Microbial extracellular electron transfer (EET) is the process that electrons generated from redox reactions transfer between inside of cells and extracellular electron donors/acceptors. This process accompanies with the energy transformation and substance conversion. Studies of microbial EET have attracted increasing interests in recent years because it is found to be significant to understand element biogeochemical cycle, anti-corrosion of metals, bioelectrochemical systems, etc. Electrochemical techniques have played important roles in EET mechanisms analysis, because these techniques are simple and available in studying electron transfer reactions at the interfacial region between electrode and solution. In this review, electrochemical integrated techniques used to study EET pathways including microelectrode, scanning electrochemical microscopy, three-electrode cell combined with optical microscopy and electrochemical spectroscopy are summarized. The functions and advantages of these integrated techniques are illustrated in detail. The EET pathways from macroscopic to microcosmic aspects are reviewed, which include four hierarchies:whole biofilm, redox reaction in microenvironment of biofilm, single cell, redox proteins or molecular. This review proposes that several advanced electrochemistry combined techniques can be useful for the investigation of microbial EET mechanisms in the future.
Contents
1 Introduction
2 Study of the electron transfer of microenvironment in biofilm by microelectrode and scanning electrochemical microscopy
3 Study of the electron transfer of single cell by three-electrode cell combined optical microscope
4 Study of the redox of protein or molecule by electrochemical spectroscopy
4.1 Electrochemical UV-visible spectroscopy
4.2 Electrochemical infrared spectroscopy
4.3 Electrochemical Raman spectroscopy
5 Conclusion and outlook