A surface-modified nanoparticle composition comprising surface-functionalized transition metal oxide nanoparticles, each comprising a respective transition metal oxide core having a surface layer thereon comprising bound organic carboxylates represented by the formula R1—CO2—, wherein R1 is a hydrocarbyl group having from 6 to 30 carbon atoms, and at least one organoammonium cation represented by the formula R2R3NH2+, wherein R2 represents a hydrocarbyl group having from 6 to 30 carbon atoms, and R3 represents H or an alkyl group having from 1 to 4 carbon atoms.