We developed a method to characterize polymer-supported polyacrylamide crosslinked hydrogel networks using a range of well-defined poly(N, N-dimethylacrylamide)-coated gold nanoparticles with diameters ranging from 3 to 48 nm under ultrafiltration conditions of 16 bar. The membranes resulted in permeabilities ranging between 0.199 and 6.343 x 10-18 m2. There was a direct correlation between the size exclusion and the permeability rate coefficient, km; the higher the km value the larger the average pore size. Our results further demonstrate that the gold nanoparticles could be trapped within the membrane at the end of a cul-de-sacs found within the gel network, which often leads to membrane fouling. We believe that this method of using gold nanoparticles to characterize crosslinked membranes provides insight into the gel network, and will provide a unique tool to analyze new membranes. (C) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013