Thermally Adaptive Surface Microscopy for brain functional imaging

Fluorescence microscopes can capture the dynamics of living cells with high spatio-temporal resolution in a single plane. However, monitoring rapid and dim fluorescence fluctuations, e.g. induced by neuronal activity in the brain, remains challenging for 3D-distributed emitters due to out-of-focus fluorescence background, a restricted photon budget, and the speed limit of conventional scanning systems. Here, we introduce a Thermally Adaptive Surface strategy, allowing the parallel imaging of 3D-distributed objects at speeds only limited by the camera framerate or photon budget. This microscope add-on leverages on an array of thermally tuneable microlenses that offers low chromatic aberration and high transmission, and can be combined with patterned illumination to provide optical sectioning. We demonstrate its potential in vivo, by simultaneously monitoring fast fluorescent dynamics at different depths in the zebrafish larval brain, at 0.5 kHz rate within a 360x360x90 µm^3 observable volume.