Figure 7 A) The simulated enhanced electric field distribution
near the tips (top row) and around the core (bottom row) of AuNS. E is
the polarisation direction and K is the propagation direction. The
wavelength of the incident light is 785 nm; B) The simulated LSPR peaks
of AuNS@BSA with different thicknesses of protein layers around the core
(PC – protein corona and its thickness).
To further study this phenomenon we performed MD simulations to reveal
the potential link between gold surface curvature (shape of GNPs) and
the adsorption of BSA protein. Four types of gold surface models were
constructed (Figures 8 A–D ): plane (P), truncated cone large
(TCL), truncated cone small (TCS), and spherical tip (ST). For other
details regarding the simulation please see Supporting
Information . Initially, the protein was placed away from the gold
surface with a minimum distance of 0.8 nm. The protein was adsorbed on
the gold surface within a 1 ns simulation. The energy of the system was
averaged over a 1 ns simulation after adsorption under a canonical
ensemble. The temperature was set to be 300 K. To quantify the
adsorption strength between BSA and the gold surface, the adsorption
energy \(E_{\text{ad}}\) was calculated as (Equation 1):
\(E_{\text{ad}}=\ -\left(E_{Gold@BSA}-E_{\text{BSA}}-E_{\text{Gold}}\right)\)(1)
where \(E_{Gold\&BSA},\ E_{\text{BSA}}\ \)and \(E_{\text{Gold}}\) are
energies of Gold@BSA, BSA and gold surface structures respectively. A
larger adsorption energy indicates a stronger interaction between BSA
and the gold surface, so the BSA is more likely to remain adsorbed and
less likely to desorb under the local thermal
fluctuations.[41] For each gold surface model, the
extreme and average adsorption energies along 10 directions are
presented in Figure 8 E . The complete results including each
orientation can be found in the Supporting Information Table
S3 . When the curvature of the gold surface increases, the number of
gold atoms within the force cut-off distance of BSA decreases, and the
van der Waals force decreases. Thus, with the increase of the radius of
curvature, the adsorption energy decreases significantly. Such results
illustrate that BSA is less likely to be adsorbed on the surface with
large curvatures, such as the spikes on the gold nano star surface,
which supports the experimental finding that BSA is seldom found on the
AuNS tips.