When bacteria make their way into wounds, they literally threaten life and limb—unless they are detected as quickly as possible. A new sensor can nestle in bandages and alert a nearby smartphone when the bacterial population tips over into dangerous territory.
Healthy human skin is covered with bacteria such as Staphylococcus aureus and Escherichia coli, which are quick to colonize an open wound. To prevent the bacteria from spreading through the body, which can permanently injure or kill a person, the infected wound may need to be cleaned and treated with antibiotics or—in the most extreme situations—the affected limb may require amputation. Medical professionals identify infections by unwrapping a wound and then checking it for observable signs or by swabbing it and conducting a laboratory test. But removing the dressing can slow down the healing process. Plus, observations are subjective, swab tests take time and both options require that a patient be physically present.
To address these issues, some research teams are developing devices that sit under bandages and continuously monitor indirect signs of infection, such as changes in wound temperature or acidity. And scientists at the National University of Singapore have now created an even more direct infection sensor.
The sensor can detect an enzyme called deoxyribonuclease, or DNase. It acts as a reliable infection indicator because disease-causing bacteria produce the enzyme in large amounts, whereas bacteria on healthy skin do not, so testing for it reduces the chance of a false positive result. Furthermore, DNase builds up before other signs of infection appear. This new alert system—dubbed the wireless infection detection on wounds, or WINDOW, sensor—is described in a paper published on Friday in Science Advances.
WINDOW’s enzyme-sensing parts are constructed from a gooey material called DNA hydrogel, or DNAgel, made of entangled chains of DNA. The researchers developed a particular kind of DNAgel that remains stable in watery environments, such as the human body, but begins to break down in the presence of DNase. They connected the material to a chip that senses when the gel decays and responds by sending a signal to a smartphone. This signal is broadcast using a battery-free wireless technique called near-field communication (NFC), the same technology that allows people to make a payment with just the tap of a credit card.
“By coupling this DNAgel with that sensor [chip], we can make a completely battery-free device that can fit under a bandage on the wound,” says study co-author John Ho, an electrical engineer at the National University of Singapore. A person with a chronic wound, or someone sent home after a surgical operation, might monitor their own status by tapping a smartphone next to their dressing a couple times per day. If the phone receives an infection alert, it can send a message to a doctor or tell the patient to return to the hospital for an antibiotic treatment.
Other researchers have tried different approaches to infection detection, including high-tech imaging to monitor bacterial spread and “electronic noses” to sniff out an infection’s chemical signals. “There’s a raft of stuff out there that people, in principle, have proved” works, says June Mercer-Chalmers, a project manager at the University of Bath in England, who was not involved with the new study but worked on a team that developed a low-cost ultrafast swab test for infections. The issue, she says, comes down to a tool’s practicality: whether it requires a lot of cumbersome equipment, if it has steep barriers to legal approval and how cost-effective it is. She points out that the WINDOW sensor requires electronic parts and smartphone access, which might put it out of reach for some people outside of higher-cost hospitals. Ho says the material cost of each WINDOW sensor is under $10 and notes that it could be constructed with existing electronic manufacturing methods.
Thus far Ho’s team has exposed the DNAgel to wound swabs from 18 people with diabetic foot ulcers, some of whom had S. aureus infections, to see how much the material degraded in the presence of the bacteria. The researchers also used the device on six living laboratory mice whose wounds were exposed to the same bacterial species, and it successfully detected infections within 24 hours, before any physical signs had become visible. Because the WINDOW sensor is still in its early days, Ho plans to continue testing it on larger groups of patients and on wounds infected with other types of bacteria. “Hypothetically this should work with many other types of strains as well [because they] have similar DNase-secreting mechanisms,” he says.