The Effect of pH and Viscosity on Magnetophoretic Separation of Iron Oxide Nanoparticles

Abstract

Magnetic nanoparticles (MNPs) are used for magnetophoresis-based separation processes in various biomedical and engineering applications. Essential requirements are the colloidal stability of the MNPs and the ability to be separated even in low magnetic field gradients. Bare iron oxide nanoparticles (BIONs) with a diameter of 9.2 nm are synthesized via coprecipitation, exhibiting a high saturation magnetization of 70.84 Am2 kg−1 and no remanence. In our study, zeta potential, dynamic light scattering (DLS), and sedimentation analysis show that the aggregation behavior of BIONs is influenced by pH and viscosity. Small aggregate clusters are formed with either low or high pH values or increased viscosity. Regarding magnetophoresis-based separation, a higher viscosity leads to lower magnetophoretic velocities, similar to how small aggregates do. Additionally, cooperative magnetophoresis, the joint motion of strongly interacting particles, affects the separation of the BIONs, too. Our study emphasizes the effect of pH and viscosity on the physicochemical characteristics of MNPs, resulting in different aggregation behavior. Particularly, for high viscous working media in downstream processing and medicine, respectively, the viscosity should be taken into account, as it will affect particle migration.

Hybrid Nanoparticles of Citrate-Coated Manganese Ferrite and Gold Nanorods in Magneto-Optical Imaging and Thermal Therapy

“…These results can confirm the interactions between Ci-MnFe 2 O 4 and CTAB-GNRs and the presence of larger hydrodynamic particle sizes. Our results agree with the study of Leonie Wittmann et al [ 61 ], who investigated the effect of MNP movement along a magnetic field gradient on hydrodynamic particle size and found that larger NPs had a quicker separation time.…”

Screening of superparamagnetic iron oxide nanoparticles for their application in the human body: Influence of various coatings

“…SAXS profiles showed aggregation and primary particle sizes around 20 nm for all particles investigated (Figure 3). The highest aggregation is visible for BIONs at pH 7, which is in excellent agreement with DLS data and data from previous studies [52,75]. Even though this aggregation of nanomaterials is visible and makes it challenging to interpret the SAXS data, these results help to verify XRD data as well as TEM studies (Figure 1, Figure 2).…”

“…The space-and time-resolved extinction profiles (STEP) technology was used to understand the particle's stability and magnetophoretic behavior at pH 7.4 (Figure 1B). The sedimentation rates in a magnetic field increase with higher agglomeration and higher saturation magnetization of the particles [75]. In comparable conditions, BIONs sank with a sedimentation velocity of 1.15 mm s -1 [52].…”

“…All particles had diameters < 350 nm, and all coatings led to a colloidal stabilization. It can be assumed that the effect comes mainly from the higher viscosity of around 1.44 mPa and the binding of plasma proteins [40,75,83]. Because no degradation takes place, the small hydrodynamic diameters of the coated IONs should ensure prolonged blood circulation times.…”

Carboxymethyl-Dextran-Coated Superparamagnetic Iron Oxide Nanoparticles for Drug Delivery: Influence of the Coating Thickness on the Particle Properties

“…The hydrodynamic diameters of the particles influence the magnetophoretic behavior in water to a greater extent than the magnetization ( Figure 5 e). Agglomeration increases the sedimentation velocity, therefore explaining the increasing sedimentation rate [ 76 ]. The BIONs sink the fastest in a magnetic field compared to the coated particles, with a sedimentation velocity of 1152 µm s −1 ( SI-Table S3 ).…”