Selective sensing of sulfate anions in water with cyclopeptide-decorated gold nanoparticles.

The interaction of cyclopeptides bound to the surface of mixed monolayer-protected gold nanoparticles with sulfate anions causes the crosslinking and concomitant precipitation of the nanoparticles from aqueous solutions even in presence of an excess of competing anions, thus allowing the naked eye detection of sulfate in water.