Development of low-cost copper nanoclusters for highly selective "turn-on" sensing of Hg²⁺ ions

The development of low-cost earth abundant metal based fluorescent sensors for a rapid and selective nanomolar level detection of Hg²⁺ is essential due to the increasing world-wide concern of its detrimental effect on humans as well as the environment. Herein, we present a perylene tetracarboxylic acid functionalized copper nanoclusters (CuNCs) based "turn-on" fluorescence probe for highly selective detection of toxic Hg²⁺ ions. The fabricated CuNCs exhibited high photostability with emission maximum centered at 532 nm (λ_ex = 480 nm). The fluorescence intensity of CuNCs was remarkably enhanced upon the addition of Hg²⁺ over other competing ions and neutral analytes. Notably, the 'turn-on' fluorescence response exhibits highly sensitive detection limit as low as 15.9 nM (S/N ∼ 3). The time resolved fluorescence spectroscopy suggested the energy transfer between CuNCs and Hg²⁺ ions following either inhibited fluorescence resonance energy transfer (FRET) or surface modification of CuNCs during Hg²⁺ sensing. This study offers the systematic design and development of new fluorescent 'turn-on' nanoprobes for rapid and selective recognition of heavy metal ions.