Aberration correction in STED microscopy to increase imaging depth in living brain tissue

We demonstrate an approach based on adaptive optics to improve the spatial resolution of STED microscopy inside thick biological tissue by a priori correction of spherical aberrations as a function of imaging depth. We first measured the aberrations in a phantom sample of gold and fluorescent nanoparticles suspended in an agarose gel with a refractive index closely matching living brain tissue. Using a spatial light modulator to apply corrective phase shifts, we imaged neurons in living brain slices and show that the corrections can substantially increase image quality. Specifically, we could measure structures as small as 80 nm at a depth of 90 m inside the biological tissue, and obtain a 60% signal increase after correction.