Practice question

Ion Torrent semiconductor sequencing, introduced by Life Technologies, determines sequence without optics. Each microwell contains template-coated beads and a polymerase. When a deoxynucleotide complementary to template is incorporated, a covalent phosphodiester bond forms and a proton, hydrogen ion, is released as byproduct. This release transiently acidifies microwell solution, typically by 0.02 pH units, detected by an ion-sensitive field-effect transistor beneath well. Signal amplitude reflects homopolymer length. Detection principle is therefore pH change, not light, electrical charge of DNA itself or fluorescence employed in other platforms.