Enzyme-amplified SERS immunoassay with Ag-Au bimetallic SERS hot spots
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Enzyme-amplified SERS immunoassay with Ag-Au bimetallic SERS hot spots Xuan-Hung Pham1, Eunil Hahm1, Tae Han Kim1, Hyung-Mo Kim1, Sang Hun Lee1, Sang Chul Lee2, Homan Kang3, Ho-Young Lee2, Dae Hong Jeong4, Hak Soo Choi3 (), and Bong-Hyun Jun1 () 1
Department of Bioscience and Biotechnology, Konkuk University, Seoul 143-701, Republic of Korea Department of Nuclear Medicine, Seoul National University Bundang Hospital, Seongnam 13620, Republic of Korea 3 Gordon Center for Medical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA 02114, USA 4 Department of Chemistry Education, Seoul National University, Seoul 151-742, Republic of Korea 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 24 April 2020 / Revised: 14 July 2020 / Accepted: 24 July 2020
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.
KEYWORDS surface-enhanced Raman scattering (SERS)-based immunoassay, Au-Ag alloy, surface-enhanced Raman scattering, silica template, immunoglobulin G (IgG) detection
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Introduction
Immunoassays have been widely used in the diagnosis, screening, and prognosis of human diseases [1]. In particular, sandwich immunoassays are especially useful in determining the number of antibody molecules, where a secondary antibody is typically labeled with specialized markers, such as scintillation counting [2], fluorescence [3], chemiluminescence [4], electrochemical signal [5], enzymes [6], and quantum dots [1]. Although radiolabeled immunoassays (RIA), enzyme-linked immunosorbent assays (ELISA), and fluorescence-based techniques have most frequently be
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