3D Hotspots Platform for Plasmon Enhanced Raman and Second Harmonic Generation Spectroscopies and Quantitative Analysis

Abstract

devices, [6] and Raman, [7] fluorescence, [8,9] even infrared [10] spectroscopy. Nonetheless, the lack of high-efficiency substrates with uniformly distributed hotspots greatly hinders the widespread and practical application of plasmon-enhanced spectroscopies (PESs), such as plasmon enhanced second harmonic generation (PESHG) and surface-enhanced Raman scattering (SERS). Hence, constructing hotspot platforms with high-efficiency is of great importance. At present, 0D, 1D, and 2D hotspots based on different types of metal nanostructures are the most frequently used enhancement structures, such as 0D single isolated nanospheres, [11] 1D nanowires [12] or nanorods, [13,14] and 2D nanoarrays, [15][16][17][18] synthesized using various nanofabrication techniques. However, these low spatial dimensions limit the number of hotspots that can be generated and thus impede further improvements in the detection sensitivity of PESs.Due to the higher density of hotspots and larger surface area for adsorbing probe molecules, 3D hotspot platforms can give stronger and more stable SERS signals than that of 0D, 1D, or 2D nanostructures. However, the rational design and simple construction of 3D SERS substrates with controllable and reproducible nanoscale hotspots and stronger Raman enhancement factors via a facile and green approach is a longstanding challenge and numerous efforts have been devoted to their fabrication. Ag NP decorated cactus-like 3D SERS substrates [19] and 3D hot-junction formation of gold nanoparticles on 2D silicate nanoplatelets [20] had been designed, which exhibited good reproducibility and considerable SERS signal amplification. Also, it had been demonstrated that SERS enhancements of 3 orders of magnitude could be generated during evaporation of a drop containing pure Ag NPs solution compared with the dried substrate. [21] Unfortunately, the SERS signals were not stable and rapidly decreased after the complete evaporation of water. To alleviate this drawback, aqueous glycerol was added in the Ag NPs sol to slow the evaporation, [22] which extended the duration of maximum Raman signal. However, the Raman signal kept decreasing with time due to charge exchange among aggregated Ag NPs. Considering this charge

Smart design of high‐performance surface‐enhanced Raman scattering substrates

“…(F) Ultrathin SiO 2 shells coated Ag‐SHINs and 3D hotspot platforms. Reproduced with permission: Copyright 2019, Wiley 53 …”

“…To tackle these issues, Tian et al improved the technology by adding aqueous glycerol to slow the evaporation process, and ultrathin SiO 2 shells were used to prevent charge transfer (Figure 3F). 53 As a result, the uniformity and stability of SERS activity are improved remarkably with increasing the evaporation time. The LOD for 4‐MBA is up to 10 −8 mol/L, suggesting that this 3D hotspots platform has great potential in plasmon‐enhanced linear and nonlinear spectroscopy, as well as for practical sensor applications.…”

Controllable Self-Assembly of SERS Hotspots in Liquid Environment

“…As Yang's group described, four states transformation of moist agglomerates without halogen ions added would occur with the decrease of the liquid phase. 54,55 Adhesive forces made a significant difference in the distribution of nanoparticles and drove the particles closer together. In the process of the droplet evaporation, the intensity of spectra first increased gradually and reached the strongest points and then decreased immediately.…”

Three-dimensional porous SERS powder for sensitive liquid and gas detections fabricated by engineering dense “hot spots” on silica aerogel

“…Hence, three dimensional (3D) SERS active substrates have recently attracted great attention. [28][29][30][31][32][33] At present, two main technical routes have been reported to fabricate the 3D SERS substrates. One is to assemble the metallic nanostructures layer by layer at liquid-liquid or liquid-air interface.…”