Positron emission tomography(PET)imaging has received special attention owing to its higher sensitivity,temporal resolution,and unlimited tissue penetration.The development of tracers that target specific molecules is therefore essential for the development and utility of clinically relevant PET procedures.However,64Cu as a PET imaging agent generally has been introduced into biomaterials through macrocyclic chelators,which may lead to the misinterpretation of PET imaging results due to the detachment and transchelation of 64Cu.In this study,we have developed ultrasmall chelator-free radioactive [64Cu]Cu nanoclusters using bovine serum albumin(BSA)as a scaffold for PET imaging in an orthotopic lung cancer model.