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Surface-enhanced Raman scattering(SERS)enables rapid detection of single molecules with high specificity.However,quantitative and sensitive SERS analysis has been a challenge due to the lack of reliable SERS-active materials.In this study,we developed a quantitative SERS-based immunoassay using enzyme-guided Ag growth on Raman labeling compound(RLC)-immobilized gold nanoparticle(Au NP)-assembled silica NPs(SiO2@Au-RLC@Ag).The enzyme amplified Ag+reduction as well as Ag growth on the RLC-immobilized Au NP-assembled silica NPs(SiO2@Au-RLC),which resulted in a significant increase in SERS signal.In the presence of target antigens such as immunoglobulinG(IgG)or prostate-specific antigen(PSA),Ab1-Antigen-Ab2 immune complex with alkaline phosphatase triggered an enzyme-catalyzed reaction to convert 2-phospho-L-ascorbic acid(2-phospho-L-AA)to ascorbic acid(AA).As produced AA reduced Ag+to Ag,forming an Ag hot spot on the surface of SiC2@Au-RLC,which enhanced the SERS signal of SiO2@Au-RLC@Ag in a solution with a target antigen concentration.The plasmonic immunoassay for IgG detection showed a high linearity of SERS intensity in the range of 0.6 to 9.0 ng/mL with a detection limit(LOD)of 0.09 ng/mL,while an LOD of 0.006 ng/mL was obtained for PSA.The results indicate that the sensitivity of our novel SERS-based immunoassay is higher than that of conventional enzyme-based colorimetric immunoassays.