Semiconductor sequencing is another sequencing by synthesis method that is based on detection of H+ ions released during the polymerization of DNA. With this technique, Life Technologies released the Personal Genome Machine in 2011 as, "a rapid, compact and economical bench top machine."
One great thing about this technology is that there is no need for a modified nucleotide, or oligonucleotides as we have seen in reversible chain terminators and Sanger sequencing.
Emulsion PCR allows for enriched beads to be placed in microwells (see micro-machined well). Just underneath these microwells are pH sensors that are able to detect the most miniscule changes in pH.
Remember that pH is just a logarithmic scale that measures the amount of hydrogen ions (H+) in a solution. The lower the pH, the more hydrogen ions there are.
A particular dNTP is released. If the growing sequence requires that particular dNTP, then a H+ ion and pyrophosphate group is released.
The signal is picked up by the ISFET sensor and translated into a base call. Any homopolymers (multiple of the same base) result in a strong signal.
Unattached dNTP molecules are washed out, and the cycle repeats with a new dNTP.
|Ion Torrent Personal Genome Machine||Ion Proton System|
|Bases per run||1 Gb||Up to 10Gb|
|Read Length||35-400 bp||200 bp|
|Run time||4.5 hours||2-4 hours|
Watch how the Ion Torrent system works.
A more detailed look into the Ion Proteon Sequencer.
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