In summary, we have illustrated that the surface-based biosensing technique QCM-D can provide insights into amyloid growth mechanisms of modified fibrils which may be unavailable in bulk measurements due to flocculation, changes in dyesensitivity and persistent modifying agents. We demonstrate that dissipation-frequency (DF)-plots allow the discrimination of addition/removal of mass originating from fibril core and non-core regions as well as surface binding of proteins. Combining our QCM-D results with kinetic modeling, we show that proteolytic truncation of the disordered flanking regions of fibrils does not abolish their ability to elongate through the addition of unmodified monomer. Furthermore, such proteolysis leads to the generation of additional growth-competent ends at neutral pH, where monomer-dependent secondary nucleation is very inefficient, and hence suggests the existence of a new secondary pathway with potential relevance for the proliferation of amyloid pathology in vivo.