Electric Polarization-Dependent Absorption and Photocurrent Generation in Limnospira indica Immobilized on Boron-Doped Diamond
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-07-17 |
| Journal | ACS Omega |
| Authors | Nikolay V. Ryzhkov, Nora Colson, Essraa Ahmed, Paulius Pobedinskas, Ken Haenen |
| Institutions | Belgian Nuclear Research Centre, Swiss Federal Laboratories for Materials Science and Technology |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Discovery: External electrical polarization directly modulates the light absorption characteristics of immobilized Limnospira indica (P6 strain) cyanobacteria, a phenomenon previously undocumented in BPEC literature.
- Performance Enhancement: Negative polarization (-0.6 V vs Ag/AgCl) significantly increased the light absorption amplitude of the cyanobacteria, particularly in the green-red visible spectrum (up to 12% increase in the PEDOT:PSS matrix).
- Electrode Functionality: The BDD/PEDOT:PSS biophotoelectrode demonstrated efficient dual functionality, operating effectively as both a photocathode (negative bias) and a photoanode (positive bias).
- Cathodic Efficiency: Cathodic photocurrent generation was found to be more efficient than anodic generation, utilizing the entire visible spectrum, suggesting potential for rational biophotocathode design.
- Matrix Role: The conductivity of the immobilization matrix is crucial; PEDOT:PSS facilitated polarization-dependent absorption changes and higher current outputs, whereas the low conductivity of agar hydrogel prevented significant electrical modulation.
- Material System: The use of Boron-Doped Diamond (BDD) as the current collector provides a stable, biocompatible, and chemically inert platform with a wide electrochemical potential window (3-3.5 V).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| BDD Film Thickness | 180 | nm | Microwave Plasma CVD deposition |
| BDD Band Gap | 5.47 | eV | Wide band gap semiconductor |
| BDD Potential Window | 3 - 3.5 | V | Wide electrochemical stability |
| B/C Ratio (TMB/H2) | 20,000 | ppm | Boron doping concentration during CVD |
| Methane Concentration (CH4) | 1 | % | Gas flow during BDD growth |
| CVD Microwave Power | 4000 | W | BDD growth parameter |
| CVD Pressure | 40 | Torr | BDD growth parameter |
| Substrate Temperature | 730 | °C | BDD growth temperature |
| Applied Potential Bias (Testing) | +0.6 and -0.6 | V | vs Ag/AgCl reference electrode |
| Typical BPEC Current Density (Intact Cells) | Up to 1 | mA/cm2 | Literature benchmark |
| Indicative High Current Density | 100 | ”A/cm2 | Performance benchmark |
| Max Photocurrent Wavelength | 375 | nm | UV light illumination |
| Absorbance Increase (PEDOT:PSS, -0.6 V) | 11 - 12 | % | Green-red visible light spectrum |
| Cyanobacteria Cultivation Temperature | 30 | °C | Standard growth conditions |
| Cyanobacteria Illumination (Growth) | 0.5 | mW/cm2 | White LED light |
Key Methodologies
Section titled âKey Methodologiesâ- BDD Electrode Synthesis: Fused silica substrates were cleaned via O2 plasma, then seeded with 7 nm ultradispersed detonation nanodiamond colloid. BDD films (180 nm thick) were grown using Microwave Plasma Enhanced Chemical Vapor Deposition (CVD) at 730 °C, 40 Torr, and 4000 W, utilizing a CH4/H2/Trimethylboron (TMB) plasma (1% CH4, 20,000 ppm B/C ratio).
- Cyanobacteria Cultivation: Axenic cultures of L. indica PCC 8005 (P6 morphotype) were grown in Zarroukâs medium at 30 °C under low-intensity white LED light (0.5 mW/cm2).
- Bioelectrode Immobilization: Harvested cells were immobilized by drop-casting onto the BDD surface using two matrices:
- Agar hydrogel (0.75% agar, optionally with 100 mM [Fe(CN)6]3+ redox mediator).
- Conductive conjugated polymer (0.5-1% PEDOT:PSS in water).
- Spectroelectrochemical Measurement: A three-electrode setup (BDD working electrode, Pt counter, Ag/AgCl reference) in PBS solution was used. Absorbance transients were monitored in situ using a deuterium/tungsten halogen lamp while applying switched DC potential biases (+0.6 V or -0.6 V).
- Photocurrent Measurement: Chronoamperometry was performed using a potentiostat. The biophotoelectrode was periodically illuminated (1 min light, 1 min dark) using mounted monochromatic LEDs (375 nm to 625 nm). Photocurrents were calculated by subtracting the extrapolated steady-state dark current baseline.
Commercial Applications
Section titled âCommercial ApplicationsâThe integration of BDD electrodes with living photosynthetic organisms enables several advanced bioelectrochemical technologies:
- Regenerative Life Support Systems (RLSS): Essential for long-duration space missions (e.g., Mars colonization) where BPECs can recycle CO2, generate O2, and produce electricity and biomass simultaneously.
- Biophotovoltaic (BPV) Devices: Development of sustainable, low-power energy sources utilizing microbial photosynthesis, particularly optimized for cathodic output via controlled polarization.
- Bioelectrochemical Systems (BES): Used for solar-to-chemical production, including sustainable hydrogen generation (H2 evolution) under anaerobic conditions, leveraging the BDD/cyanobacteria interface.
- Biosensing and Environmental Monitoring: BDDâs chemical inertness and wide potential window make it ideal for biosensors that rely on electrochemical reactions driven by photosynthetic components.
- High-Performance Electrodes: BDD substrates are utilized in harsh environments (e.g., high radiation, extreme temperatures) where traditional carbon electrodes fail, ensuring long-term stability for microbial systems.
View Original Abstract
We present the change of light absorption of cyanobacteria in response to externally applied electrical polarization. Specifically, we studied the relation between electrical polarization and changes in light absorbance for a biophotoelectrode assembly comprising boron-doped diamond as semiconducting electrode and live <i>Limnospira indica</i>PCC 8005 trichomes embedded in either polysaccharide (agar) or conductive conjugated polymer (PEDOT-PSS) matrices. Our study involves the monitoring of cyanobacterial absorbance and the measurement of photocurrents at varying wavelengths of illumination for switched electric fields, i.e., using the bioelectrode either as an anode or as cathode. We observed changes in the absorbance characteristics, indicating a direct causal relationship between electrical polarization and absorbing properties of <i>L. indica</i>. Our finding opens up a potential avenue for optimization of the performance of biophotovoltaic devices through controlled polarization. Furthermore, our results provide fundamental insights into the wavelength-dependent behavior of a bio photovoltaic system using live cyanobacteria.