Asymmetric flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry for quality control of the grafting state of polystyrene on gold nanoparticles

Nanoplastics are omnipresent not only in the environment, but can also be transmitted to humans, mainly via the food chain and by contaminating respiratory air. These pollutants have the ability to cross biological barriers, carried into the bloodstream and reach different organs. In order to better understand the mechanisms of their uptake and transport into human cells and better assess their potential risks, the ability to localize and quantify nanoplastics in biological material is crucial. Electron microscopy (EM) represents a common method to study the uptake and intracellular fate of nanoparticles. However, polymeric materials are more difficult to visualize in cells due to the low contrast with cellular components. In this work, approximately 20 nm gold nanoparticles grafted onto polystyrene were synthesized as a model of metal-polymer hybrid nanoparticles in order to resolve the problem of low contrast and visualize nanoplastic-like particles in cells. A multi-technique approach has been developed to characterize those particles. Asymmetric flow field flow fractionation coupled with inductively coupled plasma mass spectrometry (AF4-ICP-MS) is presented as a control quality technique to characterize the grafting percentage of polystyrene onto gold nanoparticles as well as the grafting distribution and the concentration of the synthetized nanoparticles. Thus, grafting percentage of (57 ± 2)% and (100 ± 1)% were obtained for the two samples of Au@PS nanoparticles, respectively synthesized initially and after optimization of the synthesis process. Complementarily, Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM) were used jointly with AF4-ICP-MS in order to determine the particles size and get complementary information about the grafting state. Thus, hydrodynamic diameters of (26 ± 1) nm and (35 ± 3) nm were found for the synthesized Au@PS nanoparticle samples.