Nanowires Replace Newton’s Glass Prism

Illustration of a single-nanowire spectrometer for ultraminiaturized spectroscopy platforms. (Source: U. Cambridge / Ella Maru Studio)

The device, made from a single nanowire a thousand times thinner than a human hair, 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.

In the 17th century, Isaac Newton, through his obser­vations on the splitting of light by a prism, sowed the seeds for a new field of science studying the inter­actions between light and matter. Today, optical spectro­meters are essential tools in industry and almost all fields of scientific research. Through analyzing the charac­teristics of light, spectrometers can tell us about the processes within galactic nebulae, millions of light years away, down to the charac­teristics of protein molecules. However, even now, the majority of spectro­meters are based around principles similar to what Newton demons­trated with his prism: the spatial separation of light into different spectral components. Such a basis funda­mentally limits the size of spectro­meters in respect: they are usually bulky and complex, and challenging to shrink to sizes much smaller than a coin. Four hundred years after Newton, Cambridge researchers have overcome this challenge to produce a system up to a thousand times smaller than those previously reported.

The 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-minia­turized system than conven­tional spectrometers can allow,” said 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.”

“When you take a photo­graph, the infor­mation stored in pixels is generally limited to just three components – red, green, and blue,” said Tom Albrow-Owen. “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.” “Our approach could allow unpre­cedented minia­turization of spectro­scopic devices, to an extent that could see them incor­porated directly into smartphones, bringing powerful analytical tech­nologies from the lab to the palm of our hands,” said Tawfique Hasan, who led the study.

One of the most promising potential uses of the nanowire could be in biology. Since the device is so tiny, it can directly image single cells 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 ultracompact 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 team has filed a patent on the tech­nology, and hopes to see real-life appli­cations within the next five years. (Source: U. Cambridge)

Reference: Z. Yang et al.: Single-nanowire spectrometers, Science 365, 1017 (2019); DOI: 10.1126/science.aax8814

Link: Cambridge Graphene Centre, University of Cambridge, Cambridge, UK

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