Graphene Nanogaps For DNA

Solid-state and protein nanopores are of great interest for DNA sequencing because of the possibility of reading longer stretches of DNA. But nanopores have trouble achieving single-base resolution. In a theoretical study, Henk W. Ch. Postma of California State University, Northridge, suggests a variation on the nanopore concept—graphene nanogaps. Postma proposes using a narrow gap in a graphene sheet attached to a pair of gold electrodes to measure the transverse conductance of DNA (Nano Lett., DOI: 10.1021/nl9029237). Each base has a characteristic conductance, and graphene’s single-atom thickness should make it possible to achieve single-base resolution during sequencing. The nanogap needs to be large enough for single-stranded DNA to slide through, but it can’t be larger than 1.6 nm. “For every 0.1-nm increase in width, the current decreases by about an order of magnitude,” Postma says. He proposes measuring the conductance with nonlinear current-voltage analysis, which would allow determination of whether current changes are due to gap-width variations or due to different bases. Postma’s calculations suggest that graphene nanogaps up to 1.6 nm will lead to error-free sequencing.