The ζ-potential of nanoparticles plays an important role in nanoparticle-protein interactions, with ζ-potential changes observed following incubation with protein-containing media for all samples. The most significant observed change in ζ-potential with relative to the reference particles was in positively charged amine-modified nanoparticles, which showed a change from +50.4mV to -18.1 mV in ζ-potential (following 2-hour incubation, and a further change observed in samples incubated for 24-hour--20.3 mV. A small change in ζ-potential was observed for the unmodified nanoparticles from -33.5 mV to -31.6 mV following a 24-hour incubation. The negatively charged carboxylate-modified nanoparticles showed a larger change in ζ-potential from baseline (-34.0 mV) to 2-hour incubation (-24.3 mV) with a similar ζ-potential measured at 24-hour incubation (-24.8 mV) (Figure ). These results overall indicate that nanoparticle interactions with protein occur to a lesser extent with the negativelycharged polystyrene latex nanoparticles.