Tyramine-mediated aggregation amplification of Au@Ag nanocubes Raman tags for sensitive multiplex SERS biosensing

Surface-enhanced Raman scattering (SERS) sensing has gained extensive attention in various fields. However, conventional SERS signal tags still show limited sensitivity for biomolecule detection. In this study, a sensitive multiplex SERS immunosensor for tumor markers detection was proposed by integrating tyramine-mediated aggregation amplification (TMAA) with Au@Ag core-shell nanocubes (Au@Ag NCs) Raman tags. Specifically, tyramine and 4-mercaptobenzoic acid (4-MBA, Raman-active molecule) were first functionalized on Au@Ag NCs to act as SERS signal tags. In the presence of H₂O₂, horseradish peroxidase (HRP) catalyzed the rapid deposition of tyramine-Au@Ag NCs tags onto the labeled antibodies, thereby producing the aggregation of 4-MBA/Au@Ag signal tags for Raman signal amplification. Compared with the conventional SERS signal tags, the Au@Ag NCs-based TMAA-mode achieved an approximately 4-fold enhancement in SERS signal. By coupling the TMAA strategy with encoded silica photonic crystal beads (SPCBs), a multiplex SERS immunosensor was established for tumor markers detection. The proposed immunosensor exhibited wide linear ranges of 0.001-1000 ng/mL for AFP and 0.0001-1000 ng/mL for CEA, with low detection limits of 0.85 pg/mL and 0.12 pg/mL, respectively. This research offers a promising and cost-effective SERS signal amplification platform for the early diagnosis of cancer.