In summary, bifunctional anti-CXCR4-NaGdF4 NDs have been successfully fabricated for MRI-guided biotherapy of cancer by a two-step procedure through ligand exchange reaction between oleate and CPPs in tryptone, and the amidation reaction between activated carboxyl group of tryptone and amine group of anti-CXCR4. The gene discussed is CXCR4; the disease is cancer.