A method for spatially high-resolution investigation of a structure, marked with a fluorescing substance, of a specimen, the substance being capable of being repeatedly converted from a first state into a second state, the first and second states differing from one another in terms of at least one optical property, encompasses the following steps. Firstly, bring the substance, in a specimen region to be sensed, into the first state; and inducing the second state by way of an optical signal, spatially delimited subregions within the specimen region to be sensed being blanked out in controlled fashion. A protein-target protein-in living cells is used as a structure that is marked with the fluorescing substance, by the fact that a ligand complex encompassing the fluorescing substance is bound to an enzyme via an enzymatic reaction in the cell, the enzyme being expressed as a fusion protein together with the target protein to be investigated.
Method for Spatially High-Resolution Investigation of a Structure, Marked With a Fluorescing Substance, of a Specimen