A Eu3+/Tb3+-functionalized MOF ratiometric fluorescence sensor for ciprofloxacin detection and its agarose hydrogel for anti-counterfeiting application

Abstract

Luminescent metal–organic frameworks (MOFs) have potential application in the visual detection of antibiotics. This work presented a europium/terbium-functionalized MOF of Eu_0.125Tb_0.875-DDB (H₄DDB = 1,3-di(3′,5′-dicarboxylphenyl)benzene) and an agarose hydrogel of Eu_0.125Tb_0.875-DDB@agarose. Eu_0.125Tb_0.875-DDB acted as a ratiometric fluorescence sensor for the detection of ciprofloxacin (CPFX), showing the linear relationships I₄₈₈/I₆₁₂ = 0.00479C_CPFX + 0.06906 (where I₄₈₈/I₆₁₂ is the ratio of emission intensities at 488 and 612 nm) within the CPFX concentration (C_CPFX) range of 3–20 µM and I₄₈₈/I₆₁₂ = 0.00178C_CPFX + 0.129 within the C_CPFX range of 20–45 µM. The limits of detection (LODs) for these two C_CPFX ranges were 0.315 and 0.848 µmol L⁻¹ (µM), respectively. Furthermore, the sensing of CPFX by Eu_0.125Tb_0.875-DDB had no interference from common cations/anions, amino acids, and antibiotics. The accuracy of the fluorescence assay using Eu_0.125Tb_0.875-DDB was demonstrated in lake water and milk samples, with the measured C_CPFX close to the spiked C_CPFX. A smart-phone assisted method was used to recognize the blue values (B) of the images of Eu_0.125Tb_0.875-DDB@agarose sheets, thus establishing a quantitative model of B = 0.98857C_CPFX + 110.8381, with an LOD of 0.9189 µM. An allochroic rose mold of Eu_0.125Tb_0.875-DDB@agarose exhibited anti-counterfeiting through a series of color changes under UV light irradiation for a certain time. This work provides not only a fluorescence assay for the visual detection of CPFX by a heterometallic MOF but also an agarose hydrogel for anti-counterfeiting applications.