Laser sensor could improve benzene detection

Researchers at KAUST (King Abdullah University of Science & Technology) claim to have developed a laser sensor that can detect ‘extremely low’ concentrations of benzene in real time.

© 2020 KAUST; Anastasia Serin

The team, led by Aamir Farooq in collaboration with Saudi Aramco, believes the new sensor could be used to efficiently scan target areas daily for benzene emissions. 

Benzene originates from natural sources and human activities, mainly existing in industrial settings ranging from crude oil and petrochemical processing facilities to service stations. With the potential to cause cancer and the blood-related disease aplastic anaemia, the volatile compound poses a serious health risk to workers. Dangerous exposure can also occur through vehicle exhaust, biomass-based heating fuels and some consumer products.

Typical approaches to control benzene emissions rely on gas chromatography and mass spectrometry, but demand stringent maintenance schedules, complex sampling protocols and time-consuming measurements. Commercially available sensors can also present interference problems from other ambient air components and detection limits exceeding 100 parts per billion, failing to meet recommended thresholds.

Portable device instantly analyses airborne hazards

According to researchers, their laser sensor exhibits high selectivity and sensitivity to benzene with a detection limit of two parts per billion, and the ability to to perform measurements ‘in seconds’ without preliminary calibration.

Published in the IEEE Sensors Journal, their study explains how they designed a sensor with walls comprising two parallel concave mirrors that form a cavity around the sample. The cavity traps the laser beam, which reflects back and forth between the mirrors.

“In this way, it travels a dramatically larger distance through the sample than the inter-mirror separation,” said PhD student Mhanna Mhanna, who performed the experiments. “It enables us to detect concentrations that are three orders of magnitude lower than in a conventional sensor.”

The compact laser-based sensor developed by Mhanna Mhanna (left) and Amir Farooq (right) can detect benzene at levels ‘as low as two parts per billion’ (Credit: © 2020 KAUST)

Farooq’s team said they optimised the light absorption of benzene by selecting the laser wavelength and mathematically eliminating any interference from methane, ethylene and water vapour. This is said to have provided accurate benzene concentrations in the presence of interfering components..

The sensor detected higher benzene concentrations in parking garages on weekdays than on weekends, consistent with traffic conditions, when tested on real life samples from various locations. Service stations showed the highest levels, but amounts were well below the recommended thresholds.

Mhanna explained that the sensor could be attached to drones or carried by hand, and researchers are now looking at ways of making it more portable.