Medical Design Briefs - December 2021 - 24

Monitoring Glucose Levels, No Needles Required
The wearable,
noninvasive glucose
monitoring
device prototype is the
first of its kind.
Penn State University
State College, PA
Noninvasive glucose monitoring
devices are not currently commercially
available in the United States, so people
with diabetes must collect blood
samples or use sensors embedded
under the skin to measure their blood
sugar levels. Now, with a new wearable
device created by Penn State
researchers, less intrusive glucose
monitoring could become the norm.
Led by Huanyu " Larry " Cheng,
Dorothy Quiggle Career Development
Professor in Penn State's Department
of Engineering Science and
Mechanics, the researchers published
the details of the noninvasive, lowcost
sensor that can detect glucose in
sweat in the journal Biosensors and
Bioelectronics.
The researchers
constructed the
device first with laser-induced
graphene (LIG), a material consisting
of atom-thick carbon layers in various
shapes. With high electrical conductivity
and a convenient fabrication time
of just seconds, LIG appeared to be an
ideal framework for the sensing device
- but there was a significant caveat.
" The challenge here is that LIG is
not sensitive to glucose at all, " Cheng
says. " So, we needed to deposit a glucose-sensitive
material onto the LIG. "
The team chose nickel because of its
robust glucose sensitivity, according to
Cheng, and combined it with gold to
lower potential risks of an allergic
reaction.
The researchers hypothesized that
the LIG outfitted with the nickel-gold
alloy would be able to detect low concentrations
of glucose in sweat on the
skin's surface.
A material with high glucose sensitivity
was a priority. Sweat exhibits
remarkably low glucose concentrations
compared to blood - but, according
to Cheng, there is a strong correlation
between glucose levels in sweat and
blood. While the concentration of glu24
Cov
Penn
State researchers developed a prototype of a wearable, noninvasive glucose sensor, shown
here on the arm. (Credit: Jia Zhu)
cose in sweat is about 100 times less
than the concentration in blood, the
team's device is sensitive enough to
accurately measure the glucose in
sweat and reflect the concentration in
blood.
The nickel-gold alloy's sensitivity
allowed Cheng's
team to
exclude
enzymes, which are often used to
measure glucose in more invasive,
commercially available devices or in
noninvasive monitors proposed by
other
researchers. These enzymes,
however, can degrade quickly with
time and changing temperatures.
" An enzymatic sensor has to be kept
at a certain temperature and pH, and
the enzyme can't be stored in the long
term, " Cheng says. " A nonenzymatic
glucose sensor, on the other hand, is
advantageous in terms of stable performance
and glucose sensitivity
regardless of these changes. "
Nonenzymatic sensors require alkaline
solution, which can damage the
skin and typically limits device wearability.
To curb this issue, Cheng and his
team attached a microfluidic chamber
to the LIG alloy.
This chamber is smaller than previously
developed configurations to promote
wearability and porous to allow
www.medicaldesignbriefs.com
ToC
for a range of movement, such as
stretching or crushing.
It is connected to a collection inlet
that passes sweat into the solution
without allowing the solution to touch
the skin. The basic solution interacts
with the glucose molecules to produce
a compound that reacts with the alloy.
This reaction triggers an electrical signal,
indicating the concentration of
glucose in the sweat.
With a smaller alkaline solution
chamber, the entire device is roughly
the size of a quarter and is flexible
enough to maintain a secure attachment
to the human body, Cheng says.
In a proof-of-concept test, the re -
searchers used a skin-safe adhesive to
attach the reusable device to a person's
arm one hour and three hours
after a meal. The subject performed a
brief workout - just enough to produce
sweat - right before each measurement
time.
A few minutes after collecting the
sweat, the researchers found that
the detected glucose concentration
dropped from the first measurement
to the next. The glucose measurements
from the device were verified by
measurements made with a commercially
available glucose monitor.
Medical Design Briefs, December 2021
http://www.medicaldesignbriefs.com
Medical Design Briefs - December 2021

Table of Contents for the Digital Edition of Medical Design Briefs - December 2021
