New security and medical sensor devices made possible by metallic nanostructures

Miniscule ring and disk combine to detect chemicals and substances<em> - News release</em>

Imperial College London news release

For immediate use
Tuesday 7 April 2009

Scientists have designed tiny new sensor structures that could be used in novel security devices to detect poisons and explosives, or in highly sensitive medical sensors, according to research published tomorrow (8 April) in Nano Letters.

The new 'nanosensors', which are based on a fundamental science discovery in UK, Belgian and US research groups, could be tailor-made to instantly detect the presence of particular molecules, for example poisons or explosives in transport screening situations, or proteins in patients' blood samples, with high sensitivity.

An image of the metallic ring and disk. The scale bar shows 200 nanometres.

The researchers were led by Imperial College London physicists funded by the Engineering and Physical Sciences Research Council. The team showed that by putting together two specific 'nanostructures' made of gold or silver, they can make an early prototype device which, once optimised, should exhibit a highly sensitive ability to detect particular chemicals in the immediate surroundings.

The nanostructures are each about 500 times smaller than the width of a human hair. One is shaped like a flat circular disk while the other looks like a doughnut with a hole in the middle. When brought together they interact with light very differently to the way they behave on their own.

The scientists have observed that when they are paired up they scatter some specific colours within white light much less, leading to an increased amount of light passing through the structure undisturbed. This is distinctly different to how both structures scatter light separately. This decrease in the interaction with light is in turn affected by the composition of molecules in close proximity to the structures. The researchers hope that this effect can be harnessed to produce sensor devices.

Lead researcher on the project Professor Stefan Maier from Imperial's Department of Physics, and an Associate of Imperial's Institute for Security Science and Technology, said:

"Pairing up these structures has a unique effect on the way they scatter light – an effect which could be very useful if, as our computer simulations suggest, it is extremely sensitive to changes in surrounding environment. With further testing we hope to show that it is possible to harness this property to make a highly sensitive nanosensor."

Metal nanostructures have been used as sensors before, as they interact very strongly with light due to so-called localised plasmon resonances. But this is the first time a pair with such a carefully tailored interaction with light has been created.

The device could be tailored to detect different chemicals by decorating the nanostructure surface with specific 'molecular traps' that bind the chosen target molecules. Once bound, the target molecules would change the colours that the device absorbs and scatters, alerting the sensor to their presence. The team's next step is to test whether the pair of nanostructures can detect chosen substances in lab experiments.

Professor Maier concludes: "This study is a beautiful example of how concepts from different areas of physics fertilise each other – in essence our nanosensor system is a classical analogue of electromagnetically induced transparency, a famous phenomenon from quantum mechanics."

The research was conducted by the team at Imperial College London in collaboration with IMEC and the Catholic University in Leuven, Belgium, and Rice University in Houston, Texas.

-Ends-

For more information please contact:
Danielle Reeves, Imperial College London press office
Tel: +44 (0)20 7594 2198
Out-of-hours duty press office: +44 (0)7803 886248
Email: Danielle.reeves@imperial.ac.uk

Notes to editors:

1. 'Fano Resonances in Individual Coherent Plasmonic Nanocavities', Nano Letters, Issue 4, April 8 2009.

Niels Verellen, Yannick Sonnefraud, Heidar Sobhani, Feng Hao, Victor V. Moshchalkov, Pol Van Dorpe, Peter Nordlander, and Stefan A. Maier.

-IMEC, Kapeldreef 75, 3001 Leuven, Belgium.
-INPAC-Institute for Nanoscale Physics and Chemistry, Nanoscale Superconductivity and Magnetism and Pulsed Fields Group, K. U. Leuven Celestijnenlaan 200 D, B-3001 Leuven, Belgium.
-Experimental Solid State Group, Physics Department, Imperial College, London SW7 2AZ, U.K.
-Laboratory for Nanophotonics, Department of Physics and Astronomy, M.S. 61, Rice University, Houston, Texas 77005-1892

2. About Imperial College London

Consistently rated amongst the world's best universities, Imperial College London is a science-based institution with a reputation for excellence in teaching and research that attracts 13,000 students and 6,000 staff of the highest international quality.

Innovative research at the College explores the interface between science, medicine, engineering and business, delivering practical solutions that improve quality of life and the environment - underpinned by a dynamic enterprise culture.

Since its foundation in 1907, Imperial's contributions to society have included the discovery of penicillin, the development of holography and the foundations of fibre optics. This commitment to the application of research for the benefit of all continues today, with current focuses including interdisciplinary collaborations to improve health in the UK and globally, tackle climate change and develop clean and sustainable sources of energy.

Website: www.imperial.ac.uk

3. About the Engineering and Physical Sciences Research Council

The Engineering and Physical Sciences Research Council (EPSRC) is the UK's main agency for funding research in engineering and the physical sciences. The EPSRC invests more than £740 million a year in research and postgraduate training, to help the nation handle the next generation of technological change.

Website: www.epsrc.ac.uk