Unbinding process of adsorbed proteins under external stress studied by atomic force microscopy spectroscopy

We report the study of the dynamics of the unbinding process under a force load f of adsorbed proteins (fibrinogen) on a solid surface (hydrophilic si lica) by means of atomic force microscopy spectroscopy. By varying the load ing rate r(f), defined by f = r(f) t, t being the time, we find that, as fo r specific interactions, the mean rupture force increases with r(f). This u nbinding process is analyzed in the framework of the widely used Bell model . The typical dissociation rate at zero force entering in the model lies be tween 0.02 and 0.6 s(-1). Each measured rupture is characterized by a force f(0), which appears to be quantized in integer multiples of 180-200 pN.