Ultrasensitive plasmon-free SERS platform at femtomolar detection from 2D van der Waals heterostructure with synergistic effects

Abstract

Surface-enhanced Raman spectroscopy (SERS) is nondestructive and sensitive analytical technique for molecule detection. Two-dimensional (2D) materials have attracted significant attention as an ideal platform for SERS to resolve the drawbacks of noble metal-based SERS substrates based on electromagnetic mechanism. However, the inferior limit of detection of 2D materials is still challenging to achieve ultrahigh sensitive SERS platform. Here, we introduce one-step solution phase deposition process for synthesizing uniform large-area ReOxSy thin films and demonstrate ultrasensitive SERS platform based on graphene/ReOxSy vertical heterostructure. The electronic structure and surface property of ReOxSy are changed by controlling the oxygen concentration in the ReOxSy lattice during the growth process, which leads to the improved Raman enhancement effect through the complementary resonances and dipole-dipole interaction between ReOxSy and probe molecules. For the graphene/ReOxSy heterostructure, the charge transfer and exciton resonances in ReOxSy are further enhanced through the interlayer coupling effect with underlying graphene. As a result, the graphene/ReOxSy vertical heterostructure based SERS substrate shows ultrahigh sensitivity at femtomolar detection, along with remarkable flexibility, reproducibility, and operational stability. Our results can provide significant insights into the study of 2D material-based ultrasensitive SERS based on chemical mechanisms.