CXCR4 and neoplasm: The BALB/c nude mouse bearing MDA-MB-231 tumor was used for evaluating the tumor-targeting capacity of anti-CXCR4-NaGdF4 NDs through intravenous injection of anti-CXCR4-NaGdF4 NDs and Try-NaGdF4 NDs via tail vein, respectively.