MPs were produced in < 75% purity (see Supplementary Figures for the primary data). These data strongly support the idea that the IP+ grafting chemistry is suitable for the creation of libraries of MPs. After thorough washing and equilibration in an aqueous buffer, the beads were blocked with Starting Block to discourage non-specific protein binding, then incubated for one hour with Alexaflour 647-labeled SA (A647-SA, 150 nM) at room temperature. After thorough washing, the amount of fluorescence retained by the beads in each well was measured using a fluorescent plate reader. This protocol was conducted in triplicate. The five bead-displayed MPs that retained the highest levels of A647-SA in each run were synthesized as C-terminal fluorescein conjugates and their solution affinities for unlabeled SA were determined by titration followed by an increase in fluorescence polarization (Figure ). These data showed IP + -linked MP29 to be the best SA ligand with a KD of approximately 7.0 µM (Figure ). These data demonstrate that the IP + chemistry is suitable for the construction of useful screening libraries of novel MPs.