Ricin determination by temperature controlled phase-separation immunoassay

A novel immunoassay of ricin in serum was developed. The antigen of ricin ( Ag-ricin) was labeled with isothiocyano-fluorecein (FITC). The antibody of Ag-ricin (Ab(ricin)) was conjugated to poly-N-isopropylacrylamide (PNIP) to form Ab(ricin) bound thermally reversible hydrogel PNIP-Ab(ricin). A compe titive immunoassay method based on the competition of FITC-Ag-ricin and fre e ricin with limited amount of PNIP-Abricin was established. The separation in the: assay process was achieved by precipitation of the immune-complex above its lower critical solution temperature (LCST). The fluorescence inte nsity was determined and the standard curve was obtained. The linear range was 30-200 ng/ml. The detection limit was 30 ng/ml. The recoveries of ricin from serum were satisfactory.