A simple paper-based nickel nanocluster-europium mixed ratio fluorescent probe for rapid visual sensing of tetracyclines.

In this work, a ratiometric fluorometric sensor based on nickel nanoclusters (NiNCs)-europium complex (NiNCs-Eu) was constructed for the highly selectivity detection of tetracyclines (TCs) in water samples. In the presence of TCs, the blue fluorescence of the sensor NiNCs-Eu was quenched at 430 nm and the characteristic red fluorescence of Eu-TCs appeared at 620 nm because of the combined help of inner filter effect (IFE) and antenna effect. Under the optimized conditions (100 mM Eu (100 µL); temperature (25℃); reaction time (10 min), HEPES buffer solution (pH = 7.0)), the sensor offered a wide detection range of tetracycline (TC) and oxytetracycline (OTC) from 0.1 to 50 μM with the detection limit (LOD) of 25 nM and 21 nM, respectively. Moreover, the sensor was able to detect of TC and OTC in tap and lake water with high recovery rate (89.10%-97.60%). In addition, the portable paper-based sensor was constructed using filter paper embedded with NiNCs-Eu. The distinct fluorescent color of the paper-based sensor varied from bright blue to red against different concentrations of TC and OTC. These above findings demonstrated the potential for wide application of as-prepared ratio metric fluorescence sensor for visual detection of TCs in water samples.