Magnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria

Abstract

Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro-and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET).

Surface-ligand-induced crystallographic disorder–order transition in oriented attachment for the tuneable assembly of mesocrystals

“…The coercivity of the magnetic chains arranged in the <111> direction showed a pronounced dependency on this angle, with a minimum at θ = 0° and maximum at θ = 90°. This result agrees with the theoretical prediction of the chain-of-spheres model and magnetic chains formed by magnetotactic bacteria 33 – 35 . However, this angle dependency tended to diminish as the BNCs became disordered.…”

“…Interestingly, the ac-MCs aligned along the <111> easy axis of the magnetocrystalline anisotropy owing to the interaction anisotropy, which induces the uniaxial anisotropy of nanochains due to magnetostatic coupling between mesocrystals (Fig. 6e ) 19 , 33 . In contrast, the mesocrystals with misaligned BNCs did not exhibit a particular orientation (Supplementary Fig.…”

Magnetically Controlled Reversible Photomagnetic Nanoactuators for Dynamic Contrast Enhancement in Optical Coherence Tomography

“…Next, we investigated whether PMNAs can exhibit magnetic responses and subsequently magnetic field‐induced changes in their optical responses. When exposed to an external magnetic field, PMNAs were assembled into a chain assembly with a length of ≈4.5 ± 2.2 µm due to magnetostatic coupling [ 33 , 34 , 35 , 36 ] between neighboring PMNAs (Figure 1e,f ; Figure S3 , Supporting Information). Specifically, upon the external magnetic field excitation, PMNAs exhibit the magnetic interactions between neighboring particles (i.e., magnetostatic coupling) due to the presence of Fe 3 O 4 core, which overcomes thermal fluctuations and electrostatic repulsion between nearby PMNAs, thereby yielding a chain assembly along the magnetic field direction [ 33 , 36 , 43 , 44 ] (Figure S4 , Supporting Information).…”

Soft Viscoelastic Magnetic Hydrogels from theIn SituMineralization of Iron Oxide in Metal-Coordinate Polymer Networks

“…The majority of the particles formed in our catechol-functionalized networks through coprecipitation were <10 nm in diameter, with the occasional presence of larger aggregates of <50 nm . We thus sought to grow larger iron oxide nanoparticles in this study, which is possible through a different approach of forming Fe 3 O 4 namely, via the partial oxidation approach − .25ex2ex Fe 2 + + 2 OH − → Fe ( OH ) 2 3 Fe ( OH ) 2 + NO 3 − → Fe 3 normalO 4 + 4 normalH 2 O + NO 2 − …”