Arjan P. Quist

DEFECT FORMATION ON SURFACES BOMBARDED BY ENERGETIC MULTIPLY CHARGED PROTEINS : IMPLICATIONS FOR THE CONFORMATION OF GAS-PHASE ELECTROSPRAYED IONS

Indirect information on the conformation of highly charged molecular ions may be obtained by monitoring their collisional cross sections and the course of simple gas-phase reactions such as hydrogen-deuterium exchange. In this work, another indirect but more visually oriented approach is explored: electrosprayed protein ions are accelerated toward a highly oriented pyrolytic graphite surface and the resulting single-ion defects are imaged by scanning force and tunneling microscopy. All protein impacts generated shallow hillocks: the shapes depended on the identity and charge state of the incident protein. Lysozyme and myoglobin, both compact, globular proteins in the native state, produced compact, almost circular hillocks. However, hillocks generated by myoglobin that had been denatured in the solution phase were elongated, and the elongation was positively correlated with the charge state of the ion. It appears that structural information about gas-phase multiply charged proteins can be derived from imprints generated by energetic protein impacts on surfaces.

A scanning force microscopy study of human serum albumin and porcine pancreas trypsin adsorption on mica surfaces

Abstract Scanning force microscopy is more and more expanding as a tool for biological research. Here we report about the observation of molecular adsorption on mica surfaces. Human serum albumin and porcine pancreas trypsin were adsorbed on freshly cleaved mica from the solution phase. The new tapping mode (intermittent contact) scanning force microscopy technique was employed to image the molecules on the surface. We observed clusters of molecules and features which we interpret as single molecules adsorbed on the mica. For albumin, we could sometimes resolve structures corresponding to the three main domains of which albumin is composed. Analysis of lateral sizes and height, as well as scanning artefacts, are discussed. We observed the ability of the tapping mode to modify the distances between the respective domains in albumin and to split clusters into smaller parts.

Scanning force microscopy studies of surface defects induced by incident energetic macromolecular ions

Abstract Scanning force microscopy (SFM) has been employed to study morphological changes associated with single-ion-impacts on SiO2, highly oriented pyrolytic graphite (HOPG), and single-crystals of the amino acid L-valine. Massive biomolecular ions are generated using an electrospray ionization source and a quadrupole mass spectrometer. The target is biased for post-acceleration and resulting impact velocities are around 50 km/s. Impacts of molecular ions with masses between 5.7 kDa (bovine insulin) and 66.3 kDa (bovine albumin) are studied. Surfaces are probed with SFM operated in both the continuous contact (repulsive force) mode and an intermittent contact mode which eliminates damaging lateral forces during scanning. The use of different SFM modes allows an assessment to be made of the role of artefacts in the obtained images. Surface topological features due to individual ion impacts were identified and had the appearance of low hillocks on SiO2 and HOPG, and shallow craters on L-valine. Results of a study of defect size versus incident projectile molecular mass are presented for approximately constant impact velocity. Slow but energetic massive polyatomic ions are expected to create regions of high energy volume density leading to cratering. Hillock formation may reflect a premature end to the crater formation process due to rapid diffusion of deposited energy into the bulk.

Desorption of nanoclusters (2–40 nm) from nanodispersed metal and semiconductor layers by swift heavy ions

Abstract New experimental data on the desorption of nanoclusters (2–40 nm) from nanodispersed layers of metals (Ag, Pt, In, Bi) and semiconductors (Ge, UO2, PbS) by fission fragments (FF) are reported and compared to the previously obtained data on desorption of nanoclusters of gold. It is shown that the desorption of nanoclusters from nanodispersed layers of metals and semiconductors due to electronic processes induced by swift heavy ions is a universal phenomenon. The yield of the desorbed nanoclusters depends on the cluster material and cluster size as well as on the material of the target substrate and varies within the range from ∼5 to ∼0.001 FF−1. The angular distributions of the nanoclusters do not depend on the cluster material, but only on the cluster size: the mean polar angle of desorption decreasing from 45° to 23° while cluster size increasing from 2 to 40 nm. The majority of the nanoclusters is desorbed in the form of molten, liquid droplets. The results are discussed.

Micropatterned surfaces: techniques and applications in cell biology.

Importance of the field: Engineering of cell culture substrates provides a unique opportunity for precise control of the cellular microenvironment with both spatial as well as temporal resolutions. This greatly enhances studies of cell–cell, cell–matrix and cell–factor interaction studies in vitro. Areas covered in this review: The technologies used for micropatterning in the biological field over the last decade and new applications in the last few years for dynamic control of surfaces, tissue engineering, drug discovery, cell–cell interactions and stem cell studies are presented. What the reader will gain: The reader will gain knowledge on the state of the art in micropatterning and its wide ranging applications in cell patterning, with new pathways to control the cell environment. Take home message: Micropatterning of cells has been studied and developed enough to be widely applied ranging from single cell assays to tissue engineering. Techniques have evolved from many-step processes to direct writing of biologically selective patterns.

Impacts of polyatomic ions on surfaces: conformation and degree of fragmentation of molecular ions determined by lateral dimensions of impact features

Abstract Massive, multiply-charged molecular ions produced by an electrospray ionization source are accelerated and directed onto flat target surfaces. Scanning force microscope (SFM) techniques are employed to examine the giant defects that are produced by individual incident ions. These defects appear as oblong hillocks, the widths of which indicate a typical distance over which the deposited energy density reaches a high enough level to permanently disrupt the surface structure. When the lengths of these hillocks exceed the widths, then the lengths yield qualitative information about the conformation of the incident molecular ions. Conversely, observation of low, small circular hillocks constitutes evidence for extensive fragmentation. Here, it is demonstrated in a simple visual fashion that electrosprayed poly(ethylene glycol) is easily fragmented by collisions with residual gas, and that electrosprayed native albumin molecules are partly denatured in the gas phase. Electrosprayed denatured albumin molecules appear in an extended, narrow configuration much longer than typical dimensions of the native molecule. Coulomb forces no doubt play a role in determining the structure of the gas-phase ions. These experimental results provide the first direct view of the conformation of electrosprayed molecules.

KEV-POLYATOMIC-ION-IMPACT-NUCLEATED OXIDATIVE ETCH PITTING IN HIGHLY ORIENTED PYROLYTIC-GRAPHITE

The tendency of freshly cleaved highly oriented pyrolytic graphite (HOPG) to form nanometer-sized circular pits during high temperature oxidative etching is an example of a controllable, nanoscale tailoring of a surface with a number of potential applications. Here we explore the possibility of modulating the number density, shapes, and dimensions of such etch pits by deliberately nucleating defects at or near the surface by bombardment with kiloelectronvolt polyatomic projectiles. We observed that bombardment of HOPG by 176 keV apomyoglobin ions resulted in the nucleation of a large population of deep hexagonal etch pits upon baking. The depths of the pits also give new information on the depth to which a material is damaged by impinging energetic polyatomic projectiles.