Abstract: Disclosed herein is a nanocomposite comprising a core-shell nanoparticle and a core-shell quantum dot. The core-shell nanoparticle comprises a phosphor core, a shell layer, and a cleavable peptide. The core-shell quantum dot comprises a center core, an intermediate layer, an outer layer, a silica layer, and an arginylglycylaspartic acid (RGD) peptide. The core-shell nanoparticle and the core-shell quantum dot are linked to each other via forming a peptide bond between the cleavable peptide and the RGD peptide. Also disclosed are the uses of the nanocomposite in making a diagnosis of tumors.