Nanoscale dynamics in macromolecular crowding conditions

Macromolecular crowding, where proteins occupy up to 40% of cellular volume, strongly affects molecular transport. While generalized Stokes–Einstein relations describe dilute systems, they often fail in crowded media where protein structure and interactions dominate. Our recent XPCS work at ESRF showed that PEGylated gold nanoparticles (AuNP@PEG) in crowded bovine serum albumin (BSA) solutions experience nanoscopic viscosities deviating from macroscopic rheology. We now propose XPCS studies at ID10-COH on AuNP@PEG in αB-crystallin (weakly interacting), BSA (moderately interacting), and lysozyme (strongly interacting). By varying protein concentration and nanoparticle surface chemistry, and combining with rheology and NMR diffusion, we will directly compare transport across scales. The results will clarify how crowding and protein properties govern deviations from classical diffusion models, with implications for intracellular dynamics and nanomedicine.