Page last updated at 14:00 GMT, Wednesday, 10 September 2008 15:00 UK

Diatom nanostructures bend light

By Elizabeth Mitchell
Science reporter, BBC News

Diatoms
Diatoms are well known for the intricate designs of their silica cell walls

Simple marine algae called diatoms have evolved intricate structures that allow them to manipulate light.

Visible light is strongly diffracted when it passes through tiny holes in their silica-based cell walls, scientists say.

Understanding the physical principles that allow diatoms to trap solar energy more efficiently may also help develop new synthetic replicas.

This research was presented at the BA Science Festival in Liverpool.

Nature started to evolve complex colour and light manipulating systems during the Cambrian explosion - about 500 million years ago.

Scientists have been inspired by the natural systems that are found in wide range of organisms - including peacocks, butterflies and beetles.

These single-celled marine algae are found in almost all aquatic environments on Earth.

Diatom valve
When magnified, we see how colour is created by the valve’s ultrastructure

They come in all shapes and sizes - but are all encased within silica-based walls that are well known for their intricate designs.

The scientists studied one of the most common species of diatom - Coscinodiscus wailesii.

Nanostructures

Each half of its "petri-dish" shell has two layers that are covered with a regular pattern of tiny pores called "nanostructures" - which can be highly-magnified using an electron microscope.

"If you look through the large holes you can see some much finer structures," explained Professor Pete Vukusic, of the University of Exeter.

The scientists performed elaborate optical experiments and found that these structures diffracted light very strongly.

Why have diatoms evolved these nanostructures?

Their mechanical strength offers protection from predation but their ability to control the way light passes through them may offer another evolutionary advantage.

Butterflies
Natural light-scattering systems are inspiring scientists to manipulate light

Diatoms are photosynthetic organisms: they convert light energy from the sun into the energy they need for reproduction.

They contain hundreds of chloroplasts - internal structures that are responsible for harvesting the light.

"Depending on which way round the diatom is, some choloroplasts will be disadvantaged relative to others," said Professor Vukusic.

"The optic experiments suggest that the presence of the nanostructure allows a much more even spread of the light throughout the diatom," he explained.

Diatom valve
Electron microscopy reveals "nano-structures" on the valve's surface

These light-manipulating properties could be exploited to assist the development of many biosynthetic devices - including tiny light-activated drug-delivery tools.

"Diatoms are available everywhere - freely, widely and cheaply.

"Our hope is that our research will be one of the foundations from which diatom applications may move forward," said Professor Vukusic.


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