PEG-covered ultra-small Gd\u2082O\u2083 nanoparticles for positive contrast at 1.5T MR clinical scanning

The size distribution and magnetic properties of ultra-small gadolinium oxide crystals (US-Gd\u2082O\u2083) were studied, and the impact of polyethylene glycol capping on the relaxivity constants (r\u2081, r\u2082) and signal intensity with this contrast agent was investigated. Size distribution and magnetic properties of US-Gd\u2082O\u2083 nanocrystals were measured with a TEM and PPMS magnetometer. For relaxation studies, diethylene glycol (DEG)-capped US-Gd\u2082O\u2083 nanocrystals were reacted with PEG-silane (MW 5000). Suspensions were adequately dialyzed in water to eliminate traces of Gd\ub3\u207a and surfactants. The particle hydrodynamic radius was measured with dynamic light scattering (DLS) and the proton relaxation times were measured with a 1.5 T MRI scanner. Parallel studies were performed with DEG\u2013Gd\u2082O\u2083 and PEG-silane\u2013SPGO (Gd\u2082O\u2083, < 40 nm diameter). The small and narrow size distribution of US-Gd\u2082O\u2083 was confirmed with TEM ( 3c3 nm) and DLS. PEG-silane\u2013US-Gd\u2082O\u2083 relaxation parameters were twice as high as for Gd\u2013DTPA and the r\u2082/r\u2081 ratio was 1.4. PEG-silane\u2013SPGO gave low r\u2081 relaxivities and high r\u2082/r\u2081 ratios, less compatible with positive contrast agent requirements. Higher r\u2081 were obtained with PEG-silane in comparison to DEG\u2013Gd\u2082O\u2083. Treatment of DEG\u2013US-Gd\u2082O\u2083 with PEG-silane provides enhanced relaxivity while preventing aggregation of the oxide cores. This study confirms that PEG-covered Gd\u2082O\u2083 nanoparticles can be used for positively contrasted MR applications requiring stability, biocompatible coatings and nanocrystal functionalization.Peer reviewed: YesNRC publication: Ye