Elaborate Design of Two Novel Fluorescent Zinc-based Metal-Organic Frameworks for Highly Efficient Tetracycline Antibiotics Detection

The abuse of tetracycline antibiotics has caused great harm to human health and ecosystems. Developing inexpensive, convenient and sensitive methods for the detection of tetracycline antibiotics is highly desirable. Herein, based on the H₄ddp ligand [H₄ddp=3-(3,5-dicarboxyphenyl)pyridine-2,6-dicarboxylic acid], two novel zinc-based metal-organic frameworks (MOFs) {[Zn₃(ddp)₂(H₂O)₄]·3H₂O}_n (Zn1-ddp) and {[Zn₃(ddp)₂(H₂O)₄]·3H₂O}_n (Zn2-ddp) were successfully designed by delicate structural regulation. Both Zn1-ddp and Zn2-ddp exhibited excellent water and chemical stability and showed excellent fluorescence quenching performance for tetracycline antibiotics. Notably, the more advanced framework structure and better fluorescent performance make Zn1-ddp more sensitive than Zn2-ddp in fluorescent detection with a detection limit of 0.29 µmol/L for tetracycline (TC), 0.09 µmol/L for doxycycline (DOX), 0.10 µmol/L for minocycline (MIN) and metacycline (MEL), 0.19 µmol/L for chlortetracycline (CTC), and 0.67 µmol/L for oxytetracycline (OTC) among tetracycline antibiotics. The fluorescence quenching mechanism of Zn1-ddp and Zn2-ddp for tetracycline antibiotics detection was deeply investigated. The reasons for the superior detection performance of Zn1-ddp over Zn2-ddp were also analyzed in depth through Fourier transform infrared spectrophotometry (FTIR), X-ray photoelectron spectroscopy (XPS) analysis and framework structure analysis. The developed method opens up a new perspective for antibiotics detection based on zinc-based MOFs.