Optical tweezers use a highly focused laser to trap micrometric transparent objects and manipulate them.
This technique allows to micromanipulate beads, parasite, cells and put them in contact with a partner substrate, monitoring in transmission or fluorescence microscopy the outcomes of the interaction. Using a micrometric trapped bead as a probe and the laser as a very soft spring, we also measure forces with a pN force resolution.

Upper image sequence : a tube of membrane is pulled from a T cell with a fluorescently labelled membrane. The cell is moved away from the trapped bead which position is kept constant. Lower part : typical force vs. time profile of pulling such a nanotube.

We used our setup to (a) present toxoplasma oocytes to macrophages and follow the phagocytosis (b) measure molecular forces between artificial substrates (c) press and pull on cellular surfaces to measure cell mechanics, in particular membrane cell tension. We developped methodologies for experiments, in particular regarding decorations of beads with given molecules, and open-source softwares for data processing.

Thierry Galliano, Guillaume Gay, Laurent Limozin, Pierre-Henri Puech*. OT_Analysis: a software for rich analysis of force curves when probing living cells with optical tweezers. Journal of Open Source Software, 8(90), 4877, https://doi.org/10.21105/joss.04877

Fabio Manca, Gautier Eich, Omar N’Dao, Lucie Normand, Kheya Sengupta, Laurent Limozin, Pierre-Henri Puech. Probing mechanical interaction of immune receptors and cytoskeleton by membrane nanotube extraction. Scientific Reports 13, Article number: 15652 (2023). https://www.nature.com/articles/s41598-023-42599-9