Stacked Graphene-Al₂O₃ Nanopore Sensors for Sensitive Detection of DNA and DNA–Protein Complexes

We report the development of a multilayered graphene-Al₂O₃ nanopore platform for the sensitive detection of DNA and DNA–protein complexes. Graphene-Al₂O₃ nanolaminate membranes are formed by sequentially depositing layers of graphene and Al₂O₃, with nanopores being formed in these membranes using an electron-beam sculpting process. The resulting nanopores are highly robust, exhibit low electrical noise (significantly lower than nanopores in pure graphene), are highly sensitive to electrolyte pH at low KCl concentrations (attributed to the high buffer capacity of Al₂O₃), and permit the electrical biasing of the embedded graphene electrode, thereby allowing for three terminal nanopore measurements. In proof-of-principle biomolecule sensing experiments, the folded and unfolded transport of single DNA molecules and RecA-coated DNA complexes could be discerned with high temporal resolution. The process described here also enables nanopore integration with new graphene-based structures, including nanoribbons and nanogaps, for single-molecule DNA sequencing and medical diagnostic applications

Electrochemistry at the Edge of a Single Graphene Layer in a Nanopore

We study the electrochemistry of single layer graphene edges using a nanopore-based structure consisting of stacked graphene and Al₂O₃ dielectric layers. Nanopores, with diameters ranging from 5 to 20 nm, are formed by an electron beam sculpting process on the stacked layers. This leads to a unique edge structure which, along with the atomically thin nature of the embedded graphene electrode, demonstrates electrochemical current densities as high as 1.2 × 10⁴ A/cm². The graphene edge embedded structure offers a unique capability to study the electrochemical exchange at an individual graphene edge, isolated from the basal plane electrochemical activity. We also report ionic current modulation in the nanopore by biasing the embedded graphene terminal with respect to the electrodes in the fluid. The high electrochemical specific current density for a graphene nanopore-based device can have many applications in sensitive chemical and biological sensing, and energy storage devices