Vacuum ultraviolet postionization of aromatic groups covalently bound to peptides

Experiments demonstrate that peptides with ionization potentials (IPs) above 7.87 eV can be single-photon-ionized in the gas phase with a molecular fluorine laser following prior chemical derivatization with one of several aromatic tags acting as chromophores. 4-(Dimethylamino)benzoic acid, 1-naphthylacetic acid, and 9-anthracenecarboxylic acid (denoted Benz, Naph and Anth, respectively) behave as chromophores, allowing single-photon ionization for vacuum ultraviolet (VUV) laser light by lowering the IP of the tagged peptide. Anth-tagged peptides that are laser-desorbed from a substrate and subsequently postionized produce mass spectra dominated by the intact radical cation, although protonated ions and fragmented species are also observed. Electronic structure calculations on Anth-tagged peptides indicate that in addition to lowering the ionization potential, the presence of the aromatic tag increases charge localization on and delocalization across the ring structure, which presumably stabilizes the radical cation. Measurements on several tagged peptides confirm this calculation and show that the stabilizing effect of the tag increases with the size of the conjugated system in the order Benz < Naph < Anth. The tagged hexapeptide Anth-GAPKSC exhibits the parent ion, whereas the Benz- and Naph-tagged peptides do not. These results are supported by the experimental comparison of Anth-tagged vs untagged tryptophan, further suggesting that VUV postionization of tagged high-IP species is a promising method for expanding the capabilities of mass spectrometric analyses of molecular species.     

Increasing surface capacity for on-probe affinity capture MALDI-MS via gold particle attachment to allyl amine plasma polymers

In this study, we demonstrate that the protein binding capacity of a surface modified matrix-assisted laser desorption/ionization (MALDI) target can be increased significantly by architecturing the surface of the MALDI probe using gold microparticles. In the present approach, a MALDI target, initially modified via pulsed rf plasma deposition of an allyl amine polymer thin film, is subsequently architectured via reaction with 2-iminothiolane and surface attachment of gold microparticles. The modified probe is then exposed to thiolated biotin to introduce an avidin binding element on the surface of the gold beads. The protein binding capacity of this architectured target is compared with a similarly plasma polymer modified MALDI target that is directly biotinylated. Application of various surface concentrations of avidin to the two probes and MALDI-MS analysis of avidin contained in the solution removed from the probe reveals that saturation of the gold-particle architectured target occurs at a factor of 15-30 higher applied surface concentration, as compared with the unarchitectured target. Furthermore, MALDI-MS analysis of the avidin retained on the two probes reveals that the limit of detection is lowered by a factor of 15-20 on the gold-particle architectured target as compared with the unarchitectured target.     

Covalent attachment of a bioactive hyperbranched polymeric layer to titanium surface for the biomimetic growth of calcium phosphates

This work is investigating the chemical grafting on Ti surface of a polymer/calcium phosphate coating of improved adhesion for enhanced bioactivity. For this purpose, a whole new methodology was developed based on covalently attaching a hyperbranched poly(ethylene imine) layer on Ti surface able to promote calcium phosphate formation in a next deposition stage. This was achieved through an intermediate surface silanization step. The research included optimization both of the reaction conditions for covalently grafting the intermediate organosilicon and the subsequent hyperbranched poly(ethylene imine) layers, as well as of the conditions for the mechanical and chemical pretreatment of Ti surface before coating. The reaction steps were monitored employing FTIR and XPS analyses, whereas the surface morphology and structure of the successive coating layers were studied by SEM combined with EDS. The analysis confirmed the successful grafting of the hybrid layer which demonstrated very good ability for hydroxyapatite growth in simulated body fluid.     

Covalent attachment of gold nanoparticles to DNA templates

Functionalized gold nanoparticles have been covalently bound to internal, modified sites on double-stranded DNA. Gold nanoparticles coated with mercaptosuccinic acid or thioctic acid were bound to amino-modified thymine bases on double-stranded DNA. Visible absorption spectra, gel electrophoresis, and atomic force microscopy were used to analyze the products. Thiol groups were added to one end of the gold/nanoparticle product, which was then attached to a gold surface. This method has the potential to allow controlled placement of particles with subnanometer precision and to allow attachment of the product to fixed contacts for nanodevice fabrication.     

A fluorescence-based method for determining the surface coverage and hybridization efficiency of thiol-capped oligonucleotides bound to gold thin films and nanoparticles

Using a fluorescence-based method, we have determined the number of thiol-derivatized single-stranded oligonucleotides bound to gold nanoparticles and their extent of hybridization with complementary oligonucleotides in solution. Oligonucleotide surface coverages of hexanethiol 12-mer oligonucleotides on gold nanoparticles (34 +/- 1 pmol/cm2) were significantly higher than on planar gold thin films (18 +/- 3 pmol/cm2), while the percentage of hybridizable strands on the gold nanoparticles (1.3 +/- 0.3 pmol/cm2, 4%) was lower than for gold thin films (6 +/- 2 pmol/cm2, 33%). A gradual increase in electrolyte concentration over the course of oligonucleotide deposition significantly increases surface coverage and consequently particle stability. In addition, oligonucleotide spacer sequences improve the hybridization efficiency of oligonucleotide-modified nanoparticles from approximately 4 to 44%. The surface coverage of recognition strands can be tailored using coadsorbed diluent oligonucleotides. This provides a means of indirectly controlling the average number of hybridized strands per nanoparticle. The work presented here has important implications with regard to understanding interactions between modified oligonucleotides and metal nanoparticles, as well as optimizing the sensitivity of gold nanoparticle-based oligonucleotide detection methods.     

Development and application of C60-fullerene bound silica for solid-phase extraction of biomolecules

Sample pretreatment is the most important procedure to remove the matrix for interfacing with mass spectrometry (MS). Additionally, for the samples with low concentration, the process of preconcentration is required before MS analysis. We have newly developed a solid-phase extraction stationary phase based on C60-fullerene covalently bound to silica for purification of biomolecules of different characteristics. Silica particles of different porosity are modified with aminopropyl linker and then covalently bound to C60-fullerenoacetic acid or C60-epoxyfullerenes. The developed materials have been successfully applied as an alternative to commercially available reversed-phase materials for solid-phase extraction. C60-fullerene silica is able to retain small and hydrophilic molecules like phosphopeptides, which can be easily lost by reversed-phase sorbents. The novel materials are applied for desalting and preconcentration of proteins and peptides, especially phosphopeptides. In addition, the C60-fullerene silica is applied for the solid-phase extraction of selected flavonoids with recoveries of approximately 99%. The recoveries are compared with the commercially available solid-phase extraction materials.     

Solid-phase synthesis and photochromic switching of a polymeric photochromic layer on a gold surface

The preparation of a novel carboxymethylated dextran photochromic polymer on a gold surface is presented here. Ethylester-dihydroindolizine is attached by amine coupling to a carboxymethylated dextran polymer on the gold surface of a Surface Plasmon Resonance (SPR) sensor. The photoinduced switch between the two isomers of the ethylester-dihydroindolizine photochromic polymer was investigated by fiber optics based surface plasmon resonance. The different solvent effect on the SPR shift is also reported. A larger absolute shift was obtained in solvents with low relative dielectric constants, than in solvents with a larger relative dielectric constant. A blue shift was observed with organic solvents and a red shift for the aqueous solvent. Moreover, by changing the solvent, the refractive index of the surrounding media in contact with the gold surface also changes and the wavelength used to excite the surface plasmon can be shifted outside the excitation/relaxation range of the photochromic system.     

Double layer calculations for the attachment of a colloidal particle with a charged surface patch onto a substrate

The attachment of a particle onto a substrate with a like surface charge may be greatly facilitated in the presence of an oppositely charged surface patch on the particle. Calculations are presented for the effect of various parameters on particle attachment. These include the patch charge, patch size, particle size and the ionic strength of the medium.     

The write field of a ring head for a double layer perpendicular medium

The write field of a ring head used with the preferred medium for perpendicular recording (CoCr with an underlayer of softmagnetic material) is discussed and compared with the write field of a Thin- -Film Single Pole (TF-SP) head on the basis of two-dimensional calculations. It is found that the saturation of the underlayer plays an important role in the shape as well as the magnitude of the calculated write field.     

Simple surface modification techniques for immobilization of biomolecules on SU-8

SU-8, an epoxy based negative photoresist polymer has found wide range of applications in the field of microfabrication based biosensors. SU-8 surfaces need to be modified in order to immobilize bioreceptors. We studied the possibility of grafting desired functional groups by means of simple chemical treatments under normal laboratory conditions. These chemical treatments involve the use of crosslinkers that are expected to react with epoxy groups or hydroxyl groups generated by acid/alkali treatment. Here, a comparison of the results obtained on surface modification using glycine and 11-mercapto undecanoic acid as crosslinkers is presented. Human Immunoglobin G (HIgG) was covalently immobilized to carboxylic acid on SU-8 surface using carbodiimide/succinimide chemistry. The activity of immobilized HIgG was verified by using fluorescence imaging of FITC tagged goat anti HIgG bound to the surface. Fluorescence imaging was used to determine the chemistry best suited to functionalize SU-8 surface for biosensor applications.     

Immobilization of biomolecules on the surface of inorganic nanoparticles for biomedical applications

Abstract

Various inorganic nanoparticles have been used for drug delivery, magnetic resonance and fluorescence imaging, and cell targeting owing to their unique properties, such as large surface area and efficient contrasting effect. In this review, we focus on the surface functionalization of inorganic nanoparticles via immobilization of biomolecules and the corresponding surface interactions with biocomponents. Applications of surface-modified inorganic nanoparticles in biomedical fields are also outlined.     

Voltage regulation of fluorescence emission of single dyes bound to gold nanoparticles

An organic dye, SAMSA, bound to gold nanoparticles, displays random photoactivated fluorescence blinking whose rate depends on the size of the nanoparticles. We report experiments indicating that (1) the dye emission wavelength is red-shifted (10-30 nm) by applying an external low voltage (1-10 V) and that (2) the fluorescence emission of single dyes can be resonantly driven by tuning the alternating external bias frequency from 1 to 3 Hz, depending on the nanoparticle size. These properties appear highly valuable and promising for devising light emitting nanostructures.     

Coupled problem of thermomechanics for a conducting layer subjected to a uniform pulsed electromagnetic action

A coupled dynamic problem of thermomechanics is formulated for a conducting layer with plane-parallel boundaries subjected to a nonstationary electromagnetic action. As key functions of the problem, we use the tangential component of the vector of magnetic-field intensity, temperature, and the normal components of the tensor of dynamic stresses. We propose a procedure for the determination of these functions based on their cubic approximation in the thickness coordinate and the Laplace transformation with respect to time. On the basis of the obtained general solutions, we present the solutions of the problem for a sinusoidal electromagnetic action with pulsed modulating signal. The influence of the parameter of coupling of the strain and temperature fields on the stresses and temperature is analyzed.     

Immobilization of biomolecules on the surface of inorganic nanoparticles for biomedical applications

Various inorganic nanoparticles have been used for drug delivery, magnetic resonance and fluorescence imaging, and cell targeting owing to their unique properties, such as large surface area and efficient contrasting effect. In this review, we focus on the surface functionalization of inorganic nanoparticles via immobilization of biomolecules and the corresponding surface interactions with biocomponents. Applications of surface-modified inorganic nanoparticles in biomedical fields are also outlined.     

Plasma-based surface modification of polystyrene microtiter plates for covalent immobilization of biomolecules

In recent years, polymer surfaces have become increasingly popular for biomolecule attachment because of their relatively low cost and desirable bulk physicochemical characteristics. However, the chemical inertness of some polymer surfaces poses an obstacle to more expansive implementation of polymer materials in bioanalytical applications. We describe use of argon plasma to generate reactive hydroxyl moieties at the surface of polystyrene microtiter plates. The plates are then selectively functionalized with silanes and cross-linkers suitable for the covalent immobilization of biomolecules. This plasma-based method for microtiter plate functionalization was evaluated after each step by X-ray photoelectron spectroscopy, water contact angle analysis, atomic force microscopy, and bioimmobilization efficacy. We further demonstrate that the plasma treatment followed by silane derivatization supports direct, covalent immobilization of biomolecules on microtiter plates and thus overcomes challenging issues typically associated with simple physisorption. Importantly, biomolecules covalently immobilized onto microtiter plates using this plasma-based method retained functionality and demonstrated attachment efficiency comparable to commercial preactivated microtiter plates.     

X-ray topography contrast of edge dislocations perpendicular to the 6H-SiC crystal surface

Features of the X-ray topography (XRT) images of edge dislocations perpendicular to the (0001) surface of a 6H-SiC single crystal are described. The contrast of topographs obtained in the regime of anomalous X-ray transmission is compared to the contrast of images obtained using section X-ray topography in the transmission geometry.     

Oblique-incidence sputtering of Ru intermediate layer for decoupling of intergranular exchange in perpendicular recording media

During the Ru deposition process for granular type perpendicular magnetic recording media, both a reduction in the Ru intermediate layer thickness and lowering of sputtering gas pressure were successfully achieved by focusing on a self-shadowing effect. Oblique-incidence sputtering with a 60° incident angle under an Ar gas pressure of 0.6 Pa yielded (1) columnar Ru grains with a growth direction of 30° from the film normal, (2) c-plane sheet texture by epitaxial growth on the Pt underlayer, and (3) a flat envelope of the surface and a deep gap at grain boundaries. This change in the Ru structure significantly contributes to reducing exchange coupling among magnetic grains, especially in the initial growth region in an overlying granular medium.     

Fractal structure of uniform corrosion surface for Fe-based alloys

Abstracts are not published in this journal     

In situ raman spectroscopy studies of metal ion complexation by 8-hydroxyquinoline covalently bound to silica surfaces

Raman spectroscopy is applied to an investigation of the interfacial chemistry of silica-immobilized 8-hydroxyquinoline (8HQ) for binding of metal ions over a wide range of solution conditions. Since the derivatized silica has a high specific binding capacity, the mass of silica equilibrated with solution needs to be small for studies of reactions with trace-level (microM) metal ions; otherwise, the solution volume required to reach equilibrium becomes excessive. To address this problem, a small-volume flow cell is designed for this work using a fiber-optic Raman probe inserted directly into the packed end of a microcolumn, allowing excitation and collection of Raman scattering from less than 10 mg of derivatized silica. This cell is attached to a flow system that allows control of solution conditions while the response of the 8HQ-silica material is acquired by continuous monitoring of Raman scattering from the sample. Raman spectra of the deprotonated, neutral, protonated, and copper-complexed forms of the ligand can be distinguished, allowing proton-transfer and metal ion binding reactions of the ligand to be investigated. To account for the effects of changing surface potential on these reactions, zeta-potential measurements are made on the 8HQ-silica particles under the same solution conditions that are employed in the Raman scattering measurements. The observed pH dependence of metal ion binding was corrected for the effect of surface potential using the Boltzmann equation, and the resulting equilibrium constant for binding of Cu2+ was independent of metal ion concentration over a 100-fold range from 30 microM to 5 mM.     

Effects of compressive stress perpendicular to the surface of four percent silicon-iron single crystals

Effects of compressive stress perpendicular to the surface of 4 percent silicon-iron single crystals on their magnetic properties were investigated. Picture frame single crystal specimens which were used had [100] and [111] orientation, respectively. The hysteresis loops at low field (0 < H <450 A/m) were measured under the applied stress. For the 4 percent Si-Fe [100] specimen, a large decrease of induction under stress occurs at lower fields, and for the 4 percent Si-Fe [111] specimen, the induction increases with increasing applied stress at lower fields but decreases at higher fields and coincides with the same value of the zero stress case when H is greater than about 400A/m. The stress versus Br/Bmcurves of the 4 percent Si-Fe [100] and [111] specimens were plotted to show the change of the induction under applied stress.