Discrimination of Protein Amino Acid or Its Protonated State at Single-Residue Resolution by Graphene Nanopores

The function of a protein is determined by the composition of amino acids and is essential to proteomics. However, protein sequencing remains challenging due to the protein's irregular charge state and its high-order structure. Here, a proof of principle study on the capability of protein sequencing by graphene nanopores integrated with atomic force microscopy is performed using molecular dynamics simulations. It is found that nanopores can discriminate a protein sequence and even its protonation state at single-residue resolution. Both the pulling forces and current blockades induced by the permeation of protein residues are found to be highly correlated with the type of amino acids, which makes the residues identifiable. It is also found that aside from the dimension, both the conformation and charge state of the residue can significantly influence the force and current signal during its permeation through the nanopore. In particular, due to the electro-osmotic flow effect, the blockade current for the double-protonated histidine is slightly smaller than that for single-protonated histidine, which makes it possible for discrimination of different protonation states of amino acids. The results reported here present a novel protein sequencing scheme using graphene nanopores combined with nanomanipulation technology.