Evaluation of protein separation mechanism and pore size distribution in colloidal self-assembled nanoparticle sieves for on-chip protein sizing

The separation behavior of 6.5-66 kDa proteins in silica particle array-based sieves formed by colloidal self-assembly in microchips is reported across a pore size range of 22-103 nm. The protein separation and resolution improves markedly with decreasing pore size. The variation of electrophoretic mobility with molecular weight of SDS-protein complexes and with particle size was evaluated using the Ogston sieving equation for a random pore gel structure, and using the modified Giddings equation developed by Wirth for uniform pore structures. The Wirth/Giddings equation provides the best fit for estimation of molecular weight of proteins, and demonstrates that even though experimental evidence shows there is some dispersion in measured pore sizes, these structures can best be described as having a uniform pore size.