Fluorescent proteins as biosensors by quenching resonance energy transfer from endogenous tryptophan: detection of nitroaromatic explosives.

Ensuring domestic safety from terrorist attack is a daunting challenge because of the wide array of chemical agents that must be screened. A panel of purified fluorescent protein isoforms (FPs) was screened for the ability to detect various explosives, explosive simulants, and toxic agents. In addition to their commonly used visible excitation wavelengths, essentially all FPs can be excited by UV light at 280 nm. Ultraviolet illumination excites electrons in endogenous tryptophan (W) residues, which then relax by Förster Resonance Energy Transfer (FRET) to the chromophore of the FP, and thus the FPs emit with their typical visible spectra. Taking advantage of the fact that tryptophan excitation can be quenched by numerous agents, including nitroaromatics like TNT and nitramines like RDX, it is demonstrated that quenching of visible fluorescence from UV illumination of FPs can be used as the basis for detecting these explosives and explosive degradation products. This work provides the foundation for production of an array of genetically-modified FPs for in vitro biosensors capable of rapid, simultaneous, sensitive and selective detection of a wide range of explosive or toxic agents.