Blending electrochemical methods with the benefits of biological reaction specificity in bio-electrochemical systems presents a potential for the development of effective and sustainable processes for the manufacture of several products. Various microorganisms have the capacity to transfer electrons beyond the cell surface to insoluble components. This capability allows for application of these organisms in cellular bio-electrochemical systems including microbial electro-synthesis and microbial fuel cells.
However, low productivity of the bio-electrochemical systems has limited industrial implementation of this concept. This is because most bio-electrochemical systems depend on the attachment of the organism on an electrode and biofilm formation. Biofilms are polymeric porous surface attachments that are composed of water, polysaccharides, lipids, microorganisms, nucleic acids, and proteins. These dynamic systems can adapt to changes in the environment. Therefore, in the application of bio-electrochemical system, optimization of biofilm formation is fundamental in view of efficient electron transfer between the electrode and the organism.
In-depth knowledge of the attachment of electro-active bacteria to electrode surfaces remains a shortcoming for cellular bio-electrochemical system development. Characterizing biofilm formation, viability and growth is pivotal to enhance biofilm maintenance in several applications such as microbial fuel cells. Various methods have been developed, which range from classical electrochemical techniques to various spectroscopical and optical approaches, in a bid to analyze the attachment of electroactive organisms at electrodes.
Markus Stöckl at DECHEMA Research Institute in Frankfurt, Germany and Christin Schlegel at the Technical University of Kaiserslautern, Germany and colleagues investigate the development and characterization of a flow cell that enabled the parallelized application of electrochemical impedance spectroscopy and confocal laser scanning microscopy for biofilm assessment. The proposed flow cell enabled electrochemical characterization of biofilm processes by noninvasive and nondestructive methods. Their work is published in Electrochimica Acta.
For constant observation of the biofilm growth, the authors applied continuous monitoring approaches. This provided information on various stages of biofilm formation. They applied a combination of two analytical methods, confocal laser scanning microscopy and electrochemical impedance spectroscopy. They presented a custom-built flow cell with a transparent indium tin oxide electrode, which allowed for monitoring of cell attachment to a working electrode.
Cyclic voltammetry as well as electrochemical impedance spectroscopy of iron (III)/iron (II) redox couple showed that the proposed flow cell was appropriate for electrochemical analysis. The authors used Shewanella oneidensis as electro-active model organism. This was in a bid to demonstrate the application of the flow cell as bio-electrochemical system.
From electrochemical impedance spectroscopy and cyclic voltammetry, the authors observed with a model redox probe, that reliable electrochemical analysis could be performed in the flow cell. The flow cell was then applied as microbial fuel cell (MFC) with S. oneidensis as the model organism for bacterial attachment as well as generation of current. Homogeneous laminar flow allowed for the formation of stable mono to multiple layer colonies of bacteria.
The authors observed a decrease in the charge transfer resistance from impedance spectroscopy with increased current production. They also witnessed an increased cell cumber on the working electrode surface. S. oneidensis biofilm formation has been observed before, but the simultaneous application of electrochemical impedance spectroscopy and confocal laser scanning microscopy has not been described before.
With the combination of the two noninvasive approaches, a monitoring tool has been found and might give insights in the biofilm formation processes of mixed and co-cultures by various staining procedures.
Markus Stöckl, Christin Schlegel, Anne Sydow, Dirk Holtmann, Roland Ulber, Klaus-Michael Mangold. Membrane Separated Flow Cell for Parallelized Electrochemical Impedance Spectroscopy and Confocal Laser Scanning Microscopy to Characterize Electro-Active Microorganisms. Electrochimica Acta, volume 220 (2016), pages 444–452.Go To Electrochimica Acta