Medical Design Briefs - June 2021 - 34

GlobAl
INNOVATIONS
Gold Nanoparticles Enable Long-Term Implantable Sensor 'Tattoo'
Johannes Gutenberg University, Mainz, Germany
he idea of implantable sensors that
continuously transmit information
on vital values and concentrations
of substances or drugs in the body has
fascinated physicians and scientists for a
long time. Such sensors enable the constant
monitoring of disease progression
and therapeutic success. However, until
now, implantable sensors have not been
suitable to remain in the body permanently
but had to be replaced after a few
days or weeks. On the one hand, there is
the problem of implant rejection be -
cause the body recognizes the sensor as
a foreign object. On the other hand, the
sensor's color, which indicates concentration
changes, has been unstable so far
and would fade over time. Scientists at
Johannes Gutenberg University Mainz
(JGU) have developed a novel type of
implantable sensor that can be operated
in the body for several months. The sensor
is based on color- stable gold nano -
particles that are modified with receptors
for specific molecules. Embedded
into an artificial polymeric tissue, the
nano gold is implanted under the skin
where it reports changes in drug concentrations
by changing its color.
T
Gold nanoparticles embedded in a porous
hydrogel can be implanted under the skin and
used as medical sensors. The sensor is like an
invisible tattoo, revealing concentration changes
of substances in the blood by color change.
(Credit: Nanobiotechnology Group, JGU Depart -
ment of Chemistry)
■ Implant Reports Information as
an 'Invisible Tattoo'
Prof. Carsten Sönnichsen's research
group at JGU has been using gold nano -
particles as sensors to detect tiny amounts
of proteins in microscopic flow cells for
many years. Gold nanoparticles act as
small antennas for light: They strongly
absorb and scatter it and, therefore,
appear colorful. They react to alterations
in their surroundings by changing color.
Sönnichsen's team has exploited this concept
for implanted medical sensing.
To prevent the tiny particles from
swimming away or being degraded by
immune cells, they are embedded in a
porous hydrogel with a tissue-like consistency.
Once implanted under the
skin, small blood vessels and cells grow
into the pores. The sensor is integrated
in the tissue and is not rejected as a foreign
body. " Our sensor is like an invisi34
Cov
ble
tattoo, not much bigger than a
penny and thinner than one millimeter, "
says Sönnichsen, head of the
Nanobio technology Group at JGU.
Since the gold nanoparticles are infrared,
they are not visible to the eye.
However, a special kind of measurement
device can detect their color noninvasively
through the skin.
In their study published in Nano
Letters, the JGU researchers implanted
their gold nanoparticle sensors under
the skin of hairless rats. Color changes
in these sensors were monitored following
the administration of various doses
of an antibiotic. The drug molecules are
transported to the sensor via the bloodstream.
By binding to specific receptors
on the surface of the gold nanoparticles,
they induce color change that is dependent
on drug concentration. Thanks to
the color-stable gold nanoparticles and
the tissue-integrating hydrogel, the sensor
was found to remain mechanically
and optically stable over several months.
■ Long-Lasting Implantable Sensors
" We are used to colored objects bleaching
over time. Gold nanoparticles, however,
do not bleach but keep their color perwww.medicaldesignbriefs.com
ToC
manently.
As they can be easily coated
with various different receptors, they are
an ideal platform for implantable sensors, "
explains Dr. Katharina Kaefer, first
author of the study.
The novel concept is generalizable
and has the potential to extend the
lifetime of implantable sensors. In the
future, gold nanoparticle-based im -
plantable sensors could be used to
observe concentrations of different
biomarkers or drugs in the body simultaneously.
Such sensors could find
application in drug development, medical
re search, or personalized medicine
to aid in the management of chronic
diseases.
■ Interdisciplinary Teamwork Brought
Success
Sönnichsen had the idea of using gold
nanoparticles as implanted sensors in
2004 when he started his research in biophysical
chemistry as a junior professor
in Mainz. However, the project was not
realized until 10 years later in cooperation
with Dr. Thies Schroeder and Dr.
Katharina Kaefer, both scientists at JGU.
Schroeder was experienced in biological
research and laboratory animal science
and had already completed several years
of research work in the United States.
Kaefer was looking for an exciting topic
for her doctorate and was particularly
interested in the complex and interdisciplinary
nature of the project. Initial
results led to a stipend awarded to
Kaefer by the Max Planck Graduate
Center (MPGC) as well as financial support
from Stiftung Rheinland-Pfalz für
Innovation.
" Such a project requires many people
with different scientific backgrounds.
Step by step we were able to convince
more and more people of our idea, " says
Sönnichsen. " Ultimately, it was inter -
disciplinary teamwork that resulted in
the successful development of the first
functional implanted sensor with gold
nanoparticles. "
For more information, visit https://www.
uni-mainz.de.
Medical Design Briefs, June 2021
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Medical Design Briefs - June 2021

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

Medical Design Briefs - June 2021 - Intro
Medical Design Briefs - June 2021 - Cov4
Medical Design Briefs - June 2021 - Cov1a
Medical Design Briefs - June 2021 - Cov1b
Medical Design Briefs - June 2021 - Cov1
Medical Design Briefs - June 2021 - Cov2
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Medical Design Briefs - June 2021 - Cov3
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