Diffraction-unlimited optical microscopy

Optical microscopy, and fluorescence microscopy in particular, has emerged as one of the most powerful and convenient microscopic tools available today. This power does come at a price, however, in terms of a limited spatial resolution: traditionally fluorescence microscopy has been limited by diffraction to a resolution of a few hundred nanometers, far too large to discern nanostructuring in biological or material samples. Recent conceptual advances have emerged that challenge this once-thought 'unbreakable' barrier, and fluorescence microscopy with nanometer resolution is now within reach. In this review we highlight some of the approaches that have made this paradigm shift possible.