We demonstrate the reduction of oxidized to reduced glutathione in the presence of glutathione reductase enzymebased on the modulation in photoluminescent quenching efficiency between the perylene bisimide chromophoreTPPCA and gold nanoparticles (AuNPs). The TPPCA-AuNPs assembly shows a turn-on fluorescent signal in thepresence of reduced glutathione, which provides a new concept to measure the balance of glutathione in a creature.