Hydrazone-Based Europium(III) Complexes: Mechanochromic Luminescence and Turn-On Fluorescence Detection of Quinolone Antibiotics in Human Urine

In recent years, alarmingly increased use of quinoloneantibioticshas led to a large number of antibiotic residues in the bodies oforganisms and threatened their health. It is crucial to develop efficientand sensitive methods for detecting quinolone antibiotics. For theeuropium (Eu(III)) complex, its characteristic emission is affectedby the energy transfer from the excited singlet state and tripletstates of the ligands to the emission energy level of the Eu(III)ion. If external stimuli could change its coordination environmentor the stacking pattern, the intensity of the characteristic Eu(III)emission would be affected. Considering the abundant potential coordinationsites of ciprofloxacin (CIP) and norfloxacin (NOR), we designed andprepared two europium complexes based on hydrazone, [Eu2L1 (2)(phen)(2)(NO3)(2)] (L-1 = (E)-N & PRIME;-(2-hydroxybenzylidene)nicotinohydrazide;phen = 1,10-phenanthroline) (Eu-1) and [Eu2L2 (2)(CH3OH)(2)(NO3)(2)] (L-2 = (E)-N & PRIME;-(2-hydroxybenzylidene)picolinohydrazide)(Eu-2). As expected, Eu-1 and Eu-2 showed a sensitive response to quinolone antibiotics (CIP and NOR).Upon the addition of CIP and NOR to the solutions of Eu-1 and Eu-2, the evident fluorescence enhancement correspondingto both the ligand and characteristic Eu(III) emission is clearlyobserved. The limits of detection (LODs) of Eu-1 forCIP and NOR are calculated to be 6.25 x 10(-9) and 1.44 x 10(-8) M, respectively, and thoseof Eu-2 for CIP and NOR are determined to be 2.86 x10(-8) and 4.22 x 10(-8) M, respectively.The LODs and high values of K (sv) provetheir excellent sensing performance. The high sensitivities and anti-interferenceabilities make Eu-1 and Eu-2 promising turn-onfluorescence probes for detecting CIP and NOR in human urine, basedon which Eu-1 and Eu-2 have been successfullyemployed to developed paper strips for the on-site detection of CIPand NOR. In addition, Eu-1 and Eu-2 bothexhibit high-contrast mechanochromic luminescence, which is attributedto the phase transformation from a crystalline to the amorphous state. Two Eu(III) complexes Eu-1 and Eu-2 exhibited mechanochromic luminescence featuringboth simultaneousmulticolor and high contrast. They could be used as turn-on fluorescenceprobes for CIP and NOR in human urine.