1：Experimental Design and Method Selection:

The biosensor was constructed by sequentially modifying a glassy carbon electrode (GCE) with ERGO-Nafion, AuNPs, Cyt c, and Nafion using dropping-dry and electrochemical reduction methods. Electrochemical techniques such as cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to study the electrode properties and biosensor performance.

2：Sample Selection and Data Sources:

Cytochrome c from bovine heart was used as the biological component. Graphene oxide was prepared in-house, and other chemicals were purchased from commercial sources. Electrochemical data were collected using a CHI660A electrochemical analyzer.

3：List of Experimental Equipment and Materials:

Equipment includes CHI660A electrochemical analyzer, FT-IR spectrophotometer (PerkinElmer Spectra Two), SEM (Hitachi S-4800), and magnetic stirrer. Materials include GCE, Nafion, HAuCl4, H2SO4, H2O2, Cyt c, and various buffers and solutions.

4：Experimental Procedures and Operational Workflow:

The GCE was polished and cleaned. GO-Nafion mixture was dropped on GCE and electrochemically reduced to ERGO-Nafion. AuNPs were electrodeposited by CV. Cyt c and Nafion were added by dropping-dry method. Electrochemical measurements were performed in a three-electrode system.

5：Data Analysis Methods:

Data were analyzed using the CHI660A software. Linear regression was used for calibration curves, and statistical methods like RSD were applied for reproducibility assessment.