Study on the Surface Enhancement Enrichment Mechanism of Fe3O4-PDA-Au-GO Substrate for Phenanthrene Detection

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.