Chemistry and Imaging on iSeq 100

The iSeq 100 System combines complementary metal-oxide semiconductor (CMOS) technology with innovative one-channel sequencing by synthesis (SBS) chemistry to deliver high-accuracy data in a compact system.

The system uses a patterned flow cell with nanowells fabricated over a CMOS chip (Figure 1).

Figure 1: Illumina CMOS Flow Cell.

Clustering and sequencing occur in the nanowells with direct alignment of single clusters over each photodiode (pixel). Using a CMOS sensor embedded in the consumable is a simple and fast detection method.

Unlike four-channel SBS chemistry, where sequencers use a different dye for each nucleotide, the iSeq 100 System uses one dye, two chemistry steps, and two imaging steps per sequencing cycle (Figure 2). In one-channel chemistry, adenine has a removable label and is labeled in the first image only. Cytosine has a linker group that can bind a label and is labeled in the second image only. Thymine has a permanent fluorescent label and is therefore labeled in both images, and guanine is permanently dark.

Figure 2: One-Channel Chemistry by schematic representation.

Nucleotides are identified by analysis of the different emission patterns for each base across the combination of Image 1 and Image 2 that are processed by image analysis software to identify which bases are incorporated at each cluster position.

Figure 3: Image analysis during SBS Chemistry with One-Channel Detection.

The iSeq 100 System uses during cluster generation, a proprietary ExAmp chemistry to ensure that each well in the flow cell generates a single, clonal cluster. During each imaging step, light emissions are detected by the CMOS photodiodes.

For more information, see the Sequencing by Synthesis page here.

For any feedback or questions regarding this article (Illumina Knowledge Article #8434), contact Illumina Technical Support [e-mail].