Excitation energy transfer in europium complexes with doxycycline in the presence of surfactant micelles and silver nanoparticles

Doxycycline is a broad-spectrum tetracycline antibiotic used to treat infections in humans and in veterinary medicine as a prophylactic drug and growth stimulant. For this reason, residual amounts of antibiotics in milk, meat and other food products can cause resistance and the development of allergies. In this regard, constant monitoring of residual contents of tetracyclines in food products, environmental objects, and biological fluids is required. The purpose of this work was to study the effect of spherical silver nanoparticles and surfactant micelles on the intensity of sensitized fluorescence of europium ion complexes with doxycycline and to develop a new sensitive and simple method for the fluorimetric determination of doxycycline in solutions. As a result of the simultaneous influence of the energy of an external excitation source and the surface plasmon resonance of silver nanoparticles on doxycycline, the intensity of its fluorescence increases. The probability of the ligand transition to the excited state increases significantly, which contributes to the most efficient implementation of intramolecular excitation energy transfer in the Eu3+ complex with doxycycline. We have shown that in the presence of silver nanoparticles and Eu3+ ions, the fluorescence intensity of an analytical system containing doxycycline increases 125 times. In the presence of the nonionic surfactant Tween-80, the sensitized fluorescence signal of the Eu3+ chelate with doxycycline increases by more than 19 times. Solubilization of the components of the analytical reaction into micelles of surfactants helps to change their protolytic properties, dehydration, increase the stability of the complexes, and the efficiency of intramolecular energy transfer. In the combined presence of Tween-80 surfactant micelles and silver nanoparticles, an additional 27-fold increase in the fluorescence intensity of the metal ion chelate with doxycycline is observed. Based on the conducted research, a method for the fluorimetric determination of doxycycline using Tween-80 micelles, silver nanoclusters and Eu3+ ions in natural water has been proposed. The range of detectable concentrations is 1.0·10-7–1.0·10-5 M, detection limit (Limit of Detection) 6.0·10-8М (3 σ). The correctness of the definition has been controlled by the “entered–found” method.