Highly stable fluorescent coordination polymer materials for the ultrafast detection of nitrofurans in aqueous media at ppb levels

Abstract

The unsupervised usage and uncontrolled disposal of antibiotics into water bodies have detrimental effects on human health, aquatic life, and agriculture. Thus, several research studies have been conducted to detect the presence of trace amounts of such antibiotics via cost-effective and user-friendly fluorescence-based techniques. In this work, we report the synthesis of four luminescent coordination polymers (CPs), {[Co(oxdz)(bpma)(H₂O)]·H₂O}_n (1), {[Ni(oxdz)(bpma)(H₂O)]}_n (2), {[Zn(oxdz)(bpma)]·2H₂O}_n (3), and {[Cd(oxdz)(bpma)]·4H₂O}_n (4), with d⁷ (Co(II)), d⁸ (Ni(II)), and d¹⁰ (Zn(II) and Cd(II)) metal centers, respectively, utilizing an ancillary ligand, N,N′-bis(pyridylmethyl)methylamine (bpma), and a bent dicarboxylate, 4,4′-(1,3,4-oxadiazole-2,5-diyl)-dibenzoate (oxdz²⁻). Based on their single-crystal X-ray structures, these CPs exhibit different helicities depending on the geometry and coordination number preference of the metal center, the capping nature of bpma (facial vs. meridional) and the binding of the dicarboxylate groups of oxdz²⁻ (monodentate vs. bidentate). All the CPs have high thermal stability. To demonstrate their use, these CPs have been employed for the selective and ultrafast detection of trace levels of nitrofuran-based antibiotics in aqueous media. Among these, CP 4 exhibits the best efficiency (K_SV values of 6.77 × 10⁴ M⁻¹ and 5.86 × 10⁴ M⁻¹, respectively) and high sensitivity (LOD values of 197 and 172 ppb, respectively) toward nitrofurantoin (NFT) and nitrofurazone (NFZ). Its ultrafast response during real-life application (65% quenching in 20 s) and recyclability up to five times without any loss in efficiency make CP 4 eligible to safeguard human health and aquatic lives from the perilous effects of nitrofuran-based antibiotics.