Antibodies Adsorbed to the Air-Water Interface Form Soft Glasses

When monoclonal antibodies are exposed to an air-waterinterface,they form aggregates, which negatively impacts their performance.Until now, the detection and characterization of interfacial aggregationhave been difficult. Here, we exploit the mechanical response impartedby interfacial adsorption by measuring the interfacial shear rheologyof a model antibody, anti-streptavidin immunoglobulin-1 (AS-IgG1),at the air-water interface. Strong viscoelastic layers of AS-IgG1form when the protein is adsorbed from the bulk solution. Creep experimentscorrelate the compliance of the interfacial protein layer with thesubphase solution pH and bulk concentration. These, along with oscillatorystrain amplitude and frequency sweeps, show that the viscoelasticbehavior of the adsorbed layers is that of a soft glass with interfacialshear moduli on the order of 10(-3) Pa m. Shiftingthe creep compliance curves under different applied stresses formsmaster curves consistent with stress-time superposition ofsoft interfacial glasses. The interfacial rheology results are discussedin the context of the interface-mediated aggregation of AS-IgG1.