*2.8. Sample Preparation*

Living aquatic products (fish, shrimp, crab) were obtained from local markets. The above samples were tested by HPLC-FLD and the negative samples were selected as blank samples. The pretreatment of the sample was as follows: the shell and viscera of fish, shrimp and crab samples were removed, three grams of homogenized samples were added into a 15 mL conical tube, 3 mL PBS buffer was added and agitated on a vortex mixer. Subsequently, 4 mL ethyl acetate and 2 mL acetonitrile were added, shaken thoroughly for 5 min and centrifuged at 5000× *g* for 5 min. The supernatant was blown to near dry with nitrogen. Next, 1 mL 20% DMF-PBS (1:4, v:v) was used to dissolved the residue, and then 1 mL n-hexane was added and shaken acutely, static for 5 min and remove supernatant. The subnatant was detected by ic-ELISA.
