Sensor Studies Chemicals with Single Chip

A tiny new sensor uses miniaturized IR laser technology to identify and study chemicals — all on a single chip.

The new sensor, developed by researchers at the Vienna University of Technology, can analyze liquids and gases, as well as their chemical compositions. And it can all be done with a single chip.

Creating such sensors involves quantum cascade lasers and light detectors. Between these devices is a gap in the optical connection that is traditionally bridged by gold- and silicon nitride-based plasmonic waveguides. Now, the new technique makes it possible to create such a laser and detector simultaneously.

Just a drop is enough to test the chemical composition. Images courtesy of TU Vienna.

This is different from conventional methods, which require the laser light to be created and transmitted separately to the detector via lenses. Optical fibers could be used for this purpose, but they do not allow such lasers to interact with anything externally and therefore cannot be used as detectors.

“The light interacts with the electrons in the metal in a very special way, so that the light is guided outside the gold surface,” said Benedikt Schwarz, one of the researchers at the university.

With the new technique, the researchers found that the optical connection between laser and detector can harness a plasmonic waveguide made of gold and silicon oxide.

The light is emitted by the laser (top), transported on the plasmonic waveguide (blue) and hits the detector (bottom right).

Putting the laser and detector on a single chip matches the wavelength of the laser (which typically must be tuned) with the one to which the detector is sensitive.

“As both parts are created in one step, laser and detector do not have to be adjusted. They are already perfectly aligned,” Schwarz said.

The new sensor could benefit a variety of applications such as chemical, biological and medical analytics.

The research was published in Nature Communications (doi: 10.1038/ncomms5085).

For more information, visit www.tuwien.ac.at.