Unique high-performance metal-nanoparticle-free SERS substrate with rapid-fabricated hybrid 3D-Nano-Micro-Cavities anodic alumina for label-free detection

Conventional surface-enhanced Raman scattering (SERS) substrates were usually nanofabricated by coating Ag or Au metal nano particles (MNPs) to modify the surface. However, the complex and time-consuming nanofabrication prevents those good-performance substrates from the practical applications together with the instability of MNPs as a challenge. Here, a unique Roughened-Surface-with-hybrid-3D-Nano-Micro-Cavities (RS3DNMC) SERS substrate free of MNPs is proposed for high-performance enhancement using facile and rapid electrochemically micromachining aluminum foil to form randomly-distributed 3D over-etched cavities of 1 similar to 2 mu m in diameter embedded with the nanopores of anodized aluminum oxide (AAO). The metal-film-coated AAO with RS3DNMC structure creates great SERS enhancement because of two mechanisms from the significantly reduced reflectance for increasing the photonic-scattering-and-multi-reflection and the more peripheral-and-gap hotspots of 3D-nano-micro-cavities compared to the 2D flat surface. Our SERS substrate merits a high analytical enhancement factor (AEF) of 1.15x10(6) and a low limit of detection (LOD) of 1x10(-10) M for methylene blue (MB) with a good uniformity of 9.64% relative standard deviation (RSD) in a large area of 2.25 cm(2). The melamine widely remained in human body and environment was detected at LOD of 0.05 ppm that is much lower than WHO-recommended criteria (1 ppm).

Automated summary

A new type of SERS substrate is proposed, which does not require the use of metal nanoparticles. The substrate is fabricated by electrochemically micromachining aluminum foil to create a roughened surface with randomly-distributed 3D over-etched cavities and nanopores of anodized aluminum oxide (AAO). This SERS substrate demonstrates high analytical enhancement and low detection limit, making it suitable for rapid detection of substances such as methylene blue.