MoS<sub>2</sub> Nanosheets as Substrates for SERS-Based Sensing
Xiaolong Fu, Huiying Wu, Zhihong Liu, Pengzhao Wang, Jiefeng Rong, FengFu Fu, Zhenyu Lin, Yongqiang Dong
Abstract
The chemical enhancement of semiconductor-based surface-enhanced Raman scattering (SERS) substrates is an exciting hot topic. Herein, a simple hydrothermal method is developed to prepare molybdenum disulfide (MoS 2 ), which can be easily exfoliated into monolayer nanosheets (MoS 2 NSs) by sonication, even in the absence of any surfactant. The obtained MoS 2 NSs contain two types of defects, namely, one caused by the incorporation of Mo atoms of high valence states and one caused by the incorporation of S 2 2– . The density of the two types of defects can be easily tuned by controlling the ratio of Na 2 S and Na 2 MoO 4 in the raw materials. The unique properties and the clear surface make the obtained MoS 2 NSs ideal models to investigate the effect of defects on the SERS activity of MoS 2 . It is found that the SERS activity of the obtained MoS 2 NSs increases dramatically with the defects caused by Mo atoms of high valence states, while it first increases and then decreases with the increase of defects caused by S 2 2– . On the basis, MoS 2 NSs with high SERS activity and a low detection limit of 5.0 × 10 –9 mol/L toward crystal violet (CV) are obtained. Moreover, the mechanism of defects affecting the SERS activity of MoS 2 NSs is revealed. The defects on one hand provide a large amount of dangling bonds that can combine CV molecules to form MoS 2 NS–CV complex and on the other hand provide extensive induced local dipoles and enhance the overall SERS spectrum of CV.