37 research outputs found
Magnetic Wire Traps and Programmable Manipulation of Biological Cells
We present a multiplex method, based on microscopic programmable magnetic traps in zigzag wires patterned on a platform, to simultaneously apply directed forces on multiple fluid-borne cells or biologically inert magnetic microparticles or nanoparticles. The gentle tunable forces do not produce damage and retain cell viability. The technique is demonstrated with T-lymphocyte cells remotely manipulated (by a joystick) along desired trajectories on a silicon surface with average speeds up to 20 μm/s
Photoinduced suppression of the ferroelectric instability in PbTe
The interactions between electrons and phonons drive a large array of
technologically relevant material properties including ferroelectricity,
thermoelectricity, and phase-change behaviour. In the case of many group IV-VI,
V, and related materials, these interactions are strong and the materials exist
near electronic and structural phase transitions. Their close proximity to
phase instability produces a fragile balance among the various properties. The
prototypical example is PbTe whose incipient ferroelectric behaviour has been
associated with large phonon anharmonicity and thermoelectricity. Experimental
measurements on PbTe reveal anomalous lattice dynamics, especially in the soft
transverse optical phonon branch. This has been interpreted in terms of both
giant anharmonicity and local symmetry breaking due to off-centering of the Pb
ions. The observed anomalies have prompted renewed theoretical and
computational interest, which has in turn revived focus on the extent that
electron-phonon interactions drive lattice instabilities in PbTe and related
materials. Here, we use Fourier-transform inelastic x-ray scattering (FT-IXS)
to show that photo-injection of free carriers stabilizes the paraelectric
state. With support from constrained density functional theory (CDFT)
calculations, we find that photoexcitation weakens the long-range forces along
the cubic direction tied to resonant bonding and incipient ferroelectricity.
This demonstrates the importance of electronic states near the band edges in
determining the equilibrium structure.Comment: 9 page, 3 figure
Beyond a phenomenological description of magnetostriction
We use ultrafast x-ray and electron diffraction to disentangle spin-lattice
coupling of granular FePt in the time domain. The reduced dimensionality of
single-crystalline FePt nanoparticles leads to strong coupling of magnetic
order and a highly anisotropic three-dimensional lattice motion characterized
by a- and b-axis expansion and c-axis contraction. The resulting increase of
the FePt lattice tetragonality, the key quantity determining the energy barrier
between opposite FePt magnetization orientations, persists for tens of
picoseconds. These results suggest a novel approach to laser-assisted magnetic
switching in future data storage applications.Comment: 12 pages, 4 figure
Skewed brownian fluctuations in single-molecule magnetic tweezers.
Measurements in magnetic tweezers rely upon precise determination of the position of a magnetic microsphere. Fluctuations in the position due to Brownian motion allows calculation of the applied force, enabling deduction of the force-extension response function for a single DNA molecule that is attached to the microsphere. The standard approach relies upon using the mean of position fluctuations, which is valid when the microsphere axial position fluctuations obey a normal distribution. However, here we demonstrate that nearby surfaces and the non-linear elasticity of DNA can skew the distribution. Through experiment and simulations, we show that such a skewing leads to inaccurate position measurements which significantly affect the extracted DNA extension and mechanical properties, leading to up to two-fold errors in measured DNA persistence length. We develop a simple, robust and easily implemented method to correct for such mismeasurements.BN/BionanoscienceApplied Science
Magnetic Forces and DNA Mechanics in Multiplexed Magnetic Tweezers
Magnetic tweezers (MT) are a powerful tool for the study of DNA-enzyme interactions. Both the magnet-based manipulation and the camera-based detection used in MT are well suited for multiplexed measurements. Here, we systematically address challenges related to scaling of multiplexed magnetic tweezers (MMT) towards high levels of parallelization where large numbers of molecules (say 103) are addressed in the same amount of time required by a single-molecule measurement. We apply offline analysis of recorded images and show that this approach provides a scalable solution for parallel tracking of the xyz-positions of many beads simultaneously. We employ a large field-of-view imaging system to address many DNA-bead tethers in parallel. We model the 3D magnetic field generated by the magnets and derive the magnetic force experienced by DNA-bead tethers across the large field of view from first principles. We furthermore experimentally demonstrate that a DNA-bead tether subject to a rotating magnetic field describes a bicircular, Limaçon rotation pattern and that an analysis of this pattern simultaneously yields information about the force angle and the position of attachment of the DNA on the bead. Finally, we apply MMT in the high-throughput investigation of the distribution of the induced magnetic moment, the position of attachment of DNA on the beads, and DNA flexibility. The methods described herein pave the way to kilo-molecule level magnetic tweezers experiments.BN/BionanoscienceApplied Science