Although fluorescent dyes may not have the same sensitivity as radioactive probes, they are able to show real-time activity of molecules in action. Moreover, radiation and appropriate handling is no longer a concern.
With the development of fluorescent tagging, fluorescence microscopy has allowed the visualization of specific proteins in both fixed and live cell images. Localization of specific proteins has led to important concepts in cellular biology such as the functions of distinct groups of proteins in cellular membranes and organelles.  In live cell imaging, fluorescent tags enable movements of proteins and their interactions to be monitored.
Latest advances in methods involving fluorescent tags have led to the visualization of mRNA and its localization within various organisms.  Live cell imaging of RNA can be achieved by introducing synthesized RNA that is chemically coupled with a fluorescent tag into living cells by microinjection.  This technique was used to show how the oskar mRNA in the Drosophila embryo localizes to the posterior region of the oocyte.