Ag Nanoparticle/Au@Ag Nanorod Sandwich Structures for SERS-Based Detection of Perfluoroalkyl Substances

Abstract

Perfluoro- and polyfluoroalkyl substances (PFAS) are widely used throughout the world and are extensively found in the environment. The detection of PFAS has become essential to ensuring environmental sustainability and human health. Herein, AuNRs were synthesized by the seed growth method and then the samples were coated with silver shells to form Au@Ag core–shell nanorods (Au@AgNRs). Au@AgNRs monolayer was prepared by oil–water self-assembly on a silicon wafer and then was constructed as a plasmonic AgNPs/Au@AgNRs sandwich structure for surface-enhanced Raman scattering (SERS) detection of PFAS. The shell thickness of Au@AgNRs was optimized and displayed a 11.9-fold SERS intensity higher than the pristine AuNRs. Moreover, the hotspots generated by the electromagnetic field coupling between the interlayer gap achieved 3.6-fold SERS signal enhancement compared to that of the Au@AgNRs monolayer. Besides, the excellent structural uniformity (RSD ∼ 8.0%) makes it ideal for quantitative SERS detection applications. More importantly, the use of the AgNPs/Au@AgNRs sandwich structure sensor enables the highly sensitive detection of model molecules (10–11 M) and quantitative detection of a wide range of fluorinated alkyl substances of perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA), and potassium perfluoro­butanesulfonate (PPFBS), even with a portable Raman device. And the detection concentration can be down to 0.1 ppm for PFAS. This sensitive and quantitative SERS technique has promising prospects in the monitoring of fluorinated alkyl substance contaminations.

Novel Conductive and Redox-Active Molecularly Imprinted Polymer for Direct Quantification of Perfluorooctanoic Acid

“…Lastly, the ability to rapidly quantify PFAS is highly desirable in the field. For instance, current gold-standard LC-MS/MS requires complex sample preparation and analysis protocols, which take hours to days to obtain results. ,,, The typical sample preparation and testing time for surface-enhanced raman spectroscopy (SERS) is in the range of hours, which relies on a diffusion-controlled process to accumulate sufficient PFAS between neighboring nanoparticles to reach the best signal enhancement. − By contrast, PFAS detection in our proposed platform can be accomplished within a few minutes (e.g., 5 min), which lays the groundwork for rapid detection, that is urgently needed in environmental science and engineering. Although some loss of sensitivity was observed due to interfering ions in water matrices, presumably, the calibration curve can be prepared in the same water matrices but at higher concentrations than native water, which might help correct background interference.…”

Enhanced Superhydrophobic Substrate-Based 3D SERS Platform for a Portable Raman Spectrometer-Assisted Drug Detection in Plasma

“…Upon drying, analyte molecules were entrapped in 3D hotspots produced not only by the SERS substrate but also by the additional plasmonic NP clusters that accumulate on top of the SERS substrates. For example, the mixture of Ag NPs and analytes dropped onto a film of Au@Ag nanorods enabled the direct detection of perfluorinated and polyfluoroalkyl substances . Similarly, a sandwich structure composed of a gold (Au) nanostar film decorated with Au NPs facilitated the discrimination of aliphatic amino acid enantiomers .…”

Plasmon-Free Surface-Enhanced Raman Spectroscopy Using α-Type MoO3 Semiconductor Nanorods with Strong Light Scattering in the Visible Regime

“…Surface plasmon resonances (SPRs) are known as typical examples of EM processes related to localized electric fields ( E -fields) on metallic nanostructures, which contribute to the high enhancement factor (EF) of SERS ranging from 10 9 to 10 10 . , This is because the EF of Raman scattering is approximately equal to the fourth power of the localized E -field enhancement ratio. Therefore, assembled nanoparticles and artificially engineered nanostructures have been used as metal-based SERS substrates to take advantage of the EM process. , …”

“…Previous strategies for oxide semiconductor-based SERS have extensively focused on creating CT processes that resonate with incident photons using vacancy defect-mediated methods that rely on light absorptions in the visible range. SERS detection using the CM process yielded relatively low EF values ranging from 10 4 to 10. , However, heavily doped oxide semiconductors have successfully produced SPRs in the visible and near-infrared (NIR) ranges by controlling the electron carriers in the hosts. − Similar to noble metals, oxide semiconductors can also provide high E -fields generated by SPR excitations, thereby, improving the Raman signal in SERS. , In addition, plasmonic hybrid nanostructures with metals and oxide semiconductors have been proposed as a means of introducing the EM process to oxide semiconductors . Thus, the importance of the EM process caused by SPRs has been highlighted in semiconductor-based SERS substrates.…”