Exploring ultrastructure in nanomaterials, cells and biological tissues by polarized microscopy

Fluorescence to nonlinear coherent optical microscopy can reveal important spatial properties in nanomaterials, cells and biological tissues from fixed situations to in vivo dynamics. While microscopy can guide interpretation through morphological observations at the sub-micrometric scale, optical imaging cannot directly access the way molecules are organized in specific ulstrastructures, occuring at the molecular scale. This property, which is important in many fields, from nanomaterials engineering to biomechanics, is today most often studied using electron microscopy or X ray diffraction, which are not compatible with real time imaging.

We will show that reporting molecular organization in protein filaments, aggregates or lipid membranes down to the nano scale is made possible using fluorescence polarization resolved optical microscopy, which takes advantage of the orientation-sensitive coupling between optical excitation fields and molecular transition dipole moments [1]. This approach, which can be extended to super resolution microscopy, has revealed ultrastructural imaging capabilities in the cell cytoskeleton [2]. Polarized imaging has also been also applied to nonlinear optical imaging in nanostructures, revealing nanoscale plasmonic vectorial properties in metal nanostructures [3] and structrural heterogeneities in dielectric nanoparticles.

[1] S. Brasselet , “Polarization resolved nonlinear microscopy: application to structural molecular and biological imaging”, Advances in Optics and Photonics 3, pp. 205–271 (2011)

[2] C.A. Valades Cruz, H. A. Shaban, A. Kress, N. Bertaux, S. Monneret, M. Mavrakis, J. Savatier, S. Brasselet, Quantitative nanoscale imaging of orientational order in biological filaments by polarized super-resolution microscopy, Proc. Natl. Acad. Sci. 113 (7) E820-E828 (2016)

[3] N.K. Balla, C. Rendon-Barraza, L.M. Hoang, P. Karpinski, E. Bermudez, S. Brasselet, Polarized nonlinear nanoscopy of metal nanostructures, ACS Photonics 4 (2), pp 292–301 (2017)

Bio: Sophie Brasselet is an optical physicist. She obtained her Ph.D in 1997 at University Paris-Sud, France on nonlinear optical properties of polymers and spent a two years postdoc at UCSD (1998) and Stanford University (1999) in the USA, to develop single fluorescent molecules imaging in cells. After six years at ENS Cachan, France, as an assistant professor on nonlinear microscopy and optical manipulation of single molecules, she is now working as a research director at Institute Fresnel, Marseille, France. For the last fifteen years, she has developed novel nonlinear microscopy and super-resolution fluorescence tools based on polarized light, dedicated to nanomaterials and biomolecular structural imaging. Using polarized fluorescence imaging approaches down to the single molecule level, she has pioneered optical structural investigations at the nanoscale in cells. She has also extended the concept to label free nonlinear imaging, with the goal to develop tools for the understanding neuropathologies. These techniques are now applied in a large range of fields, including material sciences.