Photoactivatable Synthetic Dyes for Fluorescence Imaging at the Nanoscale.

The transition from conventional to photoactivatable fluorophores can bring the resolution of fluorescence images from the micrometer to the nanometer level. Indeed, fluorescence photoactivation can overcome the limitations that diffraction imposes on the resolution of optical microscopes. Specifically, distinct fluorophores positioned within the same subdiffraction volume can be resolved only if their emissions are activated independently at different intervals of time. Under these conditions, the sequential localization of multiple probes permits the reconstruction of images with a spatial resolution that is otherwise impossible to achieve with conventional fluorophores. The irreversible photolysis of protecting groups or the reversible transformations of photochromic compounds can be employed to control the emission of appropriate fluorescent chromophores and allow the implementation of these ingenious operating principles for superresolution imaging. Such molecular constructs enable the spatiotemporal control that is required to avoid diffraction and can become invaluable analytical tools for the optical visualization of biological specimens and nanostructured materials with unprecedented resolution.