Nanotubes signal when engine oil needs changing.

A new, easy-to-fabricate sensor made from carbon nanotubes detects when automobile-engine oil needs replacement.

As a car is driven, its lubricating oil undergoes chemical reactions with air and with combustion by-products. Those reactions degrade the oil--for instance, by causing chemicals known as hydroperoxides to build up. In previous work, other researchers had observed that carbon nanotubes become more electrically conductive when exposed to hydroperoxides.

In the new study, Seung-Il Moon of Korea University in Seoul and his colleagues blended nanotubes with glue and then printed a thin layer of the mixture onto a glass-and-metal backing to make a microchip-size sensor. They then attached the sensor to an engine dipstick and inserted it into the oil reservoir of a ear. Electrical measurements showed a steady increase in current through the sensor as the car was driven 6,000 kilometers, the team reports in the August Electrochemical and Solid-State Letters.

Additional laboratory tests indicated that changes in conductivity closely matched variations in a chemical signature known as total acid number, a sign of oil quality.

The team is continuing work on the sensor with a Korean automaker.