Schematic diagram of how a plasmonic metamaterial has been used to detect very low chemical concentrations – the gold bumps are the nanostructures that are arranged in an array. Some of the bumps have binding sites attached to them (triangular wedges). Some of the binding sites have streptavidin molecules attached (red discs). Light is incident from below (yellow beam) and reflects down from the bottom surface. The red arrow shows light that has diffracted and is interacting with the plasmonic metamaterial. (Courtesy: Sasha Grigorenko and Nature Materials)

Single molecules detected with plasmonic metamaterial

Jan 22, 2013

A new technique that could lead to chemical sensors that detect single molecules has been unveiled by researchers in the UK and France. It involves creating arrays of tiny nanostructures that interact strongly with light at a specific wavelength. When as few as one molecule of interest attaches to a nanostructure, the optical properties of the material change dramatically – signalling the presence of that chemical species.

The technique involves using “plasmonic metamaterials”, which are arrays of tiny metal structures that can be fine-tuned to interact with light in very specific ways. With these materials, it is possible to tweak the shape, size and arrangement of the structures to support collective oscillations of conduction electrons – called plasmons – at specific frequencies.

In this latest work, Sasha Grigorenko and colleagues at the University of Manchester and Aix-Marseille University have made metamaterials that are arrays of gold structures on a glass substrate. Each structure is about 90 nm tall and 100 nm across and separated by about 300 nm. The most basic array comprised a single gold pillar as the unit cell, but other arrays had double pillars or dumbbell shapes as unit cells – while others were indentations in sheets of gold.

Read more: Single molecules detected with plasmonic metamaterial – physics world.

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