Shape Separation of Colloidal Metal Nanoparticles via Size Exclusion Chromatograph

The inherent polydispersity of solution-based, colloidal nanoparticle syntheses has necessitated the development of facile post-processing methods for the purification of anisotropic nanoparticles. Here, the use of size exclusion chromatography is explored for the shape separation of colloidal silver nanocube and colloidal gold bipyramid solutions. Multiple column packing materials, pore sizes, and mobile phases were tested to address the prevalent issues of metal adsorption to the high surface area stationary phase and to distinguish differently shaped particles by size in solution. The use of diffusion through interstitial spaces to increase the retention time of silver nanocubes in cross-linked dextran columns for narrower shape distribution did not reveal a correlation between particle size and retention time. To allow particle diffusivity into the pores of the stationary phase an irregular silica gel column with sufficient pore size was chosen. In addition, the model nanoparticle system was changed to gold bipyramids to allow for more quantitative separation analysis based on the extinction spectra alone. Different concentrations of surfactant in the mobile phase were tested to optimize the difference in particle shape distribution of gold nanoparticles in the eluate. The addition of surfactant to the mobile phase may selectively flocculate anisotroptic nanoparticles from solution, forming large aggregates monodisperse in particle shape. To resolve the issue of cationic surfactant interactions with the stationary phase, an alkyl functionalized silica is proposed to simultaneously facilitate diffusion and mitigate adsorption.