Tryptophan optical probe, preparation method therefor and use thereof

An optical sensor comprising:

• a tryptophan-sensitive polypeptide having tryptophan-binding function and an optically active polypeptide, wherein the tryptophan-sensitive polypeptide has a sequence having at least 80% sequence identity with SEQ ID NO:
• 1 and having tryptophan-binding function, and wherein the optically active polypeptide is a fluorescent protein or a functional variant thereof and is operably fused into the tryptophan-sensitive polypeptide at one or more positions of the tryptophan-sensitive polypeptide selected from the group consisting of:
• 263/265, 263/266, 263/267 and 263/268, wherein the optical sensor responds to tryptophan with the change in optical property.