The present invention relates to a new type of metabolizable flower-like gold nanodandelion (GND), which possesses features: (1) large scale green synthesis with high monodispersity and a circa 100% yield; (2) cellular/physiological degradability; (3) precision control of the shape, petal number and size; (4) highly efficient radiotheranostics encompassing better enhanced CT contrast and pronounced x-ray induced ROS generation than conventional spherical AuNP.