The defined presentation of nanoparticles to cells and their surface controlled uptake.

New approaches and standardized test procedures to study the impact of nanoparticles (NPs) on living cells are urgently needed for the evaluation of potential hazards relating human exposure to NPs. Here we study semiconductor quantum dots (QDs) preparation on solid surfaces and the subsequent internalization by cells seeded on top of the NP layer. Controlled densities of NPs are adsorbed to solid surfaces coated with extra-cellular macromolecules. The fraction of QDs taken up by the cells is assessed by automated fluorescence microscopy z-scans. We find that NPs aggregate during the uptake process, forming clusters inside cells that are able to enter the cell nucleus. NP uptake is dependent on surface functionalization and can be hindered by increasing the strength of the adhesion force between NPs and the surface. Studying time dependent uptake, we show that particles are able to exit cells.