A nanoparticle contains a core including superparamagnetic nanoparticles and having an outer surface, and siloxanyl moieties covalently coupled to the outer surface of the core and having Formula (I): In formula (I): X1 and X2 independently represent methylene, ethylene or propylene; R represents an optionally substituted pyridyl group, or —S—R is a group derived from a targeting ligand containing —SH group and effective to bind specifically with a predetermined targeted cell in an object; n and m independently represent an integer ranging from 1 to 3; and p represents an integer ranging from 9 to 45. The nanoparticles are suitable for use as a magnetic resonance imaging contrast agent.