NONLINEAR KINETICS OF FERRITIN ADSORPTION

The adsorption of ferritin at a methylized quartz surface was measured with off-null ellipsometry and transmission electron microscopy. An i nitial lag-phase was seen, followed by an accelerating adsorption lead ing to mass transport limitation of the reaction. The rate of adsorpti on then decreased at a surface concentration far below monolayer cover age, and a continuously decreasing rate of binding was seen. The slope of the binding rate was linear with the logarithm of time (fractal ki netics). The adsorbed ferritin molecules were distributed in clusters as seen by transmission electron microscopy. Clusters grown during the mass transport limited adsorption had crystalline structure at short range and low fractal dimensions (d(f) = 0.89) over long range. Cluste rs grown during adsorption with fractal kinetics showed random structu re at short range and a high fractal dimension d(f) = 1.86 over all ra nges. These findings indicate some new important mechanisms responsibl e for the complex kinetics of macromolecular reactions at solid-liquid interfaces. The results are discussed in relation to recently develop ed theories of self-organized criticality.