Portland, Ore. - Researchers at Vanderbilt University have updated the idea of the "canary in the coal mine" with a microphysiometer containing real human cells that reacts quickly to all manner of toxins.
Coal miners handled old-school hazards by sending down a caged bird to test for "bad air." Birds react similarly to humans in the presence of arbitrary toxins, but because of their faster metabolism, they react more quickly, thereby offering an early warning. Today, electronic sensors tuned to specific contaminants have all but replaced such broad-stroke early-warning measures. But anti-bioterrorism developers that need to sense arbitrary toxins must either build arrays of sensors for every known substance or go back to the caged-bird model.
"Terrorists could use any toxin as a weapon," said David Cliffel, assistant professor of chemistry at Vanderbilt University (Nashville, Tenn.). "Even if we have a sensor for sarin and anthrax and the other well-known biological agents, we will still have a need for the microphysiometer, because it can sense any toxin that has short-term effects."
Like a caged bird, the microphysiometer has live cells inside-"immortalized" human cells that have been adapted to accept an artificial nutrient stream that keeps them alive indefinitely. These cells sit atop sensors that quickly detect any abnormalities. The nutrient stream is exposed to the environment before being delivered to the immortalized human cells, thereby mixing in any biological agents in the environment. As a result, the cells react to toxins within minutes.
"We envision a multiple-chambered device that has different types of immortalized cells in each one," Cliffel said. "One for liver cells, one for heart cells, one for lung cells and one for nerve cells."
Immortalized cell cultures from every part of the body are widely available from commercial scientific supply houses. Other researchers have used them to construct simple physiometers, albeit only for a single sensor that usually tests acidity (pH). Cliffel's contribution was to add multiple sensors in the chamber for each type of cell cultured within the device. He also is working toward a microfluidic version that could be portable for use in the field. Today the microphysiometer is tethered to the top of a laboratory table.
Cliffel led a development group working under the auspices of the Vanderbilt Institute for Integrative Biosystems Research and Education. His group included postdoctoral assistants Sven Eklund and Dale Taylor working with senior research associate Eugene Kozlov and research professor Ales Prokop from the chemical-engineering department. The group proved the concept of a microphysiometer by creating a single-chamber, four-sensor version cannibalized from a commercial device that measures changes in pH only.
The microphysiometer itself is a series of reservoirs, switches, rotary pumps and chambers made from thin membrane sheets that contain colonies of 100,000 to 1 million cells. In addition to acidity, Cliffel's group added sensors for oxygen, glucose and lactic acid, enabling the device to monitor and chart moment-by-moment variations in the cells. "Cells consume oxygen and glucose and produce lactic and carbonic acids," said Cliffel. "By measuring with these four sensors we can quickly determine whether the cells are consuming oxygen and glucose normally, while producing lactic and carbonic acids normally, or whether these actions have been adversely affected by a toxin."
In tests with the single-chamber, four-sensor prototype the group was able to detect two pesticides-parathion and paraoxon-and two common pollutants, a gas additive (methyl tertiary-butyl ether) and hexachromium.
In another test, hamster ovary cells were exposed to fluoride which, as expected, blocked their ability to digest glucose.The sensors showed the characteristic buildup of excess glucose and oxygen as the cells failed to digest it, plus a dropping in their rates of lactating and acidification. "We saw the cells basically go into hibernation," said Cliffel. "Then, we flushed out the fluoride, and they almost immediately started working normally again."
Future devices will add separate chambers for different types of cells, such as nerve, heart, lung and liver cells, he said. "One thing we want to do is create a library of profiles showing the typical reaction for each sensor to each type of known toxin or contaminant. Then we will be able to spot truly novel bioagents when they don't fit any profile," said Cliffel.
Cliffel's research was funded by the Defense Advanced Research Projects Agency.