1：Experimental Design and Method Selection:

A sandwich immunoassay strategy was designed using Fe3O4 superparticle@SiO2 nanocomposites as IR probes. The method leverages the IR fingerprint signals of SiO2 for detection, with magnetic field assistance to enhance sensitivity and reduce assay time.

2：Sample Selection and Data Sources:

Human IgG was used as the analyte. Blood samples from anonymous volunteers were collected and processed to obtain plasma. Interfering agents like BSA, GLU, LYS, HIgM, and HIgA were used for selectivity tests.

3：List of Experimental Equipment and Materials:

Materials included Fe3O4 nanoparticles, DTAB, PVP, TEOS, APTES, glutaraldehyde, goat-anti-human IgG, human IgG, BSA, and others from suppliers like Sigma Aldrich and Beijing Chemical Works. Equipment included TEM (JEOL JEM-2100), XRD (Rigaku D/MAX 2500), SQUID magnetometer (Quantum Design MPMS-XL), and FTIR spectrometer (Nicolet IS10).

4：0). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Fe3O4 superparticles were prepared via solvophobic method, coated with SiO2 using a one-pot emulsion-droplet-based method, and functionalized with antibodies via glutaraldehyde crosslinking. Gold-coated substrates were prepared and used for antibody immobilization. The immunoassay involved incubating analyte with probes, magnetic separation, capture on substrates with or without magnetic field, and FTIR measurement.

5：Data Analysis Methods:

The integral area of the IR absorption band between 1250 cm?1 and 900 cm?1 was used for quantitative analysis. Detection limits were calculated using the 3Sb/m criterion, and linear correlations were assessed.