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Univ. Paris-Saclay

Sujet de stage / Master 2 Internship

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Development of a spray-plunging method for cryoTEM observations at short timescale

Contact: GOBEAUX Frederic, , frederic.gobeaux@cea.fr, +33 1 69 08 55 21
Summary:
The aim of this internship is to develop a method combining microfluidics, spray and rapid-freezing to prepare samples for cryo-TEM. This subject can be adapted for different academic levels (up to Master 2).
Possibility of continuation in PhD: Non
Deadline for application:30/04/2022

Full description:
Our “green economy” (photovoltaics, lithium batteries) largely relies on the rare-earth (RE) elements; but their extraction raises heavy ecological concerns, and their recycling is scarce. Any progress in the separation and precipitation processes will benefit the global environmental balance.

Our recent study of the co-precipitation of cerium ions by oxalic acid in water, a key step in some recovery process of RE, has revealed the spontaneous formation of “mineral nanodroplets” right after reagent mixing (Durelle et al. to be submitted). These nanodroplets consist in a reactant-rich liquid that convert into cerium oxalate crystals after several tens of seconds. These droplets have been imaged with cryoTEM 7.5 s after the mixing. This newly reported nanophase could benefit separation and recovery processes, but its conditions and mechanisms of formation needs a deeper investigation.

Its thorough characterization implies being able to probe the system just after mixing, when the system still consists of free ions. This is achievable thanks to ultrafast microfluidic mixers (tmix < 1 ms), fabricated using soft-lithography techniques, and recently used by our team to study calcium carbonate precipitation by X-ray scattering.

The aim of this internship is to develop a set-up enabling to freeze a solution as quickly as possible after mixing the reactants. In practice, we need to combine microfluidic mixers with a freeze-plunger (see Chen & Frank and Feng et al.). Both components already exists, but they need to be interfaced with a spray in order to quickly collect the solution at the mixer exit on an electron microscope grid plunging into liquid ethane. The intern will have to develop this sprayer with microfluidic tools and find the correct conditions and parameters to obtain observable samples.

References:
Chen, B.; Frank, J. Two Promising Future Developments of Cryo-EM: Capturing Short-Lived States and Mapping a Continuum of States of a Macromolecule. Microscopy (Oxf) 2016, 65 (1), 69–79. https://doi.org/10.1093/jmicro/dfv344

Feng, X.; Fu, Z.; Kaledhonkar, S.; Jia, Y.; Shah, B.; Jin, A.; Liu, Z.; Sun, M.; Chen, B.; Grassucci, R. A.; Ren, Y.; Jiang, H.; Frank, J.; Lin, Q. A Fast and Effective Microfluidic Spraying-Plunging Method for High-Resolution Single-Particle Cryo-EM. Structure 2017, 25 (4), 663-670.e3. https://doi.org/10.1016/j.str.2017.02.005
Technics/methods used during the internship:
Microfluidics, cryo-TEM

Laboratory
Tutor of the internship

 

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