Hazmat crews may soon get an assist from a new chemical detection device. Scientists at Georgia Tech have come up with a miniature sensor that uses polymer membranes deposited on a tiny silicon disk to measure pollutants present in aqueous or gaseous environments. The principal advantage of the device is water and air samples can be analyzed in the field, unlike conventional techniques that require samples to be transported to a laboratory for analysis.

The goal of the research is to detect volatile organic compounds in aqueous and gaseous environments. A common VOC is benzene, with a maximum contaminant level set by the Environmental Protection Agency at five micrograms per liter in drinking water. Many VOCs are present at similar very low concentrations, so effective sensors must accurately measure and discriminate extremely small mass changes.

The heart of the sensor is a microbalance that measures the mass of pollutant molecules. When pollutant chemicals get adsorbed into the surface of the sensor, a frequency change of the vibrating microbalance provides a measure of the associated mass change, according to the researchers.

Since each tiny sensor has a diameter of approximately 300 microns, or the average diameter of a human hair, a dozen sensors can be included in a space only a few millimeters in size. An array of these sensors, each sensor with a different chemically modified transducer surface, can sense different pollutants.

A typical test begins by flowing a water sample containing a known amount of pollutant over a sensor coated with a polymer membrane. When the sample flows through the cell, the mass of the microstructure increases, causing its characteristic vibration frequency, or resonance frequency, to decrease. Over time, the device can detect the amount of aromatic hydrocarbons such as benzene present in water.