New nanostructure enhances sensitivity of biosensors

Biosensors convert a biological response into an optical or electrical signal and can be used to sense anomalies such as toxic chemicals and particles in the air, or enzymes, molecules, and antibodies in the body that could indicate diabetes, cancer, and other diseases.

According to Northwestern, an optical biosensor works by absorbing a specific bandwidth of light and shifting the spectrum when it senses minor changes in the environment. The narrower the band of absorbed light is, the more sensitive the biosensor.

‘Currently, plasmonic absorbers used in biosensors have a resonant bandwidth of 50 nanometres,’ said Koray Aydin, assistant professor of electrical engineering and computer science in the McCormick School of Engineering at Northwestern University, Illinois. ‘It is significantly challenging to design absorbers with narrower bandwidths.’

Aydin and his team have created a new nanostructure with a bandwidth of 12 nanometres, an ultra narrow band absorber that can be used for a variety of applications, including better biosensors.

‘We believe that our unique narrowband absorber design will enhance the sensitivity of biosensors,’ Aydin said in a statement. ‘It’s been a challenge to sense very small particles or very low concentrations of a substance.’

This research was described in the paper ‘Ultra narrow band absorbers based on surface lattice resonances in nanostructured metal surfaces,’ published in ACS Nano.

Typical absorber designs are said to use two metal sheets with a non-metallic insulating material in between.

By using nanofabrication techniques in the lab, Aydin’s team found that removing the insulating layer - leaving only metallic nanostructures - caused the structure to absorb a much narrower band of light. The absorption of light is also high, exceeding 90 per cent at visible frequencies.

Aydin said this design can also be used in applications for photothermal therapy, thermo-photovoltaics, heat-assisted magnetic recording, thermal emission, and solar-steam generation.

‘The beauty of our design is that we found a way to engineer the material by using a different substrate,’ Aydin said.