Fabrication of Raman reporter molecule–embedded magnetic SERS tag for ultrasensitive immunochromatographic monitoring of Cd ions and clenbuterol in complex samples

A rapid, simple but sensitive analytical method for the simultaneous monitoring of heavy metal ions and illegal additives in complex samples remains lacking. We reported a difunctional capture–detection surface-enhanced Raman scattering (SERS) immunochromatographic assay (ICA) for the direct detection of the heavy metal residue Cd ion (Cd²⁺) and illegal additive clenbuterol (CLE) with high sensitivity and specificity herein. A novel magnetic SERS tag (Fe@RAu) with a Raman reporter molecule–embedded raspberry-like Au shell was fabricated via a one-step reduction reaction that not only simplified the fabrication of common magnetic SERS nanomaterials but also improved SERS activity to increase detection sensitivity. The difunctional SERS–ICA enabled the fast magnetic enrichment of the target small molecules in complex specimens and ultrasensitive and quantitative determination of CLE/Cd²⁺ on the two test lines of the ICA system. The limits of detection of the developed method for CLE and Cd²⁺ were as low as 0.48 and 1.88 pg/mL, respectively, and about 2000 and 500 times lower than those of conventional AuNP-based ICA strips. The excellent practicability of Fe@RAu–ICA for real food samples analysis was also demonstrated, revealing the potential of the proposed assay for rapid and on-site screening of small-molecule pollutants.