Computational screening of biomolecular adsorption and self‐assembly on nanoscale surfaces

The quantification of binding properties of ions, surfactants, biopolymers, and other macromolecules to nanometer‐scale surfaces is often difficult experimentally and a recurring challenge in molecular simulation. A simple and computationally efficient method is introduced to compute quantitatively the energy of adsorption of solute molecules on a given surface. Highly accurate summation of Coulomb energies as well as precise control of temperature and pressure is required to extract the small energy differences in complex environments characterized by a large total energy. The method involves the simulation of four systems, the surface‐solute–solvent system, the solute–solvent system, the solvent system, and the surface‐solvent system under consideration of equal molecular volumes of each component under NVT conditions using standard molecular dynamics or Monte Carlo algorithms. Particularly in chemically detailed systems including thousands of explicit solvent molecules and specific concentrations of ions and organic solutes, the method takes into account the effect of complex nonbond interactions and rotational isomeric states on the adsorption behavior on surfaces. As a numerical example, the adsorption of a dodecapeptide on the Au {111} and mica {001} surfaces is described in aqueous solution. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

Driving forces for protein adsorption at solid surfaces

Under most conditions proteins show a strong tendency to adsorb at interfaces. The general principles underlying the interaction between proteins and solid surfaces in an aqueous environment are discussed. These principles are illustrated by experimental results obtained with well-defined systems. The approach is mainly based on thermodynamic arguments.     

Mobile precursor mediated protein adsorption on solid surfaces

The interaction between a protein molecule and a surface is ubiquitous to a number of important technologies, such as bio-sensing, biomaterials, and nanomedicine. This process is also essential to complex biological functions, such as protein–cell surface interactions. Here we explore the application of fundamental concepts developed in the field of surface science to the understanding of protein–surface interactions. In particular, we focus on the role of mobile precursor states in the reversible and irreversible adsorption of protein molecules. We attempt to apply these simple concepts to the analysis of the kinetics and thermodynamics of protein–surface interactions. We conclude by discussing how one may take advantage of these simple concepts in designing and controlling protein–surface interactions for various bio-interface based technologies.     

Selective adsorption of protein molecules on phase-separated sapphire surfaces

Site-selective adsorption of protein molecules was found on sapphire surfaces that exhibit a phase separation into two domains: weakly charged hydrophobic domain and negatively charged hydrophilic one. Ferritin and bovine serum albumin molecules, which are negatively charged in a buffer solution, are adsorbed to the hydrophobic domains. Avidin molecules, which are positively charged, are adsorbed to the other domain. Fibrinogen molecules, which consist of both negative and positive modules, are adsorbed to the whole sapphire surface. Hemoglobin molecules, whose net charge is almost zero, are also adsorbed to the whole surfaces. These results indicate that electrostatic double layer interaction is the primary origin of the observed selectivity. Dependence of protein adsorption or desorption behaviors on the pH value can also be interpreted by the proposed model.     

FTIR-ATR-spectroscopic analysis of the protein adsorption on polymer blood contact surfaces

Summary Model experiments have been carried out in a flow-through attenuated total reflectance (ATR-) cell mounted in a Fourier Transform Infrared- (FTIR-) spectrometer to study in situ the adsorption of some important blood proteins on several organic and inorganic surfaces from D₂O-solutions. The model compounds used were fibrinogen, albumine and ₁-acid glycoprotein as well as polystyrene, polyetherurethane and germanium (the material of the ATR-prism).The intensities of the amide I bands of the respective adsorbed proteins were in the 10 m AU-range and have been plotted as a function of contact time between solution and surface for different reaction conditions. (Isolated, ground and negatively charged surfaces, before and after rinsing with D₂O, different pD-values.) From the data it was concluded, that the proteins adsorb in two layers, the first, irreversibly bound within a few seconds to minutes and the second build up slowly. This second layer could be removed by application of negative charge (–9 V) in the case of fibrinogen on polystyrene, and to a lesser extend for albumine and ₁-acid glycoprotein but not by rinsing with D₂O. From these IR spectra of fibrinogen, structural changes upon buildings up and desorption of the second layer as compared to the first could be derived.

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FTIR-ATR spektroskopische Analyse der Proteinadsorption an polymeren Blutkontaktoberflächen

Zusammenfassung In einem mit einer ATR-Durchflußzelle ausgestatteten Fourier-Transformations-Infrarotspektrometer wurden Modellexperimente zum In-situ-Studium der Adsorption einiger wichtiger Blutproteine an verschiedenen organischen und anorganischen Oberflächen aus D₂O-Lösung durchgeführt. Als Modellsubstanzen wurden Fibrinogen, Albumin und ₁-Glycoprotein sowie Polystyrol, Polyetherurethan und die Oberfläche des Ge-Reflexionselementes eingesetzt. Die Intensitäten der Amid-I-Banden der jeweiligen adsorbierten Proteine lagen im Bereich vonE=0,01 und wurden als Funktion der Kontaktzeit für verschiedene Reaktionsbedingungen dargestellt (isolierte, geerdete bzw. negativ geladene Oberflächen, vor und nach D₂O-Spülung, verschiedene pD-Werte). Es konnte gezeigt werden, daß die Proteine zunächst rasch eine irreversible Schicht bilden (Sekunden bis Minuten), worauf sich langsam eine zweite Schicht aufbaut. Diese konnte durch Aufladung des Reflexionselementes auf –9 V im Fall von Fibrinogen auf Polystyrol signifikant, für Albumin und ₁-Glycoprotein nur in geringerem Ausmaß wieder entfernt werden. D₂O-Spülung allein greift diese zweite Schicht nicht an. Aus den IR-Spektren dieses Fibrinogenexperiments konnten weiters Strukturänderungen während des Auf- und Abbaues der zweiten Schicht im Vergleich zur ersten abgeleitet werden.

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This work was supported by the Austrian Science Foundation (Fonds zur Förderung der wissenschaftlichen Forschung in Österreich); Proj. no. 3427.     

Elucidation of protein adsorption behavior on polymeric surfaces: toward high-density, high-payload protein templates

The elucidation of protein adsorption behavior on polymeric surfaces is very important, since their use as arrays and carriers of biomolecules is ever growing for a wide variety of bioapplications. We evaluate protein adsorption characteristics on chemically homogeneous and heterogeneous polymeric surfaces by employing polystyrene-block-polymethylmethacrylate (PS-b-PMMA) diblock copolymer, PS homopolymer, PMMA homopolymer, and PS/PMMA blend as protein templates. We also investigate distance-dependent protein adsorption behavior on the interfacial region between PS and PMMA. We observe selective protein adsorption exclusively onto PS areas for the chemically heterogeneous PS-b-PMMA and PS/PMMA blend templates. On blend films, protein adsorption is highly favored on the PS regions located near the PS:PMMA interface over that on the PS areas situated away from the interface. Protein density on PS domains is inversely proportional to the separation distance between two neighboring PS:PMMA interfaces. We also observe a higher protein density on the PS-b-PMMA than on the PS or PMMA homopolymer templates. This effect is due to the fact that chemically heterogeneous PS-b-PMMA presents periodically spaced PS:PMMA interfaces on the nanometer scale, whereas no such interfaces are present on homopolymer films. The density of protein molecules on the heterogeneous PS-b-PMMA surface is approximately 3-4-fold higher than on the homogeneous PS surface for the identical experimental conditions. These results demonstrate that self-assembling, chemically heterogeneous, nanoscale domains in PS-b-PMMA diblock copolymers can be used as excellent, high-payload, high-density protein templates. The unique advantages of the diblock copolymer may prove the spontaneously constructed protein nanotemplates to be highly suitable as functional substrates in many proteomics applications.     

Laser-induced nanoscale superhydrophobic structures on metal surfaces

The combination of a dual-scale (nano and micro) roughness with an inherent low-surface energy coating material is an essential factor for the development of superhydrophobic surfaces. Ultrashort pulse laser (USPL) machining/structuring is a promising technique for obtaining the dual-scale roughness. Sheets of stainless steel (AISI 304 L SS) and Ti-6Al-4V alloys were laser-machined with ultraviolet laser pulses of 6.7 ps, with different numbers of pulses per irradiated area. The surface energy of the laser-machined samples was reduced via application of a layer of perfluorinated octyltrichlorosilane (FOTS). The influence of the number of pulses per irradiated area on the geometry of the nanostructure and the wetting properties of the laser-machined structures has been studied. The results show that with an increasing number of pulses per irradiated area, the nanoscale structures tend to become predominantly microscale. The top surface of the microscale structures is seen covered with nanoscale protrusions that are most pronounced in Ti-6Al-4V. The laser-machined Ti-6Al-4V surface attained superhydrophobicity, and the improvement in the contact angle was >27% when compared to that of a nontextured surface.     

Synthetic surfaces for ribonuclease adsorption

Intact RNA and DNA are of central importance to biochemical research and biotechnology. The preservation of these nucleic acids requires the absence of nuclease activity. Here, radical-mediated polymerization of vinylsulfonate on resin and glass surfaces is shown to produce a high-density poly(vinylsulfonate) coating that sequesters ribonucleases from aqueous solutions quickly and completely. The adsorptive efficacy of this coating exceeds that of other known coatings by > or =10(7)-fold. Surfaces coated with poly(vinylsulfonate) could be used to maintain the integrity of ribonucleic acids in a variety of contexts.     

Polymer adsorption on heterogeneous surfaces

The adsorption of polymers on an energetically heterogeneous surface can be modelled using a self-consistent field lattice theory. The surface consists of sites having different adsorption energies. It turns out that the distribution of the sites over the surface is one of the main parameters determining the adsorption behaviour.     

Non-specific adhesion on biomaterial surfaces driven by small amounts of protein adsorption

This work explores how long-range non-specific interactions, resulting from small amounts of adsorbed fibrinogen, potentially influence bioadhesion. Such non-specific interactions between protein adsorbed on a biomaterial and approaching cells or bacteria may complement or even dominate ligand–receptor mating. This work considers situations where the biomaterial surface and the approaching model cells (micron-scale silica particles) exhibit strong electrostatic repulsion, as may be the case in diagnostics and lab-on-chip applications. We report that adsorbed fibrinogen levels near 0.5 mg/m² produce non-specific fouling. For underlying surfaces that are less fundamentally repulsive, smaller amounts of adsorbed fibrinogen would have a similar effect. Additionally, it was observed that particle adhesion engages sharply and only above a threshold loading of fibrinogen on the collector. Also, in the range of ionic strength, I, below about 0.05 M, increases in I reduce the fibrinogen needed for microparticle capture, due to screening of electrostatic repulsions. Surprisingly, however, ionic strengths of 0.15 M reduce fibrinogen adsorption altogether. This observation opposes expectations based on DLVO arguments, pointing to localized electrostatic attractions and hydration effects to drive silica–fibrinogen adhesion. These behaviors are benchmarked against microparticle binding on silica surfaces carrying small amounts of a polycation, to provide insight into the role of electrostatics in fibrinogen-driven non-specific adhesion.     

Covalently modified silicon and diamond surfaces: resistance to nonspecific protein adsorption and optimization for biosensing

We report the direct covalent functionalization of silicon and diamond surfaces with short ethylene glycol (EG) oligomers via photochemical reaction of the hydrogen-terminated surfaces with terminal vinyl groups of the oligomers, and the use of these monolayers to control protein binding at surfaces. Photochemical modification of Si(111) and polycrystalline diamond surfaces produces EG monolayers linked via Si-C bond formation (silicon) or C-C bond formation (diamond). X-ray photoelectron spectroscopy was used to characterize the monolayer composition. Measurements using fluorescently labeled proteins show that the EG-functionalized surfaces effectively resist nonspecific adsorption of proteins. Additionally, we demonstrate the use of mixed monolayers on silicon and diamond and apply these surfaces to control specific versus nonspecific binding to optimize a model protein sensing assay.     

Poly(N-vinylpyrrolidone)-modified surfaces repel plasma protein adsorption

The present work aimed to study the interaction between plasma proteins and PVP-modified surfaces under more complex protein conditions.In the competitive adsorption of fibrinogen(Fg) and human serum albumin(HSA),the modified surfaces showed preferential adsorption of HSA.In 100%plasma,the amount of Fg adsorbed onto PVP-modified surfaces was as low as 10 ng/cm~2,suggesting the excellent protein resistance properties of the modified surfaces.In addition, immunoblots of proteins eluted from the modified surfaces after plasma contact confirmed that PVP-modified surfaces can repel most plasma proteins,especially proteins that play important roles in the process of blood coagulation.     

Novel tertiary amine oxide surfaces that resist nonspecific protein adsorption

Novel surfaces derivatized with tertiary amine oxides have been prepared and tested for their ability to resist nonspecific protein adsorption. The oxidation of tertiary amines supported on triazine units was carried out using mCPBA to give a format allowing conjugation of biologically active ligands alongside them. Adsorption to these surfaces was tested and compared to adsorption to a set of commercial and custom oligo-/poly(ethylene glycol) (OEG/PEG) supports by challenging them with a protein display library presented on bacteriophage lambda. The new class of amine oxide surfaces is found to compare favorably with the performance of the OEG/PEG supports in the prevention of nonspecific binding.     

Silane layers on silicon surfaces: mechanism of interaction, stability, and influence on protein adsorption

In this work the mechanism of (3-aminopropyl)triethoxysilane (APTES) interaction with silicon surfaces is investigated at the molecular level. We studied the influence of experimental parameters such as time, temperature, and concentration on the quality of the APTES layer in terms of chemical properties, morphology, and stability in aqueous medium. This was achieved using a highly sensitive IR mode recently developed, grazing angle attenuated total reflection (GA-ATR). This technique provides structural information on the formed APTES layer. The topography of this layer was investigated by atomic force microscopy in aqueous medium. The hydrophilicity was also studied using contact angle measurement. Combining these techniques enables discussion of the mechanism of silane grafting. Considerable differences were observed depending on the reaction temperature, room temperature or 90 °C. The data suggest the presence of two adsorption sites with different affinities on the oxidized silicon layer. This also allows the optimal parameters to be established to obtain an ordered and stable silane layer. The adsorption of proteins on the APTES layer was achieved and monitored using in situ quartz crystal microbalance with dissipation monitoring and ex situ GA-ATR analyses.     

Grafted ionomer complexes and their effect on protein adsorption on silica and polysulfone surfaces

We have studied the formation and the stability of ionomer complexes from grafted copolymers (GICs) in solution and the influence of GIC coatings on the adsorption of the proteins β-lactoglobulin (β-lac), bovine serum albumin (BSA), and lysozyme (Lsz) on silica and polysulfone. The GICs consist of the grafted copolymer PAA₂₈-co-PAPEO₂₂ {poly(acrylic acid)-co-poly[acrylate methoxy poly(ethylene oxide)]} with negatively charged AA and neutral APEO groups, and the positively charged homopolymers: P2MVPI₄₃ [poly(N-methyl 2-vinyl pyridinium iodide)] and PAH?HCl₁₆₀ [poly(allylamine hydrochloride)]. In solution, these aggregates are characterized by means of dynamic and static light scattering. They appear to be assemblies with hydrodynamic radii of 8 nm (GIC-PAPEO₂₂/P2MVPI₄₃) and 22 nm (GIC-PAPEO₂₂/PAH?HCl₁₆₀), respectively. The GICs partly disintegrate in solution at salt concentrations above 10 mM NaCl. Adsorption of GICs and proteins has been studied with fixed angle optical reflectometry at salt concentrations ranging from 1 to 50 mM NaCl. Adsorption of GICs results in high density PEO side chains on the surface. Higher densities were obtained for GICs consisting of PAH?HCl₁₆₀ (1.6?÷?1.9 chains/nm²) than of P2MVPI₄₃ (0.6?÷?1.5 chains/nm²). Both GIC coatings strongly suppress adsorption of all proteins on silica (>90%); however, reduction of protein adsorption on polysulfone depends on the composition of the coating and the type of protein. We observed a moderate reduction of β-lac and Lsz adsorption (>60%). Adsorption of BSA on the GIC-PAPEO₂₂/P2MVPI₄₃ coating is moderately reduced, but on the GIC-PAPEO₂₂/PAH?HCl₁₆₀ coating it is enhanced.     

pH effect on protein G orientation on gold surfaces and characterization of adsorption thermodynamics

The pH effect on adsorbed antibody-binding protein (protein G) orientation on gold (Au) and its adsorption thermodynamic characteristics were investigated using quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The adsorbed protein G orientation was measured by binding response of two antibody-antigen systems: the model bovine serum albumin (BSA) and the foodborne pathogen E. coli O157:H7. Surface coverage was not significantly affected by pH, but its orientation was. The most properly oriented protein G for antibody binding was achieved at near-neutral pH. Adsorption was verified by XPS measurements using nitrogen (N) 1s, oxygen (O) 1s, and Au 4p peak heights. Adsorption energetics were determined by van't Hoff and Langmuir kinetic analyses of adsorption data obtained at 296, 303, and 308 K. Large characteristic entropy change of protein adsorption was observed (ΔS° = 0.52 ± 0.01 kcal/mol·K). The adsorption process was not classical physisorption but exhibited chemisorption characteristics based on significant enthalpy change (ΔH° = -25 ± 6 kcal/mol).     

Ethanol adsorption on SrTiO3 surfaces

Using a quantum chemical method developed for crystalline systems and a periodic large unit cell (LUC) model, ethanol, CH₃CH₂OH, adsorption on the SrTiO₃ (001) surfaces is studied, considering both cubic and tetragonal lattices of the crystal. The investigation is carried out for the ethanol molecule as a whole complex and considering its decomposition into the ethylene and water. The structural and electronic effects involved in the adsorption are discussed. The obtained results predict a higher possibility of ethanol adsorption on the Ti? O₂ face of the SrTiO₃ (001) surfaces for both crystallographic lattices. The favored ethanol adsorption as a whole complex testifies the possibility of the ethanol molecule formation from the ethylene and water on the SrTiO₃ (001) surface with the former acting as a catalyst. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006