Large-scale fabrication of flexible macroscopic SERS substrates with high sensitivity and long-term stability by wet-spinning technique: Uniform encapsulation of plasmon in graphene oxide fibers

Graphene oxide has attracted wide interest for theoretical research and application exploration in surface enhancement Raman scattering (SERS). However, how to break the geometric limitations of the nanoscale and extend its properties to the macroscopic level remains an urgent problem. Here, we prepared flexible graphene oxide/Au nanoparticles (GO/AuNP) fibers with high sensitivity and reproducibility for SERS sensing using wet spinning method. Benefitting from the plasmonic coupling of GO/AuNP fibers in vertical direction and uniform adsorption of the target molecules, the limit of detection for fiber was as low as 5 × 10^-11 M for rhodamine 6G (R6G) and crystal violet (CV) molecules. In addition, due to the optimal distribution of AuNP in the macroscopic assembly of GO/AuNP hybrid, the fiber substrates provided uniform and stable signals for both temporal (6 months) and spatial (RSD = 8.18 %) scales, exhibited excellent reliability and durability. Moreover, an ultra-low concentrations of the pesticide thiram residues could be rapidly traced by direct sampling from the apple peel with a sensitivity of 5 × 10^-9 M, which is much lower than the residue limit set by the US environmental protection agency. We envision that this work could provide new insights into the large-scale and economical fabrication of high-performance flexible SERS sensors for real world applications.