(331f) Interfacial Aging of Blood Serum Studied by Active Microrheology

The magnetically driven motion of 300 nm diameter Nickel rods is used to monitor changes in the surface viscosity of blood serum. Our results show that the surface viscosity of serum increases from 10-9 to 10-5 Ns/m over two hours while the surface pressure saturates in minutes. This aging of serum is attributed to the aging of albumin, the most abundant protein in blood. Albumin is a hydrophobic protein forming a 4 nm thick monomolecular film at the air-water interface. The increase in surface viscosity is not accompanied by a corresponding increase in elasticity, suggesting that the protein film anneals with time, resulting in a more densely packed film leading to increased resistance to shear. This aging of protein molecules remains undetected by other spectroscopic methods indicating that microrheology can provide sensitive information about protein-protein interactions at the interface. The nanometer dimensions of the rods provide the same sensitivity as passive microrheology with an improved ability to measure more viscous films as well as the dynamics of aging.