ADVANCES
22 Scientific American, February 2022HE ALTHWound Guard
Gel-based sensor can send
infection alerts to a smartphoneWhen bacteria make their way into
wounds, they literally threaten life and
limb—unless they are detected as quickly
as possible. Now a new sensor can nestle
in bandages and alert a nearby smart-
phone when the bacterial population tips
over into dangerous territory.
Healthy human skin is covered with bac-
teria that are quick to colonize an open
wound, such as Staphylococcus aureus and
Escherichia coli. To prevent these organisms
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—an affected limb may
require amputation. Medical professionals
typically identify infections by unwrapping
and observing a wound or by swabbing it
and conducting a laboratory test. But
removing a wound’s dressing can slow down
the healing process. Plus, observations are
subjective, swab tests take time, and both
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.
This sensor can detect an enzyme called
deoxyribonuclease, or DNase. The enzyme
acts as a reliable infection indicator because
disease-causing bacteria produce it in large
amounts inside wounds, whereas bacteria
on healthy skin do not—so testing for the
substance reduces the chance of a false pos-
itive result. Furthermore, DNase builds up
before other infection signs appear. The new
alert system (dubbed the “wireless infection
detection on wounds,” or WINDOW, sen-
sor) was detailed in Science Advances.
WINDOW’s enzyme-sensing parts rely
on a gooey material called DNA hydrogel,
or DNAgel, made of entangled chains of
DNA. The researchers developed a partic-
ular 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 thisgel 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 process called
near-field communication, the same tech-
nology that allows people to make a pay-
ment with 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 Uni-
versity of Singapore. A person with a chronic
wound or someone sent home after a surgi-
cal operation might monitor their own status
by tapping a smartphone next to their dress-
ing a couple of times a day. If the phone
receives an infection alert, it can send a mes-
sage 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 devel-
oped a low-cost ultrafast swab test for in -fec tions. The issue, Mercer-Chalmers 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 and hos-
pitals systems. Ho says the material cost of
each WINDOW sensor is under $10, noting
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’s
diabetic foot ulcers, some with 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 lab mice whose wounds were ex -
posed 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 kinds of bacteria. “Hypothetically,
this should work with many other types
of strains as well [because they] have simi-
lar DNase-secreting mechanisms,” he says.
— Sophie BushwickWireless sensor detects an
enzyme released by infection.Ze Xiong