Following the successful modelling and experimental validation of the NPs behaviour during FIDA, we extended the methodology to the analysis of amyloid fibrils (Figure ). We used αSyn fibrils equilibrated in 1 M urea to allow their partial dissociation to monomers and analyzed the resulting mixture using FIDA (Figure ). The profile resembled the one obtained as the sum of NPs and monomeric αSyn (Figure e), suggesting similar, non-diffusive behaviour of the fibrils. We analyzed the curve using numerical COMSOL simulations assuming two species and obtained diffusion coefficients of 7.0×10 -11 and 1.2×10 -11 m 2 .s -1 for αSyn monomer and fibril, respectively. Both values are in excellent agreement with those measured by FIDA of αSyn monomers (Rh = 3.5 nm), and DLS analysis of fibrils (Rh = 20.3 ± 0.5 nm). The latter corresponds to a fibrillar species of around 100 nm length with 10 nm width based on the models of rod-like particles derived elsewhere . Together, our results clearly demonstrate that FIDA is a suitable method for separation and individual quantification of diffusive soluble proteins from their mixtures with non-diffusive particles.