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

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.