Fluorescence turn off-on continuous response of dual lanthanide metal organic frameworks for selective detecting fluoroquinolone antibiotics

Eu3+ and Tb3+ as central ions and 1,4-phthalic acid (H2BDC) as ligand, a dual lanthanide metal-organic framework, Eu-Tb(BDC), was synthesized by co-precipitation method. The products performed stable crystal structure and adjustable fluorescence color. Eu0.15Tb2.85 (BDC) 3.0 was selected as an optimized probe to detect norfloxacin (NFX) in urine, and the fluorescence color was found to transfer from bright yellow to dark cyan and then to strong green with increasing NFX concentration. Mechanism analysis revealed that NFX with low concentration (10−6-10−3 M) stimulated light competition with BDC ligand due to internal filtration effect (IFE), resulting in the gradual fluorescence shutdown of Eu3+and Tb3+. While further increasing concentration of NFX to 10−3-10−2 M, the antibiotic molecules coordinated with lanthanide ions and transitioned their role from competitor to assistant. Where the energy transfer due to antenna effect overwhelmed IFE, the exciting light energy were retransferred to Eu3+ or Tb3+, and the probe's fluorescence restored. Generally, the Eu-Tb(BDC) probe performed fluorescence turn off-on response to norfloxacin with continuous concentration changing. Additionally, when detecting other fluoroquinolone antibiotics, the fluorescence of Eu0.15Tb2.85(BDC)3.0 changed from bright yellow to bright blue and eventually to dark red, which was attributed to the different coordination degrees of various antibiotic molecule with Tb3+ and Eu3+. It can be used to distinguish norfloxacin from other fluoroquinolone antibiotics.