The increasing environmental prevalence of micro/nano plastics (MNPs) has raised significant concerns regarding their potential impact on human health, particularly in terms of immunotoxicity. However, the direct effects of MNPs on immune molecules, especially how they may influence protein liquid-liquid phase separation (LLPS)-a critical process implicated in various aspects of immune function-remain largely unexplored. This study addresses this gap by investigating the effects of polystyrene nanoparticles (PS NPs) with different surface modifications and sizes on LLPS in immunoglobulin Y (IgY) antibodies, critical components of the avian immune system. Our findings reveal that PS-COOH NPs uniquely induce LLPS in IgY in a size-dependent manner, while PS-NH