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Rational design of activatable photosensitizers for controlled generation of singlet oxygen remains a challenge for precise photodynamic therapy (PDT).Herein,we present an aptamer-based nanodevice for adenosine 5'-triphosphate (ATP)-activatable bioimaging and PDT.The nanodevice is constructed by modifying ATP-responsive duplex DNA units and polyethylene glycol on the surface of a gold nanoparticle (AuNP) through the thiolate-Au chemistry.The DNA units were designed by the hybridization of the ATP aptamer strand with a methylene blue (MB)-modified complementary DNA (cDNA).The close proximity of MB to the surface of AuNP results in the low photodynamic activity of MB (OFF state).Once internalized into cancer cells,the ATP-binding induced conformation switch of aptamer strand leads to the release of the MB-bearing DNA strand from AuNPs,resulting in the activatable generation of singlet oxygen under light irradiation (ON state).We demonstrate that the DNA nanodevice represents a promising platform for ATP-responsive bioimaging and specific PDT in vitro and in vivo.This work highlights a potential way for specific tumor diagnosis and therapy.