Chemical tags have been tailored for imaging technologies more so than fluorescent proteins because chemical tags can localize photosensitizers closer to the target proteins. Proteins can then be labeled and detected with imaging such as super-resolution microscopy, Ca-imaging, pH sensing, hydrogen peroxide detection, chromophore assisted light inactivation, and multi-photon light microscopy.  In vivo imaging studies in live animals have been performed for the first time with the use of a monomeric protein derived from the bacterial haloalkane dehalogenase known as the Halo-tag.  The Halo-tag covalently links to its ligand and allows for better expression of soluble proteins.