A capillary zone electrophoretic method for size characterization of gold nanoparticles

The unusual size dependent chemical and physical properties make nanoparticles attractive for quite different fields of applications1. The characterization of size distribution of solution grown nanoparticles is usually performed by dynamic light scattering and transmission electron microscopy2 (TEM). A method here is proposed for the separation of gold colloid standards, with core diameters ranging from 5 to 20 nm, using free solution capillary zone electrophoresis. The size characterization was possible by adding to the buffer poly(sodium 4-styrenesulfonate) which infers an “electrosteric” stabilization3 to colloids, exalting the difference in their electrophoretic mobilities. Applying a potential step for separation, a significant improvement was provided in terms of resolution between different sized colloids whose migration time varied linearly with particle diameter. A comparison with the size distribution derived by TEM allowed to assess that the electrophoretic profile is representative of the effective heterogeneity in size of each colloid sample. The practical utility of the method was demonstrated by measuring the size distribution of a home synthesized gold colloid which was in good agreement with the profile derived by TEM. 1. Daniel, M.C.; Astruc, D. Chem. Rev. 2004, 104, 293-346. 2. Henglein, A. J. Phys. Chem. 1993, 97, 5457-5471. 3. Pugh, T.L.; Heller, W. J. Polym. Sci. 1960, 47, 219-227.