Long Read Sequencing

Now we're going to move over to the long-read sequencers. We're gonna start with Oxford nanopore sequencing. With this sequencing technology, it uses these nanopores, which are extremely small pores with really small gaps in them - in this case, 1.8 nanometers - that are embedded in lipid membranes. These lipid membranes act as a barrier that prevent currents from going back and forth, so currents have to pass through the pore. The way the nanopore sequencer works is single-stranded DNA, or even RNA, is threaded through the pore. Depending on which bases are in the pore at a given moment, that changes the current that's read out, and detectors can measure this change in current. Over here is just a depiction of what this looks like. For instance, you might have a similar one level of current for your T's, a different one for G's, something else for C's, and then another level of current for A's. You can just measure these current traces over time and build a sequence. In reality, the traces don't look this clean, because in the pore there are actually up to six bases at a time. With six bases times four different possible bases, for your A's, C's, G's and T's, this generates up to 4,000 different possible states. So, it was really a technical tour de force to get this to work.