Analyzing the Biological Entity of Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 72

one, which is reversed upon binding to the nanoparticle surface leading to gradual
denaturation of GB1 on latex beads. Further studies should unravel the protein “hot
spots” directly responsible for the interaction. Exact knowledge of these aspects will
not only lead to a better molecular understanding of protein binding to nanoparticles
but also will ultimately enable scientists to produce “designed protein coatings” spe-
cifically aimed at lowering toxicity, altering uptake, or changing biodistribution in a
defined way, for instance, for time-dependent drug release.
In other studies, FCS was successfully applied to study protein corona thick-
ness, layer structure, or a number of adsorbed proteins (Maffre et al. 2011; Milani
et al. 2012). For instance Milani and coworkers used fluorescently labeled transferrin
to analyze adsorption on polystyrene beads. They could follow the formation of a
first monolayer, which actually represents the “hard corona.” This was followed by
formation of a secondary and a tertiary layer, which represent the “soft corona” as
those layers proved to be exchangeable in competing experiments when unlabeled
transferrin was added and the first monolayer was not. This clearly proves that the
concept of “hard” and “soft” corona holds true at least for this very simplified and
ideal system and that the postulated “memory effect” (e.g., keeping traces of “pri-
mary corona” when nanoparticles move from one body compartment to another)
could have a molecular explanation.
4.2.4 i nteraCtion With P lasma or s erum
The high complexity of serum or plasma typically makes this dispersion medium
less suitable to study detailed molecular mechanisms of interaction. However to
determine the identity of the corona and identify which proteins do or do not interact
with nanomaterial surfaces it is perfectly well suited. The study performed by Tenzer
and coworkers delivers a quite comprehensive overview of protein coronas of silica
nanoparticles of various sizes (8, 20, and 25 nm) in blood plasma (Tenzer et al. 2011).
Although they found a significant overlap in the respective coronas indicating that
a large part of the corona seems to be material specific, 37% of the corona proteins
are determined only by the particle size with no apparent pattern manifesting. They
showed that the occurrence of proteins in the corona does not directly reflect the
amount of those proteins in plasma. Some of the corona proteins, which are close
to or even below the detection limit in plasma, are highly enriched in the corona,
although other proteins, which are among the most abundant plasma proteins, could
still be detected in the corona but in terms of quantity they are certainly not holding
the same rank as could be deduced just from their serum abundance. For example
α-2-macroglobulin and complement C3 are the second and third highly abundant
proteins in plasma, yet in the corona of 125-nm silica nanoparticles apolipoprotein
A1 (8th place in serum) and prothrombin with a 35-fold enrichment take the second
and third place. Complement C3 and α-2-macroglobulin are only the 5th and 13th
most abundant proteins in the corona.
Apart from size, the surface charge is another major parameter influencing the
composition of the protein corona. Influence of the surface charge of latex nanoparti-
cles has been analyzed in several publications (Cedervall et al. 2007; Lundqvist et al.
2008; Aggarwal et al. 2009). In the study performed by Lundqvist and coworkers it