There were several generations of sequencers, and the driving idea is to cut the DNA in very very short pieces that could be analyzed separately and accurately.
However the tiny reads have to be reassembled and it is a hard challenge. So much for all the pop science articles.
There are sequencers that are able to process long reads. Not surprisingly their error rate is awful.
Oxford Nanopore smallest sequencer (as big as a USB dongle) is still valuable with lot of data processing. But a one shot usage of their device costs near $800 and it is slooooow
Their core idea is to make a DNA molecule go through a nanometer pore, and to measure how the current flow is varying as each nucleotide goes through the pore.
Basically their device is very similar to a water reverse osmosis unit with an electrical potential applied to the water chamber.
The real added value of Oxford Nanopore is in the software, not in the hardware.
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