Fig. 6. A schematic representation of the adsorption process of BSA onto HM NPs. BSA molecules penetrate the stagnant layer in the vicinity of the HM NP surface (BSAT) from the bulk solution (BSAbulk) at a rate constant of k1. The diffusion of BSA back to the bulk solution occurs at a rate constant of k2. BSA molecules might overcome the energy barrier of adsorption, which depends on various factors, such as the steric and electrostatic forces between proteins and particles as well as the osmotic repulsion from a water layer on the particle surface, and bind to the surface of HM NPs without conformational changes in a transient state at a rate constant of k3 (BSAO). Then, adsorbed BSA molecules undergo conformational changes within 30–60 min at a rate constant of k4 and change to an unfolded state (BSAU). However, when the surface coverage exceeds a threshold, BSA molecules refold at a rate constant of k5 (BSAO). It is worth mentioning that the values of k4 and k5 depend on the protein surface coverage changing over time. Reprinted with permission from ref. 194. Copyright 2019. American Chemical Society.
