1：Experimental Design and Method Selection:

The study involved the synthesis of GQDs from citric acids, making them rich in carboxyl and hydroxyl groups, which enabled the combination with lead ions. The fluorescence intensity was quenched by Pb2+ through an electron transfer process. The addition of D-PA recovered the fluorescence due to the strong coordination between D-PA and Pb2+.

2：2+. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: Human urine samples were collected from healthy adult volunteers and diluted for 20 folds before analysis.

3：List of Experimental Equipment and Materials:

Materials included D-Penicillamine (D-PA, 98%) and citric acid (AR, 99.5%) purchased from Aladdin Reagents Company. Instruments included a JEM-F200 transmission electron microscope, Nano-ZS90 laser particle sizer, XSAM 800 electron spectrometer, TU-1901 UV-Vis spectrophotometer, and F-7000 fluorescence spectrophotometer.

4：5%) purchased from Aladdin Reagents Company. Instruments included a JEM-F200 transmission electron microscope, Nano-ZS90 laser particle sizer, XSAM 800 electron spectrometer, TU-1901 UV-Vis spectrophotometer, and F-7000 fluorescence spectrophotometer. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: The determination of D-PA was performed in PBS solution with pH=7.0 at room temperature. The fluorescence emission spectra were recorded immediately after adding D-PA solutions with different concentrations.

5：0 at room temperature. The fluorescence emission spectra were recorded immediately after adding D-PA solutions with different concentrations. Data Analysis Methods:

5. Data Analysis Methods: The fluorescence recovery efficiencies were calculated and found to be proportional to the concentration of D-PA.