Sequencing-By-Synthesis (SBS) Technique
The sequencing-by-synthesis (SBS) technology, the foundation of Illumina sequencing instruments, was launched by Solexa Inc. in 2006. One year later, Illumina (San Diego, CA) acquired Solexa. Illumina refined, optimized and continued the commercialization of the SBS-technique.
By employing specific adaptors, the fragmented template DNA is covalently bound to a glass slide (flow cell) where the sequencing reaction takes place. Starting with the bound template DNA molecule, a PCR-like step is used to form clusters of identical molecules (bridge amplification). The sequencing reaction is performed cycle-wise and applies reversible terminator chemistry and fluorescently labeled nucleotides. Exactly one nucleotide is incorporated to the template DNA in a complimentary way for each sequencing cycle. The fluorescence group is then cleaved and the emerging signal detected. Finally, the blocking group is removed to allow the incorporation of the next nucleotide in the following sequencing cycle.
The market offers various sequencing instruments with SBS-technology, for instance, the Genome Analyzer IIx (GAIIx), the successor models of the HiSeq series (HiSeq 1000, HiSeq 2000, HiSeq 1500, HiSeq 2500) or the benchtop-sized MiSeq. NextSeq500 with a medium throughput has recently been released. So far, current NIPT procedures use only the HiSeq platform for validation.