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Evanescent field patterning for optogenetic activation of live cells

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About 10 years ago a Nobel Prize was awarded to the invention of fluorescent proteins. Genetically encoded fluorescent molecules opened the route for a previously unimaginable amount of functional imaging experiments. The recent development of optogenetics probe is another revolution, since the isomerization state of this new kind of engineered proteins can be controlled, in living cells, with light illumination (generally in the 400 – 540 nm range). Upon optical activation these molecules interact with cellular partners, initiating specific biological activity (such as the contractile machinery, adhesion, motility, etc.). Cell response can be modulated by the spatio-temporal properties of the signal. Hence, having a better spatio-temporal control of the photoactivation process is a key point to understand the dynamics of cellular biological processes.

With this goal in mind, we propose to develop a setup for programmable patterned evanescent field illumination, in order to directly activate the basal membrane of a cell adhering on a substrate, rather than the standard cytosolic activation. This implies two conditions : i) the laser beam incident on the coverslip/aqueous medium must have a incidence angle above the critical angle to be totally reflected ; ii) its angular distribution should be tailored to obtain the desired pattern. Since these two conditions must fulfill the constraint of diffraction law, there is a compromise between penetration depth and spatial resolution.

The first step will consist in simulating the simplest optical configuration in which a mask is used to spatially modulate the illumination beam. In this case, the penetration depth, as well as the spatial resolution of the transmitted pattern, will be calculated. In a second step, wavefront control will be performed by the means of a Digital Micromirror Device, in order to optimize the illumination geometry by using a holographic approach.

This internship requires a background in optics/physics. It will take place at the Laboratory for Interdisciplinary Physics (LIPhy), in close collaboration with biologists of the Institute for Advanced Biosciences. It will involve optical simulations and first experiments on an optical bench to define the best optical configuration compatible with a microscope environment.

Contact :

Irène Wang – tél. 04 76 51 47 29 – irene.wang@univ-grenoble-alpes.fr
Antoine Delon – tél. 04 76 63 58 01– antoine.delon@univ-grenoble-alpes.fr