New microsensor measures volatile organic compounds in water and a...( Researchers at the Georgia Institute...)

Researchers at the Georgia Institute of Technology have developed a miniature sensor that uses polymer membranes deposited on a tiny silicon disk to measure pollutants present in aqueous or gaseous environments. An array of these sensors with different surface coatings could be used during field-testing to rapidly detect many different chemicals.

Since this new sensor allows water and air samples to be analyzed in the field, it is an improvement over classical techniques that require samples be carried back to the laboratory for analysis. This research, funded by the National Science Foundation, was presented on August 20 at the American Chemical Societys 234th National Meeting.

The heart of the disk-shaped sensor is a microbalance that measures the mass of pollutant molecules.

When pollutant chemicals get adsorbed to the surface of the sensor, a frequency change of the vibrating microbalance provides a measure of the associated mass change, said Oliver Brand, associate professor in Georgia Techs School of Electrical and Computer Engineering.

Cantilever-type balances, which move up and down like a diving board, are common when measuring the amount of a chemical in the gas phase. However, the mechanical vibrations of the balance used to detect the mass changes are damped in liquids, causing the sensitivity of the balance to decrease. Thus, Brand and graduate students Jae Hyeong Seo, Stuart Truax and Kemal Safak Demirci searched for structures whose vibrations were less affected by the surrounding medium.

The researchers chose a silicon disk platform for the sensor. The disk shears back and forth around its center with a characteristic resonance frequency between 300 and 1,000 kHz, depending on its geometry. With proper actuation and sensing elements integrated onto the microstructures, Brand can electrically excite the resonator and sense these rotational oscillations.

Since each sensor has a di
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