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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Piezochromic Carbon Dots with Two-photon Fluorescence.

Piezochromic materials, which show color changes resulting from mechanical grinding or external pressure, can be used as mechanosensors, indicators of mechano-history, security papers, optoelectronic devices, and data storage systems. A class of piezochromic materials with unprecedented two-photon absorptive and yellow emissive carbon dots (CDs) was developed for the first time. Applied pressure from 0-22.84 GPa caused a noticeable color change in the luminescence of yellow emissive CDs, shifting from yellow (557 nm) to blue-green (491 nm). Moreover, first-principles calculations support transformation of the sp2 domains into sp3 -hybridized domains under high pressure. The structured CDs generated were captured by quenching the high-pressure phase to ambient conditions, thus greatly increasing the choice of materials available for a variety of applications.

Ultrafast carrier dynamics of carbon nanodots in different pH environments.

Ultrafast carrier relaxation dynamics in fluorescent carbon nanodots is investigated by femtosecond transient absorption spectra at different pH environments so as to understand the mechanism of fluorescence for the first time. Utilizing multi-wavelength global analysis to fit the measured signal via a sequential model, four different relaxation channels are found, which are attributed to electron-electron scattering and surface state trapping, optical phonon scattering, acoustic phonon scattering and electron-hole recombination respectively. The results reveal that the surface states are mainly composed of different oxygen-containing functional groups (epoxy, carbonyl and carboxyl) and carbon atoms on the edge of the carbon backbone and can effectively trap a large number of photo-excited electrons. The deprotonation of carboxyl groups at high pH will change the distribution of π electron cloud density between the carbon backbone and surface states and consequently, compared with the excited electrons in the acidic and neutral environments, those in the alkaline environment can be more easily trapped by the surface within 1 ps, thereby giving rise to stronger fluorescence emission.

Optical emission generated from silicon under dual-wavelength femtosecond double-pulse laser irradiation.

In femtosecond double-pulse laser-induced breakdown spectroscopy, collinear double-pulse performance is investigated experimentally using various laser wavelength combinations of 800 nm and 400 nm Ti: sapphire lasers. The induced plasma emission line collected by BK7 lenses is the Si (I) at 390.55 nm. The double-pulse time separation ranges from -300 ps to 300 ps. The line intensity is dependent on the time separation of the dual-wavelength femtosecond double-pulse, and its behavior is unlike that of single-wavelength femtosecond double-pulses. Optical emission intensity can be enhanced by selecting appropriate time separation between sub-pulses. This result is particularly advantageous in the context of femtosecond laser-induced breakdown spectroscopy.

Depolymerization of Free-Radical Polymers with Spin Migrations.

The mechanism of depolymerization is one of the most essential issues in chemical engineering and materials science. In this work, we investigate the depolymerization reactions of three typical free-radical poly(alpha-methylstyrene) tetramers by using first-principles density functional theory. The calculated results show that these reactions all need to overcome the energy barriers in the range of 0.58 to 0.77 eV, and that breaking the C-C bond at the chain end leads to the dissociation of alpha-methylstyrene monomers from the polymers. Electronic-structure analysis indicates that the reactions occur easily at the CR3 unsaturated end, and that the frontier molecular orbitals that participate in the reactions are mainly localized at the unsaturated ends. Meanwhile, spin population analysis presents the unique net spin-transfer process in free-radical depolymerization reactions. We hope the current findings can contribute to understanding the free-radical depolymerization mechanism and help guide future experiments.

Influence of ambient pressure on the ablation hole in femtosecond laser drilling Cu.

The holes were drilled by femtosecond laser pulse (800 nm, 100 fs) on Cu sheets at different ambient pressures. The pressure range was from 1 Pa to atmospheric pressure. The number of pulses to drill through the target, the stable photodiode signal, and the hole diameter were obtained as functions of ambient pressure. The morphology of the hole was observed by a scanning electron microscope (SEM). The result showed that the ambient pressure had significant influence on the morphology of the hole.

Environmental-confinement-induced stability enhancement of chiral molecules.

We computationally study the transition process of a chiral difluorobenzo[c]phenanthrene (DFBcPh) molecule within non-polar fullerene C(260) to explore the confinement effect. We find blue-shifts in the infrared and Raman spectra of the molecule inside the fullerene relative to those of isolated systems. Six types of spectrum features of the molecule appear in the 0-60 cm(-1) band. Interestingly, the energy barrier of the chiral transformation of the molecule is elevated by 15.88 kcal mol(-1) upon the confinement by the fullerene, indicating improvement in the stability of the enantiomers. The protection by C(260) lowers the highest occupied molecular orbital energy level and lifts the lowest unoccupied molecular orbital energy level of the chiral molecule such that the chiral molecule is further chemically stabilized. We concluded that the confinement environment has an impact at the nanoscale on the enantiomer transformation process of the chiral molecule.

Potential energy curves and lifetimes of low-lying excited electronic states of CSe studied by configuration interaction method.

In this work, we performed a high level ab initio study on the low-lying electronic states of CSe, utilizing MRCI+Q (the internally contracted multireference configuration interaction, and Davidson's correction) method with scalar relativistic and spin-orbit coupling effects taken into account. The potential energy curves of 18 Λ-S states associated with the lowest dissociation limit of CSe molecule, as well as those of 50 Ω states generated from the Λ-S states were computed. The spectroscopic parameters of bound states were evaluated, which agree well with existing theoretical and experimental results. With the aid of calculated spin-orbit matrix elements and the Λ-S compositional variation of the Ω states, the spin-orbit perturbations of low-lying states to the A(1)Π and a(3)Π states are analyzed. Finally, the transition dipole moments of A(1)Π, A'(1)Σ(+), a(3)Π0+, and a(3)Π1 to the ground X(1)Σ(+) state as well as the lifetimes of the four excited states were evaluated.

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.

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.