Nanowires replace Newton’s glass prism

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A University of Cambridge team has designed a nanowire-based spectrometer that doesn’t require dispersive elements like a prism, therefore permitting greater miniaturisation than conventional systems

Artist's impression of single-nanowire spectrometer. Credit: Ella Maru Studio

Scientists have designed an optical spectrometer made from single nanowire that is small enough to be used in smartphones. The device, described in a paper published in Science in September, doesn’t require components such as prisms, which enables a further degree of miniaturisation than traditional optical systems.

According to the researchers from University of Cambridge, UK, the system is the smallest spectrometer ever designed. It could be used in potential applications such as assessing the freshness of foods, the quality of drugs, or even identifying counterfeit objects, all from a smartphone camera.

Today, the majority of spectrometers are based around principles similar to what Isaac Newton demonstrated with his prism in the 17th Century – the spatial separation of light into different spectral components. Such a basis fundamentally limits the size of spectrometers – they are usually bulky and complex, and challenging to shrink to sizes much smaller than a coin.

The Cambridge team, working with colleagues from the UK, China and Finland, used a nanowire whose material composition is varied along its length, enabling it to be responsive to different colours of light across the visible spectrum. Using techniques similar to those used for the manufacture of computer chips, they then created a series of light-responsive sections on this nanowire.

‘We engineered a nanowire that allows us to get rid of the dispersive elements, like a prism, producing a far simpler, ultra-miniaturised system than conventional spectrometers can allow,’ said first author Zongyin Yang from the Cambridge Graphene Centre. ‘The individual responses we get from the nanowire sections can then be directly fed into a computer algorithm to reconstruct the incident light spectrum.’

Tom Albrow-Owen, co-first author, added: ‘When you take a photograph, the information stored in pixels is generally limited to just three components – red, green, and blue,’ he said. ‘With our device, every pixel contains data points from across the visible spectrum, so we can acquire detailed information far beyond the colours which our eyes can perceive. This can tell us, for instance, about chemical processes occurring in the frame of the image.’

The team’s approach could allow unprecedented miniaturisation of spectroscopic devices, ‘to an extent that could see them incorporated directly into smartphones,’ noted Dr Tawfique Hasan, who led the study, ‘bringing powerful analytical technologies from the lab to the palm of our hands.’

One of the most promising potential uses of the nanowire could be in biology, to image single cells directly without the need for a microscope. And unlike other bioimaging techniques, the information obtained by the nanowire spectrometer contains a detailed analysis of the chemical fingerprint of each pixel.

The researchers hope that the platform they have created could lead to an entirely new generation of ultra-compact spectrometers working from the ultraviolet to the infrared range. Such technologies could be used for a wide range of consumer, research and industrial applications, including in lab-on-a-chip systems, biological implants, and smart wearable devices.
The Cambridge team has filed a patent on the technology, and hopes to see real-life applications within the next five years.

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