Research - Daniel H. Reich
Some of my current research interests include:
Biological Applications of Magnetic Nanoparticles
Magnetic Nanoparticle Probes of Complex Fluids
Quantum Magnetism in Low-Dimensional Systems
In addition to the information on this page, further details can be found at the website of the JHU Materials Research Science and Engineering Center (MRSEC).
Biological Applications of Magnetic Nanoparticles
The integration of biology and the physical sciences at the nanoscale has the potential to revolutionize many areas of science and technology. The nanometer size scale is a crucial one in biology, as the dimensions of large biomolecules such as proteins and DNA, as well as those of many important sub-cellular structures, fall in this range. Recent advances in materials research have made it possible to engineer materials on these same nanometer lengthscales, and thus it is now possible to begin to design devices and artificial structures that can interact with cells and biomolecules in fundamentally new ways.
One area that is particularly promising is the use of nano-engineered magnetic particles to manipulate and study biological systems. Such particles can be selectively attached to specific types of cells, and these cells can then be moved with magnets. This allows one to, for example, separate diseased or cancerous cells from healthy cells. We are developing a novel type of magnetic nanowire as new tools for cellular manipulation. Due to their unique magnetic properties, the forces exerted by these wires on cells can be up to 1000 times larger than those generated by the particles currently in use. Indeed, we have shown that the nanowires have superior performance for certain types of cell separation processes. We are currently using magnetic interactions between the nanowires to engineer specific assemblies of cells, and to precisely position single cells on microchips. Ultimately, these novel magnetic nanowires have the potential to expand greatly the use of magnetic nanoparticles in research, and in applications such as biosensing, diagnostics, and therapeutics.
Recent publications:
A. Hultgren, M. Tanase, E. J. Felton, K. Bhadriraju, A. K. Salem, C. S. Chen, and D. H. Reich, "Optimization of Yield in Magnetic Cell Separations Using Magnetic Nanowires of Different Lengths," Biotech. Prog. 21, 509-515 (2005)
M. Tanase, E. J. Felton, D. S. Gray, A. Hultgren, C. S. Chen, and D. H. Reich, "Assembly of multicellular constructs and microarrays of cells using magnetic nanowires," Lab on a Chip 5, 569-696 (2005)
Cover feature from June, 2005 Lab on a Chip. Assembly of multicellular constructs and microarrays of cells using magnetic nanowires. Upper: two 3T3 cells bound to magnetic nanowires, magnetically trapped at the poles of an 80 micron-long ellipsoidal thin-film magnet. Lower: energy of nanowire in field of ellipsoidal micromagnet, showing attractive (red) and repulsive (blue) regions. Background: Stripes of 3T3 cells magnetically trapped on a micromagnet array.
Magnetic Nanoparticle Probes of Complex Fluids
Fluids composed of complex molecules can display a variety of surprising and unusual properties that are never seen in ordinary fluids like water. We are using novel magnetic nanoparticles to probe the local dynamics and microrheology of complex fluids. One example is nematic liquid crystals where we have used magnetic nanowires to measure the elasticly mediated forces the anisotropic nature of these materials imposes on suspended aspherical particles. We have measured the orientation-dependent elastic energy and have shown that it agrees quantitatively with long-standing theoretical predictions. We have also shown that in a spatially non-uniform liquid crystal, these forces can be manipulated to move the nanowires, and indeed to levitate them against the force of gravity.
C. Lapointe, A. Hultgren, D. M. Silevitch, E. J. Felton, D. H. Reich, and R. L. Leheny, "Elastic Torque and the Levitation of Metal Wires by a Nematic Liquid Crystal," Science 303, 652 (2004).
C. Lapointe, N. Cappallo, D. H. Reich, and R. L. Leheny, "Static and dynamic properties of magnetic nanowires in nematic fluids (invited)," J. Appl. Phys. 97, 10Q304-1-10Q304-6 (2005).
Levitation of a nickel wire within a twisted nematic liquid crystal (LC). A: The LC orientation (green), twists uniformly as a function of height to match the directions of planar anchoring at the upper and lower surfaces. When a magnetic field aligns a nanowire parallel to LC at some height in the cell (e.g., at the center of the cell in the figure), the elastic energy becomes a function of the wire's height, leading to a levitating force on a wire resting on the bottom substrate. B: Measurements demonstrate the height of a wire initially resting at the bottom rises as a function of time in response to this force.
More information on Magnetic nanoparticles in liquid crystals
Quantum Magnetism in Low-Dimensional Systems
Insulating magnetic systems are very clean systems in which to study fundamental questions in condensed matter physics. They generally have well-characterized microscopic interactions described by the Heisenberg model of localized, interacting spins on a lattice, and yet display a full panoply of complex many-body phenomena. In antiferromagnets with small spin (generally S=1/2 or S=1), anisotropies in the spin-spin coupling that render the system effectively one- or two-dimensional by decoupling it into an array of chains or layers, can enhance the destabilization of long-range order by quantum fluctuations, and lead to a variety of novel and unusual behaviors.
My research focuses on experimental studies of low-dimensional metallo-organic materials. These generally have spin-spin interaction energies of approximately 1 meV (J/K_B ~10 K), and so by applying magnetic fields H ~10 T, it is possible to introduce Zeeman energies into the system that are large compared to J. In many cases this enables one to radically change the nature of the ground state of the system, and for example, to probe a variety of quantum critical phenomena.
In one recent example, we have studied the magnetic field dependence of spin excitations in the S=1/2 linear chain antiferromagnet copper pyrazine nitrate (CuPzN). The S=1/2 antiferromagnetic spin chain is one of the most important model systems in many-body physics, displaying Luttinger liquid and quantum critical behavior. In a magnetic field it remains critical along a line in parameter space, a highly unusual situation for quantum critical systems. We have used inelastic neutron scattering to map out the full spectrum in the partially magnetized quantum critical state of CuPzN, and show for the first time several long-sought features of this state. [Phys. Rev. Lett. 91, 037205 (2003)]
Through measurements on other spin-1/2 chain systems, we have shown that in the presence of a staggered magnetic field, the excitations of the spin-1/2 chain coalesce into sharply defined bound states, and their spectrum acquires a gap, in quantitative agreement with predictions for novel excitations known as solitons and breathers, that are solutions of the quantum sine-Gordon field theory [ Phys. Rev. Lett. 93, 017204 (2004); Phys. Rev. B 71, 094411 (2005)].