In Situ Quantitative Graphene-Based Surface-Enhanced Raman Spectroscopy

Abstract

the uncertainty of the amount of detected molecules. The spectral instability is mainly due to the orientation fluctuation of molecules and/or the possible chemical reactions between the molecules and the metal substrate. [12][13][14] In principle, this can be avoided by isolating the molecules from the metal surface, for example, by coating a dielectric nanoshell on the metal nanostructures. [6,14,15] The inhomogeneous electromagnetic enhancement can be largely calibrated by implementing an internal standard species that experiences the same enhancement as the analyte molecule, so that the ratio between the Raman intensities of the analyte and the internal standard can be used for quantification. [6,16,17] The uncertainty of the amount of detected molecules is the most notorious because there have been few solutions so far, and the rough estimation of the number of molecules based on the homogenous-adsorption assumption and the detection area/volume has been generally adopted, although the probability of molecules adsorption is different on different facets of the metal nanostructures.Herein, we report a graphene-based SERS (G-SERS) substrate for analyte quantification that solves the above problems to a great extent. Graphene has shown its unique characteristics in SERS applications. [18][19][20][21] For example, graphene quenches the fluorescence of fluorophores and provides stable and clean Raman signals due to the separation of molecules from a metal. [18,19] Graphene has also been used to cover the surface of plasmonic nanostructures and the composite substrate can provide remarkable Raman enhancement. [22,23] More importantly, the single-crystalline nature of graphene guarantees that the probe molecules are homogeneously adsorbed on the surface, rendering the possibility of reliable determination of the number of molecules. Meanwhile, graphene is naturally an internal standard for the normalization of the Raman signals of analytes, so that the different enhancement experienced by molecules at different locations can be calibrated. In our substrate, a roughened metal film under graphene ensures that the overall Raman enhancement is still dominated by the sizable electromagnetic enhancement. We demonstrated in situ quantitative detection of crystal violet (CV) and rhodamine B (RhB) molecules in aqueous solutions with concentrations from 10 −8 to 10 −5 m and the real-time monitoring of a release process of RhB molecules through a permeable membrane. Our graphene-based SERS substrate promises SERS quantification Quantitative surface-enhanced Raman spectroscopy (SERS) with ultrahigh sensitivity will significantly promote its practical application in many fields, such as environment monitoring, food safety, and drug detection. However, the challenges that remain unresolved, particularly in the low concentration levels, arise from the instability of the SERS spectra and the uncertainty of the number of detected molecules. Herein, a graphene-based, flexible, and transparent substrate for SERS quantification is rep...

Monolayer Graphene Coupled to a Flexible Plasmonic Nanograting for Ultrasensitive Strain Monitoring

“…In addition to the high sensitivity, graphene's Raman signal opens up great opportunities for in situ quantitative analysis of adsorbed molecules and possibly provide more information regarding the charge transfer between molecules and graphene. Our platform may enable these investigations on strained graphene by monitoring the 2D peak, which could further enable sensors beyond perfect laboratory environments.…”

Recent Advances in Multifunctional Graphitic Nanocapsules for Raman Detection, Imaging, and Therapy

“…Luckily, the discovery and development of the SERS technique has opened up a new world for biomedical applications based on its superior merits of abundant chemical fingerprint signals and high sensitivity . Notwithstanding intensive attempts to propose novel SERS analysis methods in recent decades, SERS as a quantitative detection technique remains a notable challenge because the SERS signal is predominantly contributed by molecules in the hot spots within the commonly used, plasmonically active Au, Ag, and Cu materials or their alloy substrates . A small change in the geometric structure, such as the distance between the nanoparticles caused by the morphology alteration and aggregation of substrate, might result in a significant signal change by several orders of magnitude .…”

Trace Detection of Rhodamine B in Infant Candy by g-C3N4/Ag Nanocomposite as Surface-Enhanced Raman Scattering Substrate

“…根据 Tang 等 [30] 研究第 三个原因可能是由于复合材料 SPR 吸收相对 Ag 纳米粒 子发生了蓝移, 复合材料与分子间能量更匹配, 有利于 Figure 2 (a) UV-visible absorption spectra of silver nanoparticles, g-C 3 N 4 nanosheets, g-C 3 N 4 /Ag nanocomposites and UV-visible absorption differential spectra of g-C 3 N 4 /Ag nanocomposites and silver nanoparticles; (b) SERS spectra of 5×10 -7 mol/L RhB adsorbed on g-C 3 N 4 /Ag nanocomposites, Ag nanoparticles, and Raman spectra of 0.01 mol/L RhB solution 增强因子(enhancement factor, EF)是衡量 SERS 基 底性能优劣的重要参数, 为评价 g-C 3 N 4 /Ag 的增强效果, 实验中计算了 EF, 计算公式为 [31] : [32] . 根据 Zhang 等 [33] [34] , 当 pH 低于 3.1 时, 其为阳离子型染料, 但 pH 高 于 3.1 时, 其呈现为两性离子状态. 酸性增加导致 RhB 能够快速聚集吸附于带负电 g-C 3 N 4 /Ag 纳米复合材料的 表面 [35] , Figure 7 Schematic diagram of the preparation process…”