Bridge amplification creates a clonal cluster from each immobilized DNA fragment on the flow cell. The resulting group contains many copies of the same starting fragment rather than a single molecule, allowing fluorescent incorporation events to be imaged during sequencing. This amplification supports analysis of many DNA fragments in parallel while preserving the sequence identity of each cluster.
Each fluorescently labeled, reversible-terminator nucleotide permits one base to be added at a time. Imaging records the fluorescence associated with that incorporation, identifying the base in the growing strand. The terminator is then reversible, allowing the next cycle to proceed. Repeating this controlled process produces successive base calls for each DNA fragment.
The instrument records fluorescence after each nucleotide-incorporation cycle, and each signal identifies the base added to a fragment. Computational analysis then assembles these sequential base calls into the corresponding DNA sequence. This combination of repeated imaging and computational reconstruction enables detailed analysis while supporting the technology’s accuracy and high-throughput operation.
The workflow first places DNA fragments on a flow cell, where bridge amplification generates a clonal cluster from each fragment. Sequencing by synthesis then adds fluorescently labeled, reversible-terminator nucleotides through repeated cycles. Imaging identifies every incorporated base, and computational analysis reconstructs the sequences for downstream biological interpretation.
Illumina sequencing can support genome analysis, transcriptome analysis, gene expression profiling, variant detection, metagenomics, and biomedical research. The same underlying data-generation approach can therefore be applied to questions about genetic composition, expressed genetic material, sequence differences, or the mixture of organisms present in a biological sample.
Its accuracy, scalability, and relatively low cost make Illumina sequencing practical for analyzing large numbers of DNA fragments and diverse biological samples. In biology, the resulting sequence information can help characterize genomes and transcriptomes, detect variants, examine gene expression, study microbial communities through metagenomics, and support broader biomedical investigations.