Microalgae cells with extracellular gold nanoparticles for enhanced photobioelectrochemical activity

Photobioelectrochemical systems (PBEs) harness the machinery of photosynthetic microorganisms to convert solar energy into electricity. However, the inefficient electron transfer at the cell-electrode interface remains as the key performance limitation. Herein, we report a plasmonic biohybrid strategy to enhance extracellular electron transfer in Chlorella-based photobioelectrodes by integrating gold nanoparticles (AuNPs) localized on the microalgae membrane. Two approaches are investigated, consisting of physical mixing of isolated cells with AuNPs and cultivating microalgae in a growth medium supplemented with AuNPs, with the second approach allowing to obtain about significantly higher photocurrent responses. Optimized bioelectrodes yield photocurrent densities of up to 132 μA cm^-2, 74% higher than bioelectrodes fabricated using unmodified cells. Spectral response analysis reveals a strong resonance at 525 nm, consistent with the plasmonic properties of AuNPs. Importantly, pigment content, growth kinetics, and membrane integrity are preserved, confirming the biocompatibility of the modification. This work presents a facile and effective route to engineer photosynthetic bioelectrodes using nanomaterials, advancing the design of high-performance PBEs for solar-to-electricity conversion.