Shedding light on chemical sensors

A group of scientists at the University of Wisconsin-Madison have published a paper that sheds light on a new use for LED’s by demonstrating their usefulness as chemical sensors.

The UW-Madison researchers have illustrated how chemical exposure can alter the surface structure of LED materials, causing the intensity of the light to fluctuate. The scientists claim that the resulting light change can be put to use in simple, highly sensitive systems that warn of chemicals in the air or water.

The finding may have a big impact on the campaign in the US to develop ‘laboratories on a chip,’ by offering an accurate, inexpensive and mass-producible method to integrate sensors on to computer chips.

The most ubiquitous chemical sensors are employed in home safety systems to detect smoke, radon or carbon monoxide, but existing technology is said to be primitive compared to the ‘smart environments’ envisaged by scientists.

Arthur Ellis, professor of chemistry and co-author of the paper, said the project, called ‘XYZ on a Chip,’ aims to demonstrate how a wide range of non-electrical processes can exploit the power and sophistication of integrated chip technology.

Light-emitting diodes, tiny chips made of semi-conducting materials, convert electrical energy into visible light. The chips also can convert light into electricity when used in a solar cell or photocell. In past research, Ellis has demonstrated that light emitted from these materials could be altered by exposure to chemicals.

Ellis’ team, including Thomas Kuech, a professor of chemical engineering and materials science, and Luke Mawst, an electrical and computer engineer, sought ways to apply this discovery to a new class of sensors.

The group began by changing the surface of the light-emitting structure to enhance its chemical sensitivity. Then they integrated it onto a chip with a nearby detector system, where both the emitter and detector can communicate.

When they placed the system in a chemical environment, the chemicals that interacted with the semiconductor surface changed the amount of light emitted – and thus detected. But rather than just indicating the presence of that chemical, the system was also sensitive to the amount of that chemical in the air.

The flexible sensors could be adjusted to detect everything from ammonia in a factory environment to biological molecules in a war zone.

One ultimate goal of the ‘lab on a chip’ research effort is to create a real-time response to environmental dangers, whether it be a chemical spill in a river or the threat of chemical warfare or bioterrorism. The current technology is nowhere near meeting that challenge, said Kuech.

The researchers’ next goal is to better understand the basic chemical reactions that are taking place on the surfaces of LED’s in order to optimise the process.