Breaking the diffraction resolution barrier in far-field microscopy by molecular optical bistability

Abstract

We demonstrate the breaking of the diffraction resolution barrier in far-field fluorescence microscopy by photoswitching ensembles of optically bistable organic molecular markers from a non-fluorescent to a fluorescent state and back. The photoswitching is accomplished by an isomerization reaction of a photochromic compound serving as a reversible energy acceptor of a fluorescent compound. The surpassing of the diffraction barrier with power levels of only a few hundred W cm(-2) of continuous wave irradiation is evidenced both in the effective point spread function and in the fluorescence images of test samples.