Mechanistic Understanding of Protein Corona Formation around Nanoparticles: Old Puzzles and New Insights

Abstract

Although a wide variety of nanoparticles (NPs) have been engineered for use as disease markers or drug delivery agents, the number of nanomedicines in clinical use has hitherto remained small. A key obstacle in nanomedicine development is the lack of a deep mechanistic understanding of NP interactions in the bio‐environment. Here, the focus is on the biomolecular adsorption layer (protein corona), which quickly enshrouds a pristine NP exposed to a biofluid and modifies the way the NP interacts with the bio‐environment. After a brief introduction of NPs for nanomedicine, proteins, and their mutual interactions, research aimed at addressing fundamental properties of the protein corona, specifically its mono‐/multilayer structure, reversibility and irreversibility, time dependence, as well as its role in NP agglomeration, is critically reviewed. It becomes quite evident that the knowledge of the protein corona is still fragmented, and conflicting results on fundamental issues call for further mechanistic studies. The article concludes with a discussion of future research directions that should be taken to advance the understanding of the protein corona around NPs. This knowledge will provide NP developers with the predictive power to account for these interactions in the design of efficacious nanomedicines.

Real-Time Optical Tracking of Protein Corona Formation on Single Nanoparticles in Serum

“…This observation contrasts with part of the literature that observes multilayers on nanoparticles of similar sizes. , Lin et al, for example, observed effective thicknesses in excess of 13 nm for a similar system (gold nanorod in a protein mixture) and attributed this to the formation of multilayers . However, it is important to note that analysis techniques based on the measurement of size or mobility of NPs in solution (such as DLS) cannot distinguish between PC formation and particle clustering . RONAS is insensitive to aggregation and, therefore, accounts for PC formation exclusively.…”

“…Indeed, it has been shown that proteins tend to rapidly form a weakly bound layer to the NPs, but as adsorption time increases, these weak interactions are progressively replaced by stronger (and eventually irreversible) interactions. , In addition, at low protein concentrations, the slow association rate enables the early adsorbed proteins to have more time to rearrange into a more stable configuration. These configurations, which may be structural relaxations, provide reduced space for subsequent proteins, resulting in a more compact PC structure . Taken together, these mechanisms explain the gradual plasmon shift for high dilution factors.…”

“…49 However, it is important to note that analysis techniques based on the measurement of size or mobility of NPs in solution (such as DLS) cannot distinguish between PC formation and particle clustering. 44 RONAS is insensitive to aggregation and, therefore, accounts for PC formation exclusively.…”

“…Because aggregates of particles can be distinguished from monomers, single particle analysis is poised to become a major asset in the study of the PC and its heterogeneity. 44 Despite the need to investigate NP-protein interactions, only a limited number of studies have focused on the in situ formation of PCs at the single-nanoparticle level. For instance, the direct visualization of individual proteins formed on the surface of silica NPs has permitted their quantification and localization using stochastic optical reconstruction microscopy (STORM).…”

“…Information collected at the single particle level can reveal distributions of behavior that cannot be observed in ensemble measurements. Because aggregates of particles can be distinguished from monomers, single particle analysis is poised to become a major asset in the study of the PC and its heterogeneity …”