Method and compositions for detecting botulinum neurotoxin

A method for detecting a botulinum neurotoxin, the method comprising, a) providing a construct capable of fluorescent resonance energy transfer (FRET), comprising a linker peptide, a donor fluorophore moiety and an acceptor fluorophore moiety, a membrane-targeting domain comprising at least 5 contiguous amino acids of SNAP-25 (SEQ ID NO:7), wherein the at least 5 contiguous amino acids comprise amino acid residues 116-120 of SNAP-25, and wherein at least a portion of the linker peptide corresponds to a cleavage domain of the botulinum neurotoxin to be detected, wherein the linker peptide adopts a conformation whereby FRET occurs between the donor and acceptor fluorophore moieties, and wherein an emission spectrum of the donor fluorophore moiety overlaps with an excitation spectrum of the acceptor fluorophore moiety,

• b) contacting the construct to a sample suspected of containing a botulinum neurotoxin under a condition under which the botulinum neurotoxin cleaves the protein substrate and
• c) detecting and comparing FRET before and after the construct is contacted to the sample,
• wherein a decrease in FRET as compared to a level detected before contacting to the sample indicates the presence of botulinum neurotoxin in the sample.