Stimulated emission depletion (STED) nanoscopy of a fluorescent protein-labeled organelle inside a living cell

TLDR

The study demonstrates far‑field optical imaging of the endoplasmic reticulum in living mammalian cells with subdiffraction resolution. The authors use STED microscopy on a yellow fluorescent protein tag and perform time‑lapse recordings to track ER morphology. STED imaging achieved <50 nm lateral resolution, a 4‑fold improvement over confocal, and a 3‑fold axial resolution gain, enabling nanoscale 3‑D imaging of ER in living cells.

Abstract

We demonstrate far-field optical imaging with subdiffraction resolution of the endoplasmic reticulum (ER) in the interior of a living mammalian cell. The diffraction barrier is overcome by applying stimulated emission depletion (STED) on a yellow fluorescent protein tag. Imaging individual structural elements of the ER revealed a focal plane ( x , y ) resolution of &lt;50 nm inside the living cell, corresponding to a 4-fold improvement over that of a confocal microscope and a 16-fold reduction in the focal-spot cross-sectional area. A similar gain in resolution is realized with both pulsed- and continuous-wave laser illumination. Images of highly convoluted parts of the ER reveal a similar resolution improvement in 3D optical sectioning by a factor of 3 along the optic axis ( z ). Time-lapse STED recordings document morphological changes of the ER over time. Thus, nanoscale 3D imaging of organelles in the interior of living cells greatly expands the scope of light microscopy in cell biology.