. Here, we report that FRET process is promoted and Auger recombination process is suppressed in CdTe/CdS QDs-Rhodamine101 (Rh101) molecules system upon compression. The greatly improved FRET is attributed to the shortened donor-acceptor distance and increased the number of molecules attached to QDs induced by pressure. The reduced Auger recombination is ascribed to the formation of an alloy layer at the core/shell interface. The FRET can occur 70 times faster than Auger recombination under a high pressure of 0.9 GPa. Our findings demonstrate that high pressure is a robust tool to boost FRET and simultaneously suppress Auger recombination, and provides a new route to QDs-molecules applications.

Ultrafast dynamics on fluorescence quenching of rhodamine 6G by graphene oxide.

Fluorescence quenching of rhodamine 6G by graphene oxide (GO) was investigated using steady-state fluorescence spectroscopy and ultrafast time-resolved absorption spectroscopy. The steady-state fluorescence spectra showed that rhodamine 6G fluorescence was effectively quenched by titrating the GO to the rhodamine 6G solutions. For lower GO concentrations, transient dynamic curves followed two-exponential decay parameters. For higher GO concentrations, the dynamic curves could not be fitted well, and three-exponential decay parameters were appropriate. The results indicated that there was a new transition process (electron transfer) in the exited rhodamine 6G and GO solution.

Improvement of LIBS signal stability for NaCl solution using femtosecond laser-induced water film.

This paper studies the analysis of Na element concentration in NaCl aqueous solution using laser-induced breakdown spectroscopy (LIBS). The NaCl solution is transformed to a thin water film. The water film can provide a stable liquid surface, and overcome the disadvantage that laser focusing position cannot be fixed due to liquid level fluctuation (when nanosecond laser is used as the excitation light source, there is serious liquid splash phenomenon, which affects the signal stability). And, femtosecond pulse laser is used to excite the water film to produce the plasma, avoiding liquid splashing. The measured emission lines are Na (I) at 589.0 nm and 589.6 nm. The calibration curves of sodium are plotted by measuring different concentrations of NaCl solution. The linear correlation coefficients of Na (I) lines at 589.0 nm and 589.6 nm are 0.9928 and 0.9914, respectively. In addition, the relative standard deviation is also calculated; its range is from 1.5% to 4.5%. The results indicate that the combination of femtosecond laser and water film can significantly improve the signal stability for liquid analysis in LIBS.

ARFGAP1 binds to classical swine fever virus NS5A protein and enhances CSFV replication in PK-15 cells.

Classical swine fever virus (CSFV), an enveloped virus belonging to the genus Pestivirus of the Flaviviridae family, utilizes cell host factors for its own replication. ARFGAP1, GTPase activating protein of ADP-ribosylation factor 1, regulates COP I vesicle formation and function in cells and is involved in the life cycle of several viruses. However, the effect of ARFGAP1 on the infection of CSFV has not been illustrated. Here we showed that inhibition of ARFGAP1 either by QS11 or by lentivirus-mediated silencing repressed CSFV replication. While, subsequent experiments revealed that CSFV production were increased in cells with sufficient ARFGAP1 expression. However, ARFGAP1 was not involved in CSFV binding, entry, access to cell vesicles, and RNA replication during the early stages of infection. Then, we showed that ARFGAP1 interacted with the viral protein of NS5A, measured by immunoprecipitation, GST-pulldown, and confocal microscopy assays. Furthermore, we revealed that ARFGAP1 could alleviated CSFV NS5A-induced endoplasmic reticulum stress (ERS). Altogether, these results demonstrate that ARFGAP1, a NS5A binding protein, is involved in CSFV replication.

Rab1b-GBF1-ARFs mediated intracellular trafficking is required for classical swine fever virus replication in swine umbilical vein endothelial cells.

Classical swine fever virus (CSFV), a plus-sense RNA virus, utilizes host intracellular membrane organelles for its replication. Our previous studies have shown that disruption of the intracellular membrane-trafficking events can inhibit CSFV replication. However, the underlying mechanism of this process in CSFV infection has not been elucidated. To determine the role of Golgi-associated anterograde and retrograde trafficking in CSFV replication, we revealed the effect of vesicular transport between Golgi and ER inhibitors Brefeldin A (BFA) and 2,2-methyl-N-(2,4,6,-trimethoxyphenyl) dodecanamide (CI-976), the GBF1 inhibitor golgicide A (GCA) on virus production. Our results showed that disruption of vesicular trafficking by BFA, CI-976, and GCA significantly inhibited CSFV infection. Subsequent experiments revealed that knockdown of Rab1b by lentiviruses and negative-mutant Rab1b-N121I transfection inhibited CSFV infection. Furthermore, we showed that the Rab1b downstream vesicular component effectors GBF1, and class I and class II ADP-ribosylation factors (ARFs) were also involved in virus replication. In addition, confocal microscopy assay showed that CSFV infection disrupted the Golgi apparatus resulting in extended Golgi distribution around the nucleus. We also showed that cell secretory pathway, measured using Gaussia luciferase flash assay, was blocked in CSFV infected cells. Taken together, these findings demonstrate that CSFV utilizes Rab1b-GBF1-ARFs mediated trafficking to promote its own replication. These findings also provide new insights into the intracellular trafficking pathways utilized for CSFV life cycle.

Rab18 binds to classical swine fever virus NS5A and mediates viral replication and assembly in swine umbilical vein endothelial cells.

Classical swine fever virus (CSFV), a positive-sense RNA virus, hijacks cell host proteins for its own replication. Rab18, a small Rab GTPase, regulates intracellular membrane-trafficking events between various compartments in cells and is involved in the life cycle of multiple viruses. However, the effect of Rab18 on the production of CSFV remains uncertain. In this study, we showed that knockdown of Rab18 by lentiviruses inhibited CSFV production, while overexpression of Rab18 by lentiviruses enhanced CSFV production. Subsequent experiments revealed that the negative-mutant Rab18-S22 N inhibited CSFV infection, while the positive-mutant Rab18-Q67 L enhanced CSFV infection. Furthermore, we showed that CSFV RNA replication and virion assembly, measured by real-time fluorescence quantitative PCR (RT-qPCR), indirect immunofluorescence assay (IFA), and confocal microscopy, were reduced in cells lacking Rab18 expression. In addition, co-immunoprecipitation, GST-pulldown, and confocal microscopy assays revealed that Rab18 bound to the viral protein NS5A. Further, NS5A was shown to be redistributed in Rab18 knockdown cells. Taken together, these findings demonstrate Rab18 as a novel host factor required for CSFV RNA replication and particle assembly by interaction with the viral protein NS5A.

Quantum dynamics of atomic Rydberg excitation in strong laser fields.

Neutral atoms have been observed to survive intense laser pulses in high Rydberg states with surprisingly large probability. Only with this Rydberg-state excitation (RSE) included is the picture of intense-laser-atom interaction complete. Various mechanisms have been proposed to explain the underlying physics. However, neither one can explain all the features observed in experiments and in time-dependent Schrödinger equation (TDSE) simulations. Here we propose a fully quantum-mechanical model based on the strong-field approximation (SFA). It well reproduces the intensity dependence of RSE obtained by the TDSE, which exhibits a series of modulated peaks. They are due to recapture of the liberated electron and the fact that the pertinent probability strongly depends on the position and the parity of the Rydberg state. We also present measurements of RSE in xenon at 800 nm, which display the peak structure consistent with the calculations.

Spectral resolved study of filamentation effect on the nonlinear absorption in carbon disulfide.

A Z-scan system using spectrometers as detectors is established to investigate nonlinear absorption and white light continuum separately, in which absorption coefficient that is coincident with previous work was obtained. After Z-scan experiments, spot photographs were captured to further study the spatial properties of filaments in CS2, and we obtained similar space between dual filaments with previous work. Using the experimental setup, we find that plasma generation is the main effect impacting the nonlinear absorption and refraction process, and this impact can be eliminated in the case of CS2. Therefore, effect of filamentation can be neglected for CS2. Though it is easy to generate filaments in CS2 at relatively low intensity, fitting the Z-scan curve with three-photon model at 800 nm for CS2 is reasonable. In addition, the thickness of sample can affect extracted absorption coefficient of CS2 by affecting the length of filamentation.

Ultrafast carrier dynamics in all-inorganic CsPbBr3 perovskite across the pressure-induced phase transition.

The excited-state carrier dynamics of lead halide perovskites play a critical role in their photoelectric properties, and are greatly affected by lattice structural changes. In this work, the carrier dynamics of all-inorganic CsPbBr3 peroveskite, as a function of pressure, are investigated using in situ high-pressure femtosecond transient absorption spectroscopic experiments. Compression is found to drive crystal structural evolution, thereby markedly changing the behavior of charge carriers in CsPbBr3. Before the phase transition, simultaneous prolonging of the carrier relaxation and Auger recombination is achieved alongside a narrowing in the bandgap. The results favor improved efficiency and photovoltaic performance.

Pressure-Induced Tunable Electron Transfer and Auger Recombination Rates in CdSe/ZnS Quantum Dot-Anthraquinone Complexes.

Electron transfer (ET) and Auger recombination (AR) processes in quantum dots (QDs) are key mechanisms for the advance of QD-based devices. However, it still remains a challenge to promote ET and suppress AR simultaneously. Here, we use in situ high-pressure ultrafast transient absorption spectroscopy to explore the impact of pressure on the ET between CdSe/ZnS and anthraquinone (AQ) and AR dissolved in cyclohexane. Remarkably, under compression, ET lifetimes are shorten, while suppression of AR lifetimes is present. The promotion of ET is attributed to the shortened distance between CdSe/ZnS and AQ induced by pressure. We rationalize that for the AR suppression, pressure may enhance the formation of an alloy layer at the core/shell interface. These findings indicate that compression is an effective approach to promote ET and suppress AR simultaneously. This study highlights a brand-new approach for modulating ET and AR and provides new routes toward QD-based applications.

Effect of hydrogen bond on solvation dynamics of coumarin153 in cyclohexane-phenol solvent mixtures by time-resolved optical Kerr fluorescence.

Time-resolved optical Kerr fluorescence system was used to investigate time-resolved red-shift of coumarin 153 in different solvent mixtures. The mixtures included four mole fractions of phenol-cyclohexane solvents (0, 0.013, 0.08, and 0.3), and anisole-cyclohexane solvents with the mole fraction of 0.3. The measured time-resolved fluorescence showed that, in the solvent mixtures containing phenol, the time-dependent frequency shift accelerated with the increase in the mole fraction of phenol-cyclohexane mixtures. However, the time-dependent red-shift in the fluorescence was not observed in the anisole-cyclohexane mixture, the solvent polarity could not influence the spectral Stokes shift compared with phenol. The results indicated that coumarin 153 formed an excited hydrogen bond with phenol, and the excited hydrogen bond was strengthened with an increase in the mole fraction of phenol. And, these processes also suggested that the increase in the phenol ratio improves a large number of hydrogen bond formed between phenol and carbonyl group of coumarin 153, the charge distribution will be faster towards lower the free energy of the system due to the stronger dipole moment. Therefore, the corresponding solvation response in phenol-cyclohexane mixtures with higher mole fractions decays very rapidly.

Lighting Up the Invisible Twisted Intramolecular Charge Transfer State by High Pressure.

The twisted intramolecular charge transfer (TICT) state plays an important role in determining the performance of optoelectronic devices. However, for some nonfluorescent TICT molecules, the "invisible" TICT state could only be visualized by modifying the molecular structure. Here, we introduce a new facile pressure-induced approach to light up the TICT state through the use of a pressure-related liquid-solid phase transition of the surrounding solvent. Combining ultrafast spectroscopy and quantum chemical calculations, it reveals that the "invisible" TICT state can emit fluorescence when the rotation of a donor group is restricted by the frozen acetonitrile solution. Furthermore, the TICT process can even be effectively regulated by the external pressure. Our study offers a unique strategy to achieve dual fluorescence behavior in charge transfer molecules and is of significance for optoelectronic and biomedical applications.