Fabrication of large-area nanostructures of pine needles with a dewdrop array for surface-enhanced Raman spectroscopy

Abstract

Surface-enhanced Raman spectroscopy (SERS) depends on the development of a nanostructured substrate on which the excitation of a localized surface plasmon enhances the Raman scattering signals. Herein, we proposed a large-area three-dimensional (3D) pine needle with a dewdrop array (PNDA) nanostructure that can be easily fabricated via a film deposition technique with the help of a self-assembled polystyrene microsphere template and ultra-thin anodized aluminum oxide mask. Electromagnetic hotspots generated at the cracks or gaps between adjacent island structures of the PNDA are responsible for the SERS enhancement factor of 6.7 × 10⁶ when the structural parameters of the PNDA substrate are optimized. Experiments demonstrated that the rhodamine 6G (R6G) molecule can be probed with the PNDA substrate at the lowest concentration of 10⁻⁹ M using SERS. The homogeneity of the substrate was confirmed by verifying the relative standard deviation (RSD) of Raman spectra at different sites (6.5% at 611 cm⁻¹ and 8.3% at 1652 cm⁻¹). Moreover, crystal violet (CV) molecules were probed using our SERS experiment at the lowest detection concentration of 10⁻⁸ M. The results confirm that the PNDA structure is a reliable and sensitive SERS substrate to detect trace amounts of pollutants in an aquatic environment.