Reversible versus Irreversible Binding of Transferrin to Polystyrene Nanoparticles: Soft and Hard Corona

Abstract

Protein adsorption to nanoparticles (NPs) is a key prerequisite to understand NP-cell interactions. While the layer thickness of the protein corona has been well characterized in many cases, the absolute number of bound proteins and their exchange dynamics in body fluids is difficult to assess. Here we measure the number of molecules adsorbed to sulfonate (PSOSO(3)H) and carboxyl-(PSCOOH) polystyrene NPs using fluorescence correlation spectroscopy. We find that the fraction of molecules bound to NPs falls onto a single, universal adsorption curve, if plotted as a function of molar protein-to-NP ratio. The adsorption curve shows the build-up of a strongly bound monolayer up to the point of monolayer saturation (at a geometrically defined protein-to-NP ratio), beyond which a secondary, weakly bound layer is formed. While the first layer is irreversibly bound (hard corona), the secondary layer (soft corona) exhibits dynamic exchange, if competing unlabeled is added. In the presence of plasma proteins, the hard corona is stable, while the soft corona is almost completely removed. The existence of two distinct time scales in the protein off-kinetics, for both NP types studied here, indicates the possibility of an exposure memory effect in the NP corona.

Non-specific interactions between soluble proteins and lipids induce irreversible changes in the properties of lipid bilayers

“…In this respect, non-specic inter-protein interactions were detected for a transferrin coated nanoparticle incubated in blood plasma, for which a so corona of proteins was identied by uorescent correlation spectroscopy. 38 Within this so corona protein exchange occurred in the timescale of two minutes and faster, showing the highly dynamic nature of such inter-protein non-specic interactions. 38 Indeed, the existence of such a so protein corona arises from typical non-specic protein-protein interactions in the crowded protein environment induced by the higher concentration of proteins at the interface between the solution and any surface.…”

“…38 Within this so corona protein exchange occurred in the timescale of two minutes and faster, showing the highly dynamic nature of such inter-protein non-specic interactions. 38 Indeed, the existence of such a so protein corona arises from typical non-specic protein-protein interactions in the crowded protein environment induced by the higher concentration of proteins at the interface between the solution and any surface. Our results suggest that such reversible, dynamic and "so" proteinprotein interactions also occur in the close vicinity of lipid bilayers and together with non-specic protein-lipid interactions may indeed have an irreversible effect on the lipid bilayer structure, in terms of their permeability against soluble dyes and the colloidal stability of the vesicles.…”

The Impact of Nanoparticle Protein Corona on Cytotoxicity, Immunotoxicity and Target Drug Delivery

“…Based on the exchange time of its composition, the PC is classified into hard and soft (Figure 2). The hard corona is considered the first tightly bound layer of proteins that has a long exchange time (many hours), while the soft corona is represented by the second layer of proteins (not directly bound to the NP) that undergoes fast exchanges over time (seconds or minutes) [11]. The proteins adsorbed on NPs are considered to be in a continuous flux of desorption/adsorption mainly controlled by the so-called 'Vroman effect' [32] as the group of Vroman observed this phenomenon at the plasma-solid interface in 1962 [33].…”

“…On the other hand, the physicochemical characterization of bare NPs before exposure to body fluids remains crucial to reveal the correlations between the properties of NPs and PC composition (Figure 1). During the recent years, a large number of studies have been devoted to the characterization of NP-PC complexes [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Furthermore, the scientific community is now moving from the The impact of nanoparticle protein corona on cytotoxicity, immunotoxicity and target drug delivery The bare NP (synthetic identity) that has a specific shape, size and charge is injected into the body.…”

Biomolecular coronas provide the biological identity of nanosized materials

“…For several nanoparticles such as gold 12 , polystyrene 8,13,14 , silica 5,8,14,15 , titania 15 and zinc oxide 15 , a near-monolayer of biomolecules (called the 'hard' corona) bind tightly, but not completely irreversibly, to the nanoparticle surface. On top of this 'hard' corona is a 'soft' corona consisting of a more loosely associated and rapidly exchanging layer of biomolecules 8,[12][13][14]16 (Fig. 1b).…”