Magnetic nanoparticles have a broad field of applications including biomedicine, magnetocaloricrefrigeration, magnetic sealing and magnetic storage. For most applications it is of crucial importance that their physical and chemical characteristics are well defined and controllable. The non-aqueous sol-gel method allows synthesizing magnetic particles with the desired properties. Particles with tunable size and high crystallinity can be obtained employing mild conditions, using high-boiling solvents like benzyl alcohol (BnOH) or triethylene glycol (TEG). A profound knowledge of the formation and growth processes of the particles is essential to be able to produce particles that are tailored to the needs of the application.
Therefore, the non-aqueous sol-gel method was investigated extensively regarding the growth process of manganese-zinc ferrites synthesized in TEG, and of iron oxide nanoparticles synthesized in TEG as well as in BnOH. It is shown that the growth as well as the composition of the obtained noparticles are strongly influenced by the used solvent. The particle formation was traced over the course of the synthesis for the three systems, via a combination of various analytical methods, and models of particle growth were developed. The growth of iron oxide nanoparticlessynthesized in BnOH follows the conventional model of LaMer involving nucleation steps and subsequent growth, while for the particles synthesized in TEG a sol-gel like formation process was noted. The manganese-zinc ferrites display additionally growth via oriented attachment, giving the
particles a unique shamrock-like shape.
Furthermore, the hydrophilic iron oxide nanoparticles synthesized in TEG were functionalized by coupling priorly reacted 3-glycidoxypropyltrimethoxysilane (GLYMO) and N ,N -bis (carb-oxymethyl)-L-lysine (NTA) to the surface of the particles for a direct mode magnetic separation of antibody fragments based on affinity interaction between small metal ions and a polyhistidine tag. This separation system showed good performance for the ex situ purification of the anti-body fragment (ABF) D1.3 scFV. The system was optimized with respect to product quantity and quality by modifying the concentration of added functionalization ligand. First results for the separation of protein A directly from the culture broth, the in situ separation, suggest that the developed magnetic separation system caneasily be implemented into the scale-up in situ separation of other biomolecules.