Patent ID: 7638294

Claim:
A method of determining the presence or activity of a clostridial toxin, comprising the steps of: (a) treating with a sample, including a clostridial toxin, under conditions suitable for clostridial toxin protease activity, a clostridial toxin substrate, said clostridial toxin substrate comprising (i) a donor fluorophore; (ii) an acceptor having an absorbance spectrum overlapping the emission spectrum of said donor fluorophore; and (iii) a clostridial toxin recognition sequence comprising a cleavage site, wherein said cleavage site intervenes between said donor fluorophore and said acceptor; and (b) measuring fluorescence polarization of said treated clostridial toxin substrate by exciting said fluorophore with plane polarized light; wherein an increase in said fluorescence polarization is indicative of the activity of said clostridial toxin in said sample due to cleavage of said treated clostridial toxin substrate by said clostridial toxin; and wherein a decrease in said fluorescence polarization is indicative of the presence of said clostridial toxin in said sample due to complex formation of said clostridial toxin with said treated clostridial toxin substrate.