Figure 4.

(A) Filtration of gold nanoparticles in a 5–30 nm size ladder. Gold nanoparticle solutions (0.01% solids) were filtered through three different pnc-Si membranes and one commercial PES membrane. Absorbance readings were used to calculate the nanoparticle concentrations and losses. The figure shows the ratio of concentrations in the filtrate vs. feed solutions as a function of nanoparticle size. Dashed lines are the apparent cut-off for each wafer. (B) Images of stock, retentate and filtrate solutions for separations with wafer F. Tubes are labeled with particle size and R for retentate, F for filtrate. Stock particles are in the center with no letter designation. (C) Purification of 10 nm particles from a mixture of 10 nm and 15 nm particles using wafer G. Dynamic light scattering spectra of 15 nm stock gold nanoparticles (black); 10 nm stock (blue); the starting solution containing equal concentrations of 10 nm and 15 nm particles (green); and the filtrate (red). (D) Fractionation of a protein mixture by SDS PAGE. The protein size ladder contains 6 proteins with distinct molecular weights ranging from 37k to 400k when the proteins are in their native state (see Supplement for details on protein structure and sizes).