Temperature Imaging using Quadriwave Shearing Interferometry. Applications in Thermoplasmonics

International audienceThe use of illuminated gold nanoparticles as ideal nanosources of heat is the basis of numerous research activities and applications in physics, chemistry, biology and medicine. This field defines the area recently named Thermoplasmonics [1]. In most of the activities related to Thermoplasmonics, probing the temperature at the vicinity of the metal nanoparticles is not an easy task. In this context, we recently developed a novel optical microscopy technique, named TIQSI, aimed at mapping the temperature around plasmonic nanoparticles [2]. The approach is based on the measure of the thermal-induced variation of the refractive index surrounding the sources of heat. The TIQSI technique cumulates all the advantages a thermal microscopy technique may require: i) high resolution (diffraction limited), ii) high readout rate (less than one image per second), iii) high temperature sensitivity (<1°C), iv) large accessible temperature range, v) temperature can be measured without fluorescence labelling or any other kind of thermal probe, v) no need to use sophisticated devices such as heterodyne detection, acousto-optic modulator, spectrometer, etc, like previous thermal imaging techniques. In this presentation, we will first introduce the TIQSI technique, its principle and capabilities. We will then present several recent applications made it possible by this new thermal imaging technique. In particular, we shall explain how this technique have been already used to quantitatively measure the absorption cross section of gold nanoparticles [3] and graphene sheets, how it can be used to map the temperature in real time in living cells [4], how it can help to design temperature distributions at will at the microscale using gold nanoparticles [5,7], and how it can be used to investigate thermal-induced phenomena in hydro- dynamics and phase transitions [6]

Thermal Imaging of Nanostructures by Quantitative Optical Phase Analysis

International audienceWe introduce an optical microscopy technique aimed at characterizing the heat generation arising from nanostructures, in a comprehensive and quantitative manner. Namely, the technique permits (i) mapping the temperature distribution around the source of heat, (ii) mapping the heat power density delivered by the source, and (iii) retrieving the absolute absorption cross section of light-absorbing structures. The technique is based on the measure of the thermal-induced refractive index variation of the medium surrounding the source of heat. The measurement is achieved using an association of a regular CCD camera along with a modified Hartmann diffraction grating. Such a simple association makes this technique straightforward to implement on any conventional microscope with its native broadband illumination conditions. We illustrate this technique on gold nanoparticles illuminated at their plasmonic resonance. The spatial resolution of this technique is diffraction limited, and temperature variations weaker than 1 K can be detected

Mapping the Local Organization of Cell Membranes Using Excitation-Polarization-Resolved Confocal Fluorescence Microscopy

International audienceFluorescence anisotropy and linear dichroism imaging have been widely used for imaging biomolecular orientational distributions in protein aggregates, fibrillar structures of cells, and cell membranes. However, these techniques do not give access to complete orientational order information in a whole image, because their use is limited to parts of the sample where the average orientation of molecules is known a priori. Fluorescence anisotropy is also highly sensitive to depolarization mechanisms such as those induced by fluorescence energy transfer. A fully excitation-polarization-resolved fluorescence microscopy imaging that relies on the use of a tunable incident polarization and a nonpolarized detection is able to circumvent these limitations. We have developed such a technique in confocal epifluorescence microscopy, giving access to new regions of study in the complex and heterogeneous molecular organization of cell membranes. Using this technique, we demonstrate morphological changes at the subdiffraction scale in labeled COS-7 cell membranes whose cytoskeleton is perturbed. Molecular orientational order is also seen to be affected by cholesterol depletion, reflecting the strong interplay between lipid-packing regions and their nearby cytoskeleton. This noninvasive optical technique can reveal local organization in cell membranes when used as a complement to existing methods such as generalized polarization

COMPARAISON DES DIFFERENTES METHODES D'EVALUATION DE FIDES

International audienceSummary The FIDES guide assesses the reliability of electronic systems with different methods depending on the level of information available. Depending on the progress of the product design, the definition will be more or less detailed. So, it is not always possible to make a complete component reliability study. This publication proposes to compare the results obtained through these different methods, detailed or simplified, defined in the FIDES guide (UTEC 80811): component method (or part stress), part count, families count and COTS board. The study is conducted on 5 boards from different military systems. This analysis will be supplemented by a concrete case of evaluation of a COTS consumer board to show the possibilities and interest of these methods. The objective of this two-step study is to verify the relevance of FIDES macroscopic methods ("part/family count") compared to the traditional method at the component level "Part stress".Résumé Le guide FIDES permet d'évaluer la fiabilité de systèmes électroniques à partir de différentes méthodes en fonction du niveau d'information disponible. En effet, suivant l'avancement du développement d'un produit, le dossier de définition sera plus ou moins détaillé et ne permet pas toujours de réaliser une étude de fiabilité complète composant par composant. Cette publication propose de comparer les résultats obtenus à travers ces différentes méthodes, détaillées ou simplifiées, définies dans le guide FIDES (UTE C 80811) : méthodes composant (« Part stress »), comptage par famille d'article (« families count »), comptage par type d'article (« part count »), carte COTS. L'étude est réalisée sur 5 cartes issues de différents systèmes militaires. Cette analyse sera complétée d'un cas concret d'évaluation d'une carte COTS grand public pour montrer les possibilités et l'intérêt de ces méthodes. L'objectif de cette étude en 2 temps est de vérifier la pertinence des méthodes macroscopiques (par comptage) de FIDES par rapport à la méthode fine traditionnelle au niveau composant

Optical detection and measurement of living cell morphometric features with single-shot quantitative phase microscopy

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Quantitative retardance imaging of biological samples using quadriwave lateral shearing interferometry

We describe a new technique based on the use of a high-resolution quadri-wave lateral shearing interferometer to perform quantitative linear retardance and birefringence measurements on biological samples. The system combines quantitative phase images with varying polarization excitation to create retardance images. This technique is compatible with living samples and gives information about the local retardance and structure of their anisotropic components. We applied our approach to collagen fibers leading to a birefringence value of (3.4 +/- 0.3) . 10(-3) and to living cells, showing that cytoskeleton can be imaged label-free