Even though biological tissues are highly dynamic at many different scales, traditional optical microscopes can often enable to track only a portion of them. While the optical diffraction limit prevents the detection of submicrometric displacements, and imposes a trade-off between spatial and temporal resolution, the scattering properties of tissues prevent the imaging in depth. Besides, fluorescence imaging only looks at a small subset of targets, and usually misses the complexity and compacity of cells.

In this presentation, I will present a novel non conventional optical microscope, named dynamic full field optical coherence tomography. It takes advantage of optical interferences to provide label-free detection of many different biological objects at several hundred microns deep inside tissues, and to measure their axial displacements with nanometric accuracy. We designed a new imaging paradigm that uses the intrinsic biological dynamics to create a contrast based on the active intracellular transport, and specifically detects living cells inside tissues.

Taking advantage of such technology, I will show a first main application for the label-free characterization of ex vivo retina samples, in which we could detect most cells in all layers of the retina, as well as their morphological parameters, and their metabolic activity.

I will then switch to a very different application which consists in measuring the flow dynamics of small vesicles secreted in the cerebrospinal fluid (CSF) in zebrafish spinal cord. This allowed us to perform the first quantification of CSF flow in central canal and helped us to understand the mechanisms that drive CSF circulation. Our data also suggests that CSF is involved in long-range communication between neurons distributed along the spinal cord, and involved in the sensory-motor integration, as well as in the development of the antero-posterior axis.