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Magnetotactic bacteria produce magnetite nanoparticles called magnetosomes at ambient conditions via a protein‐stabilized transient amorphous precursor to obtain precise control over particle size and morphology. In a bioinspired approach, such biomineralization processes are emulated, mimicking proteins involved in magnetosome formation using the positively charged analog poly‐L‐arginine. While the additive is expensive, it remains elusive whether the change in magnetite formation mechanism arises solely from the polymer's cationic nature. This study uses different mass‐produced and sustainably sourced polycations to induce the biomineralization‐reminiscent formation of magnetite nanoparticles. These findings present how to achieve control over nanoparticle size (from 10 to 159 nm) and morphology (compact and sub‐structured) as well as magnetic properties (superparamagnetic, stable‐single‐domain, vortex state) at ambient temperature and pressure using these additives. Furthermore, the formation of large nanoparticles with the addition of poly(diallyldimethylammonium chloride) (PDADMAC) at low alkalinity highlights how magnetotactic bacteria may produce magnetite nanoparticles under similar conditions. Confirming the polycations' ability to electrostatic stabilize amorphous ferrihydrite, it is anticipated that parametric in vitro studies on polymer properties will provide valuable insights into magnetite biomineralization and aid in rationally designing magnetic nanomaterials. [ABSTRACT FROM AUTHOR]

Magnetic nanomaterials find increasing application as separation agents to rapidly isolate target compounds from complex biological media (i.e., blood purification). The responsiveness of the used materials to external magnetic fields (i.e., their saturation magnetization) is one of the most critical parameters for a fast and thorough separation. In the present study, magnetite (Fe3O4) and non-oxidic cementite (Fe3C) based carbon-coated nanomagnets are characterized in detail and compared regarding their separation behavior from human whole blood. A quantification approach for iron-based nanomaterials in biological samples with strong matrix effects (here, salts in blood) based on platinum spiking is shown. Both materials are functionalized with polyethyleneglycol (PEG) to improve cytocompatibility (confirmed by cell toxicity tests) and dispersability. The separation performance is tested in two setups, namely under stationary and different flow-conditions using fresh human blood. The results reveal a superior separation behavior of the cementite based nanomagnets and strongly suggest the use of nanomaterials with high saturation magnetizations for magnetic retention under common blood flow conditions such as in veins. [ABSTRACT FROM AUTHOR]

High magnetic responsiveness is critical for nanomagnets in biomedicine, and fast and complete separation is essential for blood purification or targeted drug delivery, to diminish potential risks. However, studies on the collection efficiency of iron‐based nanoparticles are rare. On page 4888, W. J. Stark and co‐workers present a new quantification approach based on platinum doping of magnetite and carbon‐coated cementite nanoparticles. Their findings show that a good separation efficiency from human whole blood calls for nanomaterials with high saturation magnetizations. [ABSTRACT FROM AUTHOR]