Development of a fluorescence immunoassay for measurement of paclitaxel in human plasma

A new fluorescence immunoassay for the quantitative determination of paclitaxel (Pac) under equilibrium conditions was developed. Anti-Pac IgG2a antibody was immobilized through its Fc region to protein A covalently bound to the inside surface of a silanized glass capillary column and the antigen-binding sites of anti-Pac saturated with rhodamine-labeled Pac (Rh-Pac). Analyte Pac was circulated through the column in a closed loop and the steady-state fluorescence of the Rh-Pac displaced from the immobilized antibody was recorded after 6 min. The Rh-Pac fluorescence emission intensity was directly related to the concentration of the Pac analyte over a broad dynamic range of up to 400 ng/ml with a linear range up to 200 ng/ml and lower detection limit of 5.85 ng/ml. While there was no interference from the baccatin III and 10-deacetylbaccatin III, cephalomannine was found to interfere in Pac determination. When applied for measurement of Pac in human plasma, the concentration of Pac determined by the fluorescence assay was found to be in excellent agreement with the Pac added, confirming the potential of the fluorescence immunoassay for clinical application.