Enhanced Tumor-Accumulation of Upconversion Nanoparticles for Upconversion Luminescence/Magnetic Resonance Dual-Mode Bioimaging of Colorectal Tumor Using a Tumor Affinity Peptide with PSP Motif

Abstract

Up to date, it is still a great challenge to construct tumor targeting nanoparticles with high sensitivity and resolution for improving the non-invasive detection ability of colorectal cancer (CRC) at early stage. In this study, we have prepared NaErF4:Yb@NaGdF4:Yb core@shell upconversion nanoparticles (UCNPs) with high upconversion luminescence (UCL) emission in red light region through adjusting the doping ratios of Er element and Yb element in the core. For biomedical application, the carboxyl-terminated silica shell has been introduced to transfer the as-prepared UCNPs from organic phase to aqueous phase, as well as to conjugate peptide ligands derived from L-SP5 peptide (i.e., L-SP5-H and L-SP5-C), respectively. Due to the tumor-binding affinity of PSP motif in peptide ligands, the as-prepared peptide functionalized UCNPs (UCNP@SiO2-L-SP5-H and UCNP@SiO2-L-SP5-C) can be used as active tumor targeting contrast agents for UCL/T1-weighted magnetic resonance (MR) dual-mode imaging. Both the in vitro and in vivo experimental results demonstrate that the as-prepared UCNP@SiO2-L-SP5-C has relatively high affinity with HCT116 CRC subtype. Particularly, UCNP@SiO2-L-SP5-C can even visualize ultrasmall subcutaneous xenografted HCT116 tumor (c.a. 13 mm3 in volume) by in vivo UCL imaging.