Bioconjugates of quantum dot nanocrystals possess unique optical properties that allow them to serve as exceptional biological imaging and sensing reagents. Protein kinases are an important family of enzymes that phosphorylate serine, threonine, or tyrosine side chains and are critical in cell signaling and cancer biology, but despite their biomedical and pharmaceutical significance, their activity has been little explored using quantum dot technology. We demonstrate that self-assembled peptide-quantum dot conjugates can serve as surrogate substrates in a simple homogeneous assay for protein kinase activity. Enzymatic phosphorylation of the peptide-conjugates is detected by means of a complementary FRET-acceptor labeled antiphosphotyrosine antibody, with formation of the immunocomplex resulting in energy transfer between the quantum dot and FRET acceptor molecules. This approach should facilitate the development of new assays for protein kinases and other enzymes based on quantum dot FRET donors.