Terbium doped heterometallic metal–organic compound with carboxylate and imidazole-containing ligands for naked-eye detection of nitro containing antibiotics†

Antibiotics are used for treating bacterial infections in humans. Antibiotic residues have become well-known water pollutants. For the detection of antibiotics in water, we have synthesized heterometallic metal–organic compounds, [YSr(PDA)₃(H₂O)₄]·Him·3H₂O, compound 1 and [Y_0.9Tb_0.1Sr(PDA)₃(H₂O)₄]·Him·3H₂O, compound 1:Tb, using a solvothermal method (where PDA = 2,6-pyridinedicarboxylic acid and Him = protonated imidazole). The single crystal X-ray diffraction pattern of compound 1 revealed a three-dimensional supramolecular structure. The characterization of compound 1 was performed using Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM). Compound 1:Tb was readily soluble in the aqueous medium and exhibited green emission upon excitation with a UV light of 280 nm. This largely Stokes-shifted luminescence property was used for the highly sensitive and naked-eye detection of various antibiotics in aqueous media. Compound 1:Tb showed huge luminescence quenching of 91%, 88%, and 83%, along with high Stern–Volmer constants of 5.35 × 10⁴ M⁻¹, 3.71 × 10⁴ M⁻¹ and 2.93 × 10⁴ M⁻¹ for nitrofurazone, nitrofurantoin, and furazolidone, respectively. The detection limits (LOD) were calculated to be as low as 0.49, 0.83 and 0.71 μM for nitrofurazone, nitrofurantoin, and furazolidone, respectively. Results demonstrated that the heterometallic metal–organic compound can detect nitrofuran antibiotics in an aqueous medium, proving that compound 1:Tb could be a potential luminescent sensor for useful applications. The detection was tested for real water samples, including pond and tube wells. With the help of time-resolved luminescence data and DFT calculations, the sensing mechanism of antibiotics by 1:Tb was established.