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Unraveling the Interfacial Electron Transfer Dynamics of Electroactive Microbial Biofilms Using Surface-Enhanced Raman Spectroscopy

Authors

  • Hoang K. Ly,

    1. Institut für Chemie, Sekr. PC14, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany)
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  • Dr. Falk Harnisch,

    1. Institute of Environmental and Sustainable Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig (Germany)
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  • Dr. Siang-Fu Hong,

    1. Institute of Environmental and Sustainable Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig (Germany)
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  • Prof. Dr. Uwe Schröder,

    1. Institute of Environmental and Sustainable Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig (Germany)
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  • Prof. Dr. Peter Hildebrandt,

    1. Institut für Chemie, Sekr. PC14, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany)
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  • Dr. Diego Millo

    Corresponding author
    1. Institut für Chemie, Sekr. PC14, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany)
    2. Biomolecular Spectroscopy/LaserLaB Amsterdam, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam (The Netherlands)
    • Institut für Chemie, Sekr. PC14, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany)
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Abstract

The electron transfer (ET) processes of electroactive microbial biofilms have been investigated by combining electrochemistry and time-resolved surface-enhanced resonance Raman (TR-SERR) spectroscopy. This experimental approach provides selective information on the ET process across the biofilm–electrode interface by monitoring the redox-state changes of heme cofactors in outer membrane cytochromes (OMCs) that are in close vicinity (i.e., within 7 nm) to the Ag working electrode. The rate constant for heterogeneous ET of the surface-confined OMCs (sc-OMCs) of a mixed culture derived electroactive microbial biofilm has been determined to be 0.03 s−1. In contrast, according to kinetic simulations the ET between sc-OMCs and their redox partners, embedded within the biofilm, is a much faster process with an estimated rate constant greater than 1.2 s−1. The slow rate of heterogeneous ET and the lack of high-spin species in the SERR spectra rule out the direct attachment of the sc-OMCs to the electrode surface.

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