Immunosorbent analysis of ricin contamination in milk using colorimetric, chemiluminescent and electrochemiluminescent detection

Analytical methodology to detect active ricin in food matrices is important because of the potential use of foodborne ricin as a terrorist weapon. Monoclonal antibodies (mAbs) that bind ricin were used as both capture and detection ligands in sandwich enzyme-linked immunosorbent assay (ELISA) and electrochemiluminescent (ECL) immunosorbent assays. ELISA employed two types of substrate for colorimetric or chemiluminescent detection. Although both fat content and protein content of samples influenced the recovery of ricin, the lower limit of detection (LOD) in ELISA and ECL systems permitted detection of 0.1 ng/mL for milk samples containing 0-4% fat. The assay systems detect pure ricin- or crude ricin-containing castor extract, but do not significantly respond to isolated ricin chains, heat-denatured ricin or the related agglutinin, Ricinus communis agglutinin 1 (RCA-1). Using the standard 96-well-plate formats, the assays detect less than 0.01% of an adult human lethal dose in a typical serving of milk.