**4. Conclusions**

To summarize, there is a need to understand the influence of submicron polystyrene particle properties, such as size and chemical composition, on the various endpoints of particle toxicity. In the presented research, we investigated whether polystyrene particles influence the electrokinetic potential of erythrocytes and thrombocytes. Two types of polymers were used, and each experiment was conducted several times. In addition, different particle sizes and concentrations, as well as exposure durations to the polymer, always provided the same results, i.e., the internalization of PS-100, PS-200, and PS-NH2- 100 particles into the cells and the attachment of PS-NH2-200 particles to cell membranes. Our study clearly shows that the size and surface chemistry of PS particles determine the extent to which they affect the electrical properties of thrombocyte and erythrocyte membranes.

**Author Contributions:** Conceptualization, M.Z. and M.N.; methodology, M.Z., J.K., J.B. and M.N.; validation, M.Z., J.K., J.B. and M.N.; formal analysis, M.Z., J.K. and M.N.; investigation, M.Z.; resources, M.Z., J.K. and M.N.; data curation, J.K. and M.N.; writing—original draft preparation, M.Z., J.K. and M.N.; writing—review and editing, M.Z., J.K., M.W. and M.N.; visualization, M.Z., J.K. and M.N.; supervision, M.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** The FTIR spectrometer was funded by the EU as part of the Operational Program Development of Eastern Poland 2007-2013 (projects Nr POPW.01.03.00-20-034/09-00 and POPW.01.03.00-20- 004/11-00, the Centre of Synthesis and Analysis BioNanoTechno, University of Bialystok, Poland).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
