ADSORPTION AND OPTICAL-PROPERTIES OF FERRITIN LAYERS ON GOLD STUDIED WITH SPECTROSCOPIC ELLIPSOMETRY

Thin layers of ferritin adsorbed on gold substrates were studied in si tu in buffer with spectroscopic ellipsometry. A four-phase model was u sed to determine their optical properties. The top layer was the prote in layer and the bottom layer an effective medium layer used to model interaction between the protein molecules and the gold substrate. An a nalysis of the time dependence of the ellipsometric data showed that t he adsorption can be described as a two-state process, The molecules a dsorb first in a precursor state from which they can adsorb in a secon d state involving an electronic interaction with the gold substrate. T he interaction with the gold was found to grow stronger with time. At the same time the layer thickness decreased and the layer density incr eased, The evaluation of ellipsometrically determined thicknesses and surface concentrations is also discussed. (C) 1995 Academic Press, Inc .