Yes / To develop an efficient nanotechnology fluorescence-based method to track cell proliferation to avoid the limitations of current cell-labeling dyes. Material & methods: Synthesis, PEGylation, bifunctionalization and labeling with a fluorophore (Cy5) of 200 nm polystyrene nanoparticles (NPs) were performed. These NPs were characterized and assessed for in vitro long-term monitoring of cell proliferation. Results: The optimization and validation of this method to track long-term cell proliferation assays have been achieved with high reproducibility, without cell cycle disruption. This method has been successfully applied in several adherent and suspension cells including hard-to-transfect cells and isolated human primary lymphocytes. Conclusion: A novel approach to track efficiently cellular proliferation by flow cytometry using fluorescence labeled NPs has been successfully developed.