Photoinduced Enhanced Raman Spectroscopy with Hybrid Au@WS2 Nanosheets

Two-dimensional (2D) layered transition-metal dichalcogenides (2DMX2) are materials with unique optoelectronic properties, high surface-to-volume ratio, and high carrier mobility. The combination of noble metal nanoparticles (MNPs) with 2DMX2 opens new avenues in conceiving more efficient plasmonic sensors, allowing one to optimize both electromagnetic and chemical signal enhancement. Photoinduced enhanced Raman spectroscopy (PIERS) exploits the electron migration from semiconductors to MNPs, upon UV light irradiation, to further boost the chemical enhancement in the surface-enhanced Raman scattering (SERS) of molecules deposited on hybrid 2DMX2–MNP nanostructures. Here, we propose a new PIERS sensor architecture based on tungsten disulfide (WS2) nanosheets produced by liquid-phase exfoliation (LPE) and functionalized with citrate-stabilized Au MPNs. Electron injection from WS2 to AuNPs is observed when the Au@WS2 is exposed to ultraviolet light, yielding an increase of the charge carriers' density ≈ 1.8%. The PIERS sensor performances are tested by detecting 4-mercaptobenzoic acid at a concentration of 10 μM. The overall PIERS signal enhancement is ∼106, whereas the photoactivation of WS2 yields a signal improvement of factor 4 with respect to SERS from Au@WS2 before UV irradiation. Our sensor is of low cost, easy to fabricate, and has the potential to detect biomolecules and chemical molecules at trace levels.