1：Experimental Design and Method Selection:

The study involved the synthesis of Cu2+-modified carbon nitride nanosheets (Cu2+-C3N4) as a peroxidase mimic catalytic substance and gold nanobipyramids (Au NBPs) as a chromogenic substrate for multicolor display. The methodology included the optimization of reaction conditions and the evaluation of the biosensor's performance in detecting NSE.

2：Sample Selection and Data Sources:

The study used NSE antigen and antibody, along with other biological compounds for specificity tests. Real serum samples were also analyzed to evaluate the biosensor's applicability.

3：List of Experimental Equipment and Materials:

Instruments included a UV2310II spectrophotometer, HITACHI HT7700 TEM, and Canon DSLR EOS 600D Digital Camera. Materials included melamine, citric acid, HAuCl4, CTAB, AgNO3, AA, HRP, and others.

4：Experimental Procedures and Operational Workflow:

The synthesis of Au NBPs and Cu2+-C3N4 nanosheets, modification of secondary antibodies with Cu2+-C3N4 nanosheets, and the detection of NSE in serum samples were detailed. The process involved incubation, washing, and colorimetric analysis steps.

5：Data Analysis Methods:

The study utilized UV-vis spectroscopy for spectral analysis and TEM for morphological characterization. The colorimetric responses were analyzed visually and spectroscopically.