3D RGO@MoS2/Ag NPs based SERS platform for label-free detection of IL-6

The efficient and sensitive monitoring of the interleukin-6 (IL-6) is crucial for the clinical tracking and diagnosis of chronic obstructive pulmonary disease (COPD). Herein, a novel surface-enhanced Raman scattering substrate (RGO@MoS 2 /Ag NPs), comprising an efficient charge-transfer and adsorption layer of reduced graphene oxide (GO) encapsulated in molybdenum disulfide (MoS 2 ) and an electromagnetic enhancement layer of Ag nanoparticles, was developed for the highly sensitive, label-free detection of IL-6. Experimentally, a precursor film consisting of (NH 4 ) 2 MoS 4 and GO was first deposited onto a rough g -C 3 N 4 substrate via spin-coating process. Subsequently, the above precursor film was subjected to a two-step high-temperature annealing process for preparing the RGO@MoS 2 charge transfer layer. Finally, Ag NPs were sputtered onto the RGO@MoS 2 film to induce the localized surface plasmons for the further enhancement of the SERS performance. Leveraging the high specific surface area and exceptional charge transfer properties of RGO@MoS 2 , together with the high-density “hot spots” generated by surface Ag NPs, the fabricated SERS substrate exhibited remarkable electromagnetic and chemical enhancement effects. By using the rhodamine 6G (R6G) as the Raman reporter, it was determined that the lowest detection limit could be as low as 10 −9  M on the optimal SERS substrate, with an enhancement factor of 2.2 × 10 9 . Meanwhile, the substrate also exhibited good uniformity, with a relative standard deviation of 9.84%. Finally, the prepared SERS substrate was used to detect the IL-6, it showed good linear response in the range of 5.0-1000 pg/mL, with a detection limit as low as 0.41 pg/mL.