Synthesis, Biocompatibility, and Relaxometric Properties of Heavily Loaded Apoferritin with D-Glucuronic Acid-Coated Ultrasmall Gd₂O₃ Nanoparticles

Apoferritin (APO) with a diameter of ~12 nm is a naturally occurring protein assembly in living organisms. APO is made of 24 protein subunits that form a nanocage with an inner diameter of ~8 nm. Thus far, the loading of only a few nanoparticles inside the nanocage of APO has been reported. In this study, the mass loading of D-glucuronic acid (GA)-coated ultrasmall gadolinium oxide (Gd₂O₃) nanoparticles (UGNPs) (GA-UGNPs) (d_avg = 1.9 nm) inside and outside the nanocage of APO was investigated. The in vitro cytotoxicity and relaxometric properties were investigated. This study indicates that APO is an extremely useful bio-material, which can be used for mass loading of various nanoparticles for biomedical applications. Graphical abstract: [Figure not available: see fulltext.]