Interactions of nanoplastics with human albumin and hemoglobin: Structural and spectroscopic insights

Nanoplastics (NPls) are emerging environmental contaminants with increasing evidence of human exposure and bioaccumulation. Their ability to interact with essential plasma proteins raises concerns about potential effects on protein structure, and possible downstream biological activity. Herein, we investigated the interactions of europium-doped nanoplastics (Eu-NPls) on human albumin (Alb) and hemoglobin (Hhb). Circular dichroism (CD) spectra revealed that Eu-NPls may interact with proteins resulting in a decline in α-helical content and a concomitant rise in β-sheet and disordered fractions after 24 h exposure, consistent with partial unfolding and destabilisation. FTIR and 2D-correlation analyses further confirmed significant perturbations in the Amide I/II regions, highlighting time- and dose-dependent secondary structure reorganisation. Fluorescence spectroscopy showed progressive quenching of tryptophan residues, while SDS-PAGE indicated conformational destabilisation without extensive aggregation. Molecular docking provided complementary mechanistic insight, indicating that NPl-protein interactions are predominantly driven by hydrophobic and aromatic surface contacts of the polystyrene matrix within accessible protein cavities. These results demonstrate that Eu-NPls interact strongly with Alb and Hhb, leading to measurable structural alterations. This work provides mechanistic evidence of Eu-NPl-protein interactions, indicating the need for further studies to determine whether such structural perturbations translate into functional effects under physiologically relevant conditions.