Targeting dyes for biology

Measurements of the structure, function, and interactions of proteins are crucial to our understanding of living systems. Biologists and chemists have developed a variety of methods to study these proteins both in vitro and in vivo. Among the methods to observe proteins, fluorescence spectroscopy has proven to be a unique tool in cell biology and biophysics, capable of revealing the dynamic nature of many processes. The prime requirement for observing a protein of interest (POI) using fluorescence spectroscopy is that the protein has to be labeled with a fluorescent probe. While in vitro labeling of biomolecules for biochemical methods is relatively straightforward as it relies on standard functional groups in purified proteins (typically cysteines) for covalent labeling, labeling POIs in living cells is a very formidable task. Labeling inside the cell requires balancing trade-offs between spatiotemporal control, specificity, selectivity, and modularity (e.g., the ability to swap one dye for another). Developments in fluorescent probes and microscopy techniques over the last two decades have given us tools that address all these challenges, thus making fluorescent labels the tool of choice for live cell imaging.