What are the major platforms for next generation sequencing (NGS)?

Many sequencing platforms have been developed for next-generation sequencing (NGS) applications, including Roche/454 sequencing, Ion Torrent/proton sequencing, Illumina sequencing, and ABI/SOLiD (Sequencing by Oligonucleotide Ligation and Detection).

• Roche/454 sequencing: It is the first commercially available platform for NGS, which uses pyrosequencing based on the sequencing by synthesis approach. As each nucleotide is incorporated into the DNA molecule, a pyrophosphate is released, allowing a cascade of enzymatic reactions to give off light that is detected and used to identify the nucleotide added.
• Ion Torrent/Proton sequencing: This platform is based on semiconductor technology, which also employs the sequencing by synthesis approach. During the incorporation of dNTP to a growing DNA strand, hydrogen ions are released and detected. The sequencing reaction takes place on a complementary metal-oxide semiconductor chip. Once hydrogen ions are released, a high positive voltage is formed in the microenvironment, which can be detected by a transistor-based device and is eventually converted into a voltage signal.
• ABI/SOLiD sequencing: The SOLiD platform works on the basis of sequencing by ligation approach, which uses the mismatch sensitivity of DNA ligase to determine the nucleotide sequence. When the sequence of fluorescently tagged oligo probes matches with the strand to be sequenced, DNA ligation occurs, producing fluorescence signal that can be used to indicate the sequence information.
• Illumina sequencing: Illumina sequencing is currently the most popular NGS platform on market, and is responsible for more than 90% of the world’s sequencing data generated. It is based on the sequencing by synthesis approach, in which fluorescence signals are detected as fluorescently tagged dNTPs are added to a growing DNA chain. Images are taken after each dNTP incorporation reaction, and high-quality sequence data can be obtained by analyzing and processing these images.