Driving forces for layer-by-layer self-assembly of films of SiO2 nanoparticles and heme proteins

Heme protein hemoglobin (Hb) or myoglobin (Mb) and silica nanoparticles in a variety of charge states were assembled layer-by-layer into films on solid surfaces to investigate the driving forces for film assembly. Cyclic voltammetry (CV), quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS), and U-V-vis and reflectance absorption infrared (RAIR) spectroscopy were used to characterize the different {SiO2/protein}(n) films. Even when the proteins and silica were both negatively charged, stable layer-by-layer {SiO2/protein}(n) films were successfully fabricated, although amounts of protein were smaller than when nanoparticles and proteins had opposite charges. Results suggest the importance of localized Coulombic attractions between the negative nanoparticle surface and positively charged amino acid residues on the Mb or Hb surfaces in the assembly and for the stability of {SiO2/protein}(n) films.