Principle
In GSD microscopy fluorescent markers are used. In one condition the marker can freely be excited from ground state and returns spontaneously via emission of a fluorescence photon. However if light of appropriate wavelength is additionally applied the dye can be excited to a long-lived dark state, i.e. a state where no fluorescence occurs. As long as the molecule is in the long-lived dark state (e.g. a triplet state), it cannot be excited from the ground state. Switching between these two states (bright and dark) by applying light fulfills all preconditions for the RESOLFT concept and subdiffraction imaging and images with very high resolution can be obtained. For successful realization, GSD microscopy requires either special fluorophores with high triplet yield, or removal of oxygen by use of various mounting medium like Moviol or Vectashield.
The implementation in a microscope is very similar to Stimulated Emission Depletion Microscopy, however it can operate with only one wavelength for excitation and depletion. Using an appropriate ring-like focal spot for the light that brings the molecules into the dark state, the fluorescence can be quenched at the outer part of the focal spot. Therefore fluorescence only still takes place at the center of the microscope's focal spot and the spatial resolution is increased.
Read more about this topic: GSD Microscopy
Famous quotes containing the word principle:
“The sons of Judah have to choose that God may again choose them.... The divine principle of our race is action, choice, resolved memory.”
—George Eliot [Mary Ann (or Marian)
“Now, what I want is, Facts. Teach these boys and girls nothing but Facts. Facts alone are wanted in life. Plant nothing else, and root out everything else. You can only form the minds of reasoning animals upon Facts: nothing else will ever be of any service to them. This is the principle on which I bring up my own children, and this is the principle on which I bring up these children. Stick to Facts, sir!”
—Charles Dickens (1812–1870)
“It were as wise to cast a violet into a crucible that you might discover the formal principle of its colour and odour, as seek to transfuse from one language into another the creations of a poet. The plant must spring again from its seed, or it will bear no flower—and this is the burthen of the curse of Babel.”
—Percy Bysshe Shelley (1792–1822)