Biomedical subjects

Mara Prentiss

Publications and source records attributed to Mara Prentiss.

6 recordsLinked to original sources

PubMed2005

Radial confinement of light in an ultracold anisotropic medium.

We demonstrate radial confinement and waveguiding of light in an ultracold anisotropic gas. The waveguiding medium is a laser cooled ensemble of rubidium atoms confined in a trap of large aspect ratio. A recoil induced resonance (RIR) is used to create strong dispersion and large gain in this ensemble. The combination of the anisotropic trap and the RIR give rise to a spatially varying group refractive index resulting in a slow-light optical waveguide. Waveguided pulses of light experience strong gain (approximately 50), low group velocities (c approximately 1500 m/s), and long group delays (delta approximately 7 micros) due to the enhanced path length.

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PubMed2005

Dissociation of ligand-receptor complexes using magnetic tweezers.

We present a new tool for measuring ligand-receptor complex bonds at the single-molecule level using magnetic tweezers. Our apparatus allows massively parallel (100-1000) measurements on many single complexes perturbed by constant forces. Compared to other single-molecule techniques, our method is simple, inexpensive, robust, and widely compatible with other techniques. We immobilized specific receptor molecules on the surface of superparamagnetic beads and corresponding ligand molecules on a fixed surface. The beads were allowed to contact the surface so that ligand-receptor binding occurred. A permanent magnet then generated a constant force that pulled the receptors away from the ligands. The rates at which bound species separated at various forces allowed us to characterize the potential energy landscape of the bond and extrapolate bulk solution kinetic rates and transition-state distances. These values agreed with those obtained using bulk and single-molecule methods.

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PubMed2005

Atom Michelson interferometer on a chip using a Bose-Einstein condensate.

An atom Michelson interferometer is implemented on an "atom chip." The chip uses lithographically patterned conductors and external magnetic fields to produce and guide a Bose-Einstein condensate. Splitting, reflecting, and recombining of condensate atoms are achieved by a standing-wave light field having a wave vector aligned along the atom waveguide. A differential phase shift between the two arms of the interferometer is introduced by either a magnetic-field gradient or with an initial condensate velocity. Interference contrast is still observable at 20% with an atom propagation time of 10 ms.

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PubMed2004

Dynamic control of liquid-core/liquid-cladding optical waveguides.

This report describes the manipulation of light in waveguides that comprise a liquid core and a liquid cladding (liq/liq waveguide). These waveguides are dynamic: Their structure and function depend on a continuous, laminar flow of the core and cladding liquids. Because they are dynamic, they can be reconfigured and adapted continuously in ways that are not possible with solid-state waveguides. The liquids are introduced into the channels of a microfluidic network designed to sandwich the flowing core liquid between flowing slabs of the cladding fluid. At low and moderate Reynolds numbers, flow is laminar, and the liq/liq interfaces are optically smooth. Small irregularities in the solid walls of the channels do not propagate into these interfaces, and liq/liq waveguides therefore exhibit low optical loss because of scattering. Manipulating the rate of flow and the composition of the liquids tunes the characteristics of these optical systems.

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PubMed2003

Asymmetric dimers can be formed by dewetting half-shells of gold deposited on the surfaces of spherical oxide colloids.

Asymmetric dimers consisting of gold microcrystals and spherical silica colloids have been fabricated by depositing thin films of gold onto the spherical colloids to form half-shells, followed by annealing at elevated temperatures. The capability and feasibility of this procedure have been demonstrated with silica and titania beads of 0.2-2 mum in diameter and gamma-Fe2O3/polystyrene@SiO2 core-shell particles 0.5 mum in size. The dimensions of gold microcrystals could be conveniently varied in the range of 100-650 nm by controlling the thickness of gold films and/or the diameter of the spherical colloids. This method provides another route to asymmetric dimers made of colloidal particles that could be different in size, chemical composition, surface functionality, density or sign of surface charge, bulk property, or a combination of these properties.

Journal Article↗

PubMed2003

DNA unzipped under a constant force exhibits multiple metastable intermediates.

Single molecule studies, at constant force, of the separation of double-stranded DNA into two separated single strands may provide information relevant to the dynamics of DNA replication. At constant applied force, theory predicts that the unzipped length as a function of time is characterized by jumps during which the strands separate rapidly, followed by long pauses where the number of separated base pairs remains constant. Here, we report previously uncharacterized observations of this striking behavior carried out on a number of identical single molecules simultaneously. When several single lambda phage molecules are subject to the same applied force, the pause positions are reproducible in each. This reproducibility shows that the positions and durations of the pauses in unzipping provide a sequence-dependent molecular fingerprint. For small forces, the DNA remains in a partially unzipped state for at least several hours. For larger forces, the separation is still characterized by jumps and pauses, but the double-stranded DNA will completely unzip in less than 30 min.

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