NUCLEATION AS THE RATE-LIMITING STEP IN THE INITIAL ADSORPTION OF FERRITIN AT A HYDROPHOBIC SURFACE

Adsorption of ferritin on a methyl silanized quartz surface was measured with in situ ellipsometry and transmission electron microscopy (TEM). An initial lag phase in the adsorption process followed by a rapid increase in the amount of bound ferritin was recorded by ellipsometry. The time dependence of the rapid adsorption exhibited an exponential form. The initial lag phase corresponds to a nucleation process manifested by the TEM studies. Adsorption was initiated at 10(9) sites per square centimetre, which corresponds well to the thickness measured by ellipsometry. The accelerated adsorption recorded by ellipsometry corresponds to an accelerating growth of protein clusters at the surface as seen by TEM. The present data indicate that the initial rate of adsorption of ferritin is limited by nucleation and not by diffusion. The exponential acceleration of nucleation and growth-like kinetics lead to depletion of protein in the reaction zone, which is the mechanism behind the often-seen mass transport limitation of macromolecular reactions at solid-liquid interfaces.