Growth of Spherical Gold Satellites on the Surface of Au@Ag@SiO₂ Core–Shell Nanostructures Used for an Ultrasensitive SERS Immunoassay of Alpha-Fetoprotein

Abstract

The identification and detection of cancer biomarkers in early stages is an important issue for the therapy of cancer. However, most methods are time-consuming and have limited sensing sensitivity and specificity. In this work, we prepared a novel plasmonic multilayered core–shell–satellite nanostructure (Au@Ag@SiO2–AuNP) consisting of a gold nanosphere with a silver coating core (Au@Ag), an ultrathin continuous silica (SiO2) shell, and a high coverage of gold nanosphere (AuNP) satellites. The Au@Ag core is a prominent surface enhanced Raman scattering (SERS) platform, and the thin SiO2 layer exhibits a long-range plasmon coupling between the Au@Ag core to the AuNP satellites, further leading to enhanced Raman scattering. Meanwhile, the outer AuNP satellites have a high biocompatibility and long-term stability. Combining the above advantages, the well-designed metallic nanoassemblies would be a promising candidate for SERS-based applications in biochemistry. For specific detection of alpha-fetoprotein (AFP), we utilized the SERS-active core–shell–satellite nanostructures modified with AFP antibody as immune probes and nitrocellulose membrane (NC) stabilized captured anti-AFP antibodies as solid substrate. To improve the detection performance, we further systematically optimized the parameters, including the silver coating thickness of the Au@Ag core and the density and size of the satellite AuNPs. Under the optimized conditions, AFP could be detected by the SERS-based sandwich immunoassay with an ultralow detection limit of 0.3 fg/mL, and the method exhibited a wide linear response from 1 fg/mL to 1 ng/mL. The limit of detection (LOD) was considerably lower than conventional methods in the literature. This work relies on the unique Au@Ag@SiO2–AuNP nanostructures as the immune probe develops a new outlook for the application of multilayered nanoassemblies and demonstrates the great potential in early tumor marker detection.

Ultrasensitive detection of SARS-CoV-2 spike protein in untreated saliva using SERS-based biosensor

“…The as-prepared Ag NPs had a strong extinction maximum at 416 nm and then slightly red-shifted to 420 nm after labeling with Raman reporter via the Ag-S bond ( Song et al, 2016 ), which was caused by the variation in the refractive index around the nanoparticles ( Li et al, 2019 ). After conjugating with anti-SARS-CoV-2 antibodies, the LSPR band significantly red-shifted from 420 nm to 431 nm, indicating that the SARS-CoV-2 spike antibodies were successfully anchored on the Ag NPs@4MBA ( Yang et al, 2019 ). Besides, a new extinction peak appeared at around 670 nm, which was caused by the plasmon resonance of Ag NPs aggregates.…”

Nanoengineering with RAFT polymers: from nanocomposite design to applications

“…To build such structures, planet and satellite NPs must be bound with a proper linker to form a colloidally stable nanostructure. For the task of accomplishing a precise assembly of the planet-satellite nanostructure, various synthetic approaches based on small molecular linkers, [374][375][376] polymer linkers, 109,113,154,168,175,207 and DNA conjugation 369,373,377,378 have made significant progress recently.…”

Surface modification of plasmonic noble metal–metal oxide core–shell nanoparticles

“…39 A hybrid system consisting of both Ag@SiO 2 and gold nanoclusters was used for the simultaneous detection of Cu 2+ and PPi 40 and Au@Ag@SiO 2 core-shell nanostructures were used as an ultrasensitive SERS immunoassay of alpha-fetoprotein. 41 EDC/NHS crosslinking chemistry has been used also for the immobilization of folate on the surface of Ag or Au nanoparticles coated with silica. The folic acid/folate receptor interaction can be targeted for imaging cancer cells by the attachment of imaging-probe molecules to the folate moiety ( Fig.…”