Canadian scientists are on a roll when it comes to copying DNA. Yingfu Li and co-workers from McMaster University in Hamilton have developed a cheap and efficient way of amplifying DNA that could prove very useful for the DNA diagnostic industry.

Many diagnostic technologies aren't sensitive enough to detect single molecules of DNA and so DNA amplification is often essential. The polymerase chain reaction is usually relied on to make the necessary DNA copies, but it requires sophisticated temperature-cycling instrumentation.

Rolling circle amplification (RCA) was developed in the mid 1990s, as an alternative way of amplifying DNA but at a constant reaction temperature. It uses DNA polymerase enzymes to copy circular DNA strands repeatedly. A short linear DNA primer binds to the circular template DNA and is extended by polymerase so that it is complementary to the template. Because the template DNA is circular, it effectively rolls along the growing primer, allowing many copies to be made in a linear, end-to-end fashion.

Polymerase enzymes form end-to-end copies (blue) of a circular DNA template (red)

Now, Li's team has found a cheap, highly stable solid support for the DNA primers - microgel colloidal particles. Colloidal particles are attractive supports in RCA because they can be dispersed in solution, giving the primer/polymerase/template conjugate plenty of configurational freedom for efficient amplification, but also collected easily for analysis. 

According to the team, a convenient DNA amplification method on a suitable support is 'still highly demanded.' Gold nanoparticles and magnetic particles have been used in the past but can be problematic, for example, due to their lack of stability and expense. 

The Canadian team has shown that its microgels allow efficient RCA. What's more, the method is low cost, the DNA-microgel constructs are highly stable and collection and hence DNA detection is straightforward because the microgels swell when reaction temperature, pH or salt levels are changed.

Freya Mearns