Tom Byvank

On-chip magnetic separation and encapsulation of cells in droplets

Single cell study is gaining importance because of the cell-to-cell variation that exists within cell population, even after significant initial sorting. Analysis of such variation at the gene expression level could impact single cell functional genomics, cancer, stem-cell research, and drug screening. The on-chip monitoring of individual cells in an isolated environment would prevent cross-contamination, provide high recovery yield, and enable study of biological traits at a single cell level. These advantages of on-chip biological experiments is a significant improvement for a myriad of cell analyses methods, compared to conventional methods, which require bulk samples and provide only averaged information on cell structure and function. We report on a device that integrates a mobile magnetic trap array with microfluidic technology to provide the possibility of separation of immunomagnetically labeled cells and their encapsulation with reagents into picoliter droplets for single cell analysis. The simultaneous reagent delivery and compartmentalization of the cells immediately following sorting are all performed seamlessly within the same chip. These steps offer unique advantages such as the ability to capture cell traits as originated from its native environment, reduced chance of contamination, minimal use of the reagents, and tunable encapsulation characteristics independent of the input flow. Preliminary assay on cell viability demonstrates the potential for the device to be integrated with other up- or downstream on-chip modules to become a powerful single-cell analysis tool.

Magnetic Microstructures for Control of Brownian Motion and Microparticle Transport

A platform of microscopic magnetic wires and discrete bits of disks patterned on a surface offers dynamic control over the motion of fluid borne magnetic particles. The energy landscape associated with the local domain wall field originating from zigzag wire vertices is tuned by weak external fields to vary Brownian trajectories between strong confinements and delocalized spatial excursions. The corresponding spatial coverage of single particle trajectories allows the energy profile of such a magnetic trap to be mapped. Remote manipulation and guided transport of these objects across various opaque and transparent rigid surfaces as well as flexible films supporting discrete magnetic disks is presented.

Two dimensional triangulation of breakdown in a high voltage coaxial gap.

We describe a technique by which magnetic field probes are used to triangulate the exact position of breakdown in a high voltage coaxial vacuum gap. An array of three probes is placed near the plane of the gap with each probe at 90° intervals around the outer (anode) electrode. These probes measure the azimuthal component of the magnetic field and are all at the same radial distance from the cylindrical axis. Using the peak magnetic field values measured by each probe, the current carried by the breakdown channel, and Ampères law we can calculate the distance away from each probe that the breakdown occurred. These calculated distances are then used to draw three circles each centered at the centers of the corresponding magnetic probes. The common intersection of these three circles then gives the predicted azimuthal location of the center of the breakdown channel. Test results first gathered on the coaxial gap breakdown device (240 A, 25 kV, 150 ns) at the University of California San Diego and then on COBRA (1 MA, 1 MV, 100 ns) at Cornell University indicate that this technique is relatively accurate and scales between these two devices.

Programmable Self-Assembly, Disassembly, Transport, and Reconstruction of Ordered Planar Magnetic Micro-Constructs

We present a method to seamlessly self-assemble, disassemble, transport, and reconstruct ordered 2-D structures of fluid-borne microspheres on a surface using an array of magnetic zigzag wire traps. Competition between and control over: 1) the trapping forces of underlying magnetic patterns; 2) magnetic dipole repulsion; and 3) Brownian motion gives rise to reproducible cluster structures. Weak external magnetic fields (<;175 Oe) tune the spacing between particles and enable the assembled structures to be remotely manipulated and reassembled on the platform. This method could be used in biological and photonic applications by utilizing the microspheres, for example, as carriers of host biomolecules or as linkers to fluorescent emitters.

Plasma jets subject to adjustable current polarities and external magnetic fields

In the present research, collimated plasma jets form from ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform axial magnetic field (1 T) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foils central axis. Experimental results are compared with numerical simulations (PERSEUS). The influence of the Hall effect on the jet development is observed under opposite current polarities. Additionally, the magnetic field compression within the jet is examined. Further studies will compare the laboratory-generated plasma jets and astrophysical jets with embedded magnetic fields.