Mercaptopropionic acid-assisted synthesis of green and blue emissive copper nanoclusters for multimodal sensing, logic gate, and white light applications

A time-controlled synthesis strategy for luminescent copper nanoclusters (CuNCs) was adopted via a two-step process. First, non-emissive copper nanoparticles (CuNPs) were formed by reducing copper salt with ascorbic acid (AA), and then the CuNPs were converted into green (G-CuNCs, λem = 520 nm) and blue emissive CuNCs (B–CuNCs, λem = 440 nm) after time-controlled treatment (2 h and 43 h) with mercaptopropionic acid (MPA). Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) analysis unambiguously demonstrate the etching of CuNPs with the reduction of core size (from 6.09 nm for CuNPs to 2.67 nm and 1.92 nm for G-CuNCs and B–CuNCs, respectively) and a simultaneous lowering of the contribution of the +2 oxidation state of Cu species. Moreover, B–CuNCs showed selectivity and sensitivity towards Fe3+ and glutathione (GSH) via fluorescence (Fl) turn-off-on mechanism; the limit of detections (LODs) for respective analytes were 6.2 nM and 281 nM. The Fl turn-off mechanism by Fe3+ involves both static and dynamic quenching processes, whereas restoration of the Fl intensity of B–CuNCs was triggered by the GSH-induced reduction of Fe3+ to Fe2+ and subsequent release of Fe3+ from the surface of B–CuNCs. A logic gate was constructed based on the Fl response of the B–CuNCs toward the analytes. Finally, the synthesized B–CuNCs and G-CuNCs were employed for white light emission (WLE) with Commission Internationale d'Eclairage (CIE) coordinates of (0.33, 0.32) with the aid of another red-emitting GSH-capped gold nanocluster (GSH-AuNCs).