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Biomedical subjects

Richard E Palmer

Publications and source records attributed to Richard E Palmer.

11 recordsLinked to original sources
PubMed2006

Immobilisation of proteins by atomic clusters on surfaces.

In this Opinion article, we describe a nanotechnology-based approach to immobilize and orient proteins onto surfaces using atomic clusters prepared by physical methods. This is relevant to future protein biochips where dilute arrays of protein binding sites, each designed to immobilize no more than one protein molecule, would be ideal. In the case of a surface consisting of size-selected atomic gold clusters, proteins containing free cysteine residues can chemisorb directly to the bare cluster surface, thus effecting oriented immobilisation. The selection of atomic gold clusters in the size range 1-100 atoms (<3nm in diameter) is intended to ensure that, typically, only one protein can bind directly to the cluster surface. These nanoclusters of a smaller size scale than that of the protein present minimal contact between the gold and the protein, and hence imply a reduced risk of protein denaturing compared with gold films or extended surfaces.

Binding Sites↗
PubMed2006

Sintering of passivated gold nanoparticles under the electron beam.

Time-lapse studies of a film of passivated gold nanoparticles under electron beam irradiation have been performed using a transmission electron microscope, revealing the microscopic dynamics of the sintering process at the single nanoparticle level. It is found that the sintering of individual passivated gold nanoparticles under electron irradiation is local and mainly depends on the sensitivity of the passivating ligands to the electron beam. A multilayer film is less stable than monolayer film, consistent with the enhanced generation of secondary electrons. The observations also reveal a significant difference between the sintering of passivated nanoparticles and bare metal particles, especially regarding the size effect on the sintering rate. The formation of a neck between adjacent nanoparticles further indicates a mechanism driven by surface diffusion rather than Ostwald ripening at the initial sintering stage.

Journal Article↗
PubMed2005

Residue-specific immobilization of protein molecules by size-selected clusters.

The atomic force microscope (AFM), operating in contact mode, has been employed in buffer solution to study two proteins; (i) green fluorescent protein (GFP), from the hydromedusan jellyfish Aequorea victoria; and (ii) human oncostatin M (OSM), in the presence of size-selected gold nanoclusters pinned on to a highly oriented pyrolytic graphite substrate. The AFM images have revealed immobilization of single molecules of OSM, which are strongly bound to the gold nanoclusters. Conversely, no strong immobilization has been observed for the GFP, as these molecules were easily displaced by the scanning tip. The contrasting behaviour of the two proteins can be explained by the exposed molecular surface area of their cysteine residues as modelled on the basis of their respective X-ray crystallographic data structures. GFP contains two cysteine residues, but neither is readily available to chemisorb on the gold clusters, because the cysteines are largely inaccessible from the surface of the protein. In contrast, OSM has a total of five cysteine residues, with different degrees of accessibility, which make the protein amenable to anchoring on the nanoclusters. Statistical analysis of the height of the OSM molecules bound to the nanoclusters is in accordance with crystallographic data, and suggests various configurations of the proteins on the clusters, associated with the presence of different cysteine anchoring sites. These results suggest that the three-dimensional conformation of protein molecules is preserved when they are chemisorbed to size-selected gold clusters, thus opening a new route towards oriented immobilization of individual protein molecules.

Cytokines↗
PubMed2005

Nanoparticle arrays patterned by electron-beam writing: structure, composition, and electrical properties.

Direct electron beam writing in nanoparticle films is employed to create nanoscale wires between prepatterned gold electrodes on SiO(2)/Si wafers. Characterization of these nanowires using AFM, SEM, and EDX reveals a core/sheath morphology, where a gold-rich core is surrounded by a sheath which is mainly of carbon. Z-contrast STEM images indicate that the central core consists of a distribution of metal cores in a carbon network. The results suggest that the nanoparticle network is created through cross-linking of the ligands of adjacent particles. The high resistivities obtained in conductivity measurements are consistent with this picture. The work illustrates the ability to generate patterned nanoparticle arrays which can be addressed electrically.

Journal Article↗
PubMed2005

Tip-state control of rates and branching ratios in atomic manipulation.

We report the atomic manipulation properties of two distinct, stable, and reproducible states of a scanning tunneling microscope tip applied to chlorobenzene/Si(111)-(7x7). We show that the tip state influences the rates of (current-driven) molecular desorption and C-Cl dissociation as well as the branching ratio between these processes, but does not change the mediating electronic channel or the required number of electrons. These manipulation properties combined with the imaging properties of the two tip-states suggest the major difference between tip-states is their coupling efficiency to the pi-states of the chlorobenzene molecule.

Chlorobenzenes↗
PubMed2004

Gold nanoparticle patterning of silicon wafers using chemical e-beam lithography.

This paper demonstrates a novel facile method for fabrication of patterned arrays of gold nanoparticles on Si/SiO2 by combining electron beam lithography and self-assembly techniques. Our strategy is to use direct-write electron beam patterning to convert nitro functionality in self-assembled monolayers of 3-(4-nitrophenoxy)-propyltrimethoxysilane to amino functionality, forming chemically well-defined surface architectures on the 100 nm scale. These nanopatterns are employed to guide the assembly of citrate-passivated gold nanoparticles according to their different affinities for amino and nitro groups. This kind of nanoparticle assembly offers an attractive new option for nanoparticle patterning a silicon surface, as relevant, for example, to biosensors, electronics, and optical devices.

Journal Article↗
PubMed1991

Psychosocial factors in chronic spinal cord injury pain.

Chronic pain is a problem among patients with spinal cord injuries, but the psychosocial factors associated with spinal cord injury (SCI) pain are not well understood. To understand SCI pain further, 54 patients (19 with quadriplegia and 35 with paraplegia) completed the Beck Depression Inventory, State-Trait Anxiety Inventory, Profile of Mood States, Acceptance of Disability Scale and SCI Interference Scale. Forty-two patients stated they had SCI pain and completed the Multidimensional Pain Inventory and the Pain Experience Scale. Results revealed that anger and negative cognitions were associated with greater pain severity. Patients who reported pain in response to a general prompt experienced more severe pain than patients who reported pain only when directly questioned about the presence of pain, but these different reporting groups did not differ on emotional variables. Those who were less accepting of their disability reported greater pain severity. Additionally, patients who perceived a significant other expressing punishing responses (e.g., expressing anger at the patients or ignoring the patients) to their pain behaviors reported more severe pain. Level of lesion, completeness of injury, surgical fusion and/or instrumentation and veteran status were not associated with pain severity. Finally, pain was associated with emotional distress over and above the distress associated with the SCI itself. Overall, psychosocial factors, not physiological factors, were most closely associated with the experience of pain. Multidimensional aspects of pain are used to explain these findings and suggest that treatment should be directed at the emotional and cognitive sequelae of chronic SCI pain.

Adult↗