Sanger sequencing

Sanger sequencing is a way to read the tiny "letters" that make up DNA, the material that carries the instructions for all living things. This method was created by a scientist named Frederick Sanger and his team in 1977. For about 40 years, it was the main tool scientists used to uncover the sequences of DNA.

The process uses special molecules that stop the DNA from copying itself at random points, creating pieces of different lengths. By separating these pieces and reading their order, scientists can figure out the exact sequence of DNA bases. In 1987, a company called Applied Biosystems made the first machine that could do this automatically, making the work faster and easier.

Even though newer, faster methods have taken over for big projects, Sanger sequencing is still very important. It can read longer pieces of DNA than many newer methods and is very accurate. Today, it is used in many important jobs, like studying the virus that causes COVID-19 and tracking outbreaks of a stomach bug called norovirus in the United States.

Method

The Sanger sequencing method needs a single piece of DNA, a special starting piece called a primer, an enzyme called DNA polymerase, normal building blocks for DNA, and special modified blocks called ddNTPs. These modified blocks stop the DNA from growing longer. Scientists mix these pieces together in four separate tests, each with one type of modified block. This helps them figure out the order of the DNA letters.

After mixing, the DNA pieces are separated by size using a special gel. This lets scientists see the order of the DNA letters. Later, scientists found ways to make this process faster by using special lights to see the DNA pieces. Today, machines can do this automatically, making it easier to read many DNA samples quickly. This method has been very important for studying diseases like SARS-CoV-2 and helping to stop their spread.

Microfluidic Sanger sequencing

Microfluidic Sanger sequencing is a special way to read DNA using tiny chips. It combines all the steps of Sanger sequencing — heating, cleaning, and separating the DNA pieces — on a small chip. This makes it faster and uses less of the expensive materials needed for regular Sanger sequencing.

This method breaks the DNA into small pieces, adds special labels, and then sorts the pieces to figure out the exact order of the DNA bases. It can read longer stretches of DNA than some other methods, which helps in studying complicated parts of the genome. The chip is made from glass and special materials, with tiny channels and chambers to handle the DNA and chemicals. One platform, the Apollo 100, can prepare samples for reading in just a few hours.