Smallest biosupercapacitor provides energy for biomedical applications


Date:
August 23, 2021
Source:
Chemnitz University of Technology
Summary:
The miniaturization of microelectronic sensor technology,
microelectronic robots or intravascular implants is progressing
rapidly. However, it also poses major challenges for research. One
of the biggest is the development of tiny but efficient energy
storage devices that enable the operation of autonomously working
microsystems -- in more and more smaller areas of the human body
for example. In addition, these energy storage devices must be
bio-compatible if they are to be used in the body at all. Now
there is a prototype that combines these essential properties.



FULL STORY ==========================================================================
The miniaturization of microelectronic sensor technology, microelectronic robots or intravascular implants is progressing rapidly. However, it
also poses major challenges for research. One of the biggest is the
development of tiny but efficient energy storage devices that enable
the operation of autonomously working microsystems -- in more and more
smaller areas of the human body for example. In addition, these energy
storage devices must be bio-compatible if they are to be used in the
body at all. Now there is a prototype that combines these essential
properties. The breakthrough was achieved by an international research
team led by Prof. Dr. Oliver G. Schmidt, Professorship of Materials
Systems for Nanoelectronics at Chemnitz University of Technology,
initiator of the Center for Materials, Architectures and Integration of Nanomembranes (MAIN) at Chemnitz University of Technology and director
at the Leibniz Institute for Solid State and Materials Research (IFW)
Dresden. The Leibniz Institute of Polymer Research Dresden (IPF) was
also involved in the study as a cooperation partner.


==========================================================================
In the current issue of Nature Communication, the researchers report on
the smallest microsupercapacitors to date, which already functions in (artificial) blood vessels and can be used as an energy source for a
tiny sensor system to measure pH.

This storage system opens up possibilities for intravascular implants and microrobotic systems for next-generation biomedicine that could operate
in hard-to-reach small spaces deep inside the human body. For example, real-time detection of blood pH can help predict early tumor growing. "It
is extremely encouraging to see how new, extremely flexible, and adaptive microelectronics is making it into the miniaturized world of biological systems," says research group leader Prof. Dr. Oliver G. Schmidt, who
is extremely pleased with this research success.

The fabrication of the samples and the investigation of the
biosupercapacitor were largely carried out at the Research Center MAIN
at Chemnitz University of Technology.

"The architecture of our nano-bio supercapacitors offers the first
potential solution to one of the biggest challenges -- tiny integrated
energy storage devices that enable the self-sufficient operation of multifunctional microsystems," says Dr. Vineeth Kumar, researcher in
Prof. Schmidt's team and a research associate at the MAIN research center.

Smaller than a speck of dust -- voltage comparable to a AAA battery Ever smaller energy storage devices in the submillimeter range -- so-called "nano-supercapacitors" (nBSC) -- for even smaller microelectronic
components are not only a major technical challenge, however. This
is because, as a rule, these supercapacitors do not use biocompatible
materials but, for example, corrosive electrolytes and quickly discharge themselves in the event of defects and contamination. Both aspects
make them unsuitable for biomedical applications in the body. So-called "biosupercapacitors (BSCs)" offer a solution. They have two outstanding properties: they are fully biocompatible, which means that they can be
used in body fluids such as blood and can be used for further medical
studies.



==========================================================================
In addition, biosupercapacitors can compensate for self-discharge behavior through bio-electrochemical reactions. In doing so, they even benefit
from the body's own reactions. This is because, in addition to typical
charge storage reactions of a supercapacitor, redox enzymatic reactions
and living cells naturally present in the blood increase the performance
of the device by 40%.

Currently, the smallest such energy storage devices are larger than 3 mm3.

Prof. Oliver Schmidt's team has now succeeded in producing a 3,000 times smaller tubular nBSC, which, with a volume of 0.001 mm3 (1 nanolitre),
occupies less space than a grain of dust and yet delivers up to 1.6
V supply voltage for microelectronic sensors. This energy can be used
for a sensor system in the blood, for example. The power level also is
roughly equivalent to the voltage of a standard AAA battery, although the actual current flow on these smallest scales is of course significantly
lower. The flexible tubular geometry of the nano-biosupercapacitor
provides efficient self-protection against deformations caused by
pulsating blood or muscle contraction. At full capacity, the presented nano-biosupercapacitor can operate a complex fully integrated sensor
system for measuring the pH value in blood.

Thanks to Origami structure technology: flexible, robust, tiny Origami structure technology involves placing the materials required for the nBSC components on a wafer-thin surface under high mechanical tension. When
the material layers are subsequently detached from the surface in
a controlled manner, the strain energy is released and the layers
wind themselves into compact 3D devices with high accuracy and yield
(95%). The nano- biosupercapacitors produced in this way were tested in
three solutions called electrolytes: Saline, blood plasma, and blood. In
all three electrolytes, energy storage was sufficiently successful,
albeit with varying efficiency. In blood, the nano-biosupercapacitor
showed excellent lifetime, holding up to 70% of its initial capacity even
after 16 hours. A proton exchange separator (PES) was used to suppress
the rapid self-discharge.

Performance stability even under realistic conditions In order to
maintain natural body functions in different situations, the flow characteristics of the blood and the pressure in the vessels are
under constant change. Blood flow pulsates and varies according to
vessel diameter and blood pressure. Any implantable system within the circulatory system must withstand these physiological conditions while maintaining stable performance.



==========================================================================
The team therefore studied the performance of their development --
similar to a wind tunnel -- in so-called microfluidic channels with
diameters of 120 to 150 mym (0.12 to 0.15 mm) to mimic blood vessels of different sizes. In these channels, the researchers simulated and tested
the behavior of their energy storage devices under different flow and
pressure conditions. They found that the nano-biosupercapacitors can
provide their power well and stably under physiologically relevant
conditions.

Self-contained sensor technology can support diagnostics -- such as
tumor diagnostics The hydrogen potential (pH) of blood is subject
to fluctuations. Continuous measurement of the pH can thus help in
the early detection of tumors, for example. For this purpose, the
researchers developed a pH sensor that is supplied with energy by the nano-biosupercapacitor.

The 5 mym thin film transistor (TFT) technology previously established
in Prof.

Oliver Schmidt's research team could be used to develop a ring oscillator
with exceptional mechanical flexibility, operating at low power (nW to
myW) and high frequencies (up to 100MHz).

For the current project, the team used a nBSC based ring oscillator. The
team integrated a pH-sensitive BSC into the ring oscillator so that
there is a change in output frequency depending on the pH of the
electrolyte. This pH- sensitive ring oscillator was also formed into a
tubular 3D geometry using the "Swiss-roll" Origami technique, creating
a fully integrated and ultra-compact system of energy storage and sensor.

The hollow inner core of this micro sensor system serves as a channel for
the blood plasma. In addition, three nBSCs connected in series with the
sensor enable particularly efficient and self-sufficient pH measurement.

These properties open up a wide range of possible applications, for
example in diagnostics and medication.

========================================================================== Story Source: Materials provided by
Chemnitz_University_of_Technology. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Yeji Lee, Vineeth Kumar Bandari, Zhe Li, Mariana Medina-Sa'nchez,
Manfred
F. Maitz, Daniil Karnaushenko, Mikhail V. Tsurkan, Dmitriy D.

Karnaushenko, Oliver G. Schmidt. Nano-biosupercapacitors enable
autarkic sensor operation in blood. Nature Communications, 2021;
12 (1) DOI: 10.1038/s41467-021-24863-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210823125722.htm

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