Single-molecule Dynamics of Fibrinogen and Bovine Serum Albumin Adsorption on Silica Nanoparticle Coatings Observed Using High-Speed Atomic Force Microscopy.

High-speed atomic force microscopy (HS-AFM) was used to directly visualize the single-molecule adsorption dynamics of fibrinogen (FG) and bovine serum albumin (BSA) on atomically smooth mica and on silica nanoparticle (SiNP) coatings. By capturing the motion of individual proteins against a static background, HS-AFM enables the resolution of key dynamic processes, including surface diffusion, conformational adaptation, binding and unbinding events, and interfacial fluctuations on nanostructured surfaces. The results revealed two distinct, protein-specific adsorption mechanisms on SiNP coatings. BSA adsorbed via strong protein-surface interactions that promoted conformational adaptation and localized shell-like coverage of individual nanoparticles-progressively occupying interparticle interstices but leaving the overall nanoparticle topography visible. In contrast, FG adsorption followed a concentration-dependent, two-stage process; proteins first adsorbing directly to the nanoparticle surface, and at higher coverages, associated via protein-protein interactions, producing a secondary, dynamic, and loosely bound outer layer. This FG protein layer reduced the root-mean-square roughness of the underlying surface from a peak of ∼13.2 to ∼7.8 nm while introducing pronounced molecular-level fluctuations at the interface, as inferred from tip-induced smearing in HS-AFM images. These findings demonstrate that the relevant biological interface is not a static substrate, but a dynamic, structurally defined protein layer, whose properties are dictated by both nanoscale surface topography and the characteristics of the adsorbing proteins.