In contrast to αSyn, the SH3 domain of phosphatidyl-inositol-3-kinase (PI3K-SH3) contains a single tryptophan which gives the protein two distinct fluorescence emission spectra in a monomeric and fibrillar state (fluorescence is fully quenched in the fibrillar state), making it an ideal probe for studying fibril stability by DSF . Our analysis of PI3K-SH3 fibril stability by FIDA agreed well with DSF measured here (Figure , Table ) and published previously . In contrast, the SLS signal was noisy at low denaturant concentrations, presumably due to higher order assembly of fibrils and sedimentation and could not be used for the fitting. Using three model cases we successfully verified the general applicability of our novel approach for analyzing fibril stability. The only other method which could be successfully applied to all three cases was ThT fluorescence which is also simple, fast, and scalable. However, different fibrils have distinct sensitivity to ThT, and some fibril polymorphs are even "ThT-invisible" and cannot be monitored by this fluorescent dye . Although applicable in some cases, scattering techniques (SLS and DLS) suffer from large dependency of scattered light intensity on aggregate size, hindering reliable normalization of the depolymerization curves when small amounts of residual aggregates are present in the depolymerized samples at high urea concentrations. Similar issues apply to ultracentrifugation, which additionally requires higher volumes of sample (> 30 μL), specialized equipment, and long centrifugation times (> 1.5 h) at high-speed (> 150,000 x g) to ensure complete removal of the aggregates.