Making light work

A system that uses light to diagnose mutated DNA sequences could dramatically speed up the time it takes to diagnose potential problems in the treatment of diseases such as leukaemia.

The work being carried out at the Durham Institute of Photonic Materials uses a luminescent polymer, similar to those in OLED displays, as an optical antenna to detect and illuminate small segments of DNA.

The Institute’s director, Prof Andy Monkman, said that using photonics to spot genetic mutation in this way would simplify and speed up the current process of DNA sequencing.

Immune to drugs

Existing bio-chemical methods of analysis can process a maximum of around 20 samples a week, whereas Monkman hopes that the new method could deal with up to 20 a day.

‘At the moment we are using this technique to look at mutation in diseases such as leukaemia,’ said Monkman. ‘Due to a genetic mutation some patients become immune to the drugs treating the disease and so it is extremely important to identify them as quickly as possible. At the moment the process is far too time-consuming.’

The team developed a man-made protein chain (PNA) which resembles DNA — except for a protein at the end instead of an acid. The PNA is designed and produced in a protein synthesiser so that it will exclusively match a specific sequence of DNA, and a fluorescent tag is attached to the end of the PNA strand.

To check that this has attached itself to the DNA sequence, a water-soluble polymer is introduced — similar to those used in OLED display screens. This absorbs energy and fluoresces around a million times more strongly than the fluorescent tag on the DNA.

When the polymer is excited by a 400nm blue laser the energy moves along its length like an antenna and if it comes close to the PNA’s tag it will jump across and make it fluoresce strongly. This fluorescence can then be detected using a photo diode detector.

For Monkman and his team, the fluorescence is an indicator of the presence of the specified gene mutation, such as the one that makes patients resistant to drugs.

Close proximity

The only way that the polymer and the PNA could be in close enough proximity for this jump to happen is if the PNA is attached to the DNA. And this can only happen if the specified DNA mutation is present.

‘Detecting DNA mutations using light completely simplifies the process,’ said Monkman. ‘We eventually hope to develop something that can be miniaturised for use in a GP’s surgery to provide quick, accurate results.’

Monkman estimated that the technology would begin clinical trials in around 18 months, and be ready for use in hospitals within the next three to five years.