Analysis of structural specificity in antibody-antigen reactions by capillary electrophoresis with laser-induced fluorescence detection.

A rapid and simple procedure for screening antibodies for binding to an antigen is proposed. A fluorescent hapten-dye conjugate was prepared by labeling the amino moiety of the hapten with a commercially available reactive cyanine dye, Cy5 (excitation maximum: 650 nm, emission maximum: 670 nm). A fixed amount of the Cy5-hapten was titrated with serial dilution of the antibody. Each of the titration mixture was analyzed by capillary electrophoresis (25 cm x 20 microns column) monitored by laser-induced fluorescence (laser: 10 mW helium-neon, 632.8 nm). Free and antibody-bound Cy5-hapten were analyzed simultaneously on the electropherogram. Competitive immunoassay of hapten was demonstrated with low-end sensitivity of 5.10(-8) M, about 10x more sensitive than the present drug screening methods. Using morphine as an example, the screening of various antibodies (from different vendors) and cross-reactivity of morphine analogues using the present procedure will be discussed.