Dual-enhancement and dual-tag design for SERS-based sandwich immunoassays: evaluation of a metal–metal effect in 3D architecture

Abstract

The design of a sandwich-type SERS immunoassay (surface-enhanced Raman spectroscopy) is demonstrated operating in dual surface enhancement and dual-tag paradigm. The capture and detection antibodies are linked to two SERS-active substrates and form together the three-dimensional (3D) structure after specific binding to interleukin 6. A variety of metal combinations is tested (Au–Ag, Au–Au, and Ag–Ag), but an enhanced electromagnetic field is generated only due to coupling of Ag and Au nanoparticles with an Au hexagonal nanoarray. The amplified in that way Raman signals improve the limit of detection over 3 times in comparison to the assay with only one SERS-active substrate. It is also shown that the proper readout of the true-positive signal can be achieved in assays with two Raman tags, and this approach also improves LOD. For the optimal combination of the metal–metal junction and Raman tags, a linear relationship between the Raman signal and the concentration of IL-6 is obtained in the range 0–1000 pg⋅mL−1with LOD of 25.2 pg mL−1and RSD < 10%. The presented proof-of-concept of the SERS immunoassay with the dual-enhancement and dual-tag opens additional opportunities for engineering reliable SERS biosensing. Graphical abstract

Recent advances of Au@Ag core–shell SERS‐based biosensors

“…Therefore, SERS‐active metal nanoparticles provided essential enhancement to this SERS‐based immunoassay for detection of IL‐6, and a broad linear range of 0–1000 pg/ml with LOD as low as 25.2 pg/ml ‐1 (RSD < 10%) was achieved. [ 185 ]…”

“…Au@AgNPs R6G -1 × 10 −9 M [128] Ochratoxin A (OTA) Au@DTNB@Ag DTNB -0.48 pg/ml [176] AFP antigen Au-Ag alloy, Ag/AgBr NSs 4-MBA 2 fg/ml-0.8 g/ml 1.86 fg/ml [181] Thiram (pesticide) Ag@T-A@SiO 2 @Au 4-MBA 10 3 -10 8 CFU/ml 10 3 CFU/ml [221] EpCAM, ErbB2, and CD44 Ag-encapsulated Au (Ag-Au) DTDC, MGITC, and RBITC -- [147] SKBR3, HeLa, Jurkat T, LNCaP MB-Au@Ag NRs-SiO 2 DTNB, 4MBA -- [222] B16F10 ELVs Au@AgNPs --- [149] SERS Imaging EGFR-Au@Ag NR nanotags DTNB -- [223] Paclobutrazol Fe 3 O 4 @SiO 2 -Au@Ag (FSAA) -0.075-12.75 μg/g 0.075 μg/g [200] miR-196a AgNW@AuNPs NBA, 5-FAM 1 fM-100 pM 96.58 aM in PBS, and 130 aM in serum [224] Soluble sMCSP Au-Ag alloy nanoboxes 4-MBA -0.79 pM [184] Ochratoxin A (OTA) and ZEN Au NRs-cDNA, Au@4-MBA@Ag CS-OTA and Au@DTNB@Ag CS-DTNB aptamers 4-MBA, DTNB 0.01-100 ng/ml 0.018 ng/ml [177] α-fetoprotein AuNS@Ag@SiO 2 nanostars 4-MBA 3 pg/ml-3 mg/ml 0.72 pg/ml [182] Benzaldehyde and 3-Ethylbenzaldehyde MOF, ZIF-8, Au@Ag nanocubes --1 ppb [225] Penicilloyl protein (P-protein) Au-Ag alloy nanoparticles 4-MBA -0.329 pg/ml [209] Pyocyanin Au@Ag@mSiO 2 nanorattles 4-MBA -- [204] Interleukin 6 (IL-6) Au-Ag, Au-Au, and Ag-Ag 4-MBA 0-1000 pg/ml 25.2 pg ml [185] Lactic acid (LA) SFF-Au/Ag nanodendrites CV, 4-MBA 10-50 mM 10 − 9 M [226] (Continues) Thrombin and PDGF-BB Au-Ag HNPs@DTNB and Au-Ag HNPs@NBA DTNB, NBA -4.837 pg/ml for thrombin and 3.802 pg/ml for PGDF-BB [227] R6G, and FITC MoS2@Au/Ag hybrids --10 −11 M for R6G and 10 −12 M for FITC [201] Mycoplasma pneumoniae (MP) Au/DTNB@Ag/DTNB DTNB -0.1 ng/ml for human IgM [154] R6G, malachite green (MG), and uric acid (UA)…”

Ultrahigh Raman‐Fluorescence Dual‐Enhancement in Nanogaps of Silver‐Coated Gold Nanopetals

“…Petals@IR780@Ag showed single-nanoparticle sensitivity using dual-type single-nanoparticle technique and observation under the correlative Raman imaging and scanning electron microscopy (RISE) under resonance excitation, as reported in our previous works. [36,42] The enhanced EM fields produced by Ag coating create an averaged Raman enhancement 7582 times higher for the same number of fluorescence molecules [43][44][45] (Figure S6, Supporting Information) compared to petals@IR780. These uncoated nanostructures have already been found to be able to provide a SERS EF beyond 5 × 10 9 .…”

Modulating the interaction of graphenic substrates with human interleukin-6 and its monoclonal antibody: a study by Raman images

“…Raman spectroscopy in combination with spectroscopic signal enhancement techniques, as well as the use of statistical spectral analysis methods based on chemometric, have proven to be an interesting approach for the specic detection of IL-6. 14,15 Several strategies have been developed to enhance the Raman signal of biomolecules which allow their detection at low concentrations. One of them is based on the dragging of the biomolecules present in a solution towards the periphery of a solid support.…”