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Researchers from Southern California and New York are working together to integrate continuous sensing with flexible electrodes in an effort to create an intelligent sensor that can distinguish between and treat different injuries. The goal of the collaboration is to create a minimally or noninvasive sensing device that could be used to continuously monitor biomarkers—such as blood, sweat, and tears—to indicate the presence of an injury or to predict a cardiac event, for example.
Drawing on his expertise with flexible electrodes, Joseph Wang, a nanoengineering professor at the University of California–San Diego (www.ucsd.edu), is leading a team of researchers in pursuit of this sensor technology. Still in the early stages of research, Wang has partnered with Evgeny Katz of the department of chemical and biomolecular science at Clarkson University (Potsdam, NY; www.clarkson.edu). Katz has developed a system that uses an enzyme-based logic gate to measure a combination of biomarkers and then evaluates the results to make a limited diagnosis. Using a logic chain based on enzyme-driven reactions, the system has the potential to identify changes in biomarkers as signals of an injury or illness.
Despite such advancements, the team acknowledges that the path to success will not be a smooth one. In addition to working on the proper design of reliable logic gates, the team is addressing the biocompatibility and reliability challenges associated with on-body flexible electrodes. “Making sure that the bending, or mechanical stress, of the electrode doesn’t compromise its conductivity, and then maintaining long-term reliable performance are the biggest challenges,” says Wang of his current research.
The team is also examining which flexible electrode materials present the most potential for its project. Three flexible plastic substrates in particular show promise for withstanding mechanical stress. Testing on Mylar, polyethylene naphthalene, and Kapton showed that the materials can be bent to extremely small curvatures and still function well, despite a marginal increase in the electrical resistance, Wang says.
His team has also explored the fabrication and operation of a laterally rolled thick-film electrochemical amperometric enzyme electrode. “The attractive performance of this flexible screen-printed microsensor indicates great promise for continuous monitoring of health biomarkers in the tear fluid, particularly for detecting temporal changes in the pattern of these biomarkers as unique predictors of various medical or stress conditions,” Wang explains. Unlike blood, however, the use of such body fluids as sweat and tears in continuous monitoring is still being established.
Ultimately, Wang hopes that this research will help his team develop the sensing and monitoring technology to produce a sensor that can sit just under the skin, be rolled into a tight cylinder that could fit into a tear duct, or even be woven into fabric where it would be in direct contact with the body. This project has potential as a sort of medic-on-a-chip for the military as well as for a host of monitoring applications for medical devices. Those capabilities, however, are likely still a few years away.
