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The development of paper-based SERS substrates that can allow multi-component detection in real-word scenarios is of great value for applications in molecule detection under complex conditions. Here, a multifunctional SERS-based paper sensing substrate has been developed through the uniform patterning of high-density arrays of GO-isolated Ag nanoparticles on the hydrophilic porous cellulose paper strip (GO@AgNP@paper). Wet-chemical synthesis was used to provide the cover of SERS hot spots on any part of the paper, not just limited surface deposition. In virtue of the inherent ability of paper to deliver analytes by the capillary force, the detection ability of the GO@AgNP@paper substrate was greatly promoted, allowing as low as 10-19M R6G detection from microliter-volume (50 μL) samples. For the components with different polarity, the paper substrate can be used as an all-in-one machine to achieve the integration of separation and high-sensitive detection for ultralow mixture components, which improves the practical application value of SERS-based paper devices.

We have proposed a synthetic approach to produce self-supported and bendable surface-enhanced Raman scattering (SERS)-based 3D chemical sensors with high adsorptivity. Such 3D substrates consist of foam-like graphene macrostructures obtained by template-directed chemical vapour deposition on nickel foams (interconnected 3D scaffold of nickel) and uniform and high-density Ag nanoparticles wrapping around the foam graphene, via seed-mediated in situ growth process. Such 3D AgNPs/G@Ni foam substrates show high-quality SERS performance in terms of Raman signal reproducibility and sensitivity for the analyte, resulting from the high density and homogeneity of “hot spots” on AgNPs/G@Ni foam, multiple cascaded amplication (localized surface plasmon mode and optical standing waves or optical refraction) of incident laser to the 3D foam structures and powerful support from nickel scaffold. Moreover, in virtue of the high adsorptivity and sensitivity of AgNPs/G@Ni foam, the low-concentration crystal violet molecules can be easily traced in the curvilinear fish surface, by simply swabbing the surface to achieve molecules concentration effect in the practical applicability. This work shows promising potential in developing the applications of SERS in the foodstuffs processing and security field.

The physical phenomenon, surface-enhanced Raman scattering (SERS), is mainly based on the local electromagnetic fields enhancement located at the nano-gaps between metal nanostructures attributed to localized surface plasmon resonance. Therefore, nano-gaps are very important for obtaining high-density hot spots and optimal and uniform SERS signals. However, it remains a challenge to form the three-dimensional ultra-narrow nano-gaps. Here, a gyrus-inspired Gyrus-SERS substrate was fabricated with the nanostructure of Ag gyrus/graphene/Au film using an extremely simple method. The lateral and vertical hot spots respectively were obtained from the dense nano-gaps (~3 nm) between gyrus and the coupling of Ag gyrus and Au film in bilayer graphene nano-gaps (0.68 nm), which were demonstrated in experiment and theory. The proposed Gyrus-SERS platform performs an excellent SERS activity (EF~5 × 109), high sensitivity (the minimum detected concentration of R6G and CV respectively is 10−13 and 10−12 M), and outstanding reproducibility (RSD~7.11%). For practical application, the in situ detection of Malachite green (MG) residue on prawn skin was executed using the prepared flexible Gyrus-SERS substrate, which shows the wide potential in food safety field.