Molecular Behavior of Antibodies IgG-1 and IgG-4 at Buried Polymer/Solution Interfaces Probed by Sum Frequency Generation Vibrational Spectroscopy

Antibody aggregation is a widespread phenomenon that frequently occurs when antibodies interact with solid surfaces. It can significantly compromise antibody functionality, e.g., reduced antigen-binding affinity, altered pharmacokinetics, and increased immunogenicity, making it a major concern in therapeutic and diagnostic applications. Therefore, understanding the molecular interactions between antibody structures and material surfaces is critical for optimizing antibody drug formulation, storage, and filtration processes. In this study, we investigated the surface-induced aggregation behavior of two antibodies─IgG-1 and IgG-4─using polypropylene (PP) and poly(vinyl chloride) (PVC) films as representative hydrophobic and hydrophilic polymer surfaces, respectively, with a combined experimental and computational approach. In situ sum frequency generation (SFG) vibrational spectroscopy was used to monitor interfacial protein structures at varying concentrations, while solvent-accessible surface area (SASA) calculations provided structural and hydropathological insights into antibody–surface interactions. Significantly stronger SFG signals were observed for IgG-1 than for IgG-4 on both PP and PVC surfaces, across both low and high (1.2 and 12 mg/mL) concentration conditions. IgG-1 showed marked orientational rearrangement upon surface contact, in contrast to the relatively stable configuration of IgG-4. SASA calculations further supported these observations by revealing a greater exposure of hydrophobic regions in IgG-1, which likely contributes to its enhanced surface affinity and fouling propensity. Together, these results provide molecular-level insights into antibody–surface interactions and highlight molecular determinants that govern protein aggregation on polymeric filtration materials. This work offers guidance for the rational design of low-fouling biomaterials and improved antibody handling strategies in biomanufacturing and therapeutic applications.