Chemical tags for site-specific fluorescent labeling of biomolecules

This review focuses on the various approaches to covalently attach a chromophore to a biomolecule of interest in site-specific manner. Novel methods like inverse electron-demand Diels-Alder reaction, Pictet-Spengler ligation and enzyme tags like SNAP and Halo-tags are critically discussed and compared to established techniques like copper-free click reaction and native chemical ligation. Selected examples in which the tags have been exploited for in vitro or in vivo imaging are reviewed and evaluated.