A novel anthrapyridone diamine-based probe for selective and distinctive Cu2+ and Hg2+ sensing in aqueous solution

Abstract

A newly synthesized anthrapyridone-based diamine (probe 1) having two metal ion binding sites exhibited selective and sensitive sensing of Cu2+ or Hg2+ among various metal ions. Upon addition of the metal ion, the probe 1-containing solution vividly changed color, enabling visual detection of each metal ion (Cu2+ or Hg2+) without requiring any instruments. A ratiometric approach insensitive to environmental interference provided limit of detections (LODs) of 1.0 and 2.0 μM for Cu2+ and Hg2+ sensing, respectively. The green fluorescence emission of probe 1 was entirely (Cu2+) or partially (Hg2+) quenched in the presence of the metal ion, yielding an observed fluorescence-based LOD (5/200 nM for Cu2+/Hg2+). Thus, probe 1 showed a dual responsiveness for detection of the metal ion. A model probe (2) with only a single metal binding site was ineffective at sensing the metal ion (Cu2+ or Hg2+) under the same conditions, demonstrating that the presence of the two binding sites in probe 1 is essential for the sensitive detection of the metal ion. The DFT calculations suggest binding of the metal ion to the probe with a stoichiometry of 1:1 or 2:1 (M2+: probe). Probe 1 was also effective at detecting a small amount of Cu2+ in live HeLa cells or real samples such as tap and lake waters. The UV–Vis. absorbance results of probe 1 with Cu2+ and Hg2+ enabled us to build ‘NOR-YES-INHIBIT’ molecular logic gates. The metal ion sensing system presented here was extensively investigated by various techniques including UV–visible, fluorescence, NMR spectroscopy, DFT calculations, FE-SEM, and DLS.