Using tiny electrodes to measure electrical activity in bacteria
Organic microbial electrochemical transistor monitoring extracellular
electron transfer

Date:
June 17, 2020
Source:
Linko"ping University
Summary:
Scientists have developed an organic electrochemical transistor
that they can use to measure and study in fine detail a phenomenon
known as extracellular electron transfer in which bacteria release
electrons.



FULL STORY ========================================================================== Scientists at Laboratory of Organic Electronics, Linko"ping University,
have developed an organic electrochemical transistor that they can use
to measure and study in fine detail a phenomenon known as extracellular electron transfer in which bacteria release electrons.


==========================================================================
The study of bacteria and their significance for the natural world,
and for human society and health, is a growing research field, as new
bacteria are continuously being discovered. A human body contains more
bacteria than human cells, and a millilitre of fresh water can hold as
many as a million bacteria.

Respiration in a normal human cell and in many bacteria takes place
through biochemical reactions in which a compound, often glucose, reacts
with oxygen to form carbon dioxide and water. During the process, energy
is converted to a form that the cell can use. In oxygen-free environments, bacteria are found that metabolise organic compunds, like lactate, and
instead of forming water, they release, or respire, electric charges,
a by product of metabolism, into the environment. The process is known
as extracellular electron transfer, or extracellular respiration.

The phenomenon is currently used in several electrochemical systems in applications such as water purification, biosensors and fuel cells. Adding bacteria is an eco-friendly way to convert chemical energy to electricity.

One such bacteria often used in research is Shewanella oneidensis, which previous research has shown to produce electrical current when fed with arsenic, arabinose (a type of sugar) or organic acids. A similar bacterium
has recently been discovered in the human gastrointestinal system.

We do not, however, understand in detail what happens when bacteria
release charges. In order to capture and measure the amount of charge
released, electrodes are placed into the microbial systems. An individual bacterium gives a very weak signal, and thus until now, researchers
have had to be satisfied with studying extracellular electron transfer
in large systems with large numbers of bacteria.

In order to increase our understanding, scientists at the Laboratory of
Organic Electronics at Linko"ping University have employed a combination
of microelectronics, electrochemistry and microbiology. They have
developed an organic electrochemical transistor in which they have been
able to deposit Shewanella oneidensis on one of the microelectrodes, with
a surface area of only a quarter of a square millimetre. The amplification
of the signal that occurs in the transistor makes it possible for them
to study in detail what happens when various substances are added to the system. They describe in an article in Advanced Science experiments in
which they fed lactate to the bacteria.

"We have shown that we can detect very small differences in extracellular electron transfer, in other words the amount of charge released by
the bacteria. Another plus is that we can achieve very short response
times, and obtain a stable signal within ten minutes," says principal
research engineer Ga'bor Me'hes, who, together with senior lecturer
Eleni Stavrinidou, is corresponding author for the article.

"This is a first step towards understanding extracellular electron
transfer in bacteria occupying olny a small area with the help of a
transistor, and how the conversion takes place between the bacteria and
the electrode," says Ga'bor Me'hes. "One future goal is to learn how
bacteria interact with each other, and with other cells and chemical
substances in the human gastrointestinal tract." The research is being conducted within the framework of the Biocom Lab at the Laboratory of
Organic Electronics, and is financed by Vinnova, the Swedish Research
Council, the Swedish Foundation for Strategic Research, the Wallenberg
Wood Science center and the European Research Council, ERC.

It is hoped that the research will lead to optimising microbial
electrochemical systems that harvest energy, and increase
our understanding of, for example, serious gastrointestinal
conditions. Looking far inte the future, the idea has been raised among reserachers of using bacteria that respire iron compounds to support
human life on the oxygen-free planet Mars.


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


========================================================================== Journal Reference:
1. Ga'bor Me'hes, Arghyamalya Roy, Xenofon Strakosas, Magnus Berggren,
Eleni
Stavrinidou, Daniel T. Simon. Organic Microbial Electrochemical
Transistor Monitoring Extracellular Electron Transfer. Advanced
Science, 2020; 2000641 DOI: 10.1002/advs.202000641 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617121455.htm

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