Christopher M. Earhart

Functionalization of high-moment magnetic nanodisks for cell manipulation and separation

AbstractSynthetic antiferromagnetic (SAF) nanoparticles are layer-structured particles with high single-particle magnetic moments. In order to covalently bind these nanoparticles to cells, they were coated with a silica shell followed by conjugation with streptavidin. The silica coating generates both SAF@SiO2 core-shell nanoparticles and silica core-free nanoparticles. Using a simple magnetic separation, silica nanoparticles were removed and SAF@SiO2 nanoparticles were purified. After streptavidin conjugation, these particles were used to stain lung cancer cells, making them highly magnetically responsive. The stained cells can rotate in response to an external magnetic field and can be captured when a blood sample containing these cells flows through the sifter.

Designs for a Microfabricated Magnetic Sifter

A microfabricated magnetic sifter has been designed and fabricated for applications in biological sample preparation. The device enables high-throughput, high-gradient magnetic separation of magnetic nanoparticles by utilizing parallel fluid flow through a dense array (~500 /mm2 ) of micropatterned slots in a magnetically soft membrane. Finite element models have been carried out to map the magnetic field and magnetic field gradients of two variations of slot geometry resulting in two distinct capture behaviors. Experimental separations have been conducted using 20 nm diameter iron oxide nanoparticles with streptavidin functionalized surfaces. Inspection of the sifter with a scanning electron microscope revealed dense aggregates of nanoparticles captured at the regions of high magnetic field gradients calculated by the finite element models. Capture efficiencies ranging from 88.8%-100% were measured for a single pass through the sifter, and elution efficiencies ranging from 50%-70.5% were measured for a single elution step.

Synthetic antiferromagnetic nanoparticles with tunable susceptibilities

High-moment monodisperse disk-shaped Co-Fe magnetic nanoparticles, stable in aqueous solution, were physically fabricated by using nanoimprinted templates and vacuum deposition techniques. These multilayer synthetic antiferromagnetic nanoparticles exhibit nearly zero magnetic remanence and coercivity, and susceptibilities which can be tuned by exploiting interlayer magnetic interactions. In addition, a low cost method of scaling up the production of sub-100 nm synthetic antiferromagnetic nanoparticles is demonstrated.

Structural and magnetic characterizations of high moment synthetic antiferromagnetic nanoparticles fabricated using self-assembled stamps

High-moment synthetic antiferromagnetic (SAF) nanoparticles were produced using 4 in. diameter stamps made by self-assembly and nanosphere lithography of latex nanospheres. This leads to a significant increase in particle yield over a pre-existing technique which utilizes a 1 cm(2) stamp patterned using e-beam lithography. Changes in nanopillar dimensions from the self-assembled stamps and variations in the associated processing conditions can lead to the fabrication of particles with different dimensions. We demonstrate that it is possible to produce reasonably uniformly sized SAFs with diameters from 70 nm upward using self-assembled stamps. The particles exhibit low remanence at low externally applied magnetic fields, and that the saturation magnetization more than double that for conventional iron oxide nanoparticles.

Effect of Magnetic Field Gradient on Effectiveness of the Magnetic Sifter for Cell Purification

In our experiments with NCI-H1650 lung cancer cell lines labeled with magnetic nanoparticles via the Epithelial Cell Adhesion Molecule (EpCAM) antigen, we demonstrate capture efficiencies above 90% even at sample flow rates of 5 ml/h through our microfabricated magnetic sifter. We also improve the elution efficiencies from between 50% and 60% to close to 90% via optimization of the permanent magnet size and position used to magnetize the sifter. We then explain our observations via the use of finite element software for magnetic field and field gradient distributions, and a particle tracing algorithm, illustrating the impact of magnetic field gradients on the performance of the magnetic sifter. The high capture and elution efficiencies observed here is especially significant for magnetic separation of biologically interesting but rare moieties such as cancer stem cells for downstream analysis.

Silane-based functionalization of synthetic antiferromagnetic nanoparticles for biomedical applications

Synthetic antiferromagnetic nanoparticles (SAFNPs) have been successfully coated with two different kinds of silanes, 3-aminopropyltrimethoxysilane and 2-[methoxy(polyethyleneoxy)propyl]trimethoxysilane. The morphology of SAF particles is characterized by scanning electron microscopy and magnetic properties by alternating gradient magnetometry. The attachment of silane molecules is verified by Fourier-transform infrared spectroscopy and colloidal stability is studied using dynamic light scattering. These two silanes change the surface chemical properties of SAFNPs dramatically in different ways, which in turn affects the stability of these particles.