Figure 8 The adsorption configurations of the maximum
adsorption energy for A) the P (plane) model; B) the ST (spherical tip)
model (0_270_0 BSA orientation); C) the TCL (truncated cone large)
model (0_180_0 BSA orientation); D) the TCS (truncated cone small)
model (90_0_0 BSA orientation). E) The average adsorption energy for
each model. The error bar shows the maximum and the minimum value in 10
orientations.
The adsorbed amino acids, as defined by being less than 0.5 nm from the
gold surface, were also counted. For the same type of gold surface, the
adsorbed amino acid number had a positive correlation with the
adsorption energy (Supporting Information Table S3 ). However,
for different surfaces, the average adsorbed amino acid number is
similar but the adsorption energy per amino acid for the smaller
curvature surfaces is significantly higher. The types of the adsorbed
amino acids were counted, and the results are shown inSupporting Information Figure S2 .
Conclusion
In this work, we have studied GNP-protein interactions and found some
notable differences between BSA adsorption to spherical and anisotropic
(star-shaped) nanoparticles. In particular, we have considered the
effects of high ionic strength salt and varying protein concentrations
(as represented by the main protein in most biological media, BSA). We
found salt and proteins stabilise or destabilise the particles depending
on their concentrations and the particle shape. The protein layers
strongly adsorbed onto the GNPs surfaces, also known as the hard protein
corona, affect the biological identity and alter their function and
properties. We have found that the PC is not always the “enemy”.
Formation of protein layers around nanoparticles can increase their
stability in presence of salts. To utilize the benefits and omit the
drawbacks of PC formation, it requires a thorough understanding of
nanoparticle-protein interaction patterns. For spherical nanoparticles,
the PC formation was confirmed by extinction spectroscopy, zeta
potential and SERS measurements. However, in the case of anisotropic
nanostars while extinction spectroscopy and zeta potential analysis
indicated the presence of a PC, SERS analysis, did not show the presence
of protein on the surface of nanostars. With FEM simulations we have
shown that the electric field enhancement around different parts of
nanostars varies with the strongest enhancement at the tips and almost
no enhancement at the core. MD simulations, conversely, showed more
proteins would bind near the more planar core of the nanostars than at
the tips. Thus we see evidence of a PC but a lack of SERS enhancement of
the proteins on nanostars. Overall, this fascinating result means that
anisotropic nanoparticles might enjoy protein-mediated stabilization and
other benefits of PC, while having their plasmonic properties preserved
for small molecule analytes to bind to their “hot-spots” which are
free from protein binding.