Effects of Macromolecular Crowding on Nanoparticle Diffusion: New Insights from Mossbauer Spectroscopy

In this work, we used Mossbauer spectroscopy as a new approach for experimental quantification of the self-diffusion coefficient (D-Mossbauer) and hydrodynamic (HD) size of ironcontaining nanoparticles (NPs) in complex crowded solutions, mimicking cell cytoplasm. As a probe, we used 9 nm cobalt ferrite NPs (CFNs) dispersed in solutions of bovine serum albumin (BSA) with a volume fraction (phi(BSA)) of 0-0.2. Our results show that the broadening of MOssbauer spectra is highly sensitive to the diffusion of CFNs, while when phi(BSA) = 0.2, the CFN-normalized diffusivity is reduced by 86% compared to that of a protein-free solution. CFN colloids were also studied by dynamic light scattering (DLS). Comparison of the experimental data shows that DLS significantly underestimates the diffusion coefficient of CFNs and, consequently, overestimates the HD size of CFNs at phi(BSA) > 0, which cannot be attributed to the formation of the BSA monolayer on the surface of CFNs.

Automated summary

In this study, Mossbauer spectroscopy and dynamic light scattering were used to investigate the self-diffusion coefficient and hydrodynamic size of iron-containing nanoparticles in complex solutions. The results show that the diffusion of CFNs greatly affects the broadening of Mossbauer spectra.