Nanopore sequencing has been around for at least a decade in the lab. They admit that their method of using tunnel junctions to detect the DNA cannot even distinguish between different base pairs.
For background, here's the basic idea of a classical nanopore sequencer:
1. Make a solution with ions in it with a very thin membrane separating two different compartments each containing an electrode. The membrane has a very tiny hole (nanopore)
2. Apply a voltage. This will either attract or repel the salt ions, thus you get a detectable current passing through the nanopore.
3. Put DNA in the solution. The hole is hopefully small enough that the DNA can only go through as if stranded like thread through a needle. As the different base pairs move through, they block up varying amounts of the hole, manifesting as small changes in resistance across the hole.
4. Profit
The only real limiter is how thin you can make the membrane. Recently, some researchers used graphene, which is thinner than your average base pair, and so you do not get a resistance that is the convolution of many base pairs blocking up the pore at any given time. For more, google "Dekker DNA translocation through graphene nanopores" to see that they can already detect single pairs - and do it thousands of times a second.