From biofabrication to harvesting: Microalgae-mediated magnetic nanoparticles for sustainable biomass recovery

Global demand for microalgae has intensified, with Chlorella species emerging as a prominent candidate due to their diverse and nutrient-rich biochemical profile. Despite their wide-ranging applications in biofuel production and carbon sequestration, large-scale deployment of microalgae is limited by persistent techno-economic challenges. In particular, harvesting and dewatering remain critical bottlenecks due to low biomass concentrations (∼0.5–2.5 g/L) and high water content (>70%), which together contribute significantly to energy consumption and production costs. Recent advances in nanoparticle-assisted biomass recovery have positioned magnetic separation as a promising approach for microalgae harvesting, enabling up to 99.6% harvesting efficiencies for Chlorella spp. in short contact time (1–10 min). The limited availability of commercially produced biosynthesized iron oxide nanoparticles has driven interest in biological sources as sustainable alternatives. Bio-fabricated magnetic nanoparticles from plant extracts, bacteria and biopolymers demonstrate high efficiency in microalgae harvesting, while microalgae themselves contain phytochemicals that act as reducing and capping agents during nanoparticle synthesis. This review integrates insights from conventional nanoparticle-assisted harvesting with the emerging potential of microalgae-mediated nanoparticle production through in-situ or one-pot mechanisms. Comparative analysis of surface chemistry highlights connections between pre-synthesized and microalgae-produced nanoparticles, revealing key knowledge gaps for sustainable biomass recovery.