Bovine Serum Albumin Adsorption at a Silica Surface Explored by Simulation and Experiment

Abstract

Molecular details of BSA adsorption on a silica surface are revealed by fully atomistic molecular dynamics (MD) simulations (with a 0.5 μs trajectory), supported by dynamic light scattering (DLS), zeta potential, multiparametric surface plasmon resonance (MP-SPR), and contact angle experiments. The experimental and theoretical methods complement one another and lead to a wider understanding of the mechanism of BSA adsorption across a range of pH 3-9. The MD results show how the negatively charged BSA at pH7 adsorbs to the negatively charged silica surface, and reveal a unique orientation with preserved secondary and tertiary structure. The experiments then show that the protein forms complete monolayers at ∼ pH6, just above the protein's isoelectric point (pH5.1). The surface contact angle is maximum when it is completely coated with protein, and the hydrophobicity of the surface is understood in terms of the simulated protein conformation. The adsorption behavior at higher pH > 6 is also consistently interpreted using the MD picture; both the contact angle and the adsorbed protein mass density decrease with increasing pH, in line with the increasing magnitude of negative charge on both the protein and the surface. At lower pH < 5 the protein starts to unfold, and the adsorbed mass dramatically decreases. The comprehensive picture that emerges for the formation of oriented protein films with preserved native conformation will help guide efforts to create functional films for new technologies.

The conformation of bovine serum albumin adsorbed to the surface of single all‐dielectric nanoparticles following light‐induced heating

“…To coat our NPs, an aqueous solution of BSA (0.1 g/mL) was dropped (0.05 mL) onto these particles on the gold film, which was rotating at 100 Hz at room temperature in air. We determined in advance zeta potential of our c‐Si and c‐Ge NPs with an oxide shell in water to be −25 and −14 mV, respectively, a good agreement with the corresponding value for silica shell . BSA can also be easily adsorbed onto oxidized c‐Si and c‐Ge NPs via long‐range electrostatic and short‐range hydrophobic interactions at different pH levels as shown earlier .…”

“…We determined in advance zeta potential of our c‐Si and c‐Ge NPs with an oxide shell in water to be −25 and −14 mV, respectively, a good agreement with the corresponding value for silica shell . BSA can also be easily adsorbed onto oxidized c‐Si and c‐Ge NPs via long‐range electrostatic and short‐range hydrophobic interactions at different pH levels as shown earlier . The rotation of the film in combination with water evaporation led to uniform distribution of the BSA in a solid state on the surface of single NPs.…”

“…This was confirmed by confocal Raman spectroscopy (Figure A), which revealed both Raman modes of each NPs and vibrational modes of BSA in a folded state . It should be noted that BSA was expected to be randomly distributed over the NP surface and only partially in a folded state without significant alteration of the protein structure.…”

Adsorption of Bovine Serum Albumin on Carbon-Based Materials

“…It is likely that the observed maximum of BSA adsorption in the kinetic experiments in early stages reflects the conformational changes in the first layer of the adsorbed BSA molecules, which occur slower than the initial adsorption. The initial conformation of BSA adsorbed in the first layer might allow weak or co-operative attraction of other BSA molecules which ceases to exist once the BSA molecules at the surface underwent further conformational changes thus releasing the weakly retained molecules back in solution [34,35].…”

“…BSA molecules which ceases to exist once the BSA molecules at the surface underwent further conformational changes thus releasing the weakly retained molecules back in solution [34,35]. Figure 4d is the crystal structure of Bovine Serum Albumin [36].…”