A thick-film electrochemical sensor printed directly on flexible wetsuit material is now caught in the nanotechnology current as a new device can detect underwater explosives or ocean contamination.
“We have a long-term interest in on-body electrochemical monitoring for medical and security applications,” said Joseph Wang, a professor in the Department of NanoEngineering at University of California, San Diego’s Jacobs School of Engineering and co-author of a paper on the subject. “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.”
In a mix of work and pleasure, Wang said some members of his team – including electrical-engineering graduate student Joshua Windmiller – are surfers and for them the next logical step would be 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 sensors have developed to the point to where UCSD has a full U.S. patent pending on the technology and has begun talks on licensing the system to a Fortune 500 company.
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,” Wang said. “Instead, we printed a three-electrode sensor directly on the arm of the wetsuit, and inside the neoprene we embedded a 3-volt battery and electronics.”
The electrochemical sensors apply 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. In one case, if the enzyme tyrosinase interacted with the pollutant phenol, the LED light switches from green to red.
The electronics go into a device known as a potentiostat that is barely 19mm by 19mm. In addition, the battery stories on the reverse side of the circuit board.
Wang’s 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,” Wang said, “but you can have an array of electrodes, each with its own reagent to detect simultaneously multiple contaminants.”
The researchers said neoprene is a 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.
“We still need to validate and test it with the Navy,” said 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.”