Enzyme-amplified lanthanide luminescence based on complexation reaction - a new technique for the determination of doxycycline

A new spectrofluorimetric method is described for the determination of doxycycline, based on modified enzyme-amplified lanthanide luminescence. Under the optimum conditions, Eu3+-doxycycline forms a ternary complex with lysozyme in close proximity and lysozyme can remarkably enhance the characteristic fluorescence intensity of Eu3+ at 612 min in doxycycline-Eu3+ binary complex. The enhanced fluorescence intensity is in proportion to the concentration of doxycycline. The limit of detection is 1.28 x 10(-8) mol l(-1), with a linear range from 1.7 x 10(-7) to 1.7 x 10(-6) Mol l(-1). Interferences of other coexisting substances were studied. The developed method was successfully applied to the determination of doxycycline in serum, urine and real samples. The mechanism of fluorescence enhancement was also studied. (C) 2004 Elsevier B.V. All rights reserved.