Rare-earth-free up and down-conversion dual-emission carbon dots for Cu²⁺ sensing

In this work, up- and down-conversion dual-emission CDs without rare-earth (UD D-CDs) were synthesized using RhB and 1,4-Diaminoanthraquinone as precursors. The synthesized UD D-CDs exhibited dual emissions at 496 and 580 nm under 260 and 865 nm excitation, respectively. The fluorescence emission mechanism, including contributions from carbon nuclei, surface states, molecular states, and internal defect states, was discussed through the separation and purification of UD D-CDs. Based on the interaction between UD D-CDs and copper ions (Cu²⁺), a dual-mode ratio fluorescence probe was developed to detect and quantify Cu²⁺. The up-conversion ratio fluorescent probe shows a linear range of 0.0500-15.0 μM, with a detection limit as low as 2.76 nM. This method has been successfully applied to detecting Cu²⁺ in human serum and has potential applications in biochemical analysis and biological imaging. The successful preparation of up-conversion fluorescent carbon dots without rare earth elements and the ability to perform low-damage detection in high-background biological samples provide a new approach to constructing non-rare earth up-conversion probes.