Highly sensitive thin SERS substrate by sandwich nanoarchitecture using multiscale nanomaterials for pesticide detection on curved surface of fruit.

Various flexible surface-enhanced Raman scattering (SERS) substrates have been developed for the Raman detection of environmental pollutants due to their high sensitivity, low cost, and rapid sampling capabilities. However, achieving high reproducibility, reliability, and sensitivity in large areas remains challenging. In this study, we present a simple fabrication method for a layered, sandwich-nanoarchitectured SERS substrate consisting of multiscale nanomaterials of (1) 0D, Au nanoparticles (AuNPs), (2) 1D, TEMPO-oxidized nanocellulose fibers (TC), and (3) 2D, MXene (TiCT). The resulting MXene@AuNP@MXene@TC (MX@Au@MX@TC) film demonstrated enhanced SERS performance based on the synergistic effect of efficient charge transfer (CT) and the presence of numerous nanogaps. Vertical plasmonic coupling in the MX@Au@MX@TC film, combined with the uniform adsorption of the target molecules, led to an ultra-low limit of detection of 10 M and an enhancement factor of 9.9 × 10 for rhodamine 6 G (R6G). In addition, the substrate exhibited excellent reliability, providing uniform and stable signals across various spatial scales with a relative standard deviation of 2.29 %. Furthermore, the SERS substrate detected thiram (0.02 μg/cm²) via direct in-situ sampling on curved fruit surfaces, offering insights into the scalable, cost-effective production of flexible SERS substrates for practical use.