DNA-embedded Au–Ag core–shell nanoparticles assembled on silicon slides as a reliable SERS substrate

Abstract

This study aimed at developing a sensitive and reliable SERS substrate by assembling DNA-embedded Au-Ag core-shell nanoparticles (NPs) on silicon slides. First, a monolayer of well separated DNA-functionalized Au NPs (40 nm) was decorated on (3-aminopropyl)triethoxysilane modified silicon slides. The DNA-embedded Au-Ag core-shell NPs were assembled on the 40 nm Au-DNA NPs to form a core-satellite structure through DNA hybridization. Using 4-MBA as a Raman dye, the SERS performance of the substrates was evaluated after being cleaned by low oxygen and argon plasma. The Raman intensity of the assembly using DNA-embedded Au-Ag core-shell NPs was 8-10 times higher than the intensity of the assembly using Au NPs as satellites. In addition, the signal-to-noise ratio of the assembly was 2.6 times higher than that of a commercial substrate (Klarite™) when a 785 nm laser was used. The SERS enhancements of the assembled substrates were 2.2 to 2.8 times higher than the Klarite when an acquisition time of 5 s was used at an excitation wavelength of 633 nm. The assembled substrates also show a good spot-to-spot and substrate-to-substrate reproducibility at the excitation wavelengths of 633 and 785 nm. These results demonstrate that the fabrication process is simple and cost-effective for assembling DNA-embedded Au-Ag core-shell NPs on silicon slides that can be used as a reliable SERS substrate.

Three-Dimensional SERS Substrates Formed with Plasmonic Core-Satellite Nanostructures

“…When Au and Ag nanoparticles (AuNPs and AgNPs) are used for SERS detection of molecules, the distance between adjacent nanoparticles should be as short as a few nanometres to obtain high Raman enhancement 10,11 . In addition to the interparticle distance, which can be fine-tuned to optimize the SERS effects 12–14 , the size, shape, composition and surrounding environment of metal nanoparticles should also be carefully controlled to achieve sensitive and reproducible SERS detection 2 . To assemble metal nanostructures that have precisely controlled geometry and many small gaps as SERS hot spots, various top-down lithographic approaches and bottom-up self-assembly methods have been developed recently.…”

“…To assemble metal nanostructures that have precisely controlled geometry and many small gaps as SERS hot spots, various top-down lithographic approaches and bottom-up self-assembly methods have been developed recently. Molecular self-assembly is one of the bottom-up methods that can be used to assemble two- dimensional (2D) or three-dimensional (3D) nanostructures in a simple and cost-effective way 12,14–17 . While randomly aggregated AuNPs or AgNPs can already be used to enhance Raman signals, using DNA or other molecules to direct the assembly of nanoparticles allows us to have a better control of the geometries of nanoparticle-based SERS substrates and thus their SERS effects.…”

“…Given that DNA molecules of different lengths and sequences can be synthesized easily, nanoparticles can be assembled into a designed nanostructure through DNA hybridization or attachment of end-labelled functional groups 18–23 . For example, it has been demonstrated that Au-Ag core-shell nanodumbbells 12,13 and plasmonic core-satellite nanostructures can be assembled through DNA hybridization 14,24–28 or binding of other linker molecules 29–34 . The SERS effects of the nanoparticle-based nanostructures can be optimized by controlling the gaps between adjacent nanoparticles through coating Ag shells around the nanoparticles 12–14 .…”

“…For example, it has been demonstrated that Au-Ag core-shell nanodumbbells 12,13 and plasmonic core-satellite nanostructures can be assembled through DNA hybridization 14,24–28 or binding of other linker molecules 29–34 . The SERS effects of the nanoparticle-based nanostructures can be optimized by controlling the gaps between adjacent nanoparticles through coating Ag shells around the nanoparticles 12–14 . In addition, when a DNA aptamer is used as a linker to attach two nanoparticles, an analyte-controllable SERS hot spot at the nanogap between the nanoparticles can be created 28,35–37 .…”

“…Many of the core-satellite nanostructures used for SERS detection of molecules were based on detection schemes that utilized either DNA aptamers and Raman reporter molecules 28,29,36,37,51–53 or certain kinds of chemical interactions 54–56 , but the availability of suitable aptamers and chemical reactions could limit the use of the nanostructures for the detection of other molecules. Some of the SERS substrates formed with core-satellite nanostructures did not have many SERS hot spots in the z-direction, and the density of the nanostructures in the xy-plane was not maximized 14,27,57 . In this study, we did not use any specific aptamer, Raman reporter, or chemical reactions for SERS detection.…”