Nanoions: Fundamental properties and analytical applications of charged nanoparticles

Mixtures of oppositely charged nanoporticles (NPs) precipitate sharply only at the point of NP electroneutrality. This behavior-reminiscent of the threshold precipitation of inorganic ions-is specific to the nonoscale and con be attributed to the formation of like-chorged NP clusters stabilized in solution by mutual electrostatic repulsions. NP titrations based on this phenomenon provide a uniquely accurate tool for measuring charges tethered onto nonoscopic objects and for studying the thermodynamics of surface reactions at the nonoscole.