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Optical nanotopography by position modulation

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The cell membrane is the place of crucial 3D and dynamic processes (adhesions, endocytosis, virus entry and budding) which are difficult to image and track using existing microscopy techniques. Conventional techniques, such as confocal microscopy, can acquire stacks of 2D images, but they are too slow for 3D tracking and their spatial resolution in the axial direction (500 nm) is larger than the typical sizes of interest (10-100nm). Other techniques include Total Internal Reflection microscopy (TIRF) which confines excitation at the vicinity of an interface and allow imaging the adhesive side of the cell, but does not yield topographic information, or Atomic Force Microscopy which provides topography and mechanics through direct physical contact but only on the upper side of cells.

This project focuses on the development of a new method based on scanning microscopy where the PSF (Point Spread Function) is modulated in position along the z axis. The resulting modulation ratio, obtained using a lock-in approach, varies linearly with the distance to the fluorescent surface (e.g. cell membrane). This method has the advantage to be purely optical, non-invasive and suitable for both outer membranes as well as internal cellular structures. Its potential capabilities include super-resolution (down to 20 nm) topographic imaging and real-time topography tracking.

The proposed work aims at bringing a proof-of-principle demonstration of this method. It will benefit from existing experimental development : A home-built confocal microscopy setup including a piezoelectric stage for axial modulation has been developed, as well as instrument control and interfacing scripts in Python.

We are looking for a student with an interest in instrument development to evaluate and improve the performance of this setup, by measuring synthetic samples (layers of fluorescent polymer) and cell membranes. The internship will take place in an interdisciplinary team with people specialized in physics, optics and biology.

Contact :

Irène Wang – tél. 04 76 51 47 29 –
Aurélie Dupont – tél. 04 76 63 58 16–