G. Vieira

Manipulation of Magnetically Labeled and Unlabeled Cells with Mobile Magnetic Traps

A platform of discrete microscopic magnetic elements patterned on a surface offers dynamic control over the motion of fluid-borne cells by reprogramming the magnetization within the magnetic bits. T-lymphocyte cells tethered to magnetic microspheres and untethered leukemia cells are remotely manipulated and guided along desired trajectories on a silicon surface by directed forces with average speeds up to 20 microm/s. In addition to navigating cells, the microspheres can be operated from a distance to push biological and inert entities and act as local probes in fluidic environments.

Patterned magnetic traps for magnetophoretic assembly and actuation of microrotor pumps

We demonstrate a microscopic magnetic rotor pump for fluidic channels whose components are assembled in situ and powered by weak external magnetic fields (<150 Oe). A platform of patterned Permalloy microdisks and microcavities provided for the transport, trapping, and rotation of the superparamagnetic spherical microrotors. Parallel actuation of several rotors without direct physical link to external energy sources, tunable rotation speeds, and reversible drive torques offers significant advantages over macroscopic techniques to control flow within microfluidic devices. The effectiveness of trapping and transporting magnetic nanoparticles by the disks illustrate scalability to smaller, submicrometer sized devices.

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.

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.

Deterministic and Stochastic Trajectories of Magnetic Particles: Mapping Energy Landscapes for Technology And Biology

Technologies that control matter at the nano- and micro-scale are crucial to realizing engineered systems that can assemble, transport, and manipulate materials at submicron length scales. Two principles: (1) the domain wall structure of patterned magnetic structures and (2) the superparamagnetic properties of nanoparticles, have been previously used to remotely manipulate and transport magnetic entities to specific sites on a platform. In this paper, changes to the energy landscape during transport as well as the local energy profile of individual stationary traps, both of which are central to the functionality of the platform, are evaluated using directed forces and stochastic (Brownian) trajectories of trap-confined microparticles. Hybrid magnetic-fluorescent micelle nanoconstructs, which are compatible with physiological conditions and safeguard functionality of biomaterials, are shown to be viable markers to label and manipulate individual cells across the platform.