Vertically aligned Ag-decorated MoS2 nanosheets supported on polyvinyl alcohol flexible substrate enable high-sensitivity and self-cleaning SERS devices

The fabrication of stable and reproducible surface-enhanced Raman scattering (SERS) active substrates is a prerequisite for the ultra-sensitive SERS detection and sensing, but remains a great challenge. Herein, we present a facile yet efficient strategy for creating a flexible hybrid substrate by assembling Ag nanoparticles on vertical MoS2 nanosheets followed by spin-coating with polyvinyl alcohol (PVA) hydrogels. Combining the advantages of noble metal, 2D nanosheet, and hydrogel, the as-prepared SERS substrates exhibit superior detection ability and stability. Taking Rhodamine 6 G as a probing molecule, the lowest detectable concentration can be down to 1.0 x 10-12 M, and an enhancement factor is estimated to the order of 107. The finite-difference time-domain simulations reveal that the hybrid substrates provide strong electromagnetic enhancement and can generate more SERS "hot spots", therefore effectively amplify the Raman signal. Furthermore, the developed flexible MoS2 @Ag-PVA hybrid not only has a great SERS effect, but it also has outstanding catalytic characteristics due to its remarkable self-cleaning ability when exposed to visible light. Specifically, the formation of MoS2 nanosheets by chemical vapor deposition is remarkably homogenous, resulting in long-term stability and repeatability of the substrates. Additionally, the PVA coverage guarantees the flexibility and stability of the substrate, overcoming the complex handling in SERS assays. Such features make the present SERS platform to be reused for a minimum of five cycles with tolerable intensity degradation. This flexible and self-cleaning SERS technique offers a great potential for high-sensitivity detection of organic contaminants and could develop an in-situ SERS sensing platform.