Self-assembled GA-Repeated Peptides as a Biomolecular Scaffold for Biosensing with MoS₂ Electrochemical Transistors

Biosensors with two-dimensional materials have gained wide interest due to their high sensitivity. Among them, single-layer MoS₂ has become a new class of biosensing platform owing to its semiconducting property. Immobilization of bioprobes directly onto the MoS₂ surface with chemical bonding or random physisorption has been widely studied. However, these approaches potentially cause a reduction of conductivity and sensitivity of the biosensor. In this work, we designed peptides that spontaneously align into monomolecular-thick nanostructures on electrochemical MoS₂ transistors in a non-covalent fashion and act as a biomolecular scaffold for efficient biosensing. These peptides consist of repeated domains of glycine and alanine in the sequence and form self-assembled structures with sixfold symmetry templated by the lattice of MoS₂. We investigated electronic interactions of self-assembled peptides with MoS₂ by designing their amino acid sequence with charged amino acids at both ends. Charged amino acids in the sequence showed a correlation with the electrical properties of single-layer MoS₂, where negatively charged peptides caused a shift of threshold voltage in MoS₂ transistors and neutral and positively charged peptides had no significant effect on the threshold voltage. The transconductance of transistors had no decrease due to the self-assembled peptides, indicating that aligned peptides can act as a biomolecular scaffold without degrading the intrinsic electronic properties for biosensing. We also investigated the impact of peptides on the photoluminescence (PL) of single-layer MoS₂ and found that the PL intensity changed sensitively depending on the amino acid sequence of peptides. Finally, we demonstrated a femtomolar-level sensitivity of biosensing using biotinylated peptides to detect streptavidin.