Lighting up cells: labelling proteins with fluorophores. 
During the past decade, rapid improvements have been made in the tools available for labelling proteins within cells, which has increased our ability to unravel the finer details of cellular events.  One significant reason for these advances has been the development of fluorescent proteins that can be incorporated into proteins by genetic fusion to produce a fluorescent label.  In addition, new techniques have made it possible to label proteins with small organic fluorophores and semiconductor nanocrystals.