Three-Dimensional (3D) Surface-Enhanced Raman Spectroscopy (SERS) Substrates: Fabrication and SERS Applications

Abstract

This study introduces a straightforward approach to construct three-dimensional (3D) surface-enhanced Raman spectroscopy (SERS) substrates using chemically modified silica particles as microcarriers and by attaching metal nanoparticles (NPs) onto their surfaces. Tollens' reagent and sputtering techniques are utilized to prepare the SERS substrates from mercapto-functionalized silica particles. Treatment with Tollens' reagent generates a variety of silver NPs, ranging from approximately 10 to 400 nm, while sputtering with gold (Au) yields uniformly distributed NPs with an island-like morphology. Both substrates display wide plasmon resonances in the scattering spectra, making them effective for SERS in the visible spectral range, with enhancement factors (ratio of the analyte's intensity at the hotspot compared to that on the substrate in the absence of metal nanoparticles) of up to 25. These 3D substrates have a significant advantage over traditional SERS substrates because their active surface area is not limited to a 2D surface but offers a much greater active surface due to the 3D arrangement of the NPs. This feature may enable achieving much higher SERS intensity from within streaming liquids or inside cells/tissues.

Quantification of Plasma Dopamine in Depressed Patients Using Silver-Enriched Silicon Nanowires as SERS-Active Substrates

“…The equation for determining the EF factor on a 3D-type SiNWs@Ag substrate was established by relying on the concentration at the detection limit, instead of the number of molecules. This approach was chosen due to the inherent difficulty in directly deducing the number of molecules contributing to the Raman signal in the 3D substrate Figure S5 shows the Raman spectra for a normal Si wafer and an optimized SERS substrate.…”

Self-Organized SERS Substrates with Efficient Analyte Enrichment in the Hot Spots

“…Although the best control over the uniformity of the metal nanostructures on the surface and the magnitude of the interparticle distance can be achieved with electron beam lithography, this method is not viable for real-life applications because of the relatively high price. More affordable are methods based on prepatterning ,− or controlled nucleation of the metallic nanostructures on the surface or methods based on self-assembling. ,, In the case of self-assembling, the desired morphology can be formed by an oxide or other nonexpensive material and then covered with noble metal. − Alternatively, the hybrid nanostructures with predefined morphology and plasmonic properties can be first prepared in the solutions and then self-assembled on the substrate to form the hot spots between them. ,− In most approaches, preparation of efficient and rigid SERS substrates requires sophisticated and skilled preparation (in the case of nanosphere lithography, for instance) or costly equipment and materials (as in the case of lithographic methods). , Therefore, affordable fabrication of efficient SERS substrates is still an area of intense research. ,,,− Of particular interest is developing plasmonic architectures that could enable (self-)­localization of the analyte in the hot spots …”

Direct laser induced writing of high precision gold nanosphere SERS patterns

“…12–17 Moreover SERS can be combined with other advanced techniques, such as in vivo imaging 18–22 and microfluidics. 23–28 Despite the rapid development in this field, the generation of reproducible and applicable SERS substrates turns out to be a challenging task, that ranges from chemical procedures harnessing colloidal metallic solutions 29–32 and reverse micelles, 33,34 to methods like Nanosphere lithography (NSL), 35 Nanoimprint lithography (NIL) 36 and Electron-beam lithography (EBL). 37,38 Many of the substrates made in these ways are limited due to their air sensitivity and general instability ( e.g.…”