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

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.