Size separation of colloidal nanoparticles using a miniscale isoelectric focusing technique

A new method for the isolation of nanometer scale metal particles according to size is demonstrated in this paper. The colloids were derivatized with carboxylic acid groups using self-assembled bifunctional surfactant molecules. The pH at which onset of ionization occurs for the surface carboxylic acid groups was determined for silver and gold colloidal nanoparticles of different sizes using a miniscale isoelectric focusing unit. The pH at which ionization begins is a strong function of the surface curvature of the colloidal particles. It is demonstrated that this property can be used to separate mixtures of colloidal particles of different sizes. In addition to the ability to separate different sized nanoparticles, this technique may also be used to improve the polydispersity of colloids which is an important prerequisite for many applications. (C) 1999 Elsevier Science B.V. All rights reserved.