  A new type of metabolizable and efficient radiosensitizer for cancer
radiotherapy is presented in this study by combining ultrasmall Au nanoclusters
(NCs, <2 nm) with biocompatible coating ligands (glutathione, GSH). The new
nano-construct (GSH-coated Au25 NCs) inherits attractive features of both the
Au core (strong radiosensitizing effect) and GSH shell (good biocompatibility).
It can preferentially accumulate in tumor via the improved EPR effect, which
leads to strong enhancement for cancer radiotherapy. After the treatment, the
small-sized GSH-Au25 NCs can be efficiently cleared by the kidney, minimizing
any potential side effects due to the accumulation of Au25 NCs in the body.
