Organophosphates are toxic species commonly found in both pesticides and chemical warfare agents whose rapid and severe effects on human and animal health lie in their ability to block the action of acetylcholinesterase, a critical central nervous system enzyme.As a consequence, intense research efforts have been directed to develop sensitive and selective schemes for their detection. One of the most convenient and simplest means of chemical detection is generating an optical event, such as a change in absorption or fluorescence color, in the presence of an analyte of interest. It has been previously shown that lanthanide complexes, with their characteristically narrow excitation and emission bands, intense fluorescence and long excited-state lifetimes, are well suited to be used as fluorescence-based chemical sensors. For example, Eu~(3+) complexes can exhibit intense luminescence in the presence of an appropriate UV-light-absorbing ligand, via the so-called “antenna effect”. Any analyte, which can act as a competitive binder for the Eu~(3+), can “switch-off” the Eu~(3+)-based emission and potentially restore the emission of the “free” ligand. On the other hand, many metal ions do not lend themselves to metal-based emission, for example ZnEu~(2+) or La~(3+); in these cases the ligand-based fluorescence may be quenched or shifted to a different wavelength upon complexation. Taking advantage of these processes and exploiting the known binding affinity of organophosphates to lanthanide ions, we present herein a most versatile sensor platform (Scheme 1) that combines high selectivity and sensitivity with ease of signal transduction. The approach relies on the fact that 2,6-bis(1’-methyl-benzimidazolyl) (Mebip) ligands are highly fluorescent and have been shown to act as “antenna” for Eu~(3+) ions.
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