Maximally efficient exchange in thin flow cells using density gradients.

Flow cells are ubiquitous in laboratories and automated instrumentation, and are crucial for ease of sample preparation, analyte addition and buffer exchange. The assumption that the fluids have exchanged completely in a flow cell is often critical to data interpretation. This article describes the buoyancy effects on the exchange of fluids with differing densities or viscosities in thin, circular flow cells.

Accurate background correction in neutron reflectometry studies of soft condensed matter films in contact with fluid reservoirs.

Neutron reflectometry (NR) is a powerful method for looking at the structures of multilayered thin films, including biomolecules on surfaces, particularly proteins at lipid interfaces. The spatial resolution of the film structure obtained through an NR experiment is limited by the maximum wavevector transfer at which the reflectivity can be measured. This maximum is in turn determined primarily by the scattering background, from incoherent scattering from a liquid reservoir or inelastic scattering from cell materials.

Nuclear Spin Incoherent Neutron Scattering from Quantum Well Resonators.

We report the detection and quantification of nuclear spin incoherent scattering from hydrogen occupying interstitial sites in a thin film of vanadium. The neutron wave field is enhanced in a quantum resonator with magnetically switchable boundaries. Our results provide a pathway for the study of dynamics at surfaces and in ultrathin films using inelastic and/or quasielastic neutron scattering methods.

Optimization of reflectometry experiments using information theory.

A framework based on Bayesian statistics and information theory is developed to optimize the design of surface-sensitive reflectometry experiments. The method applies to model-based reflectivity data analysis, uses simulated reflectivity data and is capable of optimizing experiments that probe a sample under more than one condition. After presentation of the underlying theory and its implementation, the framework is applied to exemplary test problems for which the information gain Δ is determined.

Phase-sensitive small-angle neutron scattering experiment.

In the work reported herein, we investigate the practicality of a recently introduced variant of a general phase-sensitive method in small-angle neutron scattering that attempts to address the loss of phase-information as well as the orientational averaging simultaneously-through the use of reference structures in conjunction with finite element analysis. In particular, one possible physical realization of this approach is to employ polarized beams together with a magnetic reference connected to the sample object. We report on a first such practical implementation by successfully recovering the structure of a core-shell nanoparticle system.

Measurement and modeling of polarized specular neutron reflectivity in large magnetic fields.

The presence of a large applied magnetic field removes the degeneracy of the vacuum energy states for spin-up and spin-down neutrons. For polarized neutron reflectometry, this must be included in the reference potential energy of the Schrödinger equation that is used to calculate the expected scattering from a magnetic layered structure. For samples with magnetization that is purely parallel or antiparallel to the applied field which defines the quantization axis, there is no mixing of the spin states (no spin-flip scattering) and so this additional potential is constant throughout the scattering region.

Surface segregation driven by molecular architecture asymmetry in polymer blends.

The contributions of chain ends and branch points to surface segregation of long-branched chains in blends with linear chains have been studied using neutron reflectometry and surface-enhanced Raman spectroscopy for a series of novel, well-defined polystyrenes. A linear response theory accounting for the number and type of branch points and chain ends is consistent with surface excesses and composition profile decay lengths, and allows the first determination of branch point potentials. Surface excess is determined primarily by chain ends with branch points playing a secondary role.

Neutron reflectometry studies of the adsorbed structure of the amelogenin, LRAP.

Amelogenins make up over 90% of the protein present during enamel formation and have been demonstrated to be critical in proper enamel development, but the mechanism governing this control is not well understood. Leucine-rich amelogenin peptide (LRAP) is a 59-residue splice variant of amelogenin and contains the charged regions from the full protein thought to control crystal regulation. In this work, we utilized neutron reflectivity (NR) to investigate the structure and orientation of LRAP adsorbed from solutions onto molecularly smooth COOH-terminated self-assembled monolayer (SAM) surfaces.

Hydrogen distribution in Nb/Ta superlattices.

The distribution of hydrogen in Nb/Ta superlattices has been investigated by combined neutron reflectivity and x-ray scattering. We provide evidence to support that strain modulations determined with x-ray diffraction can be interpreted as modulations in hydrogen content. We show that the hydrogen concentration is modulated and favors Nb, in agreement with previous studies.

Halothane changes the domain structure of a binary lipid membrane.

X-ray and neutron diffraction studies of a binary lipid membrane demonstrate that halothane at physiological concentrations produces a pronounced redistribution of lipids between domains of different lipid types identified by different lamellar d-spacings and isotope composition. In contrast, dichlorohexafluorocyclobutane (F6), a halogenated nonanesthetic, does not produce such significant effects. These findings demonstrate a specific effect of inhalational anesthetics on mixing phase equilibria of a lipid mixture.

Neutron reflectivity study of substrate surface chemistry effects on supported phospholipid bilayer formation on (11 ̅20) sapphire.

Oxide-supported phospholipid bilayers (SPBs) used as biomimetic membranes are significant for a broad range of applications including improvement of biomedical devices and biosensors, and in understanding biomineralization processes and the possible role of mineral surfaces in the evolution of pre-biotic membranes. Continuous-coverage and/or stacked SPBs retain properties (e.g.

The structural orientation of antibody layers bound to engineered biosensor surfaces.

This paper describes a membrane protein array that binds immunoglobulin G at its constant regions whilst leaving the variable regions free to bind antigen. The scaffold of the array is the transmembrane domain of outer membrane protein A (tOmpA) from Escherichia coli engineered to assemble as an oriented monolayer on gold surfaces via a single cysteine residue. Other protein domains can be fused to the N and C termini of the scaffold.

An ion-channel-containing model membrane: structural determination by magnetic contrast neutron reflectometry.

To many biophysical characterisation techniques, biological membranes appear as two-dimensional structures with details of their third dimension hidden within a 5 nm profile. Probing this structure requires methods able to discriminate multiple layers a few Ångströms thick. Given sufficient resolution, neutron methods can provide the required discrimination between different biochemical components, especially when selective deuteration is employed.

Monitoring the assembly of antibody-binding membrane protein arrays using polarised neutron reflection.

Protein arrays are used in a wide range of applications. The array described here binds IgG antibodies, produced in rabbit, to gold surfaces via a scaffold protein. The scaffold protein is a fusion of the monomeric E.

AND/R: Advanced neutron diffractometer/reflectometer for investigation of thin films and multilayers for the life sciences.

An elastic neutron scattering instrument, the advanced neutron diffractometer/reflectometer (AND/R), has recently been commissioned at the National Institute of Standards and Technology Center for Neutron Research. The AND/R is the centerpiece of the Cold Neutrons for Biology and Technology partnership, which is dedicated to the structural characterization of thin films and multilayers of biological interest. The instrument is capable of measuring both specular and nonspecular reflectivity, as well as crystalline or semicrystalline diffraction at wave-vector transfers up to approximately 2.