Quantitative analysis of protein adsorption via atomic force microscopy and surface plasmon resonance

Surface properties have a significant influence on the performance of biomedical devices. The influence of surface chemistry on the amount and distribution of adsorbed proteins has been evaluated by a combination of atomic force microscopy (AFM) and surface plasmon resonance (SPR). Adsorption of albumin, fibrinogen, and fibronectin was analyzed under static and dynamic conditions, employing self-assembled monolayers (SAMs) as model surfaces. AFM was performed in tapping mode with antibody-modified tips. Phase-contrast images showed protein distribution on SAMs and phase-shift entity provided information on protein conformation. SPR analysis revealed substrate-specific dynamics in each system investigated. When multi-protein solutions and diluted human plasma interacted with SAMs, SPR data suggested that surface chemistry governs the equilibrium composition of the protein layer.     

AFM study on the adsorption and aggregation behavior of dissolved humic substances on mica

Humic substances (HS) are a category of naturally occurring, biogenic, heterogeneous organic materials found in or extracted from soils, sediments, and natu- ral waters that can generally be characterized as being yellow-to-black in color, of highly variable relative molecular masses, and refractory[1,2]. Derived from a variety of organic precursors (plant biopolymers such as lignin etc.), plant residues and animal debris via both transformation and synthesis processes[3] under the profound ge…     

Evaluation of asymmetrical structure dialysis membrane by tortuous capillary pore diffusion model

The tortuous capillary pore diffusion model (TCPDM) has been used for estimating diffusive and pure water permeability from simple structure parameters such as pore diameter, surface porosity, wall thickness and tortuosity. The validity of this model for evaluation of homogeneous membrane has been already confirmed. Recently, there is a trend toward the use of asymmetrical dialysis membranes made of synthetic polymer such as poly(acrylonitrile) (PAN), polysulfone (PS) and a polyethersulfone polyarylate (PEPA) blend polymer. The purpose of the present study is to apply the TCPDM to evaluation of commercially available hollow-fiber dialysis membranes with asymmetrical structures by simplifying them to a double-layer membrane. The TCPDM is capable of estimating pore tortuosity of asymmetrical dialysis membranes having skin and supporting layers from data on membrane thickness, pore diameter, pure water permeability and water content. Values for diffusive permeability obtained by the TCPDM are in a good agreement with experimental data. This TCPDM model is useful for evaluation of not only homogeneous membrane but also asymmetrical membrane.     

Analogy in adsorption behavior of homopolyelectrolyte mixtures as compared to analogous diblock polyampholytes

The adsorption behavior of aqueous mixtures of the homopolyelectrolytes poly(methacrylic acid) (PMAA) and poly[(dimethylamino)ethyl methacrylate] (PDMAEMA) was investigated in comparison with the adsorption of the ampholytic diblock copolymer PMAA‐b‐PDMAEMA on silicon substrates. Ellipsometry was used to determine the amount of adsorbed homopolyelectrolyte and diblock polyampholyte. Furthermore, the topography of the adsorbed polymers was investigated with atomic force microscopy (AFM) and compared with the structures observed in aqueous solutions by dynamic light scattering (DLS). For all types of investigated polyelectrolytic mixtures or the single polyampholyte, the adsorption was strongly influenced by the pH of the polymer solution. Although single homopolyelectrolytes showed only one maximum in adsorption according to their charge, the mixtures made from these homopolyelectrolytes showed two or three maxima. The third maximum near the isoelectric point of the mixture was assigned to a new species formed by aggregation of the two homopolyelectrolytes. Altogether, the adsorption behavior of the polyelectrolytic mixtures was in between the behavior of the pure homopolyelectrolytes and the analogous polyampholytes and therefore understandable from both of these polymer species. © 2002 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 40: 338–345, 2002; DOI 10.1002/polb.10091     

Cross‐Linked Multilayers of Poly(vinyl amine) as a Single Component and Their Interaction with Proteins

Novel multilayer thin films that consist solely of cross‐linked single component layers are generated by a selective cross‐linking of the poly(vinyl amine) (PVAm) layers in [PVAm/poly(acrylic acid) (PAA)]_n thin films constructed either on silica particles or silicon wafers, followed by the removal of PAA. The surface topography of the (PVAm)_n multilayer thin films, before and after the adsorption of human serum albumin (HSA), has been studied by atomic force microscopy on the freeze‐dried films. The decrease of the average roughness of the film after the adsorption of HSA showed the protein was adsorbed into the (PVAm)_n film making these films potential reservoirs for proteins.

     

Fibrinogen Adsorption on Biomaterials – A Numerical Study

A model for the adsorption of fibrinogen or, in general, non‐globular shaped proteins on solid surfaces are presented. Two‐dimensional cellular automata simulations of the adsorption of fibrinogen on two different surfaces were performed. The model includes mass transfer toward the surface, adsorption of fibrinogen molecules, and surface diffusion mechanisms for both fibrinogen molecules and clusters. We show that the major physical processes are represented in the recent model. Particularly, the influence of the surface hydrophobicity on the behavior of fibrinogen. Atomic force microscopy images of fibrinogen adsorption on Si model surfaces with different hydrophobicity are compared to the results.

     

End‐grafting copolymers of styrene and 4‐vinylpyridine on an interacting solid surface

Copolymers of styrene and 4‐vinylpyridine with a styrene fraction f varying from 1 to 0 were grafted onto a silicon substrate in the melt. The grafting reaction and the stability of the grafted chains were investigated by Fourier transform infrared and X‐ray photoelectron spectroscopy. The thickness and surface morphology of the grafted copolymer layers were characterized with ellipsometry and atomic force microscopy (AFM). The copolymer chains were successfully grafted to the surface of the silicon substrate by a reaction between the hydroxyl groups of the nitroxide moiety at the end of the copolymers and the silanol groups on the surface of the silicon wafer. A measurement of the thickness of the grafted copolymer layers showed that the ratio of grafted‐layer thickness to the unperturbed chain radius of gyration decreased with the increasing fraction of 4‐vinylpyridine in the copolymer; this indicated that the grafted layer was strongly attracted to the substrate. In addition, an accelerated grafting process was observed at grafting times ranging from 48 to 72 h for pure poly(4‐vinylpyridine) and copolymers with f values of 0.3 and 0.5. AFM observation revealed that the grafted layers densely and homogeneously covered the silicon substrate. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1332‐1343, 2005     

Chemical force microscopy: applications in surface characterisation of natural hydroxyapatite

Detailed mapping of surface chemistry with nanometer resolution has application throughout the physical and life sciences. The atomic force microscope (AFM) has provided a tool that, when using functionalised probes, is capable of providing chemical information with this level of spatial resolution. Here, we describe the technique of chemical force microscopy (CFM) and demonstrate the sensitivity of the technique using chemical force titrations against pH. We describe in detail the specific application of mapping the surface charge on natural hydroxyapatite from skeletal tissue and show that this new information leads to a better understanding of the binding of matrix proteins to the mineral surface.     

Effect of SDBS solution on the surface potential properties of the Zhaozhuang coal

It is of great significance to study the effect of surfactants on the coal surface potential for effective dust suppression in mining faces. The effect of different concentrations of sodium dodecyl benzene sulfonate (SDBS) solution on the surface potential of the Zhaozhuang coal was measured by atomic force microscopy (AFM). The experimental results show that the SDBS solution has significant influence on the surface potential of the Zhaozhuang coal. The electrical characteristics of the coal surface at the nanometer scale are different from those of macroscopic or the mesoscopic level. The surface potential of coal is basically a normal distribution, showing certain electrical characteristics. The mean value of the surface potential of the Zhaozhuang coal is increased with the increase in concentration of the SDBS solution; when the concentration of the SDBS solution is 0.3%, the mean value of surface potential is 5.59 mv, which is about two times of the mean value of the surface potential without SDBS solution added. With the increase of the concentration of the SDBS solution, the maximum value of the surface potential of the Zhaozhuang coal increases, and the minimum value decreases. It shows that the SDBS solution has a significant effect on the potential distribution law and the magnitude of the coal surface. Subsequently, on the basis of the constructed Zhaozhuang coal macromolecule model, xtb and Multiwfn simulation software were used to calculate the molecular surface electrostatic potential value and electron density value of the Zhaozhuang coal molecules after adding water molecules. The variation law for the electrostatic potential surface of the molecule was obtained after adding numbers of water molecules to the surface of the coal molecule. The simulation results show that the area proportion of absolute molecular surface electrostatic potential greater than 10 kcal/mol is increased with the growth in the number of water molecules, while the area proportion of absolute molecular surface electrostatic potential less than 10 kcal/mol is decreased. Because of the free state O─H bond polarity of water molecules, the charges on the molecular surface are rearranged in order to change the electron density on the surface of coal molecules, which affects the overall electrostatic potential of the configuration.     

Stretched polymer surfaces: Atomic force microscopy measurement of the surface deformation and surface elastic properties of stretched polyethylene

The surface structure and surface mechanical properties of low‐ and high‐density polyethylene were characterized by atomic force microscopy (AFM) as the polymers were stretched. The surfaces of both materials roughened as they were stretched. The roughening effect is attributed to deformation of nodular structures, related to bulk spherulites, at the surface. The surface‐roughening effect is completely reversible at tensile strains in the elastic regime and partially reversible at tensile strains in the plastic regime until the polymers are irreversibly drawn into fibers. AFM force versus distance interaction curves, used to measure changes in the stiffness of the surface and the surface elastic modulus as a function of elongation, show that the surfaces become softer as the polymers are drawn into fibers at high strains. At low elastic strains, however, the surface elastic modulus of HDPE increases—attributed to elastic energy stored by the amorphous regions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2263–2274, 2001     

Effect of protein solution components in the adsorption of Herbaspirillum seropedicae GlnB protein on mica

The adsorption of proteins and its buffer solution on mica surfaces was investigated by atomic force microscopy (AFM). Different salt concentration of the Herbaspirillum seropedicae GlnB protein (GlnB-Hs) solution deposited on mica was investigated. This protein is a globular, soluble homotrimer (36 kDa), member of PII-like proteins family involved in signal transducing in prokaryote. Supramolecular structures were formed when this protein was deposited onto bare mica surface. The topographic AFM images of the GlnB-Hs films showed that at high salt concentration the supramolecular structures are spherical-like, instead of the typical doughnut-like shape for low salt concentration. AFM images of NaCl and Tris from the buffer solution showed structures with the same pattern as those observed for high salt protein solution, misleading the image interpretation. XPS experiments showed that GlnB protein film covers the mica surface without chemical reaction.     

Structure of salted and discharged globules of hydrophobic polyelectrolytes adsorbed from aqueous solutions

In this article, we compare structures of protonated poly(2-vinylpyridine) globules (2D compact coils on the surface) adsorbed on the mica surface from aqueous solution when the shrinking is brought about either by discharging the molecules at an elevated pH or by adding monovalent and polyvalent salts. We study the structure of the PE coils using in situ atomic force microscopy experiments in aqueous solutions in a liquid cell. The abrupt coil-to-globule transition caused by pH changes and the discharge of polymer chains resulted in compact globules. If the pH corresponding to extended coil conformation remains unchanged, the coil shrinks due to the added salt. The size of the globule in the latter case corresponds to the unperturbed dimension of the polymer coil. There is no essential difference in the dimensions of the globules as obtained in the presence of monovalent and multivalent counterions for the studied ionic strength. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1623–1627, 2010     

利用AFM和SNOM对淋巴细胞膜表面超微结构及其光学性质的初步研究

利用原子力显微镜(Atomic Force Microscopy，AFM)对淋巴细胞表面形貌进行了形态学的初步研究，观察到了其膜表面其他显微技术所不能发现的超微结构．同时也运用扫描近场光学显微镜(Scanning Near field Optical Microscopy，SNOM)对淋巴细胞进行成像，观察了其对光的透射、吸收等光学性质，并对两种成像方法进行了比较．研究发现：淋巴细胞膜表面凹凸不平，分布着大量直径几十到几百纳米不等的小颗粒；淋巴细胞中央部位有自发荧光现象．结果表明，AFM和SNOM可作为进一步探讨淋巴细胞的结构与功能关系的有力工具．     

Laser‐induced periodic surface structure on a polymer surface: The effect of a prerubbing treatment on the surface structure

The influence of the mechanical rubbing of a polyimide (PI) film on the laser‐induced periodic structure (LIPS) was demonstrated. The periodicity and amplitude of LIPS were greater when the rubbing direction was parallel to the laser polarization direction. The amplitude became small and the periodicity of LIPS did not show an obvious change when the rubbing direction was perpendicular to the laser polarization direction. The effect of the rubbing pretreatment on LIPS was explained on the basis of the wave‐guide effect of rubbing‐induced microgrooves on LIPS formation. The orientation of PI chains induced by mechanical rubbing was relaxed after laser irradiation, and a new orientation of PI chains was formed during the LIPS formation. When the rubbing direction was perpendicular to the laser polarization direction, the orientation of PI chains remained in the rubbing direction. The laser‐irradiated, perpendicularly rubbed PI surface could be used to verify the effects of surface morphologies and intermolecular interactions on liquid‐crystal alignment. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1273–1280, 2003     

Effect of coagulant temperature and composition on surface morphology and mass transfer properties of cellulose acetate hollow fiber membranes

Cellulose acetate (CA) hollow fibers were spun via the dry‐jet wet spinning technique under various external coagulant compositions and temperatures. The surface morphology of the resulting hollow fiber was examined using field emission scanning electron microscopy (FESEM) and tapping mode atomic force microscopy (TMAFM). The pure water permeability (PWP) and the retention of dextran of the hollow fiber were also measured. The results showed that both the temperature and composition can affect greatly the surface morphology and hence the permeation performance of hollow fiber membranes when the temperature was over 55°C and the dimethyl formamide (DMF) content was higher than 15%. The on‐line draw ratio increased with the coagulant temperature and DMF content (in the range of 0 to 10%) in the external coagulant. The ultimate tensile strength also increased when the fibers were coagulated in 5–10% DMF and at 70°C. The PWP increased with the DMF content in the coagulant and the coagulant temperature. The retention of dextran decreased with the increase of the DMF content in the coagulant and the coagulant temperature. Copyright © 2005 John Wiley & Sons, Ltd.     

Interlocking layer structures formed in spin‐cast polymer blend films by surface segregation and self‐stratification

Surface morphologies formed by the phase segregation of poly(styrene‐b‐ethylene/butylene‐b‐styrene) (SEBS)/poly(methyl methacrylate) (PMMA) blend films prepared via spin coating on mica substrates were studied with atomic force microscopy accompanied by a solvent extraction treatment, X‐ray photoelectron spectroscopy, and contact‐angle measurements. Three kinds of surface structures of films were observed. Besides the ribbonlike morphology and the dispersed domains in a continuous matrix that are common in this field, we found a special interlocking layer structure characterized by a smooth SEBS layer as the cover on the top and a layer composed of hill‐like PMMA dispersed in the SEBS matrix at the bottom when the composition of the film was around 50:50 SEBS and PMMA. A series of blend films with different thicknesses were then prepared to investigate the interfacial structure, and the formation process of the interlocking layer, which could be elucidated by a schematic diagram, was discussed. The interlocking bilayer film with SEBS on the top possessed high thermal stability and the best surface roughness in comparison with other structures. It might find important technical applications in fields such as adhesion, lubrication, and protective coatings. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 532–543, 2007.     

Photodegradation of tetramethylpolycarbonate (TMPC): Correlation of properties with chemical modifications

The consequences of tetramethylpolycarbonate (TMPC) photoageing (λ > 300 nm) on the surface modifications of the material have been analysed. Roughness and stiffness measurements were performed using AFM (Atomic Force Microscopy). Gel fraction measurements, DMTA (Dynamic Mechanical Thermal Analysis) measurements and infrared analyses were also performed. The results indicate that the three-dimensional network forms as a result of crosslinking reactions. The modifications of the properties measured using each technique were followed as functions of the irradiation time, and the influence of oxygen was characterised. The surface modifications are explained in light of the modifications of the chemical structure. Quantitative correlations were obtained between the main relevant criteria characterizing the surface degradation from the chemical structure to the mechanical properties.     

Label-free detection of the aptamer binding on protein patterns using Kelvin probe force microscopy (KPFM)

Anti-lysozyme aptamers are found to preferentially bind to the edge of a tightly packed lysozyme pattern. Such edge-binding is due to the better accessibility and flexibility of the edge lysozyme molecules. Kelvin probe force microscopy (KPFM) was used to study the aptamer–lysozyme binding. Our results show that KPFM is capable of detecting the aptamer–protein binding down to the 30 nm scale. The surface potential of the aptamer–lysozyme complex is approximately 12 mV lower than that of the lysozyme. The surface potential images of the aptamer-bound lysozyme patterns have the characteristic shoulder steps around the pattern edge, which is much wider than that of a clean lysozyme pattern. These results demonstrate the potentials of KPFM as a label-free method for the detection of protein–DNA interactions. Figure Aptamers preferentially bind on the edge of a protein pattern as revealed by Kelvin force microscopy.

Temperature-programmed desorption as a tool for quantification of protein adsorption capacity in micro- and nanoporous materials

The protein adsorption capacity of porous sorbents is generally obtained by measuring the concentration of proteins desorbed from the materials after treatment by a detergent, or by measuring the decrease of protein concentration in the solution. These methods have some drawbacks and often lead to a low precision in the determination of the adsorption capacities. We describe in this paper a new method that allows to directly quantify the amount of proteins adsorbed on porous materials. This method is based on the quantitative analysis by mass spectrometry of some low mass gaseous species which evolve from the biomolecules during the heat treatment of a temperature-programmed desorption analysis (TPD-MS). The method has been applied to bovine serum albumin and cytochrome C adsorbed on an activated carbon. The adsorption uptake of the proteins on the carbon material could be measured by this direct analysis. A comparison with the depletion method was done, it shows that the two methods are complementary. The depletion method allows a determination of the total adsorption capacity, while the TPD-MS method focus on irreversible capacity.