By comparing the different overtones, we find a frequency overtone dependency of the fibril growth response, while no such dependency is present for HsP binding (Fig. ). This indicates that the dominating source of mass for fibril growth originates from liquid contributions, whereas the HsP binding frequency response is dominated by the dry mass , consistent with the ∆D to ∆F ratio of each mechanism. Our observations agree with earlier findings that the QCM frequency response can be attributed in large parts to water trapped in the fibril matrix .