Why is GFP unique in detection?
Green fluorescent protein isolated from jellyfish Aequorea victoria contains intrinsic chromophore formed autocatalytically from tripeptide Ser-Tyr-Gly cyclization and oxidation within beta-barrel structure. No external cofactor, substrate or enzymatic activation is required beyond molecular oxygen for maturation. Once folded, it absorbs blue light near 395 nm and emits green photons near 509 nm. This self-contained fluorescence distinguishes it from luciferase which needs luciferin and ATP or peroxidase requiring luminol. Consequently GFP can be expressed as genetic fusion tag enabling live cell imaging, lineage tracing and biosensor construction without exogenous chemistry.
Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.