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El Arawi D, Vézy C, Déturche R, Lehmann M, Kessler H, Dontenwill M, Jaffiol R. Advanced quantification for single-cell adhesion by variable-angle TIRF nanoscopy. BIOPHYSICAL REPORTS 2021; 1:100021. [PMID: 36425460 PMCID: PMC9680782 DOI: 10.1016/j.bpr.2021.100021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Accepted: 09/07/2021] [Indexed: 05/25/2023]
Abstract
Over the last decades, several techniques have been developed to study cell adhesion; however, they present significant shortcomings. Such techniques mostly focus on strong adhesion related to specific protein-protein associations, such as ligand-receptor binding in focal adhesions. Therefore, weak adhesion, related to less specific or nonspecific cell-substrate interactions, are rarely addressed. Hence, we propose in this work a complete investigation of cell adhesion, from highly specific to nonspecific adhesiveness, using variable-angle total internal reflection fluorescence (vaTIRF) nanoscopy. This technique allows us to map in real time cell topography with a nanometric axial resolution, along with cell cortex refractive index. These two key parameters allow us to distinguish high and low adhesive cell-substrate contacts. Furthermore, vaTIRF provides cell-substrate binding energy, thus revealing a correlation between cell contractility and cell-substrate binding energy. Here, we highlight the quantitative measurements achieved by vaTIRF on U87MG glioma cells expressing different amounts of α 5 integrins and distinct motility on fibronectin. Regarding integrin expression level, data extracted from vaTIRF measurements, such as the number and size of high adhesive contacts per cell, corroborate the adhesiveness of U87MG cells as intended. Interestingly enough, we found that cells overexpressing α 5 integrins present a higher contractility and lower adhesion energy.
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Affiliation(s)
- Dalia El Arawi
- Light, nanomaterials, nanotechnologies, ERL CNRS 7004, Université de Technologie de Troyes, Troyes, France
| | - Cyrille Vézy
- Light, nanomaterials, nanotechnologies, ERL CNRS 7004, Université de Technologie de Troyes, Troyes, France
| | - Régis Déturche
- Light, nanomaterials, nanotechnologies, ERL CNRS 7004, Université de Technologie de Troyes, Troyes, France
| | - Maxime Lehmann
- Laboratoire de Bioimagerie et Pathologies, UMR CNRS 7021, Université de Strasbourg, Faculté de Pharmacie, Illkirch, France
| | - Horst Kessler
- Department Chemie, Institute for Advanced Study, Technische Universität München, Garching, Germany
| | - Monique Dontenwill
- Laboratoire de Bioimagerie et Pathologies, UMR CNRS 7021, Université de Strasbourg, Faculté de Pharmacie, Illkirch, France
| | - Rodolphe Jaffiol
- Light, nanomaterials, nanotechnologies, ERL CNRS 7004, Université de Technologie de Troyes, Troyes, France
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Optometry for a short-sighted microscope. Biophys J 2021; 120:4301-4304. [PMID: 34509502 DOI: 10.1016/j.bpj.2021.09.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2021] [Revised: 09/01/2021] [Accepted: 09/07/2021] [Indexed: 11/21/2022] Open
Abstract
Evanescent-wave scattering is a topic in classical electrodynamics and in the study of colloidal particles near a boundary. However, how such near-surface scattering at subcellular refractive-index heterogeneities degrades the excitation confinement in biological total internal reflection fluorescence microscopy has not been well studied. An elegant theoretical work by Axelrod and Axelrod now addresses this very relevant question and reveals that-even when scattered-evanescent light preserves some of its surprising optical properties.
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Vázquez-Estrada O, Acevedo-Barrera A, Nahmad-Rohen A, García-Valenzuela A. Analysis of wavelength-scale 1D depth-dependent refractive-index gradients at an interface by their effects on the internal reflectance near the critical angle. OPTICS LETTERS 2021; 46:4801-4804. [PMID: 34598203 DOI: 10.1364/ol.434090] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Accepted: 08/15/2021] [Indexed: 06/13/2023]
Abstract
Light's internal reflectivity near a critical angle is very sensitive to the angle of incidence and the optical properties of the external medium near the interface. Novel applications in biology and medicine of subcritical internal reflection are being pursued. In many practical situations, the refractive index of the external medium may vary with respect to its bulk value due to different physical phenomena at surfaces. Thus, there is a pressing need to understand the effects of a refractive-index gradient at a surface for near-critical-angle reflection. In this work, we investigate theoretically the reflectivity near the critical angle at an interface with glass assuming the external medium has a continuous depth-dependent refractive index. We present graphs of the internal reflectivity as a function of the angle of incidence, which exhibit the effects of a refractive-index gradient at the interface. We analyze the behavior of the reflectivity curves before total internal reflection is achieved. Our results provide insight into how one can recognize the existence of a refractive-index gradient at the interface and shed light on the viability of characterizing it.
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Peng L, Tang D, Wang J, Chen R, Gao F, Zhou L. Robust incident angle calibration of angle-resolved ellipsometry for thin film measurement. APPLIED OPTICS 2021; 60:3971-3976. [PMID: 33983336 DOI: 10.1364/ao.419357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Accepted: 04/12/2021] [Indexed: 06/12/2023]
Abstract
Angle-resolved ellipsometry with back focal plane imaging has been found to be of increasing importance in recent industrial sensing by virtue of its rich information provided at various incident and azimuthal angles. To achieve high sensing accuracy, the incident angles of a back focal plane must be accurately calibrated. For this purpose, a simple and robust incident angle calibration method based on full-field Brewster angle fitting is proposed, without expensive tools or complex operations. With this method, a back focal plane image is first captured from boundary reflectance through a high-numerical-aperture objective. By extracting annular data from the image, radius-dependent ellipsometric parameters $ (\psi,{\Delta)}$ are calculated. At the end, the radii of the back focal plane are mapped to the angle of incidence by using a fitted Brewster angle as the reference. The method is validated by simulation and experiments using a homemade angle-resolved ellipsometer and a commercial spectroscopic ellipsometer. The results show that the proposed method provides a 75% error reduction approximately from generally used methods.
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Liu W, Yuan Y, Zhang C, Han Y, Zhang Z, Xu L, Hao X, Kuang C, Liu X. Quantitative objective-based ring TIRFM system calibration through back focal plane imaging. OPTICS LETTERS 2020; 45:3001-3004. [PMID: 32479443 DOI: 10.1364/ol.394116] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 04/25/2020] [Indexed: 06/11/2023]
Abstract
Being the established imaging tool for cell membrane-associated studies, total internal reflection fluorescence microscopy (TIRFM) still has some limitations. The most important one is the inhomogeneous evanescent excitation field mainly caused by the large-angle and fixed-azimuth illumination scheme, which can be eliminated by using ring-shaped illumination (ring TIRFM). However, it is challenging in assembling a ring TIRFM system with precise parameter control that works well. Here we emphasize the quantification of the ring TIRFM system and introduce a robust calibration routine to simultaneously rectify the asymmetry of the spinning light beam and determine the crucial experimental parameter, i.e., the incident angle. The calibration routine requires no specific sample preparation and is entirely based on the automatic back focal plane manipulation, avoiding possible errors caused by the sample difference and manual measurement. Its effectiveness is experimentally demonstrated by both the qualitative and quantitative comparisons of the images acquired using different samples, illumination schemes, and calibration approaches. These characteristics should enable our approach to greatly improve the practicability of TIRFM in life sciences.
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Oheim M, Salomon A, Brunstein M. Supercritical Angle Fluorescence Microscopy and Spectroscopy. Biophys J 2020; 118:2339-2348. [PMID: 32348720 PMCID: PMC7231923 DOI: 10.1016/j.bpj.2020.03.029] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2020] [Revised: 03/13/2020] [Accepted: 03/23/2020] [Indexed: 01/06/2023] Open
Abstract
Fluorescence detection, either involving propagating or near-field emission, is widely being used in spectroscopy, sensing, and microscopy. Total internal reflection fluorescence (TIRF) confines fluorescence excitation by an evanescent (near) field, and it is a popular contrast generator for surface-selective fluorescence assays. Its emission equivalent, supercritical angle fluorescence (SAF), is comparably less established, although it achieves a similar optical sectioning as TIRF does. SAF emerges when a fluorescing molecule is located very close to an interface and its near-field emission couples to the higher refractive index medium (n2 >n1) and becomes propagative. Then, most fluorescence is detectable on the side of the higher-index substrate, and a large fraction of this fluorescence is emitted into angles forbidden by Snell's law. SAF, as well as the undercritical angle fluorescence (UAF; far-field emission) components, can be collected with microscope objectives having a high-enough detection aperture (numerical aperture >n2) and be separated in the back focal plane by Fourier filtering. The back focal plane image encodes information about the fluorophore radiation pattern, and it can be analyzed to yield precise information about the refractive index in which the emitters are embedded, their nanometric distance from the interface, and their orientation. A SAF microscope can retrieve this near-field information through wide-field optics in a spatially resolved manner, and this functionality can be added to an existing inverted microscope. Here, we describe the potential underpinning of SAF microscopy and spectroscopy, particularly in comparison with TIRF. We review the challenges and opportunities that SAF presents from a biophysical perspective, and we discuss areas in which we see potential.
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Affiliation(s)
- Martin Oheim
- Saints-Pères Paris Institute for the Neurosciences, Université de Paris, CNRS, Paris, France.
| | - Adi Salomon
- Saints-Pères Paris Institute for the Neurosciences, Université de Paris, CNRS, Paris, France; Department of Chemistry, Institute of Nanotechnology and Advanced Materials, Bar-Ilan University, Ramat-Gan, Israel
| | - Maia Brunstein
- Saints-Pères Paris Institute for the Neurosciences, Université de Paris, CNRS, Paris, France; Chaire d'Excellence Junior, Université Sorbonne Paris Cité, Paris, France
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