Medical Design Briefs - June 2023 - 34

Highly Sensitive Biosensor Detects Extremely Small Changes
in Tears, Blood
Waseda University
Tokyo, Japan
W
earable wireless biosensors are
an integral part of digital
healthcare and monitoring. Commonly
used chipless resonant antennabased
biosensors are simple and affordable
but have limited applicability
due to their low sensitivity. Now, researchers
from Japan have developed
a novel, wireless, parity-time symmetry-based
bioresonator that can detect
minute concentrations of tear glucose
and blood lactate. This highly sensitive,
tunable, and robust bioresonator
has the potential to have a great impact
on personalized health monitoring
and digitized healthcare systems.
Wireless wearable biosensors have
been a game changer in personalized
health monitoring and healthcare digitization
because they can efficiently detect,
record, and monitor medically significant
biological signals. Chipless
resonant antennae are highly promising
components of wearable biosensors
because they are affordable and tractable.
However, their practical applications are
limited by low sensitivity (inability to detect
small biological signals) caused by a low
quality (Q) factor of the system.
To overcome this hurdle, researchers
led by Prof. Takeo Miyake from Waseda
University, Prof. Yin Sijie from Beijing
Institute of Technology, and Taiki Takamatsu
from Japan Aerospace Exploration
Agency, have developed a wireless
bioresonator using parity-time (PT) symmetry
that can detect minute biological
signals. Their work has been published in
Advanced Materials Technologies.1
In this study, the researchers designed a
bioresonator consisting of a magnetically
coupled reader and sensor with high Q factor,
and thus, increased sensitivity to biochemical
changes. The reader and sensor
both comprise an inductor (L) and capacitor
(C) that are parallel connected to a resistor
(R). In the sensor, the resistor is a
chemical sensor called a chemiresistor that
converts biochemical signals into changes
in resistance. The chemiresistor contains
an enzymatic electrode with an immobilized
enzyme. Minute biochemical changes
at the enzymatic electrode (in response to
34
Novel Parity-Time Symmetry-Based Wearable Biosensors
Chipless resonant antennas are highly
promising components for making low-cost,
wearable biosensors
Novel, wireless parity-time (PT) symmetric inductance-capacitance-resistance
(LCR) parallel resonator with high Q factor
Reader
Sensor
Parallel-connected
chemiresistor
Rectifier
Glucose/
lactate
- +
Re(Zin)
Inductively
coupled
Change in resistance
However, their practical use
is limited by the quality (Q)
factor of the system, leading
to low sensitivity to
biological signals
0.1
mM
0.6
mM
Tear glucose
levels
mM
0.0
00
M
4.0
mM
Blood lactate
levels
Ag/AgCl
eGOD/LOD
eCsmooth
Product
GOD/LOD
PVI-osmium
CNT
Carbon
fiber
Change in biochemical signal
High sensitivity
High tunability
High robustness
The novel amplitude-modulated PT symmetric wireless biosensor shows
high sensitivity and has immense potential for use in a wide range of
wearable devices
Wearable, Implantable, Parity-Time Symmetric Bioresonators for Extremely Small Biological Signal Monitoring
Takamatsu et al. (2023) Advanced Materials Technologies DOI: 10.1002/admt.202201704
Researchers have developed a novel, wireless, PT-symmetric wearable resonator that can detect tear glucose and blood
lactate levels in the micromolar range. The resonator is composed of an inductance-capacitance-resistance (LCR)
reader and an LCR sensor with an enzyme-based chemiresistor. The setup has a high quality (Q) factor, making it highly
sensitive. (Credit: Waseda University)
changes in the levels of biomolecules such
as blood sugar or lactate) are thus converted
into electrical signals by the sensor, and
then amplified at the reader.
" We modeled the characteristics of the
PT-symmetric wireless sensing system by
using an eigenvalue solution and in put
impedance, and experimentally demonstrated
the sensitivity enhancement at/
near the exceptional point by using parallel
inductance-capacitance-resistance
(LCR) resonators. The developed amplitude
modulation-based PT-symmetric
bioresonator can detect small biological
signals that have been difficult to measure
wirelessly until now, " Miyake says.
" Moreover, " he says, " our PT-symmetric
system provides two types of readout
modes: threshold-based switching and
enhanced linear detection. Different
readout modes can be used for different
sensing ranges. "
The researchers tested the system
(here containing a glucose-specific enzyme)
on human tear fluids and found
that it could detect glucose concentrations
ranging from 0.1 to 0.6 mM. They
also tested it with a lactate-specific enzyme
and commercially available human
skin and found that it could measure lacwww.medicaldesignbriefs.com
tate
levels in the range of 0.0 to 4.0 mM
through human skin tissue, without any
loss of sensitivity. This result further indicates
that the biosensor can be used as an
implantable device. Compared to a conventional
chipless resonant antenna-based
system, the PT-symmetric system achieved
a 2000-fold higher sensitivity in linear and
a 78 percent relative change in thresholdbased
detection, respectively.
Sharing his vision for the future, Miyake
concludes, " The present telemetry
system is robust and tunable. It can enhance
the sensitivity of sensors to small
biological signals. We envision that this
technology can be used for developing
smart contact lenses to detect tear glucose
and/or implantable medical devices
to detect lactate for efficient monitoring
of diabetes and blood poisoning. "
Reference
1. Taiki Takamatsu, et al. " Wearable, Implantable,
Parity-Time Symmetric Bioresonators for Extremely
Small Biological Signal Monitoring, " Advanced
Materials Technologies, April 8, 2023,
https://onlinelibrar y.wiley.com/doi/
full/10.1002/admt.202201704.
For more information, visit www.
waseda.jp. Contact: Takeo Miyake at
miyake@wasseda.jp or +093 692 5158.
Medical Design Briefs, June 2023
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https://onlinelibrary.wiley.com/doi/full/10.1002/admt.202201704 http://www.�waseda.jp http://www.�waseda.jp http://www.medicaldesignbriefs.com

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