The Ion Torrent from Applied Biosystems also involves the "wash-and-scan"
technique typical of the second generation methods, which involves alternately flooding the DNA with
nucleotides and scanning. It also uses emulsion PCR for amplification, like in
parallelized pyrosequencing.
However, it detects the change in pH
instead of change in color, so it only requires normal unmodified nucleotides,
which cost less. This method works because when normal nucleotides are added to DNA, they release hydrogen ions which decreases pH. In essence, the Ion Torrent is really a very small pH-change detector. (34)
   | To the left is a picture of the ION Torrent interface. Notice how it also has small micro-wells over sensing devices like several other methods. When a matching nucleotide is added, GridION detects a small spike in pH. Otherwise, pH will remain unchanged. When two consecutive nucleotides of the same type are added, in this case thymine (T), a larger change in pH is detected. |
