Analysis of DDT Isomers with Enzyme-Linked Immunosorbent Assay and Optical Immunosensor Based on Rat Monoclonal Antibodies as Biological Recognition Elements

Abstract

New rat monoclonal antibodies (mAbs) for DDT [1,1,1 -trichloro-2,2-bis (4-chlorophenyl) ethane], namely DDT 7C12, DDT 1C1, and DDT 1B2, were developed, characterized, and applied in ELISA both in coating antigen and in enzyme-tracer format. The latter used horseradish peroxidase (HRP) or glucose oxidase as enzymes. The lowest concentration of p,p'-DDT was determined with mAb DDT 7C12 and DDT-hapten HRP, with a test midpoint (IC50) of 0.5 +/- 0.2 microg/L (n=10) in 40 mM PBS (phosphate-buffered saline). The mouse anti-rat immunoglobulin lambda-light chain mAb LA1B12 was used as capture mAb. The best IC50 for o,p'-DDT in 40 mM PBS was 1.0 +/- 0.3 microg/L (n=12) and was obtained with mAb DDT 1C1 and DDT-hapten HRP, whereas mAb DDT 1B2 was very selective for p,p'-DDT with an IC50 of 4.2 + 1.6 microg/L (in 40 mM PBS, n=9). An optical immunosensor was optimized and applied for the analysis of DDT (or DDT equivalents). This immunosensor consists of a bench-top optical readout device and disposable sensor chips, which include the fluidic system. Evanescent field excitation and emission of the fluorophore Oyster-645 was used. An IC50 for p,p'-DDT [in 5% (v/v) isopropanol in 40 mM PBS] of 4 microg/L was obtained using DDT 7C12-Oyster-645. ELISA and immunosensor were used for the analysis of p,p'-DDT in unspiked and spiked surface water samples. Within the working ranges of these immunotechniques, recoveries ranged from 80 to 120%.