Purpose: Nitroxide radicals, such as 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and its derivatives, have been paid attention as contrast agents for magnetic resonance imaging (MRI) and electron paramagnetic resonance imaging (EPRI). However, due to the rapid one-electron bioreduction to diamagnetic N-hydroxy species, Nitroxide radicals has limited their use in in vivo applications. Methods: a new approach of silica coating for carrying stable radicals was prepared.