The research, published in the journal Physical Review Letters used AFM techniques to study the elasticity of two types of synthetic single-stranded DNA (ssDNA).

Previous studies have focussed on the chemical bonds between opposing bases in DNA by pulling apart the two strands of double stranded DNA (dsDNA).

This latest research has focussed on studying the interactions within single strands and uncovered the mechanical 'footprints' between bases in the same DNA strand.

"The stability of DNA is so fundamental to life that it's important to understand all factors," said Dr Piotr Marszalek, associate professor at Duke University, North Carolina, US, and lead author of the report.

"If you want to create accurate models of DNA to study its interaction with proteins or drugs, for example, you need to understand the basic physics of the molecule. For that, you need solid measurements of the forces that stabilize DNA."

While the primary goal of the researchers work was to measure the strength of base stacking interactions in DNA, Dr Marszalek said that the long term goal of the research is to study the relationship between DNA mechanics and DNA damage.

"Certain drugs, including anticancer chemicals are designed to "damage" DNA by crosslinking both strands, intercalating between the bases, or making adducts, and thus inhibit DNA transcription and replication," he said.

"By performing AFM stretching measurements on DNA that has been treated by a drug, we hope to register the change in DNA elasticity caused by the drug."

The current research focussed on the interactions between ssDNA in two strands made up of only one base linked by the phosphate backbone, either chains of adenine or thymine.

The measurements were conducted by attaching the ssDNA strands to a gold substrate at one end and an AFM tip at the other and then measuring the amount of force needed to extend the chain.

The thymine chains exhibited a smooth force versus extension curve. This was expected as there are no bonds between the thymine bases to break.

The researchers expected the curve to be more complicated for the adenine ssDNA chains as they are known to form a helix.

However, the adenine curves reveal two pronounced plateaus and the researchers speculate that the first of these indicates the unwinding of the adenine chain helix and base un-stacking.

The second plateau was not expected and the researchers believe this plateau indicates a reorientation of the bases being accompanied by the flip of the phosphate backbone bonds to new torsional states that increase the distance between neighbouring phosphate groups.

Dr Marszalek believes that this technique could be used to study how a drug affects the elasticity of DNA, whether it causes crosslinking between strands, creates a single-strand break or forms and adduct that disrupts the structure.

"We hope that this approach may one day evolve into a screening technique, which would allow new drugs to be discovered," he said.