Direct measurement of interactions between adsorbed protein layers using an atomic force microscope

An atomic force microscope (AFM) in conjunction with the colloid probe technique has been used to measure directly the interaction of adsorbed layers of the protein bovine serum albumin (BSA). The BSA was adsorbed on both a silica colloid probe and a silica surface. Measurements of force- distance curves were made at various salt concentrations and pHs. The measured force-distance curves were in good quantitative agreement with predictions based on the DLVO theory using zeta potentials (outer Helmholtz plane potentials) calculated for BSA from an independently validated site- binding-site-dissociation surface model. The paper hence provides a direct confirmation that the AFM colloid probe technique can provide a useful means of directly quantifying the interaction of biological macromolecules.