GSD microscopy

[2] It is the second concept to overcome the diffraction barrier in far-field optical microscopy published by Stefan Hell.

In one condition, the marker can freely be excited from ground state and returns spontaneously via emission of a fluorescence photon.

Switching between these two states (bright and dark) by applying light fulfills all preconditions for the RESOLFT concept and subwavelength scale imaging, and therefore images with very high resolution can be obtained.

For successful implementation, GSD microscopy requires either special fluorophores with high triplet yield,[4] or removal of oxygen by use of various mounting media such as Mowiol or Vectashield.

Therefore, fluorescence only still takes place at the center of the microscope's focal spot and the spatial resolution is increased.

Comparison of resolution between standard confocal microscopy and GSD microscopy. Left: Confocal recording of vacancies in diamonds. Single spots cannot be separated. Right: GSD recording of the same location. Single vacancies are clearly visible. The size of the pointlike vacancies, corresponding to the microscope's resolution, is about 15 nm.