Researchers have, for the first time, used a single “nanoantenna” – a device that collects and focuses light – to demonstrate that it could be used to detect particles and atoms. The work, by scientists at the Lawrence Berkeley National Laboratory (LBNL) in the US and the University of Stuttgart in Germany, could be used to make extremely sensitive gas sensors and detectors. Conventional antennas, widely used to transmit radio or TV signals, can be used at optical frequencies if they are shrunk to the nanoscale, which could have potential applications in nanophotonics. The nanoantennas can also be used to generate electronic surface waves known as “surface plamons”. This is done by confining electromagnetic waves – typically at the interface between metallic nanostructures (usually made of gold) and a dielectric (usually air) – that have dimensions smaller than half the wavelength of incident light.
When the oscillation frequency of the created plasmons matches that of the incident electromagnetic waves, a phenomenon known as “localized surface plasmon resonance” (LSPR) occurs, which concentrates the electromagnetic field into an even smaller space – around 100 nm3. Any object brought into this so-called locally confined field – or “nanofocus” – will affect the LSPR in such a way that it can then be detected using a technique called dark-field microscopy – a technique where only scattered light makes up an image.