Plasmonic nanoantenna arrays hold promise for ultrasensitive sensors

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Researchers have designed and tested plasmonic nanoantenna arrays that could lead to the development of ultrasensitive and low-cost fluorescence sensors for water monitoring.

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SEM images of nanoantenna array and in the inset a magnified view of the array elements (Credit: Bristol University)

The breakthrough has been made by researchers at the Universities of Bristol and Bedfordshire in collaboration with ABB.

The arrays, designed and tested by Dr Neciah Dorh during his PhD at Bristol University, are made from aluminium nanorods fabricated using electron beam lithography by commercial partner Kelvin Nanotechnologies. At 50nm wide and 158nm long, the nanorods are designed to resonantly enhance fluorescence emission from contaminants in water including diesel or tryptophan.

The work, published in Applied Optics, is said to show a six-fold increase in measured fluorescence emission from a dye. The research also shows that by correctly designing the array element spacing, strongly directional fluorescent emission can be obtained which would allow for highly integrated multi-wavelength sensors to be designed.

The work was carried out in Prof Martin Cryan’s research group, which is part of the Photonics Research group in the Department of Electrical and Electronic Engineering at Bristol University. Prof Cryan obtained funding from ABB as part of the ABB research grant programme.

The project was a collaboration with Dr Andrei Sarua from the School of Physics at Bristol and Dr Tahmina Ajmal from the University of Bedfordshire, who had previously worked on the Aquatest project at Bristol.

Together they developed a prototype low-cost, LED based sensor system, which they plan to develop further into a hand-held field deployable system for performing water quality monitoring.

Prof Cryan said: “The nanoantenna arrays, which can be fabricated by lower cost production techniques such as nanoimprint lithography, can bring significant sensitivity enhancement so that laboratory quality measurements could be carried out in the field.

“This would allow for deployment of remote wireless sensor networks for early warning of pollution or continuous monitoring of water quality in sensitive environments.”

Dr Dorh has co-founded a start-up, Fluoretiq, developing quantum enhanced fluorescence sensors which will help identify bacteria within minutes rather than days. Similarly, Prof Cryan’s group is developing systems that could combine the power of nanoantennas with quantum enhanced sensors to produce yet further sensitivity enhancements.