Direct image of DNA`s double helix captured for the first time

London: Scientists have for the first time captured a direct image of the double helix of DNA, the structure that encodes the genetic instructions of all living organisms.

Enzo di Fabrizio and colleagues from the University of Genoa, Italy, developed a technique to capture the double helix of DNA using a scanning electron microscope.

Deoxyribonucleic acid (DNA) molecules encode the genetic instructions used in the development and functioning of all known living organisms and many viruses.

Along with RNA and proteins, DNA is one of the three major macromolecules that are essential for all known forms of life.

Previously the DNA helix could only be detected using a technique known as X-ray crystallography, which involves scattering X rays off atoms in crystallised arrays of DNA.

Capturing the reflected rays on photo film forms the now iconic fuzzy X inside a fuzzy O pattern that James Watson and Francis Crick used to discover the double-helix structure.

However, because of the indirect nature of the image, Watson and Crick were only able to infer the existence of the double helix using complex mathematics to interpret the image.

Now Professor Di Fabrizio and his team from Genoa`s Nanostructures Department have used a scanning electron microscope to creat the first direct image of the DNA double helix.

The researchers developed a process to capture DNA threads out of a dilute solution and dry them and stretch them out across water-repellent nanoscopic silicon pillars, New Scientist reported.

By drilling tiny holes through the base of their bed of nano-nails and shining electrons through them, they were able to create high resolution images of a strand of DNA.

The remarkable image clearly shows the DNA double helix, as predicted by Watson and Crick nearly 60 years ago.

With refinement, the Genoa team hope that their new technique will allow researchers to watch single molecules of DNA as they interact with other biomolecules.

Since the electron energies are high enough to snap DNA molecules, at the moment the method only works with `cords` of DNA made of six molecules wrapped around a seventh acting as a core.

Di Fabrizio and his team now hope to use more sensitive detectors that can detect lower-energy electrons. This should allow them to see individual double helices and even unwound single strands of DNA.

"With improved sample preparation and better imaging resolution, we could directly observe DNA at the level of single bases," New Scientist quoted him as saying.

The research was published in the journal Nanoletters.