Dual-emission ratio fluorescent probes based on carbon dots and gold nanoclusters for visual and fluorescent detection of copper ions.

Blue carbon dots (BCDs) and red gold nanoclusters modified by bovine serum albumin (BSA-Au NCs) were selected as luminescent nanomaterials, and the nanohybrid materials were successfully prepared and applied to the fluorescent measurement of copper ions. The prepared ratio fluorescent probe has two emission peaks near 452 and 654 nm under an excitation of 330 nm. The fluorescence intensity was gradually quenched because Au NCs was aggregated in the presence of Cu, resulting in a gradation of the fluorescent color from red to pink to purple to blue for visual detection. BCDs have almost the same fluorescence intensity due to their light stability and chemical inertness to Cu and serve as a background reference in the sensing system. Under the optimal condition, the detection limit (LOD) is 16 nM, the linear range is 0.05-1.85 μM, and the coefficient of determination R is 0.9987 for copper determination. Compared with other single probes, the ratio fluorescent probe in the current study has good water solubility, low cytotoxicity, and is easy to synthesize. The nanoprobe provides a high-quality and sensitive visible light platform for monitoring copper ions. Graphical abstract.