The influence of nanoplastics' surface charge on the formation of protein corona and the subsequent sorption of Cd2 + and Pb2+ ions

Micro and nanoplastics (NPs) might enter in human body and with proteins resulting in the formation of the protein corona. In this study, we investigated the formation of protein coronas on negatively and positively charged polystyrene (PS) NPs and examined their effects on the sorption of Pb²⁺ and Cd²⁺. Both positively and negatively charged PS-NPs exhibited nearly identical protein corona compositions, irrespective of surface charge, except for glycoproteins, which showed significantly higher adsorption on negatively charged particles. In ultrapure water without a protein corona, no significant adsorption of Cd²⁺ or Pb²⁺ was observed on either particle type. In human serum over 72 hours, positively charged PS-NPs reduced Pb²⁺ concentrations in the surrounding medium from 100 ± 4.42% to 85.9 ± 7.63% and Cd²⁺ from 100 ± 5.88% to 88 ± 6.59%, indicating sorption of these metals onto corona-coated particles. Negatively charged PS-NPs decreased Pb²⁺ to 83 ± 3.09%. These results demonstrate that protein corona formation markedly modifies the metal sorption capacity of PS-NPs. Furthermore, Pb²⁺ consistently exhibited stronger adsorption than Cd²⁺, suggesting a metal-specific affinity of PS-NPs following corona formation. These findings demonstrated that the surface charge does not play a major role in the formation of the protein corona on nanoplastics. However, the protein corona can significantly promote the heavy metals adsorption by forming stable nanoplastics-protein corona (NP-PC) metal complexes under physiological conditions. This interaction may increase nanoplastics toxicity by enhancing the accumulation and transport of highly toxic metals within biological systems, with important implications for risk assessment.