A patterned combinatorial library of peptide-grafted polymer affinity materials is screened for target protein binding. In situ light-directed synthesis is used to produce high-density libraries that allow for the screening in parallel within an area less than 1 cm(2). From these libraries, specific peptide/polymer combinations are identified with very high target protein affinity, enabling facile detection of the target at concentrations in the low picomolar range in the presence of excess competitor.