DNA Sequencer

A DNA sequencer is a scientific instrument used to automate the DNA sequencing process. Given a sample of DNA, the instrument determines the order of the four bases—adenine, guanine, cytosine, and thymine — composing pieces of the sample. Many DNA sequencers can be also considered optical instruments as they analyzes light signals originating from fluorochromes attached to nucleotides.

Modern automated DNA sequencing instruments are able to sequence multiple samples in a batch (run) and perform as many as 24 runs a day. These perform only the size separation and peak reading; the actual sequencing reaction(s), cleanup and resuspension in a suitable buffer must be performed separately.

A simple DNA sequencer will have one or more lasers that emit at a wavelength that is absorbed by the fluorescent dye that has been attached to the DNA strand of interest. It will then have one or more optical detectors that can detect at the wavelength that the dye fluoresces at. The presence or absence of a strand of DNA is then detected by monitoring the output of the detector. Since shorter strands of DNA move through the gel matrix faster they are detected sooner and there is then a direct correlation between length of DNA strand and time at the detector. This relationship is then used to determine the actual DNA sequence.

The output of these machines requires assembly, done either manually or through software packages. This process is known as sequence assembly. The data may also contain reading errors, though good sequence coverage may alleviate this issue.