A team of researchers has designed a wearable sensor that, in preliminary testing, identified infections in open wounds before they looked any different than uninfected wounds. Their sensor, which combines principles from biology, materials science, and electrical engineering, may one day be a low-cost, time-saving alternative to existing diagnostic tools.
Many wearables on the market today, like the Apple Watch or Fitbit, use optical sensors to measure a person’s heart rate and blood oxygen levels. This wearable wouldn’t be worn on the wrist or hand — instead, researchers in Singapore have developed a hydrogel and electronic sensor the length of a human finger that attaches directly to an open wound.
The device senses infection at its source by exploiting a particular quirk of harmful bacteria. For reasons that are not entirely understood, many strains of harmful bacteria secrete an enzyme called deoxyribonuclease. It’s a reaction with that enzyme that the new wearable’s sensor ultimately converts into a signal.
The hope is that detecting infections more quickly will lead to treatment that can uproot an infection before it progresses to a complicated and potentially life-threatening illness.
“The key concept is that the hydrogel will be degraded by an enzyme secreted by bacteria, so it can reflect the presence of the bacteria,” said first author Ze Xiong. “Then, the sensor would send an alarm to the patient or clinician and they could replace the dressing of a wound or treat it with antibiotics.”
The study, published on Friday in the journal Science Advances, comes on the heels of an October study by an overlapping group of collaborators that focused on using sensors to monitor a range of biometrics in surgical wounds. The new research centers exclusively on bacterial infection, a wound complication that costs health care systems billions of dollars and frequently leads to death.
Xiong, a research fellow affiliated with three departments at the National University of Singapore, on health, innovation and technology, and electrical and computer engineering, said he drew on his interdisciplinary affiliation and background in chemistry and materials science to bring together a team that could do a bit of everything.
The hydrogel the team designed contains DNA and electrodes hooked up to an electrical sensor. When the bacterial enzyme interacts with the DNA in the gel, the conductivity of the material changes, producing an electrical signal that is measured by the sensor. Using hydrogel, which can absorb water while still maintaining its structural integrity, gave the team a huge advantage over traditional biological methods for detecting infections, Xiong said.
“The most common way to detect a biological signal is through fluorescence, but that requires a huge microscope and a bulky instrument. Hydrogels have the advantage of being 1 millimeter in thickness but still big enough to interact with a sensor.”
The team first tested the concept in cultures taken from diabetic foot ulcer patients. Then, once they’d fine-tuned the electronics of the sensor, they combined it with the hydrogel and hooked the resulting device up to several mice. They applied Staphylococcus aureus bacteria to a fraction of them — after 24 hours, the hydrogel sensors attached to the newly infected wounds had detected enough of a change to trigger a smartphone alert, while a control group exhibited next to no change.
Xiong said one of the collaborators on the study, a clinician trained in identifying infected wounds, determined there were no obvious shifts in the appearance of some of the mice’s wounds, meaning the sensor was able to recognize the bacterial infection before a visual assessment could. Still, it’s necessary to conduct further experiments with human subjects, since infections are often initially diagnosed based on a patient noticing pain or another change to their body.
Dan Luo, a biological and environmental engineering professor at Cornell University who was not involved in the research, said the results are a promising first demonstration and called them “cool.” Still, he said the team needs to collect a sizable amount of data before trying to get the device approved, starting with showing its sensitivity and specificity.
“DNA is really tough, but there are many things that can degrade it — for example, blood often contains [deoxyribonuclease],” he said.
He added that a future iteration of the device could even integrate diagnostics with treatment by engineering a DNA hydrogel that releases antibiotics in the event the DNA is degraded.
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