2D materials such as graphene have been investigated to be applied for biosensors due to their excellent electrical properties and high specific surface area. More recently, MoS2 has exhibited higher sensitivity than graphene due to its semiconducting nature . Designed peptides on the surface of 2D materials form uniform and ordered structures arise from self-assembly with non-covalent integrations. These self-assembled peptides are expected as a molecular scaffold for immobilizing probe molecules without degrading the electrical properties. It has been reported that under dry condition self-assembled peptides on the surface of the graphene and MoS2 change the electrical properties . Since the operation of the biosensor is carried out under wet condition, behavior of MoS2 field-effect transistor (FET) in solution is important. However, the response of MoS2 FET to the absorbed peptides has not been reported yet. In this work, we observed the influence of the self-assembled peptides in buffer solution on the electrical characteristics of MoS2 FET.
MoS2-FET were fabricated by transferring a single layer MoS2 to an electrode prepared by a lithography technique. For the measurement, the source-drain current with respect to the gate voltage was measured with a platinum reference electrode in 10mM phosphate buffer. After the formation of the peptide self-assembled structures, measurements were carried out in the same manner. The morphology of the self-assembled peptides on MoS2 surface was also measured by Atomic force microscopy (AFM). The peptides utilized in this work have “GAGAGA” amino acid sequence, which is inspired from silk protein, fibroin. Fibroin forms stable b-sheet structure based on the amino acid sequence of GAGAGS. We found that the GAGAGA peptides form uniform and ordered structures on MoS2 surface. In the conductivity measurements, MoS2-FET shows a shift of threshold voltage after forming peptide self-assembled structure on the surface, but no change in the transistor mobility. This result suggests that our peptides may be useful as a molecular scaffold for MoS2 biosensor.
 Sarkar, D. et al. ACS Nano 8, 3992–4003 (2014).
 Hayamizu, Y. et al. Sci. Rep. 6, 33778 (2016).