Shrinking personal monitoring devices
Miniaturized air samplers will let researchers determine what people are exposed to in real time.
When Steve Chillrud, a geochemist at Columbia University, first started planning how to send personal monitoring devices out into the city on the backs of students traveling around New York City, the result was 20 pounds (lb) of gear that fit in a standard book-sized backpack. The equipment to track their daily exposures to particulate matter at home and abroad required large batteries and collection devices, as well as a global positioning system to report locations and time.
Not only did the heavy and awkward backpacks make the students less likely to carry them—they also made police officers nervous. After the bombings in the London Underground, "they basically told us 'no way'" for anything bigger than a Walkman, Chillrud said in a presentation last fall at the International Society of Exposure Analysis meeting in Durham, N.C.
Chillrud and other U.S. researchers are searching for ways to shrink personal monitoring devices to the size of a human palm so that people can carry chemical-sensing devices with them wherever they go and get a full picture of exposure.
In tackling "the miniaturization problem," researchers are partly looking to solve a compliance problem, says David Balshaw, a program manager of the Exposure Biology Program, a part of the Genes, Environment, and Health Initiative of the National Institutes of Health (NIH). Full-sized, state-of-the-art equipment gives good data, but carrying 20 lb of gear around in a backpack deters some people from actually using it and is particularly problematic for children.
Unlike the radioactive dosimeters that lab technicians might wear to give retroactive information about their exposures over the course of several months, "what we want is prospective information—it's a big change in the technology to do that," Balshaw continues. In addition to providing cumulative information about a person's daily exposures, data gathered in real time could eventually allow people to avoid dangerous compounds altogether.
With new funding, Chillrud has teamed up with scientists at Pacific Northwest National Laboratory to make and validate a miniaturized monitoring device that has the ability to track exposures in real time, as well as collect samples for later analysis in the lab. Several concentric rings of evenly spaced ports will collect particulate matter and measure trace gases. Chillrud and his team have a patent in the works that could be finalized later this year, depending on their success in shrinking the rest of the necessary components—such as the batteries to power their device.
Other projects funded by NIH's Exposure Biology Program include a device initially developed for NASA astronauts for future missions to the Moon and Mars. The device uses a tiny cylinder filled with water to collect nanoparticles or particulate matter, as well as optical technologies to count the particles in real time.
Those explorers will be bumping up against alien dust and other unknowns, says developer Sang Young Son of the University of Cincinnati. With a "real wearable sensor," he continues, "we can deduce . . . the kind of air that every individual has been exposed to," whether on the Moon or in a Cincinnati school Earth-side.
The main challenge Son and colleagues face in miniaturizing their stationary monitor has to do with the physical changes in shrinking the cylinder of water—from macrofluidics in the larger stationary sensor (liters of water) to microfluidics (PDF size: 1021 KB) in a tiny channel. One advantage, however, will be the ability to use heat transfer at a microscale. "We can reduce power consumption," Son says. The team has set a goal of 4 years for completion of their project.
The NIH program also funded several kinds of "electronic noses" that track mixtures, including one from a team at the University of California Riverside. In the same way that a human nose takes in smells through numerous receptors, the device takes in toxins that interfere conductively with an array of sensors. The result is a complete chemical picture of volatiles and other compounds, almost in real time.
Despite the major breakthroughs now occurring, validation testing for such personal monitoring devices remains several years off. But to Balshaw, the endeavor feels immediately promising. In the next 10–15 years, tiny personal monitors may be tucked into cell phones or whatever the in vogue communications device is, he conjectures, and "some technologies are already out there" that make this seemingly futuristic monitoring closer to reality than fiction.
