Direct Observation of Postadsorption Aggregation of Antifreeze Glycoproteins on Silicates

The adsorption of antifreeze glycoproteins (AFGP) from aqueous solution onto two different silicate minerals, muscovite mica and amorphous silica−titania, has been directly observed for the first time in situ using atomic force microscopy (AFM) and optical waveguide lightmode spectroscopy (OWLS). The former yields the lateral distribution and heights of adsorbed single molecules and massed adsorpta, and the latter enables the precise number of adsorbed AFGP per unit area of surface to be determined as well as the kinetics of adsorption and desorption. On both surfaces the AFGP were initially deposited as isolated molecules. On mica they remained as such and could be imaged as compact, globular objects, in contrast to the elongated form presumed to exist in solution. On silica−titania they subsequently formed isolated conical deposits containing large numbers of molecules. The relevance of these results to the adsorption of the AFGP on ice is discussed.