π-Conjugated Small Organic Molecule-Modified 2D MoS₂ with a Charge-Localization Effect Enabling Direct and Sensitive SERS Detection

Organic semiconductors have been discovered to exhibit impressive surface-enhanced Raman scattering (SERS) activity recently. However, owing to the underdeveloped candidate materials and relatively low SERS sensitivity, practical application of SERS detection based on organic materials is still a challenge. Herein, we explored ways to further enhance the SERS sensitivity of π-conjugated fluorinated 7,7,8,8-tetracyanoquinodimethane derivatives (F_nTCNQ, n = 2, 4) by utilizing the charge-localization effect induced by two-dimensional (2D) MoS₂ flakes. A strong Raman signal enhancement in SERS has been realized via an organic/2D heterostructure constructed by F_nTCNQ nanostructures grown on a 2D MoS₂ flake. Moreover, F₂TCNQ and F₄TCNQ show different SESR sensitivities due to different numbers of cyano groups leading to different charge transfer (CT) directions. The SERS enhancement factor (EF) of methylene blue (MB) molecules on the optimal F₄TCNQ/MoS₂ nanocomposite substrate can reach as high as 2.531 × 10⁶, and the concentration of the limit of detection (LOD) is as low as 10⁻¹⁰ M. The SERS results for MB, rhodamine 6G (R6G), and 4-aminothiophenol (4-ATP) molecules demonstrate that high versatility, low cost, good stability, and easy preparation will make the F_nTCNQ/MoS₂ SERS platform promising for the detection of trace molecules. The studies on the complex microscopic interaction of organic/2D composite nanomaterials will provide some novel insights into improved SERS performance and mechanisms.