Effect of heterologous paralytic shellfish poisoning toxin-enzyme conjugates on the cross-reactivity of a saxitoxin enzyme immunoassay

A polyclonal antiserum against saxitoxin (STX) was used in a competitive enzyme immunoassay for the detection of paralytic shellfish poisoning toxins. The extent of cross-reactions was determined from the amounts of neoSTX, decarbamoylSTX and gonyautoxin 2/3 (GTX2/3) that gave 50% inhibition in the assay. Horseradish peroxidase (HRP) conjugates of the toxins and a bovine serum albumin conjugate of STX (STX-BSA) were used. When compared with STX-BSA and STX as standard, the extent varied to which heterologous conjugates affected the binding values of the other toxins to the antibodies. The antibodies did not bind GTX2/3-HRP. By use of neoSTX-HRP or decarbamoylSTX-HRP as the labelled antigen instead of STX-HRP, the detection limit for neoSTX was improved to 100 pg ml^-1.