1：Experimental Design and Method Selection:

In-situ synthesis of GO-AuNCs composites using sodium L(-) malate as a reducing agent; electrochemical characterization and sensing applications using cyclic voltammetry, differential pulse voltammetry, and current density-voltage measurements.

2：Sample Selection and Data Sources:

Graphite flakes for GO synthesis; standard solutions of DA, UA, 4-AP, and other analytes; real samples including human serum, industrial effluent, PC baby bottle, PVC food packaging, and sea water.

3：List of Experimental Equipment and Materials:

High-resolution transmission electron microscope (HR-TEM, Hitachi HF-3300), X-ray diffractometer (Empyrean, Panalytical), Raman spectrometer (Nicolet Almeca XR, Thermo Fisher Scientific), X-ray photoelectron spectroscopy (ESCALAB 250Xi, Thermo Scientific), multichannel potentiostat (Ivium-n-Stat, Ivium Technologies), electrochemical impedance spectroscopy system (IM6ex, Zahner-Elektrik GmbH & Co. KG), Keithley electrometer (6517A), glassy carbon electrodes, chemicals from Sigma-Aldrich, Alfa Aesar, and JUNSEI.

4：Experimental Procedures and Operational Workflow:

Synthesis of GO by modified Hummer's method; preparation of GO-AuNCs composites with varying sodium L(-) malate concentrations; fabrication of modified electrodes by drop-casting; morphological, structural, and electrochemical characterizations; optimization of experimental conditions; detection of analytes in buffer and real samples.

5：Data Analysis Methods:

Linear regression for calibration curves, Randles circuit model for EIS data simulation using Zview program, statistical analysis for recovery and stability.