Abstract: This invention relates to a method of determining presence, amount and/or activity of a clostridial neurotoxin in a sample, the method comprising or consisting of the following steps: (a) bringing said sample into contact with a liposome, said liposome comprising (aa) at least one receptor on its outer surface, said receptor being capable of binding said neurotoxin and comprising or consisting of (i) a glycolipid and (ii) a peptide or protein; and (ab) a substrate in its interior, said substrate (i) being cleavable by the peptidase comprised in said neurotoxin and (ii) generating a detectable signal upon cleavage, said detectable signal preferably being generated by (1) the donor of a FRET pair, said donor exhibiting increased fluorescence upon cleavage by said peptidase, (2) a luminescent compound formed upon said cleavage, or (3) an enzyme formed upon said cleavage; and (b) determining whether an increase in signal occurs as compared to the absence of said sample, wherein such increase is indicative of the