Ultrasensitive Plasmon-Free Surface-Enhanced Raman Spectroscopy with Femtomolar Detection Limit from 2D van der Waals Heterostructure

Abstract

Two-dimensional (2D) materials have been promoted as an ideal platform for surface-enhanced Raman spectroscopy (SERS), as they mitigate the drawbacks of noble metal-based SERS substrates. However, the inferior limit of detection has limited the practical applicability of 2D material-based SERS substrates. Here, we synthesize uniform large-area ReO x S y thin films via solution-phase deposition without post-treatments and demonstrate a graphene/ReO x S y vertical heterostructure as an ultrasensitive SERS platform. The electronic structure of ReO x S y can be modulated by changing the oxygen concentration in the lattice structure, obtaining efficient complementary resonance effects between ReO x S y and the probe molecule. In addition, the oxygen atoms in the ReO x S y lattice generate a dipole moment on the thin-film surface, which increases the electron transition probability. These synergistic effects outstandingly enhance the Raman effect in the ReO x S y thin film. When ReO x S y forms a vertical heterostructure on a graphene as the SERS substrate, the enhanced charge-transfer and exciton resonances improve the limit of detection to the femtomolar level, while achieving remarkable flexibility, reproducibility, and operational stability. Our results provide important insights into 2D material-based ultrasensitive SERS based on chemical mechanisms.

Surface Enhanced Raman Scattering Revealed by Interfacial Charge-Transfer Transitions

“…In another example, the SERS sensitivity of a graphene/ReO x S y vertical heterostructure was optimized by controlling the lattice oxygen concentration of ReO x S y during solution-phase growth, in which an LOD of 10 −15 M was obtained for the R6G probe. 92 An oxygen-induced band-level alignment of the CT resonance and dipole-dipole interactions with the probe molecules were both believed to be responsible for the SERS activity. More importantly, further magnified PICT and exciton resonances in ReO x S y were believed to be induced by the heterostructure through an interlayer coupling effect, which also contributed to the SERS effect.…”

2D van der Waals Heterojunction Nanophotonic Devices: From Fabrication to Performance

“…Similar Raman enhancement studies have been carried out on a graphene/ReO x S y vdWh. [114] With the help of interlayer CT and exciton resonance, the detection limit of R6G reached 10 −15 m. By using MoS 2 /SnSe 2 and MoS 2 /h-BN/SnSe 2 vdWhs, the SERS signal increased tenfold due to nonradiative energy transfer. [114] Therefore, vdWhs provided a good platform for molecular Raman signal enhancement by improving the chemical effect.…”

Surface‐enhanced Raman Scattering on 2D Nanomaterials: Recent Developments and Applications†

“…[ 76 ] These synergistic effects of enhanced charge transfer and complementary resonance effects between ReO x S y and the probe molecule outstandingly enhanced the Raman effect and improved the limit of detection to the femtomolar level. [ 77 ]…”