This study shows that the anti-amyloid Bri2 BRICHOS chaperone domain specifically targets α-synuclein aggregation and the toxic species driving neurodegeneration in Parkinson's disease. Combining aggregation kinetics, ex vivo electrophysiology and binding assays, the authors found BRICHOS mainly suppresses fibril-surface secondary nucleation, lowering oligomer generation, and also binds β-sheet-containing oligomers. Flow Induced Dispersion Analysis (FIDA), alongside ITC, SPR and NMR, measured the hydrodynamic radius of labeled BRICHOS to map its binding: no binding to monomers, binding to fibrils, and a defined affinity for isolated oligomers (KD ~78 nM). It is an example of using FIDA to measure chaperone binding affinity and selectivity in solution.