DEL4000 library selection with polyclonal human IgG. (A) Plot representing the frequency (i.e., sequence counts) of DEL4000 library members after selection on polyclonal human IgG resin, as revealed by high-throughput 454 sequencing. The chemical structures of some of the most relevant compounds enriched are indicated. The building blocks used in the 2 synthetic steps are indicated in green and red, respectively, together with an identification number. (B) Affinity chromatography of CHO cells supernatant on resin containing the compound 02-40, spiked with human IgG labeled with either Cy5 or biotin. For antibody purifications, relevant fractions were analyzed by SDS/PAGE both with Coomassie blue staining and with a specific detection method (Cy5 fluorescence and a streptavidin horseradish peroxidase-based blot, respectively). M, molecular weight marker; In, input fraction for the chromatographic process; W, pooled washed fractions; E, pooled eluted fractions. The lane (+) corresponds to Cy-5- or biotin-labeled polyclonal human IgG. In, W, and E fractions were normalized to the same volume before SDS/PAGE analysis. The SDS/PAGE gels containing the fractions from the purification of both Cy5- and biotin-labeled IgG were analyzed by conventional staining with Coomassie blue, or by using a label-specific procedure (fluorescence imaging for Cy5-labeled IgG or streptavidin-based blot for biotinylated IgG; see also SI Text).