The present invention relates to a microarray comprising at least 50,000 oligopeptide features per cm2 where the oligopeptide features represent at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, at least 99%, or 100% of the proteome of a virus or an organism. The present invention further relates to methods for the synthesis of such microarrays and methods of using microarrays comprising at least 50,000 oligopeptide features per cm2. In an embodiment of the invention, the oligopeptide features represent proteins expressed in the same species, wherein the oligopeptide features are presented in a tiling pattern representing at least about 5,000, at least about 10,000, at least about 15,000, at least about 20,000, or at least about 25,000 proteins expressed in a species. In some embodiments, the oligopeptide microarray features represent proteins expressed in the same species, wherein the microarray features are present in a tiling pattern that represents between about 5,000 and 50,000 expressed proteins, between about 10,000 and 50,000 expressed proteins, between about 15,000 and 50,000 expressed proteins, between about 20,000 and 50,000 expressed proteins, or between about 25,000 and 50,000 expressed proteins.