Unravelling Magnetic Nanochain Formation in Dispersion for In Vivo Applications

Abstract

Self‐assembly of iron oxide nanoparticles (IONPs) into 1D chains is appealing, because of their biocompatibility and higher mobility compared to 2D/3D assemblies while traversing the circulatory passages and blood vessels for in vivo biomedical applications. In this work, parameters such as size, concentration, composition, and magnetic field, responsible for chain formation of IONPs in a dispersion as opposed to spatially confining substrates, are examined. In particular, the monodisperse 27 nm IONPs synthesized by an extended LaMer mechanism are shown to form chains at 4 mT, which are lengthened with applied field reaching 270 nm at 2.2 T. The chain lengths are completely reversible in field. Using a combination of scattering methods and reverse Monte Carlo simulations the formation of chains is directly visualized. The visualization of real‐space IONPs assemblies formed in dispersions presents a novel tool for biomedical researchers. This allows for rapid exploration of the behavior of IONPs in solution in a broad parameter space and unambiguous extraction of ​the parameters of the equilibrium structures. Additionally, it can be extended to study novel assemblies formed by more complex geometries of IONPs.

Dynamics of magnetic Janus colloids studied by ultra small-angle X-ray photon correlation spectroscopy

“…2c). The observed excess intensity in the form of a streak is an indication of locally chain-like configuration of particles along the field direction 25 . Besides, the four lobes of the pattern in the horizontal direction suggests a zigzag arrangement of particles within the chain.…”

“…Throughout the past decades theories have been developed to comprehend the static equilibrium structure formed under the influence of an external field 3,[15][16][17][18] . Depending on the size of the particles these theories can be verified by optical microscopy 19 , scattering methods including small angle Xray and neutron scattering (SAXS and SANS, respectively) [20][21][22][23][24][25] , or by computer simulations [26][27][28] . In order to obtain the dynamic information of a magnetic responsive suspension, traditionally dynamic light scattering (DLS) 29,30 is used and only in the last decades modern methods such as optical particle tracking 31 , dynamic differential microscopy (DDM) 32 and X-ray photon correlation spectroscopy (XPCS) [33][34][35][36][37][38][39] became available.…”

Using small-angle scattering to guide functional magnetic nanoparticle design

“… 167 Even in the absence of particle agglomeration and chaining, long-range concentration fluctuations along the field indicating a strong anisotropy of the Brownian motion are observed under magnetic field. 168 Using a combination of scattering methods and reverse Monte Carlo simulations, Nandakumaran et al 169 explored the chain formation mechanism under magnetic field in solution. Eventually, dipolar magnetic interactions in ferrofluids induce the formation of superstructure ranging from short-range ordered aggregates via chain-like structures 170,171 to field-induced pseudocrystalline ordering in concentrated ferrofluids.…”

Using small-angle scattering to guide functional magnetic nanoparticle design

“…167 Even in the absence of particle agglomeration and chaining, long-range concentration fluctuations along the field indicating a strong anisotropy of the Brownian motion are observed under magnetic field. 168 Using a combination of scattering methods and reverse Monte Carlo simulations, Nandakumaran et al 169 explored the chain formation mechanism under magnetic field in solution. Eventually, dipolar magnetic interactions in ferrofluids induce the formation of superstructure ranging from short-range ordered aggregates via chain-like structures 170,171 to field-induced pseudocrystalline ordering in concentrated ferrofluids 172,173 .…”