Small-scale analyzer detects, analyzes aerosols

November 26, 2001

Remember mood rings? Those '70s gadgets that turned different colors as they gauged the mood of the wearer by measuring the vibes in the air or body?

Well, Da-Ren Chen, Ph.D., mechanical engineer at Washington University in St. Louis, is working on a bracelet-sized device that monitors the air quality about the wearer. Conceivably, one could attach the device to a bracelet or belt and be assured that the air is good or warned if it's bad.

While that's pretty "far out," it's just in the working stage. But recently Chen received a U.S. patent on a larger device that does the same thing. The device, which Chen designed and invented, is called the Nanometer Differential Mobility Analyzer (NanoDMA; US Patent: US 6,230,572 B1). At about seven inches tall with a circumference of a soup bowl, Chen's analyzer is nine times smaller than the industry norm, making it more portable. More importantly, though, it records aerosols - air particles - in the nanometer size range, the size that increasing evidence suggests is most dangerous to our health.

The coal mining and materials processing industries will find the Analyzer of interest, as will any industries where air quality in the work environment must be monitored. The device also can be used for fire protection and can be so fine-tuned as to be able to detect fire and also potentially the fire's source.

A nanometer is one billionth of a meter and invisible to the naked eye. A nanometer is one-thousandth of a micrometer; in comparison, a strand of human hair is typically 50 to 100 micrometers thick.

Chen's analyzer can measure nanoparticles as tiny as two nanometers. Its resolution is .2 percent compared with 10 percent for traditional analyzers, meaning it can distinguish differences between two nanoparticles with close diameters. For instance, particles with the sizes of 20 and 21 nanometers, which would be not distinguished by traditional analyzers, will be able to be classified in Chen's device. Moreover, Chen's analyzer, thanks to a separate charger that he also has patented (US Patents: 5,973,904; 6,145,391; 5,992,244), will charge a high percentage of nanoparticles. Charged particles are essential for detecting in his device. Charging the nanoparticles allows for a higher level of detection or sensitivity. A conventional apparatus will charge only eight particles out of a thousand, whereas Chen's device will charge 400 out of 1,000 particles in the 3 nanometer range; at a 7 nanometer m range, 100 percent of nanoparticles will be charged.

"The device is not only for measuring but it's for classifying, too, " said Chen, who noted that burning materials, for example, coal and fuels, produces particles in the nanometer range. "Essentially anything in the nanoparticle size can be sized with it, and it shows great promise for a number of applications. "

Chen said that his Analyzer is one-third less expensive to manufacture than current ones, and that many units have been sold to industry through a Minneapolis-based company, TSI. "I've designed the instrument to be able to do as much as it possibly can," Chen said. "Fire detection is one possibility, and it's being tested now in that capacity at the National Institute of Tests and Standards. This application will provide more insight into the initiation of a fire."
Contact: Tony Fitzpatrick 314-935-5272;; or Da-Ren Chen 314-935-7924;

Washington University in St. Louis

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