Mesoporous Silica as Nanoreactors to Prepare Gd-Encapsulated Carbon Dots of Controllable Sizes and Magnetic Properties

Gd-encapsulated carbonaceous dots (Gd@C-dots) hold great potential in clinical applications as a novel type of T-1 contrast agent for magnetic resonance imaging (MRI). However, current synthetic methods require multiple purification steps due to poor size control, making them unsuitable for high throughput. Herein, a novel, mesoporous silica nanoparticle (MSN)-templated method for the size-controlled synthesis of Gd@C-dots is reported. Briefly, MSNs nanoreactors of different pore sizes are loaded with Gd precursors. Upon calcination, carbon layers are grown around the Gd cations. The spatial restraint of the silica cavity facilitates size control of the produced Gd@C-dots. Specifically, using 3, 7, and 11 nm MSNs as templates allows the synthesis of 3.0, 7.4, and 9.6 nm Gd@C-dots, respectively. A significant size impact on the magnetic and optical properties of the nanoparticles is shown, with the smallest Gd@C-dots showing the highest r(1) relaxivity (10 mM(-1) s(-1)) and fluorescence quantum yield (30.2%). The 3.0-nm Gd@C-dots were then conjugated with a tumor-targeting ligand, c(RGDyK), and injected into U87MG xenograft tumor models. Good tumor targeting was observed in T-1-weighted MRI images; whereby the unbound nanoparticles were efficiently excreted through renal clearance, avoiding long-term toxicity to the host.