Rational surface modification of gadolinium borate nanoparticles enhancing colloidal stability in physiological media for potential neutron capture therapy and magnetic resonance imaging

Colloidal stability of nanomaterials in physiological media is an indispensable property for their biomedical applications. However, gadolinium borate (GdBO3) nanoparticles that hold promise as a theranostic agent for neutron capture therapy (NCT) and magnetic resonance imaging (MRI) of cancer tend to precipitate in phosphate buffered saline (PBS) owing to formation of insoluble gadolinium phosphate. To address this issue, in this work 10B-enriched GdBO3 nanoparticles were prepared and coated with mesoporous silica (mSiO2) of ~ 40 nm in thickness and subsequently grafted with hydrophilic polyglycerol (PG). The resulting GdBO3 @mSiO2-PG nanoparticles showed excellent colloidal stability in PBS due to the protection of the mSiO2 coating as well as superior dispersibility because of the high hydrophilicity of the PG layer. In vitro experiments revealed that GdBO3 @mSiO2-PG possessed low cytotoxicity and could be taken up by cancer cells in a concentration-dependent manner. In vivo studies indicated that GdBO3 @mSiO2-PG can circulate in mouse body for a considerably long time without obvious acute toxicity. In addition, GdBO3 @mSiO2-PG also showed promise as a T1-weighted MRI contrast agent with a proton longitudinal relaxivity of 0.67 mM−1 s−1. Our results indicate that GdBO3 @mSiO2-PG with enhanced colloidal stability in physiological media could serve as a promising multifunctional agent for cancer theranostics.