Graphene or MoS₂ nanopores: pore adhesion and protein linearization

Nanopores drilled in materials can electrophoretically drive charged biomolecules to enable their detection. Here, we explore and compare two-dimensional nanopores, graphene and MoS₂, in order to unravel their advantages and disadvantages with regard to protein detection. We tuned the protein translocation and its dynamics by the choice and concentration of the surrounding solvent. For this, we used a typical monovalent salt solution, as well as a molecular solution. We assessed, with the aid of atomistic simulations, the efficiency of both nanopores in threading the protein on the basis of measurable ionic current signals. In the case of graphene, the protein adheres on the graphene surface, hindering the translocation under physiological conditions. This stickiness is resolved with the addition of a denaturant by the formation of a hydrophilic cationic layer on the pore surface and the protein can thread the pore in a linearized configuration. On the other hand, the MoS₂ nanopores can thread the protein also in a physiological solution, leading to longer passage times, while the degree of protein linearization is lower than in the case of graphene in a molecular solution. We analyze the differences between the two nanopore materials on the basis of the complex molecular interactions between all components, the material, the target protein, and the solvent. We discuss the relevance of the results with respect to controlling the protein dynamics and enhancing the read-out ionic signals in view of an efficient detection of proteins through 2D nanopores.