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

Nanoplastics contamination is one of the pressing environmental concerns globally. Among many environmental factors in the aquatic system, 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 nanoplastics (PSNPs) aggregation. The critical coagulation concentration (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-PSNPs conjugates decreased from 1 to 0 with increasing electrolyte concentration, suggesting the attractive patch-attractive force may be screened by the steric repulsion. At a relatively high level of protein (>10 mg/L), PSNPs remained stable in BSA solution, but aggregated fast in TRY solution. Results clearly showed that the aggregation of nanoplastics was highly related to the electrical charge of protein. 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 protein. This work highlighted the necessity to account for protein type and particle size when evaluating the aggregation state and potential risk of emerging nanoplastics in aquatic systems.