A microfabricated magnetic sifter and high throughput physical fabrication of magnetic nanoparticles for applications in protein and cell separation [electronic resource]
Keywords: Materials Science and Engineering

Nanoscience and nanotechnology have been applied in recent years to cancer research, with the goal of bringing about a revolutionary change in the ways in which cancer is diagnosed and treated. Magnetic nanotechnologies, in particular, have shown significant potential in several areas, such as imaging, therapeutics, early detection, and point-of-care therapy monitoring. Most applications of magnetic nanotechnology in cancer research involve the use of nanoscale magnetic carriers. Depending on the properties of the particular carrier and the manner in which they are employed, magnetic carriers can act as MRI contrast enhancing agents, drug delivery vehicles, bio-labels for detection with magnetic biosensors, or selection agents in immunomagnetic separation platforms. The small sizes (10-100 nm), functional surface chemistries, and controllable magnetic responses of nanoscale magnetic carriers allows for interaction with and control of biological entities in both novel and powerful ways. The focus of this thesis is on a specific application of magnetic carriers -- magnetic separation of biomolecules and rare cells. After an introduction and an overview of magnetic separation principles are given in Chapters 1 and 2, Chapters 3-6 discuss the design, fabrication, and use of a novel magnetic separation device, the magnetic sifter. The magnetic sifter is a microfabricated, 7 x 7 mm planar die containing a dense array of pores (~200-5000/mm^2) in a magnetically soft membrane. When magnetized by an external field, the sifter pores generate large magnetic field gradients (~10^6 T/m) near the pore edges, which can capture nanoscale magnetic carriers with high efficiency and throughput. The gradients can be turned off by removing the external field, and the magnetic carriers can be released. The magnetic sifter is a microfluidic device, in the sense that it contains microfabricated, micron-scale pores which generate large field gradients. It is also a macrofluidic device, in that high volume throughput is achieved by parallel flow through the dense array of pores. Magnetic modeling of the magnetic sifter and a method for its fabrication are presented in Chapters 3 and 4. When paired with magnetic carriers functionalized with recognition moieties, the magnetic sifter can be used in both protein and cell enrichment schemes. The focus of Chapter 5 is on using the magnetic sifter to capture individual magnetic nanoparticles. The intended application is for enrichment of cancer protein markers prior to detection with a magnetic spin-valve biosensor. High capture efficiencies (80-100%) of magnetic nanoparticles have been achieved for a single pass through the magnetic sifter. Magnetic nanoparticles can also be released from the magnetic sifter with nearly 100% efficiency. The focus of Chapter 6 is the use of the magnetic sifter for rare cell enrichment, for applications in enumeration and enrichment of circulating tumor cells. It is shown that the magnetic sifter can capture tumor cells from whole blood with high efficiency and throughput (~60% at 5 ml/hr). Furthermore, with its planar structure and presentation of captured cells, the magnetic sifter doubles as a cell imaging platform, allowing for identification and quantification with optical microscopy. In addition to its high capture efficiency and gentle release of captured cells, the small size and scalable fabrication of the magnetic sifter are attractive for applications in point-of-care cancer diagnostics for early detection and monitoring of metastatic disease. In Chapter 7, a method for high-throughput fabrication of novel magnetic carriers, synthetic antiferromagnetic (SAF) nanoparticles is presented. The method has enabled production of large quantities of SAF nanoparticles, which have desirable properties for applications in magnetic separation. The capture and release behavior of SAF nanoparticles with the magnetic sifter has been demonstrated. High capture efficiencies are achieved at flow rates 10-20x higher than what was previously possible with commercially available magnetic carriers. Both the magnetic sifter and physically fabricated SAF nanoparticles offer unique advantages over traditional technologies. They are each, in their own right, promising new technologies for applications in cancer detection and therapy monitoring.