Surface-enhanced Raman spectroscopy (SERS) is an important tool for the analytical, trace detection of many inorganic and organic materials, especially for materials involved in medical care, food safety and environmental pollution. Numerous efforts have been dedicated to exploring periodic metallic materials with a high density of hotspots. However, for most periodic metallic materials fabricated by top-down and bottom-up approaches, the distribution of hotspots is restricted to one or two dimensions. Here, for the first time, we report the successful fabrication of a bio-inspired bicontinuous gyroid-structured Au SERS substrate with a high density of three-dimensionally (3D) distributed hotspots. The as-required gyroid-structured substrates were demonstrated to be highly sensitive, reproducible and uniform, with an enhancement factor of up to 10 9 . Finite-difference time domain (FDTD) simulations were conducted to reveal the mechanism leading to the high enhancement and we found that the interconnected helices in the gyroid structure not only increase the hotspot density but also contribute to increasing the scattering cross-section of the incident laser. The substrate was then adopted for the SERS detection of bis(2-ethylhexyl) phthalate, the most frequently used plasticizer in food, paints, house-hold items, perfumes and so on, and reached a detection limit of 1 fM, which is among the best results ever reported. Moreover, the mechanism deduced here will provide insight into the future design and selection of novel surface plasmonic resonance substrates, as many other bicontinuous interconnected systems are available. NPG Asia Materials (2018) 10, e462; doi:10.1038/am.2017.230; published online 12 January 2018
INTRODUCTIONThe fabrication of surface plasmonic resonance (SPR) materials with ultra-high plasmonic enhancement has long been a critical research area due to their broad applications as chemical sensors, biological sensors, plasmonic solar cells, photocatalysts and other environmentally friendly devices. 1-3 Among these applications, the most famous is the surface-enhanced Raman spectroscopy (SERS) detection of trace analytes, especially for analytes involved in medical care, food safety and environmental pollution. Various nanoparticle systems with novel nanomorphologies and their assemblies have been fabricated and reported to show excellent SPR performance. 2-5 However, SERS nanostructures composed of nanoparticles face significant challenges in achieving a reproducible and uniform Raman response due to the difficulty in fabricating uniform SERS active sites. Periodic metallic materials could provide hotspots with high density, reproducibility and uniformity, which completely meet the requirement of valid SERS substrates, and therefore numerous efforts have been dedicated to engineering periodic metallic materials with novel nanomorphologies,