A team of scientists at The Scripps Research Institute and the Skaggs Institute for Chemical Biology have alighted on a photochemical phenomenon with significant potential for fluorescent labeling of analytes in diagnostics and clinical applications (Science 290, 307–313, 2000). Complexes between monoclonal antibodies (mAbs) and derivatives of the aromatic hydrocarbon stilbene produce an intense blue fluorescence when irradiated. Counterintuitively, low temperatures abolish this fluorescence (freezing normally intensifies light emission). Emission spectra from fluorescence spectroscopy suggest the formation of an excited-state complex (“exciplex”) between the mAb and the stilbene derivative. Crystallographic and time-resolved spectroscopic data on the mAb–stilbene complex indicate that the fluorescence results from a dynamic interaction between the stilbene and the indole ring of a tryptophan residue in the mAb binding site. Lead author Kim Janda hopes to develop artificial nucleoside bases derivatized with stilbene (which, together with the mAb, could be used in gene sequencing) and stilbene-derivatized substances for cell labeling and tracking in the body. “Unlike traditional reporters, the fluorescence is not subject to photobleaching, and the stilbene system is robust, well characterized, and inexpensive,” he says.