In microbial electrosynthesis (MES), the integration of novel materials is crucial for optimizing efficiency and enhancing performance. These materials are predominantly utilized in the development of electrodes, which form the critical interface between electrical circuits and microbial communities. Advanced materials such as carbon-based composites, nanostructured surfaces, and conductive polymers have been instrumental in improving electron transfer rates and expanding the surface area for microbial colonization. Furthermore, novel materials are being developed for membranes and separators to enhance ion selectivity and minimize energy losses within the system. These innovations collectively contribute to more efficient MES operations by optimizing the interactions between microbes and electrodes, thereby facilitating the effective conversion of carbon dioxide into valuable chemical products. Consequently, the adoption of novel materials is pivotal in advancing MES technology, providing new avenues for sustainable energy production and effective carbon utilization. This focus on material innovation not only enhances the technical capabilities of MES but also positions it as a key technology in the transition toward a more sustainable and circular carbon economy. Here we discuss recent discoveries in this area by our lab on the use of bio-generated materials in microbial electrosynthesis.

Ever since its discovery by Myers and Nealson in 1988, Shewanella oneidensis MR-1 and other electroactive bacteria (EAB) have kept fascinating bioelectrochemists and others for the microbe’s ability to respond to oxidizing potentials delivered by polarized electrodes via extracellular transfer of charges. Realizing EAB’s potential for industrial applications, such as bioelectrosynthesis, wastewater treatment, bioremediation, etc., synthetic chemists, material scientists and electrical engineers joined the efforts to maximize the benefits of such bioelectochemical systems, particularly by improving the bioelectrical connection.

In the first part of the talk I will give my perspective on the various materials science approaches to improve extracellular electron transfer (EET), including works of direct involvement, based on the well-known conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT)1, chemically-functionalized CNTs2 and a ferrocene-based redox polymer3,4. To facilitate discussions on cross-material comparisons, I will mostly focus on one bioelectrochemical (or other) aspect at a time, such as electrochemically active surface area or microbe attachment to electrode, evaluated for multiple materials interfaces.

In the second part, I will introduce and outline future possibilities of EET signal transduction by organic electrochemical transistors (OECT) based on PEDOT:PSS, including the limited number of works published after we first introduced the organic microbial electrochemical transistor (OMECT) concept five years ago5.

For both topics, I will also show the first insights from our newest results using an n-type conducting polymer.

Cyanobacterial blooms that produce taste/odor metabolites (e.g., 2-MIB, geosmin) and toxins threaten drinking-water safety, yet conventional monitoring (nutrient analysis, physicochemical proxies, chlorophyll-a) lacks direct, real-time detection. Here, we present two complementary in-situ sensing platforms for rapid detection and quantification of phytoplankton presence and growth:

1) Ultra-Sensitive Bioelectronic Monitoring. We employ polyurethane (PU) foams dip-coated with PEDOT:PSS to create 199 cm² macroelectrodes that maximize double-layer capacitance and signal-to-noise sensitivity. We show that cohorts of Oscillatoria sp. exhibit synchronized electrical excitability. The collective cell activity is stress-dependent and produces large, coherent signals that scale linearly with electrode area - suggesting possible correlation with biomass and productivity. Electrochemical Impedance Spectroscopy (EIS) further resolves biofilm development and cell-density changes. Coordinated signaling emerges as intercellular Ca²⁺ waves, validated by fluorescent probes and suppressed by gadolinium chloride, suggesting a Ca²⁺-mediated paracrine mechanism potentially linked to 2-MIB or geosmin production.

2) Microcapillary Photometric Sensing. We use melt-extruded fluorinated ethylene propylene (FEP) strips coated with poly(vinyl alcohol) as hydrophilic “dip-stick” microcapillaries. These require no media exchange or aeration for months, and, when inoculated with Parachlorella kessleri, achieve a specific growth rate of μ = 0.37 d⁻¹ - matching a sparged Erlenmeyer and >3 times higher than an unsparged control. Their optical transparency permits non-invasive, single-cell imaging of morphology and cell-cycle events, benchmarked against high-resolution flow cytometry.

Together, these multimodal biohybrid platforms provide direct, in-situ readouts of microbial physiology, EPS formation, and metabolite risk factors - paving the way for scalable, proactive water-quality management and novel biocompatible sensing interfaces.

Photosynthesis is one of the most important processes for life on our planet, yet many important questions regarding its fundamental mechanisms remain unanswered. The rapidly developing field of bioelectronic devices that use photosynthetic organisms such as cyanobacteria wired to electrodes has given an urgency to furthering our understanding of these systems. In this talk, I will outline two areas in which scattering-based techniques have shone new light on pressing questions in this field.

Firstly, development of bioelectronic technologies such as biophotovoltaics requires a detailed understanding of the electron transfer mechanisms at the biofilm/electrode interface, which currently represents the bottleneck in improving efficiency¹. A more efficient method has been to extract the photosynthetic thylakoid membranes and deposit these directly onto the electrode^2,3. However, these systems are still highly complex and deconvoluting their components and the parameters that contribute to their electron-transfer mechanisms from a top-down perspective is non-trivial. To address this, we have used neutron reflectometry coupled with spectroelectrochemistry in situ to compare electrodes with extracted thylakoid membranes to those using a model lipid/protein mixture. This early work has demonstrated the potential of our neutron reflectometry/spectroelectrochemistry system as well as establishing a platform for further fundamental studies both of photosynthesis in model membranes and also for screening potential improvements to bioelectronic technologies.

Secondly, I will demonstrate how a combination of synchrotron X-ray methods and surface-enhanced Raman spectroscopy has allowed us to map iron oxidation states in biofilms with unprecedented accuracy. This has allowed us to resolve a long-fought controversy concerning the evolutionary reason for electron export in cyanobacteria.

Biophotovoltaics (BPV) represents an innovative biohybrid technology that couples electrochemistry with oxygenic photosynthetic microbes to harness solar energy and convert it into electricity. Central to BPV systems is the ability of microbes to perform extracellular electron transfer (EET), utilizing an anode as an external electron sink. This process simultaneously serves as an electron sink and enhances the efficiency of water photolysis compared to conventional electrochemical water splitting.

The direct coupling of the photosystem with the external anode is the theoretical basis of the BPV concept, for its capacity to explores the full potential of the oxygenic photosystem for energy production. However, there are still uncertainties in demonstrating such coupling, with conflicted results being reported in the past decade. In this work [1], we provide solid experimental basis to demonstrate that a BPV can extract electrons directly from the photosystem. We distinguished the cellular electron fluxes originating from water splitting in photosystem or those from degradation of the storage carbon via carbon metabolism, by tuning the cultivating conditions of the cyanobacteria and the operating conditions in BPV. Comparative analysis demonstrated that the current output during darkness was determined by the intracellular glycogen levels, and the current output during illumination could directly originate from the photosystems. The EET mechanism was demonstrated to be dynamic up to the environmental conditions and physiological status of the cyanobacterial cells.

Following up to the molecular dynamics of the EET pathways, we applied a comprehensive analytic approach to monitor the photosynthetic electron flows in Synechocystis sp. PCC 6803 cultivated in a ferricyanide-mediated BPV system [2]. By monitoring carbon fixation rates and photosynthetic oxygen exchange, we reveal that EET does not significantly affect cell growth, respiration, carbon fixation, or photosystem II efficiency. However, EET competes for electrons with the flavodiiron protein flv1/3, influencing Mehler-like reactions. Our findings suggest that the ferricyanide mediator facilitates photosynthetic electron extraction from ferredoxins downstream of photosystem I. Knocking out the flv1/3 protein resulted in over 270% increase of the mediator reduction rate (i.e. the EET rate).

Extracellular electron transfer (EET) is a key process in microbial electrochemical systems (MES), enabling electron exchange between microbes and solid external materials.^[1] While electroactive bacteria (EAB), such as Shewanella oneidensis MR-1, have been extensively studied for their native EET capability, non-electroactive bacteria (n-EAB), including Escherichia coli, lack intrinsic EET pathways and remain largely underutilized in MES.^[2] Recently, we reported that polyethyleneimine with ferrocene side chains (Fc-LPEI) facilitates EET in both gram-positive and gram-negative n-EAB, yet its underlying mechanism remains to be fully elucidated.^[3]

In this study, we present a comparative investigation of Fc-LPEI-enhanced EET in both EAB and n-EAB. Acting as an artificial molecular conduit, Fc-LPEI forms an efficient charge-transfer interface between bacterial cells and electrodes. Carbon felt electrodes modified with Fc-LPEI exhibited remarkable current enhancements, with E. coli showing a ~200-fold and S. oneidensis MR-1 a ~12-fold increase relative to unmodified electrodes. Scanning electron microscopy confirmed that the polymer layer enhances bacterial adhesion via electrostatic interactions, while electrochemical techniques (CA, CV, EIS) revealed reduced interfacial resistance and increased electrochemically active surface area (EASA), thereby enabling efficient electron transport.

Our detailed analysis revealed distinct EET mechanisms across the two bacterial species. In E. coli, current generation was closely associated with interactions between ferrocene moieties and secreted redox-active species or planktonic cells, indicative of a mediated electron transfer (MET)-like process. By contrast, S. oneidensis MR-1 primarily relied on direct contact-based mechanisms, wherein Fc-LPEI reinforces native electron pathways by promoting robust cell-electrode contact. Cyclic voltammetry demonstrated clear ferrocene redox peaks for E. coli, while such peaks were suppressed in MR-1, suggesting fundamentally different electron access modes. Electrochemical impedance spectroscopy further confirmed the facilitative role of Fc-LPEI: R_bac decreased from 38 kΩ to 6.5 kΩ for E. coli and from 25.3 kΩ to 0.56 kΩ for MR-1.

To investigate the electron transport pathway in MR-1, we employed cytochrome-deletion mutants (Δomc-all and ΔcymA). Our findings indicate that Fc-LPEI partially bypasses the need for outer membrane cytochromes, likely interacting with redox components in the periplasm but not across the inner membrane. A split-recombined MES configuration further demonstrated that EET in E. coli depends strongly on planktonic interactions, whereas in MR-1, direct electrode attachment remains dominant for current generation.

Lastly, we observed that applying higher electrode potentials significantly enhanced E. coli glucose consumption and current output, suggesting that metabolic activity and EET efficiency can be tuned electrochemically. These findings demonstrate that Fc-LPEI can serve as a versatile and tunable interface for dissecting and enhancing bacterial EET, providing valuable mechanistic insight and offering promising strategies for engineering sustainable bioelectronic systems.