Zwitterionic Functionalization of Persistent Luminescence Nanoparticles: Physicochemical Characterizations and In Vivo Biodistribution in Mice

After excitation in the biological transparency window, chromium-doped zinc gallate nanoparticles (ZGO NPs) emit near-infrared luminescence for more than an hour, allowing long-term imaging to be performed without background autofluorescence. However, these nanoparticles are recognized in just a few minutes by serum proteins and are then trapped in the liver. In this article, we put forth that liver uptake can be delayed when coating the surface of ZGO NPs with zwitterions. We focused on the use of a very small zwitterion molecule of 330 Da derived from sulfobetaine silane (SBS) and its grafting in one step and in water onto zinc gallate nanoparticles, and we compared the colloidal stability, the in vitro interactions with serum proteins, and the biodistribution in mice with PEGylated ZGO NPs (5000 Da) prepared in two steps in organic solvent. In vitro quantification of serum protein adsorption suggests that the similarity between the sulfobetaine and the cell membrane is enough to reduce protein adsorption as much as a PEGylation, despite the difference in coating thickness and molecular weight. This study has also proved that a combination of good protein repulsion and a smaller size compared to PEGylated NPs allows similar circulation times to be obtained in mice with zwitterionic or PEG coatings. Therefore, its use could offer new opportunities for further in vivo application of functionalized ZGO derivative NPs.