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.