A method of detecting botulinum neurotoxin serotype A (BoNT/A) activity in a sample, the method comprising the steps of: a. contacting a cell from an established cell line expressing a SNAP-25 polypeptide consisting essentially of at least a portion of human SNAP-25 comprising Q 197 -R 198 of human SNAP-25 cleavable by BoNT/A with a sample suspected of comprising BoNT/A, wherein the established cell line is susceptible to BoNT/A intoxication at about or less than 1 fmol BoNT/A per liter sample, as indicated by the enzymatic cleavage of said SNAP-25 polypeptide by BoNT/A to yield a fragment of said SNAP25 polypeptide comprising the C-terminal amino acid sequence of a peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond, wherein the sequence surrounding the BoNT/A cleavage site present in said SNAP-25 is denoted as P 5 -P 4 -P 3 -P 2 -P 1 -P 1 '-P 2 '-P 3 '-P 4 '-P 5 ', with P 1 -P 1 ' representing the scissile bond; b. isolating polypeptides from the cell; c. contacting the polypeptides with a monoclonal antibody that specifically binds to the peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond, wherein said antibody specifically binds to an epitope of said fragment of said SNAP25 polypeptide comprising the C-terminal amino acid sequence of said peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond with an equilibrium disassociation constant of less than 0.450 nM and wherein said antibody has an association rate constant for an epitope of intact SNAP-25 polypeptide comprising Q 197 -R 198 of human SNAP-25 of less than 1×10 1 M -1 s -1; and d. detecting the presence of any antibody-antigen complex comprising the antibody and the fragment of said SNAP-25 polypeptide comprising the C-terminal amino acid sequence of said peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond, wherein the amount of the antibody-antigen complex detected correlates to the amount of BoNT/A in the sample, and wherein the method is performed as a PK assay to detect the presence of BoNT/A in mammalian fluids. a. contacting a cell from an established cell line expressing a SNAP-25 polypeptide consisting essentially of at least a portion of human SNAP-25 comprising Q 197 -R 198 of human SNAP-25 cleavable by BoNT/A with a sample suspected of comprising BoNT/A, wherein the established cell line is susceptible to BoNT/A intoxication at about or less than 1 fmol BoNT/A per liter sample, as indicated by the enzymatic cleavage of said SNAP-25 polypeptide by BoNT/A to yield a fragment of said SNAP25 polypeptide comprising the C-terminal amino acid sequence of a peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond, wherein the sequence surrounding the BoNT/A cleavage site present in said SNAP-25 is denoted as P 5 -P 4 -P 3 -P 2 -P 1 -P 1 '-P 2 '-P 3 '-P 4 '-P 5 ', with P 1 -P 1 ' representing the scissile bond; b. isolating polypeptides from the cell; c. contacting the polypeptides with a monoclonal antibody that specifically binds to the peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond, wherein said antibody specifically binds to an epitope of said fragment of said SNAP25 polypeptide comprising the C-terminal amino acid sequence of said peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond with an equilibrium disassociation constant of less than 0.450 nM and wherein said antibody has an association rate constant for an epitope of intact SNAP-25 polypeptide comprising Q 197 -R 198 of human SNAP-25 of less than 1×10 1 M -1 s -1; and d. detecting the presence of any antibody-antigen complex comprising the antibody and the fragment of said SNAP-25 polypeptide comprising the C-terminal amino acid sequence of said peptide of human SNAP-25 having a carboxyl-terminus at the P 1 residue of the BoNT/A cleavage site scissile bond,