Internalized nanoparticles trigger metabolic reconfiguration to enhance extracellular electron transfer in microalgal biophotoelectrochemical cells

Microalgal biophotoelectrochemical cells (BPEC) offer a sustainable route for simultaneous wastewater treatment and bioenergy production. However, their efficiency is currently constrained by inefficient extracellular electron transfer (EET). This study demonstrated that the co-internalization of light-harvesting nanoparticles (LHN) and conductive nanoparticles (CN) into Scenedesmus quadricauda significantly amplified bioelectrochemical performance, a phenomenon supported by correlative transcriptomic analysis. The maximum current density produced by microalgae with co-internalized carbon dots (CD) as LHN and titanium dioxide (TiO₂) as CNs increased to 79.0 μA/cm² compared to the control (34.3 μA/cm²), while chemical oxygen demand (COD) removal efficiency and biodiesel yield improved 1.8-fold and 1.5-fold, respectively. Ultrastructural and elemental mapping analysis confirmed a specific spatial arrangement in which CDs were in the cytoplasm in close proximity to photosynthetic thylakoids and TiO₂ nanoparticles were positioned within the cell envelope, including the cell membrane and cell wall. Transcriptomic profiling suggested that the nanoparticles provided a correlational molecular framework that supported enhanced EET. While genes encoding light-harvesting complexes, electron transport carriers, and ribosomal machinery were significantly up-regulated to boost EET, energy-intensive peripheral pathways were down-regulated. Overall, this study provided correlative molecular evidence suggesting that nanoparticles reconfigured algal metabolism to improve cellular hardware for high-efficiency bioenergy production, offering a foundational strategy for advanced BPEC.