1：Experimental Design and Method Selection:

The study employs a C3N4-MoS2 semiconductor as the photoelectric conversion layer and uses eosin Y encapsulated into CaCO3 nanospheres as labels for antibody against CA724. Fe3O4 nanospheres are used as a magnetic platform for constructing a photoelectrochemical sandwich immunoassay.

2：Fe3O4 nanospheres are used as a magnetic platform for constructing a photoelectrochemical sandwich immunoassay. Sample Selection and Data Sources:

2. Sample Selection and Data Sources: The nanocomposite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry.

3：List of Experimental Equipment and Materials:

Includes C3N4-MoS2 semiconductor, eosin Y, CaCO3 nanospheres, Fe3O4 nanospheres, and ethylene diamine tetraacetic acid (EDTA).

4：Experimental Procedures and Operational Workflow:

The CaCO3 nanospheres are dissolved with EDTA to release eosin Y, which sensitizes the C3N4-MoS2 semiconductor, inducing photocurrent amplification.

5：Data Analysis Methods:

The photocurrent was measured under optimal conditions, showing a linear increase in the range of 0.05 mU mL?1 to 500 mU mL?1 of CA724, with a detection limit of 0.02 mU mL?1.