Determination of Trace Cu(II) Ions Using a Siraitia Grosvenorii Residue-derived Nitrogen-doped Carbon Dots-enabled Fluorescence Quenching Sensor.

Bio-based fluorescent carbon dots (CDs) have emerged as promising material for advanced sensing applications due to their exceptional sensitivity, stability and biocompatibility. However, it was till constrained by ion selectivity and solution suitability especially in physiological solutions (e.g., PBS). Herein, a novel nitrogen-doped carbon dots (N-CDs) fluorescence quenching sensor derived from Siraitia grosvenorii (named "Luo Han Guo" in China) residue was developed for selective determination of trace Cu(II) ions in different solutions. The N-CDs were synthesized through a one-step hydrothermal process utilizing agricultural waste as carbon precursor and urea as the nitrogen source, demonstrating an eco-friendly synthesis strategy. The developed sensor exhibited remarkable anti-interference capability against acid, base, salt and various metal ions while maintaining excellent photostability and biocompatibility (cell viability > 75% at 1000 ug/mL). With a limit of detection (LOD) of 0.13 µmol/L, the system showed superior sensitivity compared to conventional methods. Furthermore, the sensor demonstrated strong universality across solution types and, more importantly, suitability for trace Cu²⁺ quantification in physiological solutions. Experimental results demonstrated that the fluorescence quenching process resulted from the binding of Cu²⁺ to amino groups on CDs, forming complexes through a non-radiative photoinduced electron transfer (PET) mechanism. This PET effect synergizes with static quenching, underlying the high selectivity and sensitivity of N-CDs for Cu²⁺ detection. The integration of novel phytochemical-based sensing materials with a fluorescence quenching mechanism enables highly selective detection of trace Cu²⁺ for environmental and biomedical applications.