Analytical methods for separating and isolating magnetic nanoparticles

Abstract

Despite the large body of literature describing the synthesis of magnetic nanoparticles, few analytical tools are commonly used for their purification and analysis. Due to their unique physical and chemical properties, magnetic nanoparticles are appealing candidates for biomedical applications and analytical separations. Yet in the absence of methods for assessing and assuring their purity, the ultimate use of magnetic particles and heterostructures is likely to be limited. In this review, we summarize the separation techniques that have been initially used for this purpose. For magnetic nanoparticles, it is the use of an applied magnetic flux or field gradient that enables separations. Flow based techniques are combined with applied magnetic fields to give methods such as magnetic field flow fractionation and high gradient magnetic separation. Additional techniques have been explored for manipulating particles in microfluidic channels and in mesoporous membranes. Further development of these and new analytical tools for separation and analysis of colloidal particles is critically important to enable the practical use of these, particularly for medicinal purposes.

Size-isolation of superparamagnetic iron oxide nanoparticles improves MRI, MPI and hyperthermia performance

“…Despite the large number of previous publications describing the synthesis of iron oxide nanoparticles, the tools and technologies for their size separation are relatively limited. Techniques employed to control average particle size and polydispersity can be based on the use of magnetic/electric fields, porous media, and mass-and density-based purification [12][13][14]. Fortin and colleagues for instance synthesized citrate-coated nanocrystals of maghemite and cobalt ferrite by alkaline co-precipitation, and size-sorted the nanoparticles by successive electrostatic phase separation [15].…”

Zeptomole detection of DNA nanoparticles by single-molecule fluorescence with magnetic field-directed localization

“…The DNA-NP complexes, isolated by magnetic retrieval from the previous incubation, were pipetted into the magnetized flow chamber. A magnetic field was applied orthogonal to the flow direction, with the expectation that the magnetic moments of the nanoparticles would become aligned with the field (37, 38), causing the nanoparticles to move in solution toward the microscope slide where they could be retained by formation of a stable complex between the conjugated streptavidin and biotin immobilized on the slide surface (see Fig. 1).…”

Inverted Linear Halbach Array for Separation of Magnetic Nanoparticles

“…In these applications, features such as device efficiency and resolution depend critically on uniformity in not only the nanoparticle size but also the nanoparticle magnetic properties such as magnetization and coercivity. Unfortunately, comparatively few purification methods have been developed to sort nanoscale materials on the basis of such features [3]. …”

“…Many of the recent efforts to achieve magnetic nanoparticle separation stem from existing approaches for larger particles such as magnetic field-flow fractionation (MgFFF) [3],[4] and high gradient magnetic separation (HGMS) [5],[ 6]. In the modified methods, a variable field electromagnet preferentially retains larger, more magnetic nanoparticles, while smaller, less magnetic ones flow unimpeded.…”

“…In the modified methods, a variable field electromagnet preferentially retains larger, more magnetic nanoparticles, while smaller, less magnetic ones flow unimpeded. While these and other approaches [3] have yielded promising results, challenges remain in terms of getting higher throughput and characterizing better the separation process given the particle interaction issues.…”