These glass fibers are flexible and rugged sensors for neutrons and gamma radiation with applications in national security, medicine, and materials research.
Credit: Pacific Northwest National Laboratory
Household smoke and
carbon monoxide detectors are commonplace. Motion-triggered floodlights
illuminate driveways and parking lots. Metal detectors and biohazard
monitors guard ports and transportation hubs. Spill sensors protect
factory workers from hazardous chemicals. The safety and security
of our homes, public spaces, and workplaces rests on sensing danger
and issuing timely warnings. New sensing technologies developed
with NSF funding, and new methods for gathering and processing data
from distributed sensor systems, support a national effort to enhance
capabilities for reliably and accurately evaluating situations that
threaten our wellbeing.
A network of sensors is deployed in a burning building. They create temperature maps that allow fire fighters to move through the space safely.
Credit: Ron Peterson, Computer Science Department, Dartmouth College
At Northwestern University’s Nanoscale Science &
Engineering Center (NSEC) for Integrated Nanopatterning and Detection
Technologies, chemist and Center director Chad Mirkin uses dip-pen
lithography to deposit “lock” biomolecules on silicon substrates.
Mirkin and his coworkers write molecular patterns only a few nanometers
wide, and then expose the decorated substrates to solutions containing
“key” molecules. They are able to observe binding between pairs of
complementary molecules with both exquisite sensitivity and high
specificity. Sensors based on technologies like this will be able
to detect hazardous substances in minute quantities, but false
alarms will be a rarity. And the same sensor framework could be
adapted to detect different substances just by changing the molecular
“ink” with which the patterns are written.
Click on the micro-cantilevers to see how these molecular recognition sensors work, and view other sensor animations.
Credit: Nicolle Rager,
National Science Foundation
Another chemist who applies
the nanotechnologist’s perspective to sensor development is Robert
Hamers at the University of Wisconsin-Madison. Hamers also uses
a molecular lock and key approach—for example, he’s worked with
the binding of biotin (vitamin B-7) to the small protein avidin.
Hamers has developed methods for attaching biotin to diamond films
and electrically probing for the partner protein. He has used similar
techniques to detect specific DNA fragments. The rugged diamond-film
devices can be reliably and repeatably cycled, and the radio frequency
measurements that signal the presence or absence of the complementary
molecules lend themselves to integration in a sensor chip.
Nate Lewis’s work exemplifies a different approach
to sensing chemical or biological agents. Lewis’s technique uses
an array of sensors, each of which senses not one highly specific
molecule, but a group of related compounds. Using computational
techniques to combine the signals from several different sensors
and compare the results to known responses, he’s created an artificial
nose that can sniff out trace quantities of a variety of chemicals.
Click on the rose to see how polymers can sense smells and view other sensor animations.
Credit: Nicolle Rager,
National Science Foundation
Lab on a Wrist
The Center for Wireless Integrated Microsystems (WIMS),
an NSF Engineering Research Center directed by microelectromechanical
systems pioneer Kensall Wise, is putting together all the pieces
needed to make networkable, wristwatch-sized chemical analyzers.
Scientists and engineers from the University of Michigan, Michigan
Technical University, and Michigan State University participate
in the ERC, designing sensors, pumps, low-power microprocessors,
and radio-frequency componentry for the miniature instruments.
While the WIMS’s work will ultimately become part
of many different types of sensor and monitoring systems, they’re
concentrating current efforts on two testbeds: a cochlear implant
and an environmental monitoring system. Ted Zellers from the University
of Michigan’s School of Public Health heads the team designing the
monitoring testbed, a microscale chromatograph that could detect
hazardous gases equally well in homeland security applications or
industrial process control. To shrink this chemical analysis workhorse
down to 1 cubic centimeter, Zellers, Wise, and their students wrap
meter-long, 100 micron-wide chromatography columns into tight spirals.
They design and fabricate microscopic pumps, valves, and injectors
to capture sample gasses and transport them through the instrument.
They build electronic circuitry that generates all necessary voltages
from batteries, and transmits data via integrated micromachined
antennas and radiofrequency circuitry. Size and power consumption
must be minimized without compromising performance.
This electron micrograph shows the center of a meter-long capillary tube etched into a silicon wafer. In gas chromatography, different gasses separate as they traverse long, narrow capillary columns.
Credit: NSF Engineering Research Center for Wireless Integrated MiicroSystems, University of Michigan