The recent introduction of protein microarrays is now providing tools for the global profiling of biochemical activities.[1] Snyder and co-workers, for example, used yeast protein chips to identify kinase substrates and lipid-binding proteins.[2] Labaer and co-workers reported self- assembling protein microarrays to map pairwise interactions among 29 human DNA replication proteins.[3] Any application of a protein chip must involve a suitable labeling ...