Erythrocyte Membrane-Coated Upconversion Nanoparticles with Minimal Protein Adsorption for Enhanced Tumor Imaging.

Upconversion nanoparticles (UCNPs) with superior optical and chemical features have been broadly employed for in vivo cancer imaging. Generally, UCNPs are surface modified with ligands for cancer active targeting. However, nanoparticles in biological fluids are known to form a long-lived "protein corona", which covers the targeting ligands on nanoparticle surface and dramatically reduces the nanoparticle targeting capabilities. Here, for the first time, we demonstrated that by coating UCNPs with red blood cell (RBC) membranes, the resulting cell membrane-capped nanoparticles (RBC-UCNPs) adsorbed virtually no proteins when exposed to human plasma. We further observed in various scenarios that the cancer targeting ability of folic acid (FA)-functionalized nanoparticles (FA-RBC-UCNPs) was rescued by the cell membrane coating. Next, the FA-RBC-UCNPs were successfully utilized for enhanced in vivo tumor imaging. Finally, blood parameters and histology analysis suggested that no significant systematic toxicity was induced by the injection of biomimetic nanoparticles. Our method provides a new angle on the design of targeted nanoparticles for biomedical applications.