It goes without saying that the sooner you know an oil spill has occurred, the sooner you can set about containing it. That's why scientists from Spain's Universidade de Vigo have created a compact and inexpensive oil-detection sensor. Mounted on a buoy in areas where spills are a risk, it could detect them before they're obvious to the naked eye, and even determine the type of oil that's present.

The researchers already knew that it was possible to differentiate between various types of oil, based on the manner in which they fluoresce when exposed to ultraviolet light. Ordinarily, however, taking this approach involves the use of an expensive and fragile spectrometer.

Instead, the scientists created a simple and robust "fluorometer" in which cheap LEDs serve as the ultraviolet light source, and four photodiodes are used to measure different regions of the fluorescence spectrum – each photodiode is equipped with a cellophane filter of a different color, so it records a different signal.

The setup also incorporates a microcontroller, and a radio module for transmitting readings.

In lab tests, the system was used on simulated spills in which a thin film of oil was spread across a water surface. The instrument was able to tell the difference between three types of crude oil and two types of refined oil.

The scientists now plan on testing the technology in an actual outdoor body of water, using a solar panel for power. They will also be recording the "fluorescence fingerprints" of other types of oil, so that the system can identify those too.

"Our device could help keep better track and control of pollution, especially by detecting potential pollution sources," says project leader Jose R. Salgueiro. "Once the pollution is produced it will help to quickly detect the problem, identify the nature of the pollution and contribute to a better response."

A paper on the research was recently published in the journal Applied Optics.