FPs, including green uorescent protein (GFP) from A. victoria (GFP) and dsRed, have chromophores buried within their tertiary structures that can absorb and emit light.9 The chromophore is produced autocatalytically in an aerobic environment through a process known as maturation. Generally, an 11-stranded β-barrel makes up the tertiary structure, which protects the chromophore from the solvent. The specic microenvironment of each chromophore is shaped by the surrounding amino acids and contributes to the different spectral properties exhibited by different uorophores.