Defect-Rich Monolayer MoS2 as a Universally Enhanced Substrate for Surface-Enhanced Raman Scattering

Abstract

Monolayer 2H-MoS2 has been widely noticed as a typical transition metal dichalcogenides (TMDC) for surface-enhanced Raman scattering (SERS). However, monolayer MoS2 is limited to a narrow range of applications due to poor detection sensitivity caused by the combination of a lower density of states (DOS) near the Fermi energy level as well as a rich fluorescence background. Here, surfaced S and Mo atomic defects are fabricated on a monolayer MoS2 with a perfect lattice. Defects exhibit metallic properties. The presence of defects enhances the interaction between MoS2 and the detection molecule, and it increases the probability of photoinduced charge transfer (PICT), resulting in a significant improvement of Raman enhancement. Defect-containing monolayer MoS2 enables the fluorescence signal of many dyes to be effectively burst, making the SERS spectrum clearer and making the limits of detection (LODs) below 10−8 M. In conclusion, metallic defect-containing monolayer MoS2 becomes a promising and versatile substrate capable of detecting a wide range of dye molecules due to its abundant DOS and effective PICT resonance. In addition, the synergistic effect of surface defects and of the MoS2 main body presents a new perspective for plasma-free SERS based on the chemical mechanism (CM), which provides promising theoretical support for other TMDC studies.

A non-metallic SERS-based immunoassay founded by light-harvesting effect and strengthened chemical enhancement

“…It is noteworthy that even at ultra-low micromolar concentration, some characteristic peaks could still be clearly identified, which originated from the improved resolution of Raman spectra due to the inherent fluorescence quenching effect of the MoS 2 @RP composite nanoplates. 49,50 After a linear correlation between the SERS intensity at 1360 cm −1 and the R6G concentration in the range of 10 −2 –10 −6 M was revealed, an extremely low LOD value of 3.5 × 10 −7 M was determined based on a triple signal-to-noise ratio (Fig. 4b).…”

Chemically Engineered Sulfur Vacancies on Few-Layered Molybdenum Disulfide Nanosheets for Remarkable Surface-Enhanced Raman Scattering Activity

“…It is worth emphasizing that SERS substrates can be fabricated simply by adding NaBH 4 to MoS 2 NSs. For example, Sun et al and Quan et al created vacancies in MoS 2 monolayers by etching/annealing at high temperatures in a high-vacuum and inert gas environment and demonstrated SERS activity. , With the replacement of SV-FL-MoS 2 with FL-MoS 2 NSs, the minimum measurable concentration of R6G is 1 × 10 –6 M (Figure S3). SV-FL-MoS 2 NSs (Figure a) and FL-MoS 2 (Figure S4) as SERS substrates provide the lowest concentration of RhB corresponding to 1 × 10 –8 and 1 × 10 –6 M, respectively.…”

“…As the electron density increases, the charge transitions from the conduction of MoS 2 NSs to the LUMO of the dye molecules and vice versa. One of the causes of SERS amplification might be this electron delocalization cloud. ,,, …”

“…The two resonances mentioned above can also induce photoinduced CT resonances of neighboring molecules via vibronic coupling. These two processes are critical components of the Raman amplification mechanism in MoS vacancies. , When the sample is irradiated with a 532 nm laser (2.33 eV), electrons from the HOMO level of the R6G molecules are injected into the neighboring conduction band of the MoS 2 NSs to produce electron–hole pairs . This is the photoinduced CT process.…”

Microfluidic preparation of optical sensors for biomedical applications

“…For electromagnetic enhancement, metals are dominant SERS substrates because of their high SERS enhancement factor, which enables ultra‐sensitive molecular detection 24 . Nanostructured noble metal (such as Au, Ag, and Cu) substrates have been extensively studied 25 .…”