A new application for LEDs

17 Jun 2002

Light-emitting diodes give rise to a new class of chemical sensors.

Scientists in the US have demonstrated a way in which LEDs could work as chemical sensors. In research published in Nature (25 January), Albena Ivanisevic and colleagues at the University of Wisconsin, Madison, describe how chemicals adsorbed onto the surface of an LED can modulate the device's electroluminescent properties by altering its surface-state structure.

What this means in practice is that exposure to chemicals that interact with the surface of the diode can affect the intensity of the emitted light. If detected and measured, these changes in light intensity can be used to determine the presence of the chemicals. The finding has important implications for "lab-on-a-chip" endeavours, as it could lead to small, robust, sensitive chemical sensors with low power consumption.

The researchers first changed the surface of an LED to enhance its chemical sensitivity and then integrated it onto a chip with a nearby detector system. They found that chemicals interacting with the LED's surface altered the emitted light in a way that they could not only detect but could also correlate with the amount of chemical present. The researchers discovered optical responses for five gases: ammonia, methylamine, dimethylamine, trimethylamine and sulphur dioxide.