1：Experimental Design and Method Selection:

The ALP-mediated controlled growth of AgNPs was implemented into direct competitive plasmonic ELISA for SAL detection. Click chemistry synthesis of SAL-Bio was employed.

2：Sample Selection and Data Sources:

SAL standard was diluted with 10% methanol/PBS buffer to final concentrations varying from

3：1 ng/mL to 500 ng/mL. List of Experimental Equipment and Materials:

Instruments and reagents included AgNO3, NaBH4, NaOH, methanol, SAL, ractopamine, terbutaline, diethylstilbestrol, HATU, DIPEA, BSA, OVA, ALP, SA-ALP, AAP, PBS buffer, artificial urine, SAL polyclonal antibody, 96-well polystyrene plates, and 48-well plates.

4：Experimental Procedures and Operational Workflow:

The procedure involved preblocking and immobilizing 96-well plates with capture antibodies, adding SAL standard and SAL-Bio, incubating, washing, adding SA-ALP, incubating, washing, adding AAP, reacting, transferring mixtures to another plate with AgNPs/Ag+ solution, and recording A

5：Data Analysis Methods:

4 The absorbance at 400 nm (A400) was recorded using a microplate reader, and the calibration standard curves demonstrated a good linear relationship between A400 and the concentrations of SAL.