Interaction of proteins with nanoparticles

Nanoparticles suspended in biological fluids such as blood plasma adsorb proteins onto their surface leading to the formation of what is called a protein ‘corona’. Adsorbed proteins on nanoparticles change the original ‘identity’ of the nanoparticle surface ultimately determining the physiological response and signaling pathways at the cellular level. Because of the promising therapeutic and diagnostic applications of nanoparticles it is imperative to understand the impact of the the formation of this protein corona on both colloidal stability and protein structure.

In the Link lab we are applying optical microscopy techniques to study this ‘corona’ in situ and in real time. We expect to obtain a physico-chemical understanding of the protein corona and visualize its dynamics and evolution over time. We have started this goal by studying the interaction of bovine serum albumin (BSA, a cow analog of human serum albumin, the most abundant protein in circulation) and citrate-stabilized gold nanospheres.

We have determined the equilibrium dissociation constant (KD) of the interaction using scattering correlation spectroscopy, an experimental technique that allows measuring the hydrodynamic dimensions of nanoparticles while freely diffusing in solution. The figure below shows the characteristic decay time of an autocorrelation curve of the scattering signal of gold nanopsheres without and with the presence of BSA (A). The observed increase in the characteristic diffusion time in the presence of protein can be translated to monolayer adsorption of BSA onto the nananoparticle surface (A-inset). By varying the concentration of BSA in solution we can perform an adsorption isotherm and measure the increase in hydrodynamic radius as a function of protein concentration and extract the equilibrium dissociation constant of the interaction (B). In addition, we can count the number of individual scattering events (proportional to the number of nanoparticles sampled in solution) per autocorrelation curve and assess the impact of proteins on colloidal stability (C-D).

We have found that BSA not only does not lead to aggregation of citrate-stabilized gold nanoparticles (by observing the same of events without and with the presence of BSA), but also offers remarkable protection against aggregation under highly saline conditions of up to 1 M of NaCl.

Dissertation