Cryo-XRF study of platinum-based O2 nanosensors internalized within microalgal cells

Assessing intracellular O2 resolved spatially and temporally in the fundamentally and biotechnologically important microalgae Chlamydomonas reinharditii is crucial for understanding their physiology. We developed a luminescent sensor for O2 made of a platinum complex-labelled polymeric nanoparticle which is successfully internalized in C. reinhardtii cells and whose signal can be read out without significantly interfering with the light-driven photosynthesis. This sensor is prone to provide unprecedented dynamic measurements of O2 concentrations within photosynthetic cells and bring new insights about the complex balance between consumption and production of O2 at the subcellular level. Yet, reaching this goal requires to precisely localize the sensor within the complex 3D ultrastructure of the microalgae. The proposed correlative acquisition of epifluorescence images and XRF tomograms at ID16A on cryogenized C. reinhardtii cells will enable us to perform such a sensor localization.