Synthesis and application of metal organic framework- based composites for sensing of antibiotics

Abstract

The excessive and non-judicious use of antibiotics has a severe impact on the ecosystem and poses a serious threat to human health. The presence of antibiotic residues in the aquatic habitat needs careful appraisals due to their inherent persistence and low degradation rate. Therefore, it is crucial to develop detection platforms for antibiotic contaminants that generate a quick, easy to interpret, sensitive, and selective response towards analytes in the tested samples. In this study, fluorescent lanthanide-based metal-organic framework (Ln-MOF) composites with quantum dots (QDs) were synthesized, characterized, and explored for optical sensing of antibiotics. Particularly, a composite of Tb-BTC MOF (Terbium (III) Nitrate Hydrate and 1,3,5-Benzene tricarboxylic acid (BTC)) with GQDs (graphene quantum dots) was investigated for fluorescence sensing of tetracycline. Similarly, a composite of Eu-BTE (Europium (III) Nitrate Hexahydrate and 1,3,5-Triscarboxyphenyl-ethynylbenzene (BTE)) with RCDs (red emissive carbon dots) was examined for the fluorometric detection of ciprofloxacin. Both the composites were developed via encapsulation of respective QDs within the structure of MOFs during their synthesis. Next, the MOFs, QDs, and their composites were structurally characterized using different spectroscopic and microscopic techniques along with X-Ray Diffraction studies for determining crystallinity of synthesized materials. The structure of Tb-BTC and Eu-BTE remained intact even in composite form with GQDs and RCDs, respectively while demonstrating improved uniformity and stability, and fluorescence emission resulting in enhanced sensitivity. Overall, the GQDs@Tb-BTC and RCDs@EuBTE composites exhibiting enhanced fluorescence showed better sensitivity towards tetracycline and ciprofloxacin, respectively as compared to the MOFs alone. The limit of detection (LOD) of 0.377 μg/L and 0.22 μg/mL was observed Tb-BTC and GQDs@Tb-BTC, respectively with wide linear detection range, in case of composite (1-200 μg/L for GQDs@Tb-BTC and 20-100 μg/L for Tb-BTC). Likewise, the LOD of 0.13 μg/L over wide linear detection range of 0.1-100 μg/L and 2.14 μg/L over linear detection range of 10-100 μg/L were observed for RCDs@Eu-BTE and Eu-BTE, respectively. Therefore, the synthesized MOF/QD composites, namely, GQDs@Tb-BTC and, RCDs@Eu-BTE demonstrated excellent sensitivity and selectivity along with good reusability, stability, and anti-interference property advocating their use as efficient fluorescent probes for detection of antibiotic contaminants.