Three-electrode sensor printed on neoprene wetsuit fabric. The electronic board and battery would be embedded in the fabric, while the sensor remains in direct contact with water. Photo: UC San Diego |
Breakthroughs in
nanoengineering often involve building new materials or tiny circuits. But a
professor at the University of California, San Diego is proving that he can
make materials and circuits so flexible that they can be pulled, pushed, and
contorted—even under water—and still keep functioning properly.
Joseph Wang has
successfully printed thick-film electrochemical sensors directly on flexible
wetsuit material, paving the way for nano devices to detect underwater
explosives or ocean contamination.
“We have a
long-term interest in on-body electrochemical monitoring for medical and
security applications,” says Wang, a professor in the department of nanoengineering
in UC San Diego’s Jacobs School of Engineering. “In the past three years we’ve
been working on flexible, printable sensors, and the capabilities of our group
made it possible to extend these systems for use underwater.”
Wang notes that
some members of his team—including electrical engineering graduate student
Joshua Windmiller—are surfers. Given the group’s continued funding from the
United States Navy, and its location in La Jolla,
it was a logical leap to see if it would be possible to print sensors on
neoprene, the synthetic rubber fabric typically used in wetsuits for divers and
surfers.
The result:
development of “wearable electrochemical sensors for in situ analysis
in marine environments.” The paper, published in Analyst, was
co-authored by UCSD’s Wang, Windmiller, and visiting scholar Gabriela
Valdés-Ramírez from Mexico, as well as Michael J. Schöning and Kerstin Malzahn
from the Institute of Nano- and Biotechnologies of Germany’s Aachen University
of Applied Sciences.
UCSD has a full U.S. patent
pending on the technology, and has begun talks on licensing the system to a
Fortune 500 company.
Battery-operated electrochemical microsensor includes screen-printed, three-electrode sensor linked to electronics board (potentiostat). A) represents functioning in safe environmental conditions; B) shows red LED, indicating increased current magnitude caused by elevated phenol content in seawater. (Insets) Dashed lines indicate threshold for safe–or hazardous–phenol levels. Image: UC San Diego |
Wang’s 20-person
research group is a world leader in the field of printable sensors. But to prove
that the sensors printed on neoprene could take a beating and continue working,
some of Wang’s colleagues took to the water.
“Anyone trying to
take chemical readings under the water will typically have to carry a portable
analyzer if they want to detect pollutants,” says Wang, whose group is based in
the California Institute for Telecommunications and Information Technology
(Calit2) at UCSD. “Instead, we printed a three-electrode sensor directly on the
arm of the wetsuit, and inside the neoprene we embedded a 3 V battery and electronics.”
The electrochemical
sensors are based on applying voltage to drive a reduction-oxidation (redox)
reaction in a target threat or contaminant—which loses or gains electrons—then
measuring the current output. The wearable microsystem provides a visual
indication and alert if the levels of harmful contaminants or explosives exceed
a pre-defined threshold. It does so by mixing different enzymes into the carbon
ink layer before printing on the fabric. (For example, if the enzyme tyrosinase
interacts with the pollutant phenol, the LED light switches from green to red.)
The electronics are
packed into a device known as a potentiostat that is barely 19 mm by 19 mm.
(The battery is stored on the reverse side of the circuit board.)
Two arrays of four silver electrodes printed on neoprene. Image: UC San Diego |
In the experiments
described in the Analyst article, Wang and his team tested sensors for
three potential hazards: a toxic metal (copper); a common industrial pollutant,
phenol; and an explosive (TNT). The device also has the potential to detect
multiple hazards. “In the paper we used only one electrode,” notes Wang, “but
you can have an array of electrodes, each with its own reagent to detect
simultaneously multiple contaminants.”
The researchers
believe that neoprene is a particularly good fabric on which to print sensors
because it is elastic and repels water. It permits high-resolution printing
with no apparent defects.
The UCSD team
tested the sensor for explosives because of the security hazard highlighted by
the 2000 attack on the USS Cole in Yemen. The Navy commonly checks for
underwater explosives using a bulky device that a diver must carry underwater
to scan the ship’s hull. Using the microsystem developed by Wang and his team,
the sensor printed on a wetsuit can quickly and easily alert the diver to
nearby explosives.
Wang’s lab has
extensive experience printing sensors on flexible fabrics, most recently
demonstrating that biosensors printed on the rubber waistband of underwear can
be used continuously to monitor the vital signs of soldiers or athletes. The
researchers were uncertain, however, about whether bending the printed sensors under
water—and in seawater—would still let them continue functioning properly.
In the end, even
underwater, and with bending and other deformations, the sensors continued to
perform well. “We still need to validate and test it with the Navy,” says Wang. “While the primary security interest will be in the detection of explosives,
the Navy in San Diego
bay has also detected large concentrations of toxic metals from the paint on
Navy ships, so in principle we should be able to print sensors that can detect
metals and explosives simultaneously.”
Wang’s work in
flexible sensors grew out of 20 years’ experience with innovations in glucose
monitoring, ultimately in the form of flexible glucose strips that now account
for a $10 billion market worldwide.
Work on the
underwater sensors was supported by the Office of Naval Research.
