DVD's cheap trick boosts sensing

The method benefits from what began as imperfections in the production process Continue reading the main storyRelated StoriesCurry spice 'can spot explosives'Phone gadget to diagnose disease'Glowing' jellyfish grabs Nobel Researchers in the US have hugely boosted the sensitivity of a widespread imaging and sensing technique, using an off-the-shelf DVD.

Fluorescence spectroscopy is used to diagnose disease, image inside cells or detect toxins - but signals are weak.

A report in Nanotechnology has outlined how to boost those signals 200-fold, making use of a DVD's ready-made pits and grooves.

That could help put the technique in far more labs - or hands - worldwide.

Fluorescence describes the process in which the energy of light put into a molecule is redistributed, leading to a relatively long-lasting "glow" - it is at work in fluorescent lamps and many things that seem to glow under a "blacklight".

This has turned out to be a tremendously successful way to examine the world down at the molecular level. Scientists can "tag" molecules with a part that fluoresces and then use microscopes to see exactly what it is doing.

Some of these tags only switch on when a particular chemical is present - for instance a toxin or an explosive.

Lightning rods

At that molecular level, the light signals are profoundly weak. One way to boost them developed in recent years is to make use of what are called surface plasmons - the propensity of light waves from a sample to excite electrons in a surface beneath it, thereby boosting the signal.

This surface plasmon resonance is itself improved when the surface has nanometre-scale structure - tiny bumps or features of a size not too different from the wavelength of the light.

Making these nanometre-scale features for the task has been an inherently complex and expensive business, but there is one industry in which the costs of such precision-made structures have plummeted: DVDs.

Shubhra Gangopadhyay of the University of Missouri-Columbia and her colleagues started with commercial DVDs - sourced from a nearby store for $10 - and removed the protective outer layer to expose the nano-structure beneath.

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