SHINERS and plasmonic properties of Au Core SiO₂ shell nanoparticles with optimal core size and shell thickness

Abstract

Shell-isolated nanoparticles (NPs)-enhanced Raman spectroscopy (SHINERS) can be potentially applied to virtually any substrate type and morphology. How to take a step forward to prepare SHINERS NPs (SHINs) with superior performance is critical for the practical applications of surface-enhanced Raman scattering (SERS) in the breadth and depth. Here, we present a method to obtain 120 nm diameter gold NPs coated with ultrathin silica shells (1-4 nm). The silica shell can be controlled growth through carefully tuning a series of parameters, such as amount of 3-aminopropyl triethoxysilane used, pH, reaction time, and reaction temperature. We compare the enhancement factor of the obtained 120 nm Au with a 4 nm silica shell NPs to the 55 nm Au with a 4 nm silica shell NPs, and the activity of a 120 nm SHINs is nearly 24 times that the 55 nm SHIN from a single particle view. We also compare the enhancement factor of 1 nm silica shell Au@SiO 2 NPs with the bare Au NPs. The enhancement factor of 1 nm silica shell Au@SiO 2 NPs was found to be about twice that of the bare particles. For a deeper understanding of the source of the giant enhanced electrical field of the 1 nm silica shell Au@SiO 2 NPs, we study the plasmonic property of single 1 nm silica shell Au@SiO 2 NP on a gold film substrate through correlation of the structure of single NP using SEM with its SPR spectroscopy. We find that the multipolar interaction between the single Au@SiO 2 NP and gold film substrate is important for the SERS. Our studies on the performance of 120 nm SHINs and the plasmonic property of these particles can significantly expand the applications of SHINERS technique and improve the understanding of physical nature of SHINs.

Advances in surface-enhanced vibrational spectroscopy at electrochemical interfaces

“…The technique, termed shell-isolated nanoparticle-enhanced Raman spectroscopy, or SHINERS, has dramatically expanded the practical application of SERS, enabling measurements on effectively any substrate due to the minimal interference of the 'SHIN' resonators [82][83][84]. Procedures to synthesise SHINs are now well-documented [85], typical particles comprising a 55-120 nm spherical gold or silver core [82,86,87] [92], graphene [93,94] and other carbon materials [95,96]. Example core-shell particles are depicted in Figure 5 The substrate generality of SHINERS has greatly benefitted electrochemical Raman spectroscopy and an impressive range of native electrode substrates have been investigated including Ag [97,98], Au [99][100][101][102][103][104], Pt [99,102], Pd [102], Rh [105], Ni alloys [106,107], Cu [108] and glassy carbon (GC) [102].…”

Shell‐Isolated Nanoparticle‐Enhanced Raman Spectroscopy (SHINERS)

“…We call this new technique "shell-isolated nanoparticle-enhanced Raman spectroscopy" (SHINERS) [45][46][47], which very recently has been applied successfully to several systems. [45][46][47][52][53][54][55][56][57][58][59][60][61][62][63].…”

Insights into the heterogeneous distribution of SERS effect in plasmonic hot spots between Au@SiO2monolayer film and gold single crystal plates

“…45 Fortunately, the insulated silica shell inhibited the transfer of free electrons and allowed the gathering of them in the "particle-surface" gap area to contribute the strong SERS signal of molecules adsorbed on NPs and single crystal surfaces. 28 For the case of 785 nm laser, either the absolute or relative SERS intensities decreased compared with 633 nm laser, especially for the areas of the lms beyond the GSCPs whose SERS signals were only contributed by "particle-particle" gap mode of neighboring NPs (within 10 cps for the silica-encapsulated lm), indicating that the excitation wavelength matching with the "particle-particle" gap mode is around 633 nm rather than the 785 nm. While the absolute SERS signal disparity by two different excitation wavelengths was signicantly reduced for the area on GSCPs.…”

“…30,45 Besides that as the silica shell prevents the spread and transfer of free electrons in the "particle-surface" gap, it is easier to induce the enrichment of charges just in this gap area aer the encapsulation of silica shells. 28 So one can assume that the laser of 785 nm which matches better with "particle-surface" gap mode is more benecial to inducing the oscillation of free electrons and thus gathering of charges in the gaps to form electron holes underneath the NPs. The further gathering of charges induced by the holes allows the enhanced electromagnetic eld between particles and single crystal surfaces.…”

“…Tian and his coworkers performed a series of investigations on the coupling effect between the SHINs and single crystal metallic surface, conrming the transfer of hot spots from the "particle-particle" to "particle-surface" gap mode. [28][29][30] Therefore, the observed stronger SERS signal on the GSCPs surface is mainly contributed by the latter mode.…”