Unraveling the stability and specific electrochemical sensing of lead ions using copper nanoclusters on sulfur and nitrogen-doped graphene quantum dots

Metal nanoclusters (MNCs) exhibit unique electronic properties, quantum size effects, and high catalytic activity; however, their practical efficacy is often limited by poor stability, particularly in the case of less noble and lower cost metals such as copper compared to noble and high-cost metals such as gold and silver. Stabilization strategies involving bulky ligands compromise structural and synthesis simplicity, while the use of small molecules, for instance, thiolate ligands, offers an attractive alternative by promoting structural simplicity and stability <i>via</i> heteroatom interactions. However, their stability remains limited. Thus, here in this work, we report the synthesis of a highly stable thiolate-protected copper nanocluster anchored on sulfur and nitrogen co-doped graphene quantum dots (CuNC@S,N-GQDs), which demonstrates exceptional structural stability for ≥1 year. The NC displays superior electrochemical sensing performance toward Pb(II) ions, accomplishing specific detection with a limit of detection in the picomolar range. The high specificity is ascribed to its strong affinity to Pb(II) because of the sulphur-functional groups in the CuNC@S,N-GQD. Furthermore, the sensor exhibited excellent sensing performance in complex environmental samples, with ∼100% recovery of Pb(II) in all the spiked real water samples, confirming its suitability for environmental monitoring.