A Fiber-Optic Cocaine Biosensor

• DOI: 10.1006/abio.1995.1273
• Publication Date: 2002-10-06T20:34:52Z
• Authors: P.J. Devine; N.A. Anis; J. Wright; S. Kim; A.T. Eldefrawi; M.E. Eldefrawi
• Keywords: Immunoconjugates; Time Factors; Antibodies, Monoclonal; Biosensing Techniques; Fluoresceins; Binding, Competitive; Sensitivity and Specificity; 01 natural sciences; 0104 chemical sciences; 3. Good health; Kinetics; Spectrometry, Fluorescence; Cocaine; Calibration; Fluorescein

A fiber-optic biosensor was developed for detection of cocaine, its metabolites, and other coca alkaloids, using a monoclonal antibody (mAb) against a derivatized benzoylecgonine (BE). The mAb was immobilized noncovalently on quartz fibers and a flow fluorometer was used to detect changes in evanescent wave fluorescence. A fluorescein (FL) conjugate of BE bound to the mAb specifically in a saturable manner and with high affinity (Kd = 7.6 nM). Cocaine or other test compounds competed with FL-BE for binding to the mAb in a concentration-dependent manner, thereby reducing the initial rate or steady-state fluorescence. Addition of cocaine to the flow buffer after reaching steady-state fluorescence enhanced the dissociation of bound FL-BE, and cocaine removal allowed fiber regeneration for multiple measurements. The detection limits for cocaine, cocaethylene, norcocaine, and BE were 5, 5, 29, and 30 ng/ml, respectively, but for ecgonine it was 4600 ng/ml and for methylecgonine it was 2000 ng/ml. Tropacocaine was detected at 10 ng/ml, but atropine was detected at 2900 ng/ml. The biosensor discriminated by 833-fold between cocaine and its stereoisomer pseudococaine. Structural features necessary for high-affinity recognition by this mAb are benzoate and 3 beta configuration, both of which are found in BE, cocaine, norcocaine, and cocaethylene.