Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 8 de 8
Filter
Add more filters










Database
Language
Publication year range
1.
J Phys Chem B ; 125(50): 13718-13729, 2021 12 23.
Article in English | MEDLINE | ID: mdl-34902969

ABSTRACT

Studying the structural dynamics of lipid membranes requires methods that can address both microscopic and macroscopic characteristics. Fluorescence imaging is part of the most used techniques to study membrane properties in various systems from artificial membranes to cells: It benefits from a high sensitivity to local properties such as polarity and molecular orientational order, with a high spatial resolution down to the single-molecule level. The influence of embedded fluorescent lipid probes on the lipid membrane molecules is however poorly known and relies most often on molecular dynamics simulations, due to the challenges faced by experimental approaches to address the molecular-scale dimension of this question. In this work we develop an optical microscopy imaging method to probe the effect of fluorophores embedded in the membrane as lipid probes, on their lipid environment, with a lateral resolution of a few hundreds of nanometers. We combine polarized-nonlinear microscopy contrasts that can independently address the lipid probe, by polarized two-photon fluorescence, and the membrane lipids, by polarized coherent Raman scattering. Using trimethylamino derivative 1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and di-8-butyl-amino-naphthyl-ethylene-pyridinium-propyl-sulfonate (di-8-ANEPPS) as model probes, we show that both probes tend to induce an orientational disorder of their surrounding lipid CH-bonds in 1,2-dipalmitoylphosphatidylcholine (DPPC) lipids environments, while there is no noticeable effect in more disordered 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid membranes.


Subject(s)
Microscopy , Phosphatidylcholines , Fluorescent Dyes , Lipid Bilayers , Membrane Lipids
2.
ACS Appl Mater Interfaces ; 13(1): 1773-1782, 2021 Jan 13.
Article in English | MEDLINE | ID: mdl-33393783

ABSTRACT

Thin-film thermoelectric coolers are emerging as a viable option for the on-chip temperature management of electronic and photonic integrated circuits. In this work, we demonstrate the record heat flux handling capability of electrodeposited Bi2Te3 films of 720(±60) W cm-2 at room temperature, achieved by careful control of the contact interfaces to reduce contact resistance. The characteristic parameters of a single leg thin-film devices were measured in situ, giving a Seebeck coefficient of S = -121(±6) µV K-1, thermal conductivity of κ = 0.85(±0.08) W m-1 K-1, electrical conductivity of σ = 5.2(±0.32) × 104 S m-1, and electrical contact resistivity of ∼10-11 Ω m2. These thermoelectric parameters lead to a material ZT = 0.26(±0.04), which, for our device structure, allowed a net cooling of ΔTmax = 4.4(±0.12) K. A response time of τ = 20 µs was measured experimentally. This work shows that with the correct treatment of contact interfaces, electrodeposited thin-film thermoelectrics can compete with more complicated and expensive technologies such as metal organic chemical vapor deposition (MOCVD) multilayers.

3.
Opt Express ; 27(20): 28384-28394, 2019 Sep 30.
Article in English | MEDLINE | ID: mdl-31684592

ABSTRACT

Wavefront shaping is a powerful method to refocus light through a scattering medium. Its application to large spectral bandwidths or multiple wavelengths refocusing for nonlinear bio-imaging in-depth is however limited by spectral decorrelations. In this work, we demonstrate ways to access a large spectral memory of a refocus in thin scattering media and thick forward-scattering biological tissues. First, we show that the accessible spectral bandwidth through a scattering medium involves an axial spatio-spectral coupling, which can be minimized when working in a confocal geometry. Second, we show that this bandwidth can be further enlarged when working in a broadband excitation regime. These results open important prospects for multispectral nonlinear imaging through scattering media.

4.
Biophys J ; 113(7): 1520-1530, 2017 Oct 03.
Article in English | MEDLINE | ID: mdl-28978445

ABSTRACT

Myelin around axons is currently widely studied by structural analyses and large-scale imaging techniques, with the goal to decipher its critical role in neuronal protection. Although there is strong evidence that in myelin, lipid composition, and lipid membrane morphology are affected during the progression of neurodegenerative diseases, there is no quantitative method yet to report its ultrastructure in tissues at both molecular and macroscopic levels, in conditions potentially compatible with in vivo observations. In this work, we study and quantify the molecular order of lipids in myelin at subdiffraction scales, using label-free polarization-resolved coherent anti-Stokes Raman, which exploits coherent anti-Stokes Raman sensitivity to coupling between light polarization and oriented molecular vibrational bonds. Importantly, the method does not use any a priori parameters in the sample such as lipid type, orientational organization, and composition. We show that lipid molecular order of myelin in the mouse spinal cord is significantly reduced throughout the progression of experimental autoimmune encephalomyelitis, a model for multiple sclerosis, even in myelin regions that appear morphologically unaffected. This technique permits us to unravel molecular-scale perturbations of lipid layers at an early stage of the demyelination progression, whereas the membrane architecture at the mesoscopic scale (here ∼100 nm) seems much less affected. Such information cannot be brought by pure morphological observation and, to our knowledge, brings a new perspective to molecular-scale understanding of neurodegenerative diseases.


Subject(s)
Encephalomyelitis, Autoimmune, Experimental/metabolism , Lipids , Myelin Sheath/metabolism , Nonlinear Optical Microscopy , Animals , Disease Progression , Encephalomyelitis, Autoimmune, Experimental/pathology , Freund's Adjuvant , Lipids/chemistry , Membranes, Artificial , Mice, Inbred C57BL , Myelin Sheath/chemistry , Myelin Sheath/pathology , Myelin-Oligodendrocyte Glycoprotein , Peptide Fragments , Spinal Cord/chemistry , Spinal Cord/metabolism , Spinal Cord/pathology
5.
Opt Lett ; 42(2): 294-297, 2017 Jan 15.
Article in English | MEDLINE | ID: mdl-28081096

ABSTRACT

We demonstrate femtosecond pump-probe transient absorption spectroscopy using a programmable dispersive filter as an ultra-fast delay line. Combined with fast synchronous detection, this delay line allows for recording of 6 ps decay traces at 34 kHz. With such acquisition speed, we perform single point pump-probe spectroscopy on bulk samples in 80 µs and hyperspectral pump-probe imaging over a field of view of 100 µm in less than a second. The usability of the method is illustrated in a showcase experiment to image and discriminate between two pigments in a mixture.

6.
PLoS One ; 10(8): e0133377, 2015.
Article in English | MEDLINE | ID: mdl-26317774

ABSTRACT

Prematurity affects 11% of the births and is the main cause of infant mortality. On the opposite case, the failure of induction of parturition in the case of delayed spontaneous birth is associated with fetal suffering. Both conditions are associated with precocious and/or delayed cervical ripening. Quantitative and objective information about the temporal evolution of the cervical ripening may provide a complementary method to identify cases at risk of preterm delivery and to assess the likelihood of successful induction of labour. In this study, the cervical stiffness was measured in vivo in pregnant sheep by using Shear Wave Elastography (SWE). This technique assesses the stiffness of tissue through the measurement of shear waves speed (SWS). In the present study, 9 pregnant ewes were used. Cervical ripening was induced at 127 days of pregnancy (term: 145 days) by dexamethasone injection in 5 animals, while 4 animals were used as control. Elastographic images of the cervix were obtained by two independent operators every 4 hours during 24 hours after injection to monitor the cervical maturation induced by the dexamethasone. Based on the measurements of SWS during vaginal ultrasound examination, the stiffness in the second ring of the cervix was quantified over a circular region of interest of 5 mm diameter. SWS was found to decrease significantly in the first 4-8 hours after dexamethasone compared to controls, which was associated with cervical ripening induced by dexamethasone (from 1.779 m/s ± 0.548 m/s, p < 0.0005, to 1.291 m/s ± 0.516 m/s, p < 0.000). Consequently a drop in the cervical elasticity was quantified too (from 9.5 kPa ± 0.9 kPa, p < 0.0005, to 5.0 kPa ± 0.8 kPa, p < 0.000). Moreover, SWE measurements were highly reproducible between both operators at all times. Cervical ripening induced by dexamethasone was confirmed by the significant increase in maternal plasma Prostaglandin E2 (PGE2), as evidenced by the assay of its metabolite PGEM. Histological analyses and two-photon excitation microscopy, combining both Second Harmonic Generation (SHG) and Two-photon Fluorescence microscopy (2PF) contrasts, were used to investigate, at the microscopic scale, the structure of cervical tissue. Results show that both collagen and 2PF-active fibrillar structures could be closely related to the mechanical properties of cervical tissue that are perceptible in elastography. In conclusion, SWE may be a valuable method to objectively quantify the cervical stiffness and as a complementary diagnostic tool for preterm birth and for labour induction success.


Subject(s)
Cervical Ripening/physiology , Cervix Uteri/diagnostic imaging , Cervix Uteri/ultrastructure , Elasticity Imaging Techniques/methods , Labor, Induced/methods , Animals , Cervix Uteri/drug effects , Collagen/metabolism , Dexamethasone/pharmacology , Dinoprostone/metabolism , Female , Microscopy, Fluorescence, Multiphoton/methods , Models, Animal , Pregnancy , Radio Waves , Sheep
7.
Opt Express ; 20(23): 25834-42, 2012 Nov 05.
Article in English | MEDLINE | ID: mdl-23187400

ABSTRACT

Dipole models are one of the simplest numerical models to understand nonlinear scattering. Existing dipole model for second harmonic generation, third harmonic generation and coherent anti-Stokes Raman scattering assume that the dipoles which make up a scatterer do not interact with one another. Thus, this dipole model can be called the uncoupled dipole model. This dipole model is not sufficient to describe the effects of refractive index of a scatterer or to describe scattering at the edges of a scatterer. Taking into account the interaction between dipoles overcomes these short comings of the uncoupled dipole model. Coupled dipole model has been primarily used for linear scattering studies but it can be extended to predict nonlinear scattering. The coupled and uncoupled dipole models have been compared to highlight their differences. Results of nonlinear scattering predicted by coupled dipole model agree well with previously reported experimental results.


Subject(s)
Optics and Photonics , Scattering, Radiation , Spectrum Analysis, Raman/methods , Algorithms , Biophysics/methods , Diagnostic Imaging/methods , Lasers , Light , Metal Nanoparticles/chemistry , Metals/chemistry , Models, Statistical , Nonlinear Dynamics , Photons , Refractometry
8.
Opt Express ; 18(21): 21603-11, 2010 Oct 11.
Article in English | MEDLINE | ID: mdl-20941058

ABSTRACT

We extend a simple dipole approximation model to predict nonlinear scattering from small particles. This numerical method is known as Discrete Dipole Approximation (DDA) and has been extensively used to model linear scattering by small particles of various shapes and sizes. We show here that DDA can be used to efficiently model second harmonic scattering by small particles. Our results are compared with experimental data and other computational methods.


Subject(s)
Optics and Photonics , Algorithms , Gold/chemistry , Metal Nanoparticles/chemistry , Models, Theoretical , Physics/methods , Scattering, Radiation , Software
SELECTION OF CITATIONS
SEARCH DETAIL
...