Nanoscale Sensor Provides Clear Optical Fingerprint to ID Pollutants

A sensor made with ultrathin nanomaterials could improve environmental sensing by providing an unambiguous optical fingerprint for the detection of molecules. Traditional sensors rely on small peak shifts and intensity changes, a less precise approach to identifying molecules in the air.

A research team from Chalmers University of Technology and Technische Universität Berlin developed the highly efficient sensor using atomically thin transition metal dichalcogenides (TMDs). The material’s optimal surface-to-volume ratio, combined with strong light-matter interaction, makes it highly sensitive to changes in its surroundings.

Molecules are identified by activating dark electronic states in the sensor material, resulting in a new visible peak. The altered optical fingerprint of the material proves the presence of molecules. Courtesy of Maja Feierabend and Ermin Malic.

In addition to showing optically accessible bright excitons, TMDs show a variety of optically forbidden (dark) excitons that either exhibit a nonvanishing angular or center-of-mass momentum. The novel sensor identifies molecules by activating the dark excitons in the nanomaterial. Molecules on the surface of the nanomaterial interact with the dark states and make them visible (bright), altering the optical fingerprint to indicate the presence of molecules.

The team demonstrated that an efficient coupling between dark and bright TMD excitons and noncovalently attached molecules with a strong dipole moment could turn the dark exciton bright, resulting in an additional peak in optical spectra.

“This could open up new possibilities for the detection of environmental gases. Our method is more robust than conventional sensors, which rely on small changes in optical properties,” said researcher Maja Feierabend.

The optical fingerprint of the material is revealed when light is shined on the sensor.

Ermin Malic, Maja Feierabend and Gunnar Berghäuser: three of the authors behind the study on the new ultra-thin nanosensors. Courtesy of Mia Halleröd Palmgren.

“Our method has promising potential, paving the way for ultra-thin, fast, efficient and accurate sensors. In the future, this could hopefully lead to highly sensitive and selective sensors that can be used in environmental research,” said researcher Ermin Malic.

The team has filed a patent application for its novel sensor method. Its next step will be to work with experimental physicists and chemists to demonstrate the proof-of-principle for this new class of chemical sensors.

The research was published in Nature Communications (doi:10.1038/ncomms14776).