Evidence for the surface-diffusion mechanism of solution crystallization from molecular-level observations with ferritin

We employ atomic force microscopy to monitor in situ, in real time, the molecular processes of crystallization of ferritin, a protein that has an inorganic single-crystalline core that can be varied. We determine the statistics of molecular attachment and detachment at the growth sites and find that the ratio of the fluxes in and out of the kinks is significantly lower than expected, assuming direct incorporation of the molecules from the solution. Determinations of the energy barrier for incorporation yield approximately 30 kJ mol(-1), significantly higher than expected for this mechanism. We conclude that attachment of molecules occurs via the surface adsorption layer. The surface coverage resulting from this mechanism is approximately 0.9, suggesting a growth mode different from the classical surface diffusion mechanism.