Pleasingly, after completing a mock selection round, whilst 3.9% of the input DNA was recovered following standard affinity panning, almost no input DNA (0.0069%) was recovered following washes with 5 M guanidine (Supplementary Figure ). This confirmed that the guanidine washes were sufficient to dissociate a tight binding peptide (K D = 0.49 nM) from its target protein , most likely due to target denaturation.