The paper shows that in the presence of silver nanoparticles the efficiency of intramolecular energy transfer in the complex of europium with doxycycline increases. It is proved that sensitivity of determination increases and limit of detection of doxycycline decreases by the method of sensitized fluorescence. The justification of the observed effects is given. The amplification of the signal of sensitized fluorescence in the presence of silver nanoparticles (energy donor) is the result of

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... ant transfer of excitation energy between the nanoparticle and the antibiotic ion, which is implemented under conditions of overlapping of the local surface plasmon resonance spectrum and excitation of the doxycycline ligand located near the surface of the nanoparticle. As a result of exposure to the antibiotic external radiation source and the local field of the surface plasmon increases the efficiency of tetracycline excitation, which contributes to the effectiveness of intramolecular energy transfer in europium chelate with doxycycline, doubling the intensity and lifetime. Modification of the surface of silver nanoparticles by europium ions allows to reduce the distance between the surface of a nanoparticle and an antibiotic, to increase the intensity of the signal of sensitized fluorescence by more than 100 times. The role of the stabilizer of a non-chromophore-containing ligand, − citrateion, in the formation of the analytical signal lies in its participation in the formation of a multi-ligand Eu3+ complex on the surface of a nanoobject, which reduces the distance between the donor and the acceptor, as well as the additional removal of water molecules from the immediate environment of the complexing agent ion, suppressing the process of excitation energy dissipation. On the basis of the conducted researches the fluorimetric technique of definition of doxycycline in medicines is offered. It differs in a low limit of detection (6.0·10-9 M) and a wide range of the defined concentrations from 1.0·10-8 to 1.0·10-5 M.