Researchers identified a class of new FibrilPaint peptides (FP5–FP8) that retain amyloid-binding activity despite variations in charge, terminus chemistry, and residue order. Flow Induced Dispersion Analysis (FIDA), on a Fida 1 instrument, was used to measure the hydrodynamic radius of fluorescently labelled FibrilPaint peptides in the presence and absence of preformed Tau and Huntingtin exon-1 fibrils, with size increases confirming peptide binding and enabling determination of fibril length. It is an example of using FIDA to characterize peptide binding to amyloid fibrils and quantify particle size in solution.