Changes in structure and material properties of the surface-bound layer, such as viscoelasticity, can be inferred from changes in energy dissipation to the environment (∆D). To characterize amyloid elongation, we monitored multiple recurring growth phases of α-synuclein fibrils immobilized on a QCM-D sensor (Fig. A & B). Upon injection a rapid change in frequency and dissipation is observed. This effect originates from the viscosity and density change of solution, as the α-synuclein solution contains 0.5 v/v% ethanol (from addition of PMSF, see Methods). Such a water-ethanol mixture is expected to have an approximately 10 % higher viscosity than pure water . The frequency and dissipation perturbation is reversible when returning to pure buffer conditions (Fig. ). In the incubation period the frequency and dissipation change linearly in time, demonstrating that both dissipation and frequency changes can be used as reporters of fibril growth. Amyloid growth rates are expected to be constant throughout each growth phase, as monomer is not significantly depleted in the cell within the time of the measurements at the monomer concentrations employed . However, during the last growth phase the rate of the frequency response decreases throughout the measurement, while the rate of dissipation change remains constant. The behaviour can be explained by fibrils growing beyond their persistence length and increasingly extend away from the sensor surface where the mass sensitivity decreases. The dissipation response appears to be less affected by this phenomenon compared to the frequency response.