Abstract
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 SiO2@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.

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29 October 2020
One author name and corresponding affiliation of the original version of this article were unfortunately mislabeled.
29 October 2020
An Erratum to this paper has been published: https://doi.org/10.1007/s12274-020-3115-z
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Acknowledgements
This research was supported by the KU Research Professor Program of Konkuk University & funded by the Korean Health Technology R&D Project, Ministry of Health & Welfare (No. HI17C1264), Ministry of Science and ICT (No. NRF-2019R1G1A1006488).
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Pham, XH., Hahm, E., Kim, T.H. et al. Enzyme-amplified SERS immunoassay with Ag-Au bimetallic SERS hot spots. Nano Res. 13, 3338–3346 (2020). https://doi.org/10.1007/s12274-020-3014-3
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DOI: https://doi.org/10.1007/s12274-020-3014-3