1：Experimental Design and Method Selection:

The synthesis of C-GQDs was carried out by covalently linking coumarin derivatives to GQDs. The methodology included the use of EDC and NHS for activation of carboxyl groups on GQDs followed by reaction with coumarin derivatives.

2：Sample Selection and Data Sources:

The study used GQDs prepared from industrial grade ?ake graphites and coumarin derivatives synthesized in the lab. Real samples included fresh fruits and juice drinks for AA detection.

3：List of Experimental Equipment and Materials:

HITACHI H-7650 TEM, Tecnai G2 F30 HRTEM, AFM, PerkinElmer Spectrum One FT-IR, Thermo Fisher ESCALAB250Xi XPS, Puxi TU-1901 spectrophotometer, PerkinElmer LS55 ?uorescence spectrophotometer, Olympus IX51 biological inverted microscope.

4：Experimental Procedures and Operational Workflow:

The synthesis of C-GQDs involved blending GQDs with DMF, activation with EDC and NHS, reaction with coumarin derivatives, purification, and freeze-drying. Detection of CN?, HQ, and AA was performed by adding respective stock solutions to C-GQD solution and recording fluorescence spectra.

5：Data Analysis Methods:

Fluorescence quenching and enhancement were analyzed to determine the detection limits for CN?, HQ, and AA. The data was processed using standard deviation and slope of the linear fit curve for detection limit calculation.