Chemical sensor on a chip created to test chemical composition of liquids

Just a drop is enough to test the chemical composition.

Summary:

A tiny laser and a corresponding light detector has been developed in one production process, on a single chip. The light is transported from the laser to the detector on a specially designed waveguide. That way, the chip can measure the chemical composition of the liquid in which it is submerged

Description:

Using miniaturized laser technology, a tiny sensor has been built at the Vienna University of Technology which can test the chemical composition of liquids.

They are invisible, but perfectly suited for analyzing liquids and gases; infrared laser beams are absorbed differently by different molecules. This effect can for instance be used to measure the oxygen concentration in blood.

Specially designed quantum cascade lasers and light detectors are created by the same production process. The gap between laser and detector is only 50 micrometres. It is bridged by a plasmonic waveguide made of gold and silicon nitride. This new approach allows for the simple and cheap production of tiny sensors for many different applications.

Now a method has been developed to create a laser and a detector at the same time, on one single chip, in such a way that the wavelength of the laser perfectly matches the wavelength to which the detector is sensitive. As both parts are created in one step, laser and detector do not have to be adjusted.

Leading the Light to the Detector

In conventional systems, the laser light has to be transmitted to the detector using carefully placed lenses. Alternatively, optical fibres can be used, but they usually transport all the light inside, without letting it interact with the environment, and therefore they cannot be used as sensors.

In the new element created at the Vienna University of Technology, the optical connection between quantum cascade laser and detector works in a completely different way. It is a plasmonic waveguide, made of gold and silicon oxide. The light interacts with the electrons in the metal in a very special way, so that the light is guided outside the gold surface.That is why the light can be absorbed by the molecules on its way between laser and detector.

The sensor chip can be submerged in a liquid. By measuring the decrease of the detected light intensity due to the presence of light absorbing molecules, the composition of the liquid can be determined. The sensor was tested with a mixture of water and alcohol. The water concentration can be measured with an accuracy of 0.06%.

As the wavelength can be influenced by changing the design of the layered structure, this sensor concept can be applied to a wide variety of molecules such as carbohydrates or proteins, for many different applications in chemical, biological or medical analytics.

BY :-Sweta singh