RESUMEN

In conventional microplastic (MP) analysis, acid or alkaline digestion is a necessary pretreatment step to remove residual organic matter from environmental samples. However, such a digestion process is not only cumbersome and time-consuming, but also possibly cause severe chemical damage to the MP itself, often making accurate MP characterization difficult. This study demonstrates that broadband coherent anti-Stokes Raman scattering (CARS) microspectroscopy is useful for rapidly detecting and identifying MPs in natural soil without any digestion process. A feasibility test is performed with soil samples, which are known to require the most complicated chemical pretreatment for MP analysis, deliberately mixed with various MP particles. The C-H bond-specific CARS imaging and spectral analysis allow rapid MP particle search and chemical identification even in the presence of other residual particles and strongly fluorescent substances from the soil. It is anticipated that this nondestructive, chemical pretreatment-free CARS approach will be a beneficial tool for studying the ecological impacts of MPs absorbed by terrestrial life, such as plants and soil organisms, as well as for complementary analysis of MPs subject to chemical degradation by digestion in investigating the environmental contamination of the MPs.

Asunto(s)

RESUMEN

The spectral congestion of highly overlapping vibrational peaks of molecules in condensed phases is a persistent challenge in conventional linear vibrational spectroscopy, making it difficult to accurately determine the spectroscopic parameters. This study demonstrates the utility of time- and frequency-resolved coherent anti-Stokes Raman scattering (CARS) spectroscopy with a time-delayed picosecond probe pulse in resolving congested C-H stretching vibrational peaks of condensed organic matters. The results show that the overlapping vibrational peaks of polymeric films and oily liquids, which are not easily distinguishable in spontaneous Raman spectroscopy, can be separated in the time-resolved CARS (tr-CARS) spectra. To understand the physical basis of the enhanced spectral resolution, we examine the time series of CARS spectra obtained by varying the delay time between the pump and probe pulses. The global fit analysis indicates that the effective suppression of faster Raman free-induction-decay components and instantaneous nonresonant background signals contributes to improved spectral resolution. Additionally, the present study reveals that the CARS spectra at a sufficient probe delay time are highly sensitive to the incident and detection polarizations, further improving vibrational peak distinguishability through polarization-controlled tr-CARS.

RESUMEN

As the bioaccumulation of microplastics (MPs) is considered as a potential health risk, many efforts have been made to understand the cellular dynamics and cytotoxicity of MPs. Here, we demonstrate that label-free multicolor coherent anti-Stokes Raman scattering (CARS) microscopy enables separate vibrational imaging of internalized MPs and lipid droplets (LDs) with indistinguishable shapes and sizes in live cells. By simultaneously obtaining polystyrene (PS)- and lipid-specific CARS images at two very different frequencies, 1000 and 2850 cm-1, respectively, we successfully identify the local distribution of ingested PS beads and native LDs in Caenorhabditis elegans. We further show that the movements of PS beads and LDs in live cells can be separately tracked in real time, which allows us to characterize their individual intracellular dynamics. We thus anticipate that our multicolor CARS imaging method could be of great use to investigate the cellular transport and cytotoxicity of MPs without additional efforts for pre-labeling to MPs.

Asunto(s)

RESUMEN

Vibrational sum-frequency generation (VSFG) spectroscopy, a surface-specific technique, was shown to be useful even for characterizing the vibrational optical activity of chiral molecules in isotropic bulk liquids. However, accurately determining the spectroscopic parameters is still challenging because of the spectral congestion of chiroptical VSFG peaks with different amplitudes and phases. Here, we show that a time-variable infrared-visible chiroptical three-wave-mixing technique can be used to determine the spectroscopic parameters of second-order vibrational response signals from chiral chemical liquids. For varying the delay time between infrared and temporally asymmetric visible laser pulses, we measure the chiral VSFG, achiral VSFG, and their interference spectra of bulk R-(+)-limonene liquid and perform a global fitting analysis for those time-variable spectra to determine their spectroscopic parameters accurately. We anticipate that this time-variable VSFG approach will be useful for developing nearly background-free chiroptical characterization techniques with enhanced spectral resolution.

RESUMEN

Recently, we introduced a new switching-off technique applicable to subdiffraction-limited coherent Raman imaging, where a coherent anti-Stokes Raman scattering (CARS) signal can be selectively suppressed via competitive stimulated Raman scattering (SRS) processes between vibrational modes of a single molecular species. Here, we show that such a three-beam CARS suppression can be made via double SRS processes between vibrational modes of heteromolecular species, a mixture of paraffin oil and benzene. We achieve more than 80% suppression of the pump-Stokes-beam CARS signal for the ring-breathing mode (target mode) of benzene when the C-H stretching mode (acceptor mode) of paraffin oil is used to deplete the pump photons via the pump-depletion-beam SRS process. The freedom in the choice of acceptor mode for depletion, which could be a critical advantage of the present switching-off scheme, can be of use for overcoming current challenges of depletion-based super-resolution coherent Raman imaging of biomolecules.

RESUMEN

We introduce a new coherent anti-Stokes Raman scattering (CARS) suppression scheme based on measuring a non-resonant CARS loss signal by three-beam (pump-Stokes-depletion) double stimulated Raman scattering (SRS) processes, which can be potentially of use for super-resolution Raman microscopy. In the converging configuration with employing both pump-depletion and Stokes-depletion SRS processes, we obtained approximately 94% suppression of non-resonant CARS signal, which is about 1.5 times more efficient than that with the parallel configuration with pump-Stokes and pump-depletion SRS processes. Such an enhanced suppression efficiency in the converging configuration results from a simultaneous loss of photons both in the pump and Stokes beams by double SRS processes, leading to an efficient suppression of the pump-Stokes-pump CARS signal. Based on the present method, we further propose two potential applications: (1) non-resonant background-free CARS imaging and (2) label-free super-resolution Raman imaging, and carry out simple numerical simulations to show their feasibility.

RESUMEN

Coherent anti-Stokes Raman scattering (CARS) spectroscopy and microscopy have been used in studying the structure and dynamics of a wide range of chemical and biological systems. However, the spatial resolution of CARS microscopy is still limited by the diffraction barrier, and hence a suitable scheme to selectively switch off the CARS imaging signal is essential for super-resolution CARS microscopy. Here, we present theoretical descriptions about three different ways to selectively suppress the pump-Stokes-pump two-beam CARS signal by employing three-beam double stimulated Raman scattering (SRS) schemes. Using a semiclassical theory for the interaction of radiation with the Raman-active molecule, we obtain coupled differential equations for the intensities of the pump, Stokes, depletion, and the generated CARS signal fields. We find approximate solutions of these coupled differential equations. They are then used to show that the pump-Stokes-pump CARS signal can be selectively suppressed by increasing the added depletion beam intensity, when the three injected beam frequencies are tuned in such a way that they can induce two SRS processes simultaneously. To show that these switching-off methods can be used to develop super-resolution CARS imaging techniques, we numerically calculate the full-width-at-half-maximum of the CARS imaging point spread function assuming that the spatial profiles of the pump and Stokes beams are Gaussian functions and that the spatial profile of the depletion beam is doughnut-shaped. We anticipate that the proposed selective CARS suppression schemes will be of use in developing super-resolution, label-free CARS microscopy.

Asunto(s)

RESUMEN

Coherent Raman scattering spectroscopy and microscopy are useful methods for studying the chemical and biological structures of molecules with Raman-active modes. In particular, coherent anti-Stokes Raman scattering (CARS) microscopy, which is a label-free method capable of imaging structures by displaying the vibrational contrast of the molecules, has been widely used. However, the lack of a technique for switching-off the CARS signal has prevented the development of the super-resolution Raman imaging method. Here, we demonstrate that a selective suppression of the CARS signal is possible by using a three-beam double stimulated Raman scattering (SRS) scheme; the three beams are the pump, Stokes, and depletion lights in order of frequency. Both pump-Stokes and pump-depletion beam pairs can generate SRS processes by tuning their beat frequencies to match two different vibrational modes, then two CARS signals induced by pump-Stokes-pump and pump-depletion-pump interactions can be generated, where the two CARS signals are coupled with each other because they both involve interactions with the common pump beam. Herein, we show that as the intensity of the depletion beam is increased, one can selectively suppress the pump-Stokes-pump CARS signal because the pump-depletion SRS depletes the pump photons. A detailed theoretical description of the coupled differential equations for the three incident fields and the generated CARS signal fields is presented. Taking benzene as a molecular system, we obtained a maximum CARS suppression efficiency of about 97% with our experimental scheme, where the ring breathing mode of the benzene is associated with pump-Stokes-pump CARS, while the C-H stretching mode is associated with the competing pump-depletion SRS process. We anticipate that this selective switching-off scheme will be of use in developing super-resolution label-free CARS microscopy.

RESUMEN

A three-beam femtosecond stimulated Raman scattering (SRS) scheme is formulated and demonstrated to simultaneously induce two different SRS processes associated with Raman-active modes in the same molecule. Two SR gains involving a common pump pulse are coupled and compete: As one of the Stokes beam intensities increases, the other SRS is selectively suppressed. We provide theoretical description and experimental evidence that the selective suppression behavior is due to the limited number of pump photons used for both of the two SRS processes when an intense depletion beam induces one SRS process. The maximum suppression efficiency was ∼60% with our experimental setup, where the SR gain of the ring breathing mode of benzene is the target SRS signal, which is allowed to compete with another SRS process, induced by an intense depletion beam, of the CH stretching mode. We anticipate a potential of this new switching-off concept in super-resolution label-free microscopy.

RESUMEN

BACKGROUND: The aim of this study was to determine whether the extent of late gadolinium enhancement (LGE) is associated with left ventricular (LV) function in patients with hypertrophic cardiomyopathy (HCM). METHODS AND RESULTS: Forty-seven patients with HCM (35 males, mean age 53+/-14, 14 with LV outflow tract obstruction) underwent cardiovascular magnetic resonance imaging and comprehensive echocardiographic examination. The extent of LGE was expressed as LGE volume and LGE percentage of LV volume. LGE was present in 40 (85.1%) of 47 patients. The mean LGE volume was 36.5+/-36 cm3, and the mean percentage of LV volume was 16.4+/-17%. Following adjustment for age, mitral regurgitation and LV mass index, LGE volume and percentage positively correlated with the left atrial volume index (r=0.388, p=0.009 and r=0.425, p=0.004, respectively). However, there was no significant association of functional class, ejection fraction, mitral flow, or annular velocities with the extent of LGE. CONCLUSIONS: In HCM patients, the extent of LGE positively correlated with the left atrial volume index, a surrogate marker of chronic diastolic burden. These findings suggest that myocardial scarring may be a pathologic substrate for chronic diastolic dysfunction in patients with HCM.

Asunto(s)

RESUMEN

Coherent anti-Stokes Raman scattering (CARS) microscopy is demonstrated to be a promising optical method for the characterization of polymer films with film thickness varying between 180 nm to 4300 nm. In case of PMMA films with a thickness of few hundreds of nanometers, the observed CARS signal was mainly associated with the interference effect of large nonresonant CARS field from glass substrate and the weak resonant field of PMMA. The dependence of resonant CARS intensity of PMMA film on film thickness is in good agreement with the theoretical prediction on a CARS field. The current work offers potential possibilities of noninvasive thickness measurement of polymeric thin film of thickness less than 180 nm by multiplex CARS microscopy without depth-profiling.

RESUMEN

BACKGROUND: We compared the metabolic profiles and risk of coronary artery disease (CAD) in Koreans with non-diabetic metabolic syndrome (MetS). [We applied four criteria of MetS: the NCEP criteria, the Asian modified NCEP (a-NCEP) criteria, the WHO criteria and the Asian modified WHO (a-WHO).] METHODS: The study group composed of 2724 subjects enrolled in the cardiovascular genome center. There were 728 patients with significant CAD. The different criteria of the MetS were applied for the study population. RESULTS: Among the 2724 participants, 522 (19.2%) met the NCEP criteria, 796 (29.2%) met the a-NCEP criteria, 361 (13.3%) met the WHO criteria and 576 (21.1%) met the a-WHO criteria. The clinical parameters, lipid profile, apoA1 and apoB level were not different between the participants classified as MetS by using the different criteria. The odds ratio for CAD prediction were not significantly different according to the metabolic criteria (odd ratio: 1.755 [95% CI: 1.423-2.163] in NCEP criteria, 2.120 [1.763-2.549] in a-NCEP criteria, 1.854 [1.466-2.343] in WHO criteria, 2.205 [1.810-2.687] in a-WHO criteria). The serum level of apoA1 and apoB showed strong correlations with MetS classified by all criteria and the HOMA index and insulin level showed better correlations with WHO-MetS criteria. CONCLUSIONS: All the MetS criteria showed similar metabolic profiles and all four criteria had similar predictive value for CAD. Conventional MetS criteria, applied to the non-diabetic Asian population, may underestimate the population at risk. Our data suggests that the Asian modified criteria will decrease the risk for underdiagnosis while demonstrating similar metabolic profiles and CAD risk compared to the conventional criteria.

Asunto(s)

RESUMEN

The adsorption structures of pyrrole (C(4)H(5)N) on a Ge(100) surface at various coverages have been investigated with both scanning tunneling microscopy (STM) and ab initio density-functional theory (DFT) calculations. Three distinct features are observed in the STM images at low coverages. The comparison of the STM images with the simulation reveals that the most dominant flowerlike feature with a dark side is that the adsorbed pyrrole molecules with H dissociated form bridges between two down Ge atoms of neighboring Ge dimer rows through N-Ge bonding and beta-carbon-Ge interaction. The flowerlike feature without a dark side is also observed as a minority, which is identified as nearly the same structure as the most dominant one where a dissociated H is out of the feature. The third feature showing bright protrusions may be due to a C- and N-end-on (CN) configuration, where the pyrrole molecule is located on one dimer row. At higher coverages, the number of localized configurations increases.

Asunto(s)