Chemical labeling or the use of chemical tags utilizes the interaction between a small molecule and a specific genetic amino acid sequence.  Chemical labeling is sometimes used as an alternative for GFP. Synthetic proteins that function as fluorescent probes are smaller than GFPs, and therefore can function as probes in a wider variety of situations. Moreover, they offer a wider range of colors and photochemical properties.  With recent advancements in chemical labeling, Chemical tags are preferred over fluorescent proteins due to the architectural and size limitations of the fluorescent proteins characteristic β-barrel.  Alterations of fluorescent proteins would lead to loss of fluorescent properties.