IISER team designs angle-sensitive optical antennas for molecules

IISER team designs angle-sensitive optical antennas for molecules

Pune: A team of researchers from Indian Institute of Science, Education and Research (IISER), Pune has made a breakthrough with many applications. If we could accurately detect disease-causing molecules or an unwanted pollutant, then we can act faster and better for its prevention. Light is an excellent probe to detect and probe molecules. A powerful method is to employ Raman Scattering of light, but Raman Scattering is very weak when compared to other optical emissions. So there was a necessity to enhance, direct and differentiate Raman Scattering from molecules with high accuracy.

Precisely, this is the research area IISER team, who has been successful in harnessing the Raman Scattering signals from a few molecules using a new type of nano-cavity.
This method will help them in detecting single molecule or single nanostructure which could otherwise wouldn’t have been detected.

“Not only detection, but we can further precisely study what happens to structure of molecules when confined to nanoscale environments by employing our optical antenna,” said Prof Pavan Kumar, team leader and Associate Professor at IISER, Pune.

So far, it was difficult and expensive to separate Raman emission from the other molecular emissions such as fluorescence as they spectrally overlap. This advancement by Prof Kumar and team thus has significant implications for studying Raman Scattering of individual molecules even when there is an unwanted background signal.

While talking to Sakal Times, Prof Kumar said, “For the first time that Raman and fluorescence components of scattered light behave differently when confined to a metal nano-cavity. A metal nano-cavity is a small gap formed between a silver nanowire and gold film. Interestingly, when molecules are sandwiched in this cavity, the emission from the molecule behave very differently when compared to free molecules.”

The project has been carried out in collaboration with Centre for Nanoscale Materials, Argonne National Laboratory, USA. Prof Kumar said, “This compact and cost-effective system will enable researchers to discern Raman signals from other types of molecular emission such as fluorescence, which so far has been possible only through sophisticated and expensive techniques.”

The study also sheds new light on a fundamental questions related to how quantum electrodynamic properties of molecular cavities affect scattering of light. “Our work has implications not only in nano-optical sensors that can be a futuristic component on our mobile phones but also in fundamental optical physics where one can use light to probe molecules at extremely small scale, 1,000 times smaller than the dimension of our hair,” Kumar said.

Explaining in detail, he said, “Generally, when light interacts with the molecule, the scattered light goes in all directions giving a variety of coloured signals emitting from the molecules. In an essence, our work shows we can separate this emission from the molecules into different angles with extremely high accuracy.”

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