In this study, highly active Fe₃O₄@PDA@Au@GO surface-enhanced Raman spectroscopy (SERS) active substrate was synthesized for application in the enrichment and detection of trace polycyclic aromatic hydrocarbons (PAHs) in the environment. The morphology and structure were characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and UV–visible absorption spectrum (UV–vis spectra). The effect of each component of Fe₃O₄@PDA@Au@GO nanocomposites on SERS was explored, and it was found that gold nanoparticles (Au NPs) are crucial to enhance the Raman signal based on the electromagnetic enhancement mechanism, and apart from enriching the PAHs through π–π interaction, graphene oxide (GO) also generates strong chemical enhancement of Raman signals, and polydopamine (PDA) can prevent Au from shedding and agglomeration. The existence of Fe3O4 aided the quick separation of substrate from the solutions, which greatly simplified the detection procedure and facilitated the reuse of the substrate. The SERS active substrate was used to detect phenanthrene in aqueous solution with a detection limit of 10⁻⁷ g/L (5.6 × 10⁻¹⁰ mol/L), which is much lower than that of ordinary Raman, it is promising for application in the enrichment and detection of trace PAHs.

A method for surface-enhanced Raman spectroscopy (SERS) sensing of polycyclic aromatic hydrocarbons (PAHs) is reported. Fe₃O₄@PDA@Ag@GO is developed as the SERS substrate prepared by classical electrostatic attraction method based on the enrichment of organic compounds by graphene oxide (GO) and polydopamine (PDA) and the good separation and enrichment function of Fe₃O₄. The morphology and structure of the SERS substrate were represented by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and the UV–visible absorption spectrum (UV–vis spectra). The effect of different temperatures on SERS during synthesis was investigated, and it was found that the best effect was achieved when the synthesis temperature was 90 °C. The effect of each component of Fe₃O₄@PDA@Ag@GO nanocomposites on SERS was explored, and it was found that Ag NPs are of great significance to enhance the Raman signal based on the electromagnetic enhancement mechanism; apart from enriching the polycyclic aromatic hydrocarbons (PAHs) through π–π interaction, GO also generates strong chemical enhancement to the Raman signal, and PDA can prevent Ag from shedding and agglomeration. The existence of Fe₃O₄ is favored for the fast separation of substrate from the solutions, which greatly simplifies the detection procedure and facilitates the cycle use of the substrate. The experimental procedure is simplified, and the substrate is reused easily. Three kinds of PAHs (phenanthrene, pyrene and benzanthene) are employed as probe molecules to verify the performance of the composite SERS substrate. The results show that the limit of detection (LOD) of phenanthrene pyrene and benzanthene detected by Fe₃O₄@PDA@Ag@GO composite substrate are 10⁻⁸ g/L (5.6 × 10⁻¹¹ mol/L), 10⁻⁷ g/L (4.9 × 10⁻¹⁰ mol/L) and 10⁻⁷ g/L (4.4 × 10⁻¹⁰ mol/L), respectively, which is much lower than that of ordinary Raman, and it is promising for its application in the enrichment detection of trace PAHs in the environment.

This study focuses on the preparation of a highly active surface-enhanced Raman spectroscopy (SERS) substrate, where Ag nanoparticles synthesized by the Lee–Meisel method are loaded onto the surface of GO@PVP nanoparticles through classical electrostatic attraction. The substrate was characterized by SEM and XPS analysis. The SERS-active substrate was utilized for the detection of phenanthrene in aqueous solutions, achieving a detection limit of 10⁻⁸ g/L (5.6 × 10⁻¹¹ mol/L). In comparison to conventional Raman spectroscopy, this method exhibits a significant reduction in the detection limit and holds promise for trace polycyclic aromatic hydrocarbons (PAHs) monitoring in environmental samples.

In our prior research (2022), a Fe₃O₄@PDA@Au@GO composite was reported as a surface-enhanced Raman scattering (SERS) substrate for phenanthrene detection, with a detection limit of 10⁻⁷ g/L. The current study is a mechanistic follow-up investigation, which aims to explore the enhancement and enrichment mechanisms of the same substrate. By integrating density functional theory (DFT) calculations, adsorption experiments, and spectroscopic analyses (Raman, FTIR, XPS) before and after adsorption, the surface enhancement mechanism of the Fe₃O₄-PDA-Au-GO composite substrate is investigated. Our findings suggest that Fe₃O₄ enables efficient magnetic separation. The polydopamine (PDA) modification layer appears to enhance the uniformity and stability of the substrate surface, which is beneficial for uniform loading of Au nanoparticles (Au NPs). Graphene oxide (GO) and PDA are found to contribute to the effective enrichment of phenanthrene. Au NPs (mostly in the metallic Au⁰ state) may provide electromagnetic enhancement through localized surface plasmon resonance, and may also contribute to chemical enhancement through possible interactions with phenanthrene. Overall, the stepwise comparison presented in this study is consistent with the proposed roles of Au and GO in enhancing the SERS performance, which collectively improve the detection sensitivity.