Layered MoS2 based Electrochemical Biosensor

Recently two dimensional layered structures, such as graphene and Molybdenum disulfide (MoS₂), have got attention because of their unique physical and chemical properties. It has been reported that the integration of carbon-based materials and metal oxide nanoparticle shows synergistic effects in electrochemical application. Graphene sheets are explored due to their large active surface area, which can be embedded by intercalation methods and high mobility, on/off ratio. However, graphene doesn’t have band-gap which adds a large leakage current and reduces dynamic range of sensor hence it is difficult to use in sensing applications. In contrast, MoS₂ has a direct band gap whereas all other features are similar to graphene. Typically, MoS₂ is composed of three atomic layers which are composed by a Mo layer between Surfer layers. These layers are stacked and held each other by weak van der Waals force so molecule can be embedded. These properties lead to fabrication of MoS₂ nanosheet-based field effect biosensor for potential use in the bio-sensing applications.

It is well known that for biosensor, selective, accurate and rapid detection methods are necessary. As an example significant work has been carried out for the detection of H₂O₂ using fluorescence, chemiluminescence, titrimetry, cell imaging, spectrophotometry and electrochemical methods. Among them, electrochemical method has great advantages including high sensitivity, selectivity, low cost and simple instrumentation. Until now, horseradish peroxidase (HRP), a heme enzyme, has been commonly used to contrast an efficient H₂O₂ biosensor. However, the preparation of H₂O₂ biosensor with high performance has proven challenging. For achieving it, MoS₂ has been utilized to modify the surface of electrode and immobilize HRP because of high surface reaction activity and good catalytic efficiency.

In the present work, the electrocatalytic activity of layered MoS₂ toward the reduction of H₂O₂ with the help of HRP is demonstrated_. The chemical vapor deposition (CVD) synthesized MoS₂ thin films are transferred on gold (Au) electrode and was characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and high-resolution transmission microscopy (HR-TEM). IgG-HRP was then immobilized on MoS₂ thin film layers. Here MoS₂ work as an electrocatalyst between Au electrode and active centers of HRP.  Cyclic voltammetry (CV) results demonstrated the fast electron transfer process between HRP and the Au electrode. Figure 1 show the CV plots of IgG-HRP modified MoS₂ towards H₂O₂ for 10 to 100 mVs^-1 scan rates. It is observed that no reduction peak for 10 mM PBS (curve a). However, reduction peak were observed (curve b, c, and d) as the scan rate increases from 10 to 100 mVs^-1. This phenomenon can be attributed to electrochemical reaction of immobilized IgG-HRP on MoS₂ Au electrode and H₂O₂.

In conclusion, in the present work we successfully demonstrated MoS₂ based electrochemical biosensor platform for the detection of H₂O₂. Further H₂O₂ concentration dependent evolution is in process. We believe that this work will be helpful for the research community to develop MoS₂ based electrochemical biosensors.