Highly Resistant and Sensitive Colorimetric Immunochromatographic Assay for Sibutraminem (SBT) Illegally Adulterated into Diet Food based on PDA/AuNPs Labelling

Gold nanoparticle (AuNPs) based immunochromatographic assay strip is a valuable tool for monitoring chemicals in foods. However, the sensitive ICA strip for SBT was rarely reported due to that monoclonal antibody (mAb) against SBT with high affinity was commercially unavailable. Herein, a monoclonal antibody against SBT was prepared through a designed hapten with a carboxylendcapped space arm. The obtained mAb showed high affinity for SBT and N-desmethylsibutramine, a metabolite of SBT. Furthermore, a series of core-shell NPs, polydopamine (PDA) coated AuNPs (PDA/AuNPs) with controlled shell thickness and packing density were synthesized. The obtained PDA/AuNPs-mAb conjugate demonstrated high tolerance to salt and good stability in a wide pH range, which is beneficial to improve the matrix interference common in ICA. As a result, PDA/AuNPs-based ICA could quantify SBT in the range of 3.39–69.60 ng mL-1 with a limit of detection (LOD) of 0.98 ng mL-1. This novel ICA improved the sensitivity of the traditional AuNPs based ICA by nearly 12 times. Method validation was conducted with spiked sample of slimming food and human serum, and compared with HPLC-MS/MS. Consistent results indicated a high sensitivity, accuracy, and reliability of the PDA/AuNPs based ICA approach was achieved. To the best of our knowledge, this study reported the most sensitive immunoassay for SBT thus far.