Self-Assembled Three-Dimensional Au Films as Highly Reproducible and “Hotspots”-Rich Substrates for Multiplex SERS Detection

Three-dimensional (3D) plasmonic metal nanostructures show great promise for surface-enhanced Raman scattering (SERS) detection of analyte molecules. However, obtaining uniform "hotspots" is still a paramount challenge. Herein, we report a low-cost strategy for the scalable preparation of 3D Au films with a high density of "hotspots" using a deep eutectic solvent (DES)-mediated interfacial self-assembly of thermally evaporated Au NPs. Owing to the hydrogen-bonded structure of DES, the size and morphology of the self-assembled Au films can be precisely controlled. The as-prepared 3D Au substrate exhibits outstanding SERS detection for various analyte molecules such as crystal violet (CV), rhodamine 6G (R6G), and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) with a limit of detection (LOD) as low as 3.2 × 10^-15 M and exceptional SERS signal reproducibility. Moreover, the 3D Au-SERS substrate showed outstanding sensitivity in detecting a variety of target molecules, such as doxorubicin (DOX) with a LOD of 5.8 × 10^-12 M and heavy metal ions such as As³⁺ and Hg²⁺ with LODs as low as 5.5 × 10^-5 and 4.1 × 10^-5 g/mL, respectively. Additionally, we validate their applicability in SERS detection of nanoplastics such as polyethylene terephthalate (PET), poly(methyl methacrylate) (PMMA), and polystyrene (PS), offering a great potential in practical SERS detection of various environmental pollutants.