Quantitative Surface-Enhanced Raman Spectroscopy for Field Detections Based on Structurally Homogeneous Silver-Coated Silicon Nanocone Arrays

Abstract

Practical application of surface-enhanced Raman spectroscopy (SERS) is greatly limited by the inaccurate quantitative analyses due to the measuring parameter’s fluctuations induced by different operators, different Raman spectrometers, and different test sites and moments, especially during the field tests. Herein, we develop a strategy of quantitative SERS for field detection via designing structurally homogeneous and ordered Ag-coated Si nanocone arrays. Such an array is fabricated as SERS chips by depositing Ag on the template etching-induced Si nanocone array. Taking 4-aminothiophenol as the typical analyte, the influences of fluctuations in measuring parameters (such as defocusing depth and laser powers) on Raman signals are systematically studied, which significantly change SERS measurements. It has been shown that the silicon underneath the Ag coating in the chip can respond to the measuring parameters’ fluctuations synchronously with and similar to the analyte adsorbed on the chip surface, and the normalization with Si Raman signals can well eliminate the big fluctuations (up to 1 or 2 orders of magnitude) in measurements, achieving highly reproducible measurements (mostly, <5% in signal fluctuations) and accurate quantitative SERS analyses. Finally, the simulated field tests demonstrate that the developed strategy enables quantitatively analyzing the highly scattered SERS measurements well with 1 order of magnitude in signal fluctuation, exhibiting good practicability. This study provides a new practical chip and reliable quantitative SERS for the field detection of real samples.

Cellulose Acetate-Based Plasmonic Crystals for Surface-Enhanced Raman and Fluorescence Spectroscopy

“…To make SERS substrates viable for field or nonlab qualitative analysis, they should have low variation in the strength of generated signals obtained from different spots on the sample. Additionally, templates resulting in Raman signals with less than 15% relative standard deviation could be used for quantitative analysis Figure a,b shows the spectra from 30 randomly selected spots on the Ag-coated pillar CA sample with CV used as an analyte molecule as well as the intensity of the strongest peak in the spectrum compared to the mean value.…”

SERS Enhancement of Porphyrin-Type Molecules on Metal-Free Cellulose-Based Substrates

“…Silicon is a semiconductor material often used as a control substrate for SERS measurements due to its Raman spectrum consisting of one peak at 520 cm −1 , limiting the background signal associated with the substrate. 44 Graphene-based platforms such as graphene oxide are a class of SERS-active metal-free materials that have been recently explored due to their unique two-dimensional structure as well as physical and chemical properties, such as stability and biocompatibility. 45−47 The graphene-enhanced Raman spectroscopy (GERS) effect is considered to be absent from electromagnetic enhancement, making it a pure system for the investigation of the chemical enhancement process.…”

“…Although the CNF substrate is characterized by relatively high roughness, which may lower the reproducibility of the SERS signal, a 14.6% relative standard deviation in the signal intensity was observed, reaching the 15% threshold value desired for quantitative Raman studies. 44 Nonporphyrin molecules often used for assessing the performance of Raman substrates were also used (Figure S4) with up to 2fold overall enhancement measured. Since the highest enhancement reaching almost 2 orders of magnitude in relative peak intensity has been observed for TMPyP, further analysis has focused on the porphyrin molecules.…”

“…Figure a–e shows the SERS spectra of the five different porphyrin molecules on CNF, graphene oxide (GO), and silicon, while Figure f shows all of the spectra compared to the background signal of CNF. Silicon is a semiconductor material often used as a control substrate for SERS measurements due to its Raman spectrum consisting of one peak at 520 cm –1 , limiting the background signal associated with the substrate . Graphene-based platforms such as graphene oxide are a class of SERS-active metal-free materials that have been recently explored due to their unique two-dimensional structure as well as physical and chemical properties, such as stability and biocompatibility. − The graphene-enhanced Raman spectroscopy (GERS) effect is considered to be absent from electromagnetic enhancement, making it a pure system for the investigation of the chemical enhancement process. , Here, randomly distributed graphene oxide was used to assess the efficiency of the CNF substrate and compare it to a different plasmon-free SERS-active platform.…”

“…Ideally, for a SERS substrate, a low variation in the strength of generated signal obtained from different spots on the sample is desirable. Although the CNF substrate is characterized by relatively high roughness, which may lower the reproducibility of the SERS signal, a 14.6% relative standard deviation in the signal intensity was observed, reaching the 15% threshold value desired for quantitative Raman studies . Nonporphyrin molecules often used for assessing the performance of Raman substrates were also used (Figure S4) with up to 2-fold overall enhancement measured.…”