Breaking the Diffraction Barrier Scientists used to view the
diffraction barrier as a hefty obstacle to seeing further inside
cells. However, in the past few years, a flurry of technical
advancements have improved the resolving power of fluorescence
microscopy by quantum leaps. Collectively known as “super-
resolution” imaging, these methods are poised to provide
biologists with unprecedented images of fine cellular structures
and their dynamics inside the cell. Two general strategies for
breaking the diffraction barrier have developed independently.
The first, called STED microscopy, works by the modulation of
fluorophores - chemicals that can re-emit light upon excitation
- by patterns of light inside a diffraction-limited region. In
the second technique, applied in both PALM (short for Photo-
Activated Localisation Microscopy) and STORM (3D Stochastic
Optical Reconstruction Microscopy) microscopy, single-molecule
imaging techniques are used to measure the position of
individual molecules within a diffraction