Silica-Encapsulated Core–Satellite Gold Nanoparticle Assemblies as Stable, Sensitive, and Multiplex Surface-Enhanced Raman Scattering Probes

Abstract

Developing highly sensitive and stable surface-enhanced Raman scattering (SERS) probe systems is an actively pursued goal in sensors and diagnostics. In this study, we present silica-coated core–satellite (CS@SiO2) plasmonic nanoparticle assembly structures that potentially realize this goal. We assemble different-sized gold nanoparticles into core–satellite (CS) configurations using dithiol molecular linkers that also serve as SERS labels. Multiple hot spots in the CS structure and narrow nanogaps in each hot spot produce a significantly enhanced Raman scattering signal with an enhancement factor of ∼8 × 107. Various types of molecules can be inserted into the nanogaps using the mixed self-assembled monolayers with alkanedithiol, enabling multiplex detection. Silica encapsulation of the CS nanoassemblies stabilizes the particles and makes it easy to modify the surface to attach antibodies or DNAs. Many properties of the CS@SiO2, including a wide range of optical resonances, scalability using multiple glass slides, long-term stability in ethanol, and single-particle-level sensitivity, make the material an ideal SERS probe for sensitive and multiplexed detection of diseases and viruses.

SERS-ELISA using silica-encapsulated Au core-satellite nanotags for sensitive detection of SARS-CoV-2

“…Fig. 2 shows the assembly method for CS@SiO 2 [42] . Briefly, APTMS was coated on a glass surface, on which 75 nm citrate-capped AuNPs were immobilized on this glass surface.…”

“…2 prevents the 32 nm AuNPs from adsorbing onto the glass substrates, leading to the formation of CS NPs with 100% purity [50] . The typical yield for the CS NPs per glass substrate was 4 × 10 9 particles or 1 pM in 5 mL solution [42] . We concentrated the sample by using 9-10 glass substrates.…”

“…Citrate-stabilized AuNPs with a diameter of 75 nm (32 nm) were synthesized via the seed growth method proposed by Bastus et al [45] . The CS@SiO 2 NPs were prepared using a previous method reported by our group [42] . The 32 nm AuNPs were assembled on a 75 nm AuNP through Au–S bonds of the Raman reporter BDMT.…”

“…As previously reported [42] , for the antibody conjugation onto CS@SiO 2 , AuNP@SiO 2 , and HAuNP@SiO 2 , 2 μL of 40 mM MPTMS was reacted with 1 mL of each silica-encapsulated AuNPs for 2 h and then centrifuged (3000 rpm, 20 min) twice. Then, 2 μL of 5 μM sulfo-SMCC linker was added and reacted for 20 min.…”

“…Nanogaps are formed between the core AuNP and satellite AuNPs to enable creation of hot spots within the individual CS NP [40] . Moreover, the surface of the CS NPs is encapsulated with silica (CS@SiO 2 ) to improve the stability of the CS NPs and facilitate the surface modification for anchoring antibodies [41] , [42] , [43] , [44] , [45] , [46] . We evaluate the plasmonic coupling characteristics and stability of the CS@SiO 2 SERS nanotags by performing a SERS-ELISA on a prepared SARS-CoV-2 lysate.…”