Photon-Efficient Aberration Correction for 3D-STED Imaging of Thick Biological Specimens Using Sensorless Adaptive Optics

Stimulated emission depletion (STED) microscopy is a powerful super-resolution imaging technique for investigating the subcellular structure of biological samples in all three spatial dimensions. Its application to thick specimens is challenging, however, as sample-induced optical aberrations distort the intricate phase patterns of the STED beams and, consequently, their focal intensity distribution. Notably, the central intensity minimum, which is essential for resolution enhancement, is lifted at larger sample depths. Here we present a technique for correction of STED beam aberrations featuring minimal light exposure of the samples to avoid photobleaching and phototoxicity. We quantify STED beam aberrations by using modal wavefront sensing with spatial light modulators (SLMs) as adaptive optics (AO) elements based on reflection imaging of gold beads immobilized at the top and bottom surfaces enclosing the thick (>= 100 mu m) biological specimen. Based on this information, wavefront aberrations can be successfully compensated for all depths by linear interpolation of the correction parameters. We demonstrate the excellent imaging performance of AO 3D stimulated emission double depletion (STEDD) microscopy on cell nuclei of zebrafish embryos.