Slow and fluctuating dynamics in high concentration BSA protein solutions

We present a study on globular bovine serum albumin (BSA) protein solutions using particle tracking microrheology and dynamic light scattering over a wide concentration range (1-55 g/dl). We measured the expected drastic increase in viscosity and relaxation times with concentration, highlighting the slowing down of the dynamics associated with collective molecular motions as concentration increases. A novel aspect of our study emerged at very high concentrations, where the slow relaxation times exhibit only a mild increase with concentration, resembling the behavior observed in very soft colloids. Upon quenching the temperature to induce very slow dynamics, we observe fluctuating dynamics, suggesting a mild aging regime characterized by micro-rearrangements of BSA proteins. We use protein concentration (mass per volume) as the control parameter due to the precision of Bradford assay measurements, facilitating straightforward comparisons with other studies. Our work offers new insights into the phase behavior of BSA solutions across a wide concentration range, with implications for understanding protein solution dynamics at high concentrations.