Protein corona-induced aggregation of differently sized nanoplastics: impacts of protein type and concentration

Nanoplastic contamination is one of the pressing environmental concerns globally. Among many environmental factors in aquatic systems, ubiquitous proteins are expected to affect the physicochemical properties of nanoplastics and subsequently influence their fate, transport, and toxicity. Here, time-resolved dynamic light scattering was used to investigate the comparative effects of negatively charged bovine serum albumin (BSA) and positively charged bovine trypsin (TRY) on polystyrene nanoplastic (PSNP) aggregation. The critical coagulation concentrations (NaCl) of 20 and 100 nm PSNPs decreased from 311 and 361 mM to 10 and 43 mM after interacting with TRY, respectively, mainly due to the additional electrostatic attractive force and intramolecular bridging. The attachment efficiencies of BSA-PSNP conjugates decreased from 1 to 0 with increasing electrolyte concentration, suggesting that the patch-charge attractive force may be screened by steric repulsion. At a relatively high level of protein (>10 mg L⁻¹), PSNPs remained stable in BSA solution, but aggregated quickly in TRY solution. Results clearly showed that the aggregation of nanoplastics was highly related to the electrical charge of the proteins. Compared with 100 nm PSNPs, BSA stabilized 20 nm PSNPs more effectively, whereas TRY destabilized 20 nm PSNPs more effectively, indicating that the smaller PSNPs (20 nm) were more susceptible to the co-occurrence of proteins. This work highlighted the necessity of accounting for the protein type and particle size when evaluating the aggregation state and potential risk of emerging nanoplastics in aquatic systems.