The device can be placed under a bandage to send an infection alert directly to the smartphone

When bacteria enter the wound, they actually threaten life and limbs—unless they are discovered as soon as possible. A new sensor can be attached to a bandage and alert nearby smartphones when bacterial colonies enter a dangerous area.

Healthy human skin is covered with bacteria such as Staphylococcus aureus and Escherichia coli, and these bacteria will soon colonize open wounds. To prevent bacteria from spreading throughout the body, causing permanent injury or death, the infected wound may need to be cleaned and treated with antibiotics, or—in the most extreme cases—the affected limb may need to be amputated. Medical professionals identify infections by opening the wound and then checking for observable signs or wiping the wound and performing laboratory tests. But removing the dressing will slow down the healing process. In addition, observation is subjective, swab testing takes time, and both options require the patient to be present in person.

To solve these problems, some research teams are developing devices that are placed under bandages and continuously monitor for indirect signs of infection, such as changes in wound temperature or acidity. Scientists at the National University of Singapore have now created a more direct infection sensor.

The sensor can detect an enzyme called deoxyribonuclease or DNase. It is a reliable indicator of infection because disease-causing bacteria will produce this enzyme in large quantities, but bacteria on healthy skin will not, so testing for it can reduce the possibility of false positive results. In addition, DNase will accumulate before other signs of infection appear. This new alert system-known as wireless wound infection detection, or WINDOW, sensor-was described in a paper published in Science Advances on Friday.

The enzyme sensing component of WINDOW is made of a viscous material called DNA hydrogel or DNAgel, made of tangled DNA strands. Researchers have developed a special DNAgel that remains stable in water environments (such as the human body), but begins to decompose in the presence of DNase. They connected this material to a chip that can sense when the gel decays and respond by sending a signal to a smartphone. The signal is broadcast using a battery-less wireless technology called Near Field Communication (NFC), which allows people to pay with the tap of a credit card.

"By combining this DNAgel with the sensor [chip], we can create a device that does not require batteries at all and can be placed under the wound bandage," said John Ho, an electrical engineer at the National University of Singapore, co-author of the study . A person with a chronic wound, or a person sent home after surgery, may monitor his condition by tapping his smartphone next to the dressing several times a day. If the phone receives an infection alert, it can send a message to the doctor or tell the patient to return to the hospital for antibiotic treatment.

Other researchers have tried different infection detection methods, including high-tech imaging to monitor the spread of bacteria and "electronic noses" to sniff out chemical signals of infection. June Mercer-Chalmers, a project manager at the University of Bath in the United Kingdom, said: “In principle, people have proven that a lot of things” are effective. He did not participate in this new research, but worked in a team to develop an infection-specific Low-cost and ultra-fast swab testing. She said the problem comes down to the utility of the tool: does it require a lot of bulky equipment, whether there are huge obstacles to obtaining legal approval, and how cost-effective it is. She pointed out that the WINDOW sensor requires electronic components and smart phone access, which may prevent some people outside the higher-cost hospital from accessing it. Ho said that the material cost of each WINDOW sensor is less than $10, and pointed out that it can be built using existing electronic manufacturing methods.

So far, Ho's team has exposed DNAgel to the wound swabs of 18 people with diabetic foot ulcers, some of whom were infected with Staphylococcus aureus, to observe the degree of material degradation in the presence of the bacteria. The researchers also used the device on 6 live laboratory mice whose wounds were exposed to the same bacterial species, and successfully detected the infection within 24 hours before any signs appeared. Since the WINDOW sensor is still in its early stages, Ho plans to continue testing it on larger patient populations and wounds infected with other types of bacteria. "Assume that this also applies to many other types of strains [because they] have similar DNase secretion mechanisms," he said.

Sophie Bushwick is the associate technical editor of Scientific American. Follow Sophie Bushwick on Twitter: Nick Higgins

Evan Callaway and Nature Journal

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