Surface interactions between proteins and biomaterials are fundamental to biological processes and a means to measure these interactions with minimum perturbation to the system of interest has remained elusive. In this paper we address this problem by analysing the total unfolding force of a surface adsorbed protein, in this case fibronectin. By summing all unfolding events, domains that may be interacting with the surface are considered. We propose a protocol for comparing like with like in terms of protein behaviour based on the number of events in the sawtooth pattern. Using this method it is possible to distinguish surface behaviour between several biologically relevant surfaces including hydroxyapatite, collagen and lipids. Moreover the difference in total unfolding confirms the difference in protein interaction/conformation on the various surfaces.