Efficient magnetic harvesting of microalgae enabled by surface-initiated formation of iron nanoparticles

Magnetic separation represents a cost-effective and energy-saving strategy for harvesting targets of interest, e.g., small molecules, biomacromolecules, and cells, in complex mixture. Conventional approaches necessitate multi-step time-consuming processes, including the pre-synthesis of magnetic nanoparticles and subsequent surface modification with targeting ligands. Here, a biocompatible and rapid separation strategy was developed for six microalgal species by in situ formation of iron nanoparticles on the microalgal surface. This method streamlines the separation process of various species of microalgae (e.g., Chlorella zofingiensis) from culture medium with a high harvesting efficiency (greater than 95%) within 1 min spanning a wide pH range of 4–11. Moreover, the recovered microalgae showed intact viability and exhibited no deterioration effect on the downstream extraction process of high-value bioproducts (e.g., chlorophyll, carotenoids and lipids). This method not only provides an alternative to harvest microalgae in a facile manner, but also demonstrates a new pathway to separate other microorganisms and cells, providing more opportunities in economic bioengineering and bioresource production.