attana - sensor technologies

Surface Chemistry

  • Analyst, 2016, 141, 3993-3996 Signal enhancement in ligand–receptor interactions using dynamic polymers at quartz crystal microbalance sensorsGunnar Dunér, Henrik Anderson, Zhichao Pei, Björn Ingemarsson, Teodor Aastrup and Olof Ramström

    The signal enhancement properties of QCM sensors based on dynamic, biotinylated poly(acrylic acid) brushes has been studied in interaction studies with an anti-biotin Fab fragment. The poly(acrylic acid) sensors showed a dramatic increase in signal response with more than ten times higher signal than the carboxyl-terminated self-assembled monolayer surface.

    © The Royal Society of Chemistry 2016

  • Biosensors and Bioelectronics, Volume 76, 15 February 2016, Pages 113–130 Glyconanomaterials for biosensing applicationsNanjing Hao, Kitjanit Neranon, Olof Ramström and Mingdi Yan

    Nanomaterials constitute a class of structures that have unique physiochemical properties and are excellent scaffolds for presenting carbohydrates, important biomolecules that mediate a wide variety of important biological events. The fabrication of carbohydrate-presenting nanomaterials, glyconanomaterials, is of high interest and utility, combining the features of nanoscale objects with biomolecular recognition. The structures can also produce strong multivalent effects, where the nanomaterial scaffold greatly enhances the relatively weak affinities of single carbohydrate ligands to the corresponding receptors, and effectively amplifies the carbohydrate-mediated interactions. Glyconanomaterials are thus an appealing platform for biosensing applications. In this review, we discuss the chemistry for conjugation of carbohydrates to nanomaterials, summarize strategies, and tabulate examples of applying glyconanomaterials in in vitro and in vivo sensing applications of proteins, microbes, and cells. The limitations and future perspectives of these emerging glyconanomaterials sensing systems are furthermore discussed.

    Copyright © 2015 Elsevier B.V. All rights reserved.

  • Applied Surface Science, Volume 343, 15 July 2015, Pages 166–171 Ionization of covalent immobilized poly(4-vinylphenol) monolayers measured by ellipsometry, QCM and SPRSuji Uppalapati, Na Kong, Oscar Norberg, Olof Ramström and Mingdi Yan

    Covalently immobilized poly(4-vinylphenol) (PVP) monolayer films were fabricated by spin coating PVP on perfluorophenyl azide (PFPA)-functionalized surfaces followed by UV irradiation. The pH-responsive behavior of these PVP ultrathin films was evaluated by ellipsometry, quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). By monitoring the responses of these films to pH in situ, the ionization constant of the monolayer thin films was obtained. The apparent pKa value of these covalently immobilized PVP monolayers, 13.4 by SPR, was 3 units higher than that of the free polymer in aqueous solution.

    Copyright © 2015 Elsevier B.V. All rights reserved.

  • Advanced Materials 2015 Sep 16;27(35):5165-70 Biomimetic Approach for Ion Channels Based on Surfactant Encapsulated Spherical Porous Metal-Oxide CapsulesMahon E., Garai S., Müller A. and Barboiu M.

    Distinguished hybrid clusters with hydrophilic and hydrophobic interiors embedded within cationic surfactant shells are spontaneously inserted into lipid bilayers, showing well-defined ionic conductance behaviors. The transport via the narrow pore gates acting as selectivity filters is controlled by the dehydration energy of the cations.

    © WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Nanoscale, 2015,7, 16039-16045 Weighing the surface charge of an ionic liquidNicklas Hjalmarsson, Daniel Wallinder, Sergei Glavatskih, Rob Atkin, Teodor Aastrup and Mark W. Rutland

    Electrochemical quartz crystal microbalance has been used to measure changes in the composition of the capacitive electrical double layer for 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate, an ionic liquid, in contact with a gold electrode surface as a function of potential. The mass difference between the cation and anion means that the technique can effectively “weigh” the surface charge accurately with high temporal resolution. This reveals quantitatively how changing the potential alters the ratio of cations and anions associated with the electrode surface, and thus the charge per unit area, as well as the kinetics associated with these interfacial processes. The measurements reveal that it is diffusion of co-ions into the interfacial region rather than expulsion of counterions that controls the relaxation. The measured potential dependent double layer capacitance experimentally validates recent theoretical predictions for counterion overscreening (low potentials) and crowding (high potentials) at electrode surfaces. This new capacity to quantitatively measure ion composition is critical for ionic liquid applications ranging from batteries, capacitors and electrodeposition through to boundary layer structure in tribology, and more broadly provides new insight into interfacial processes in concentrated electrolyte solutions.

    © Royal Society of Chemistry 2017

  • mAbs, Volume 7, 2015 - Issue 1 Preclinical and early clinical development of GNbAC1, a humanized IgG4 monoclonal antibody targeting endogenous retroviral MSRV-Env proteinFrançois Curtin, Hervé Perron, Arno Kromminga, Hervé Porchet and Alois B Lang

    Monoclonal antibodies (mAbs) play an increasing important role in the therapeutic armamentarium against multiple sclerosis (MS), an inflammatory and degenerative disorder of the central nervous system. Most of the mAbs currently developed for MS are immunomodulators blocking the inflammatory immune process. In contrast with mAbs targeting immune function, GNbAC1, a humanized IgG4 mAb, targets the multiple sclerosis associated retrovirus envelope (MSRV-Env) protein, an upstream factor in the pathophysiology of MS. MSRV-Env protein is of endogenous retroviral origin, expressed in MS brain lesions, and it is pro-inflammatory and toxic to the remyelination process, by preventing the differentiation of oligodendrocyte precursor cells. We present the preclinical and early clinical development results of GNbAC1. The specificity of GNbAC1 for its endogenous retroviral target is described. Efficacy of different mAb versions of GNbAC1 were assessed in MSRV-Env induced experimental allergic encephalitis (EAE), an animal model of MS. Because the target MSRV-Env is not expressed in animals, no relevant animal model exists for a proper in vivo toxicological program. An off-target 2-week toxicity study in mice was thus performed, and it showed an absence of safety risk. Additional in vitro analyses showed an absence of complement or antibody-dependent cytotoxicity as well as a low level of cross-reactivity to human tissues. The first-in-man clinical study in 33 healthy subjects and a long-term clinical study in 10 MS patients showed that GNbAC1 is well tolerated in humans without induction of immunogenicity and that it induces a pharmacodynamic response on MSRV biomarkers. These initial results suggest that the mAb GNbAC1 could be a safe long-term treatment for patients with MS with a unique therapeutic mechanism of action.

    © 2017 The Author(s). Published with license by Taylor & Francis Group, LLC

  • ACS Applied Materials & Interfaces: One-Step Synthesis of Dual Clickable Nanospheres via Ultrasonic- Assisted Click Polymerization for Biological ApplicationsYong Hou, Shoupeng Cao, Xueming Li, Beibei Wang, Yuxin Pei, Lin Wang, and Zhichao Pei

    Dual clickable nanospheres (DCNSs) were synthesized in one step using an efficient approach of ultrasonic-assisted azide−alkyne click polymerization, avoiding the need of surfactants. This novel approach presents a direct clickable monomer-to-nanosphere synthesis. Field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and dynamic laser scattering (DLS) were used to characterize the synthesized DCNSs. Numerous terminal alkynyl and azide groups on the surface of DCNSs facilitate effective conjugation of multiple molecules or ligands onto a single nanocarrier platform under mild conditions. To exemplify the potential of DCNSs in biological applications, (1) multivalent glyco-nanoparticles (GNPs) were prepared by clicking DCNSs with azide-functionalized and alkyne-functionalized lactose sequentially for the determination of carbohydrate-galectin interactions with quartz crystal microbalance (QCM) biosensor. Using protein chip (purified galectin-3 coated on chip) and cell chip (Jurkat cells immobilized on chip), the QCM sensorgrams showed excellent binding activity of GNPs for galectins; (2) fluorescent GNPs were prepared by clicking DCNSs with azide-functionalized Rhodamine B and alkyne functionalized lactose sequentially in order to target galectin, which is over expressed on the surface of Jurkat cells. The fluorescent images obtained clearly showed the cellular internalization of fluorescent GNPs. This fluorescent probe could be easily adapted to drugs to construct lectin-targeted drug delivery systems. Thus, DCNSs prepared with our method may provide a wide range of potential applications in glycobiology and biomedicine.

    © 2014 American Chemical Society

  • Biosens Bioelectron. 2014 Mar 15;53:154-9 Atmospheric pressure plasma polymers fortuned QCM detection of protein adhesionRusu, Asandulesa, Topala, Pohoata, Dumitrascu, Barboiu

    Our efforts have been concentrated in preparing plasma polymeric thin layers at atmospheric pressure grown on Quartz Crystal Microbalance-QCM electrodes for which the non-specific absorption of proteins can be efficiently modulated, tuned and used for QCM biosensing and quantification. Plasma polymerization reaction at atmospheric pressure has been used as a simple and viable method for the preparation of QCM bioactive surfaces, featuring variable protein binding properties. Polyethyleneglycol (ppEG), polystyrene (ppST) and poly(ethyleneglycol-styrene) (ppST-EG) thin-layers have been grown on QCM electrodes. These layers were characterized by Atomic Force Microscopy (AFM), Contact angle measurements, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). The plasma ppST QCM electrodes present a higher adsorption of Concanavalin A (ConA) and Bovine Serum Albumin (BSA) proteins when compared with the commercial coated polystyrene (ppST) ones. The minimum adsorption was found for ppEG,
    surface, known by their protein anti-fouling properties. The amount of adsorbed proteins can be tuned by the introduction of PEG precursors in the plasma discharge during the preparation of ppST polymers.

    © 2013 Elsevier B.V. All rights reserved.

  • J Nanobiotechnology. 2014 Mar 21;12:8 Biotin selective polymer nano-filmsElmlund, Suriyanarayanan, Wiklander, Aastrup, Nicholls

    BACKGROUND: The interaction between biotin and avidin is utilized in a wide range of assay and diagnostic systems. A robust material capable of binding biotin should offer scope in the development of reusable assay materials and biosensor recognition elements.

    RESULTS: Biotin-selective thin (3-5 nm) films have been fabricated on hexadecanethiol self assembled monolayer (SAM) coated Au/quartz resonators. The films were prepared based upon a molecular imprinting strategy where N,N'-methylenebisacrylamide and 2-acrylamido-2-methylpropanesulfonic acid were copolymerized and grafted to the SAM-coated surface in the presence of biotin methyl ester using photoinitiation with physisorbed benzophenone. The biotinyl moiety selectivity of the resonators efficiently differentiated biotinylated peptidic or carbohydrate structures from their native counterparts.

    CONCLUSIONS: Molecularly imprinted ultra thin films can be used for the selective recognition of biotinylated structures in a quartz crystal microbalance sensing platform. These films are stable for periods of at least a month. This strategy should prove of interest for use in other sensing and assay systems.

    © 2014 Elmlund et al.; licensee BioMed Central Ltd.

  • Journal of Colloid and Interface Science (2013) Protein-resistant hyperbranched polyethyleneimine brush surfacesSubramanian Suriyanarayanan, Hung-Hsun Lee, Bo Liedberg, Teodor Aastrup, Ian A. Nicholls.

    A novel hyperbranched polyethyleneimine (PEI) modified gold surface has been designed, fabricated, and investigated with respect to its ability to resist non-specific adsorption of proteins. The facile synthesis strategy, based on self-assembly, involves immobilization of polyethyleneimine to gold surfaces modified with 11-mercaptoundecanoic acid (MuDA) monolayers using traditional carbodiimide chemistry. The hyperbranched polymer brushes were characterized by X-ray photoelectron spectroscopy (XPS). Reflection absorption infrared spectroscopy (RAIRS) and ellipsometry measurements showed the thickness of
    the PEI brushes increases with adsorption solution ionic strength. Polymer brush surface concentrations can be improved from 2560 to 3880 chains/lm2 by changing the ionic strength of the adsorption solution (PBS) by varying NaCl concentration from 0 to 650 mM. Protein adsorption (pH 7.4) was evaluated under flow injection analysis (FIA) conditions using a quartz crystal microbalance (QCM). The PEI brushes suppress protein adsorption, for example, cytochrome C, bovine serum albumin (BSA), and ribonuclease A, to less than 0.08 lg/cm2 and the protein resistance increases with increasing ionic strength of the carrier solution, performance comparable to that achieved with comparable PEG-coated surfaces. The PEI brushes were exceptionally stable, with adsorption characteristics maintained after 6 months storage in aqueous conditions (pH 7.4, 25 C, PBS). The potential of hyperbranched PEI structures as protein-resistant surfaces is discussed.

  • Doctoral thesis - KTH Royal Institute of Technology; Trita-CHE-Report, ISSN 1654-1081; TRITA-CHE Report 2012:49 Grafted Molecular Layers for Control of Surface PropertiesDunér, Gunnar

    The goal of this thesis work was to develop responsive surface grafted brushlayers for control of surface properties and to gain insights in the molecular mechanisms that control these properties. Three types of grafted layers were investigated, as outlined below. In the first system studied, poly(AAc) was synthesized by a grafting from approach, utilizing a photopolymerization reaction from a macroinitiator cast onto QCM substrates. The responsiveness in terms of frequency change, Δf, of the resulting brushes to changes in bulk pH was studied with QCM. Further, the friction properties of poly(AAc) was elucidated with colloidal probe AFM as a function of pH and counterion valency. High friction (μ=0.27) was found in presence of CaCl2 at high pH (7.5), but not under any other condition explored. It was concluded that the high friction was due to intralayer COO--Ca2+--OOC bridges. QCM-D was utilized for studying viscoelastic properties of growing poly(AAc) films during in situ photopolymerization. By Voigt modeling, the thickness, shear elasticity and shear viscosity were extracted. These parameters were observed to undergo sudden transitions at a critical thickness, and from this thickness the grafting density of the growing poly(AAc) layers was determined. In addition, the sensitivity to changes in Δf and ΔD with respect to the thickness of the poly(AAc) films was investigated, and the results showed that high sensitivity in ΔD is retained at higher film thicknesses than for Δf, and that the sensitivity with respect to noise can significantly alter the thickness that is best suited for the study of viscoelastic changes in sensor applications.

    © KTH Royal Institute of Technology 2012

  • Journal of Biological Chemistry, August 12, 2011 Unbinding of hyaluronan accelerates the enzymatic activity of bee hyaluronidaseAttila Iliás, Károly Liliom, Brigitte Greiderer-Kleinlercher, Stephan Reitinger and Günter Lepperdinger

    Hyaluronan (HA), a polymeric glycosaminoglycan ubiquitously present in higher animals is hydrolyzed by hyaluronidases (HAases). Here we used bee HAase as a model enzyme to study HA-HAase interaction. Located in close proximity to the active center, a bulky surface loop, which appears to obstruct one end of the substrate binding groove, was found to be functionally involved in HA turnover. To better apprehend kinetic changes in substrate interaction, binding of high molecular weight HA to catalytically inactive HAase was monitored by means of Quartz Crystal Microbalance technology. Replacement of the delimiting loop by a tetrapeptide interconnection increased the affinity for HA up to 100-fold, with a KD below 1 nM being the highest affinity amongst HA-binding proteins surveyed so far. The experimental data of HA-HAase interaction were further validated showing best fit to the theoretically proposed sequential twosite model. Besides the one, which had been shown previously in course of X-ray structure determination, a previously unrecognized binding site works in conjunction with an unbinding loop that facilitates liberation of hydrolyzed HA.

    © The American Society for Biochemistry and Molecular Biology 2011

  • Analyst 2011, 136, 3777-3782 Collagen I and III and their decorin modified surfaces studied by atomic force microscopy and the elucidation of their affinity toward positive apolipoprotein B-100 residue by quartz crystal microbalanceWitos J, Saint-Guirons J, Meinander K, D'Ulivo L, Riekkola ML

    Collagen, the major component of extracellular matrix (ECM) and the most abundant protein in the human body, is implicated in the development of atherosclerosis. Collagen types I and III were immobilized on fused-silica capillary to investigate their shape, size and structure by atomic force microscopy (AFM). For comparison, collagen was also immobilized on a mica surface. Our studies demonstrated that not only does the adsorption pattern on the substrate vary with the type of collagen, but also the substrate material plays an important role in the fibril formation process. Decorin, which promotes the binding of low-density lipoprotein (LDL) particles with collagen, was investigated for its effect on the fibrillogenesis. On both substrate materials, addition of decorin clearly reduced the fibril diameter of collagen surfaces. Moreover, a quartz crystal microbalance (QCM)-based biosensor approach was applied to clarify and evaluate the affinity of different collagen coatings immobilized on a silicon dioxide sensor chip toward apolipoprotein B-100, the major protein of LDL. The results confirmed the importance of collagen type and their fibrillogenesis on the binding of the positive residues of apolipoprotein B-100 on negatively charged collagen surfaces.

    © Royal Society of Chemistry 2011

  • Analytical and Bioanalytical Chemistry (2011) 400:1397–1404 Towards a Synthetic Avidin MimicWiklander J, Karlsson BCG, Aastrup T, Nicholls IA

    A series of streptavidin-mimicking molecularly imprinted polymers has been developed and evaluated for their biotin binding characteristics. A combination of molecular dynamics and NMR spectroscopy was used to examine potential polymer systems, in particular with the functional monomers methacrylic acid and 2-acrylamidopyridine. The synthesis of copolymers of ethylene dimethacrylate and one or both of these functional monomers was performed. A combination of radioligand binding studies and surface area analyses demonstrated the presence of selectivity in polymers prepared using methacrylic acid as the functional monomer. This was predicted by the molecular dynamics studies showing the power of this methodology as a prognostic tool for predicting the behavior of molecularly imprinted polymers.

    © Springer-Verlag 2011

  • Sensors and Actuators B 153 (2011) 135–144 Systematic investigation of biomolecular interactions using combined frequency and motional resistance measurementsH Anderson, G Wingqvist, T Weissbach, D Wallinder, I Katardjiev, B Ingemarsson

    The resonance frequency of acoustic biosensors is today used as a label-free technique for detecting mass changes on sensor surfaces. In combination with an appropriate continuous flow system it has earlier been used for affinity and kinetic rate determination. Here, we assess the potential of a modified acoustic biosensor, monitoring also the real-time dissipation through the resistance of the sensor, to obtain additional kinetic information related to the structure and conformation of the molecules on the surface. Actual interaction studies, including an attempt to determine avidity, are presented along with thorough verification of the experimental setup utilizing true viscous load exposure together with protein and DNA immobilizations.

    © 2010 Elsevier B.V.

  • Analytical Biochemistry vol. 398, Issue 2, 15 March 2010, Pages 161-168 Optimizing immobilization on two-dimensional carboxyl surface: pH dependence of antibody orientation and antigen binding capacityZhichao Pei, Henrik Anderson, Annica Myrskog, Gunnar Dunér, Björn Ingemarsson and Teodor Aastrup

    The performance of immunosensors is highly dependent on the amount of immobilized antibodies and their remaining antigen binding capacity. In this work, a method for immobilization of antibodies on a two-dimensional carboxyl surface has been optimized using quartz crystal microbalance biosensors. We show that successful immobilization is highly dependent on surface pKa, antibody pI, and pH of immobilization buffer. By the use of EDC/sulfo-NHS (1-ethyl 3-[3-dimethylaminopropyl] carbodiimide hydrochloride/N-hydroxysulfosuccinimide) activation reagents, the effect of the intrinsic surface pKa is avoided and immobilization at very low pH is therefore possible, and this is important for immobilization of acidic proteins. Antigen binding capacity as a function of immobilization pH was studied. In most cases, the antigen binding capacity followed the immobilization response. However, the antigen-to-antibody binding ratio differed between the antibodies investigated, and for one of the antibodies the antigen binding capacity was significantly lower than expected from immobilization in a certain pH range. Tests with anti-Fc and anti-Fab2 antibodies on different antibody surfaces indicated that the orientation of the antibodies on the surface had a profound effect on the antigen binding capacity of the immobilized antibodies.

    © 2009 Elsevier Inc.

  • Biosensors and Bioelectronics 24 (2009) 3387–3390 On the applicability of high frequency acoustic shear mode biosensing in view of thickness limitations set by the film resonanceG. Wingqvist, H. Anderson, C. Lennartsson, T. Weissbach, V. Yantchev, A. Lloyd Spetz

    The IC-compatible thin film bulk acoustic resonator (FBAR) technology has made it possible to move the thickness excited shear mode sensing of biological layers into a new sensing regime using substantially higher operation frequencies than the conventionally used quartz crystal microbalance (QCM). The limitations of the linear range set by the film resonance using viscoelastic protein films are here for the first time addressed specifically for FBARs operating at 700MHz up to 1.5 GHz. Two types of protein multilayer sensing were employed; one utilizing alternating layers of streptavidin and biotinated BSA and the other using stepwise cross-linking of fibrinogen with EDC/NHS activation of its carboxyl groups. In both cases the number of protein layers within the linear regime is well above the number of protein layers usually used in biosensor applications, further verifying the applicability of the FBAR as a biosensor. Theoretical calculations are also presented using wel established physical models to illustrate the expected behavior of the FBAR sensor, in view of both the frequency and the dissipation shifts.

    © 2009 Elsevier B.V.

  • Langmuir, 2008, 24 (14), pp 7559–7564 Surface-Confined Photopolymerization of pH-Responsive Acrylamide/Acrylate-Brushes on Polymer Thin FilmsGunnar Dunér, Henrik Anderson, Annica Myrskog, Maria Hedlund, Teodor Aastrup, Olof Ramström

    Dynamic acrylamide/acrylate polymeric brushes were synthesized at gold-plated quartz crystal surfaces. The crystals were initially coated with polystyrene-type thin films, derivatized with photolabile iniferter groups, and subsequently subjected to photoinitiated polymerization in acrylamide/acrylate monomer feeds. This surface-confined polymerization method enabled direct photocontrol over the polymerization, as followed by increased frequency responses of the crystal oscillations in a quartz crystal microbalance (QCM) instrumentation. The produced polymer layers were also found to be highly sensitive to external acid/base stimuli. Large oscillation frequency shifts were detected when the brushes were exposed to buffer solutions of different pH. The dynamic behavior of the resulting polymeric brushes was evaluated and the extent of expansion and contraction of the films monitored by the QCM setup in situ in real-time. The resulting responses were rapid and the effects were fully reversible. Low pH resulted in full contractions of the films, whereas higher pH yielded maximal expansion in order to minimize repulsion around the charged acrylate centers. The surfaces proved also highly robust, since the responsiveness was reproducible over many cycles of repeated expansion and contraction.

    © 2008 American Chemical Society

  • Langmuir 2007, 23, 11147-11156 Mode of Heavy Meromyosin Adsorption and Motor Function Correlated with Surface Hydrophobicity and ChargeNuria Albet-Torres, John O’Mahony, Christy Charlton, Martina Balaz, Patricia Lisboa, Teodor Aastrup, Alf Månsson and Ian A. Nicholls

    The in vitro motility assay is valuable for fundamental studies of actomyosin function and has recently been combined with nanostructuring techniques for the development of nanotechnological applications. However, the limited understanding of the interaction mechanisms between myosin motor fragments (heavy meromyosin, HMM) and artificial surfaces hampers the development as well as the interpretation of fundamental studies. Here we elucidate the HMM-surface interaction mechanisms for a range of negatively charged surfaces (silanized glass and SiO2), which is relevant both to nanotechnology and fundamental studies. The results show that the HMM-propelled actin filament sliding speed (after a single injection of HMM, 120 μg/mL) increased with the contact angle of the surfaces (in the range of 20-80°). However, quartz crystal microbalance (QCM) studies suggested a reduction in the adsorption of HMM (with coupled water) under these conditions. This result and actin filament binding data, together with previous measurements of the HMM density (Sundberg, M.; Balaz, M.; Bunk, R.; Rosengren-Holmberg, J. P.; Montelius, L.; Nicholls, I. A.; Omling, P.; Tågerud, S.; Månsson, A. Langmuir 2006, 22, 7302-7312. Balaz, M.; Sundberg, M.; Persson, M.; Kvassman, J.; Månsson, A. Biochemistry 2007, 46, 7233-7251), are consistent with (1) an HMM monolayer and (2) different HMM configurations at different contact angles of the surface. More specifically, the QCM and in vitro motility assay data are consistent with a model where the molecules are adsorbed either via their flexible C-terminal tail part (HMMC) or via their positively charged N-terminal motor domain (HMMN) without other surface contact points. Measurements of ú potentials suggest that an increased contact angle is correlated with a reduced negative charge of the surfaces. As a consequence, the HMMC configuration would be the dominant configuration at high contact angles but would be supplemented with electrostatically adsorbed HMM molecules (HMMN configuration) at low contact angles. This would explain the higher initial HMM adsorption (from probability arguments) under the latter conditions. Furthermore, because the HMMN mode would have no actin binding it would also account for the lower sliding velocity at low contact angles. The results are compared to previous studies of the microtubule-kinesin system and are also discussed in relation to fundamental studies of actomyosin and nanotechnological developments and applications.

    © 2007 American Chemical Society

  • Journal of Colloid and Interface Science (2007), doi:10.1016/j.jcis.2007.05.016 Forces and friction between hydrophilic and hydrophobic surfaces: Influence of oleate speciesKatarina Theander, Robert J. Pugh, and Mark W. Rutland

    The atomic force microscope has been used to investigate normal surface forces and lateral friction forces at different concentrations of sodium oleate, a frequently used fatty acid in the deinking process. The measurements have been performed using the colloidal probe technique with bead materials consisting of cellulose and silica. Cellulose was used together with a printing ink alkyd resin and mica, whereas silica was used with a hydrophobized silica wafer. The cellulose–alkyd resin system showed stronger double layer repulsion and the friction was reduced with increasing surfactant concentration. The adhesive interaction disappeared immediately on addition of sodium oleate. The normal surface forces for cellulose–mica indicated no apparent adsorption of the sodium oleate however, the friction coefficient increased on addition of sodium oleate, which we ascribe to some limited adsorption increasing the effective surface roughness. The silica–hydrophobic silica system showed a completely different surface force behavior at the different concentrations. An attractive hydrophobic interaction was evident since the surfaces jumped into adhesive contact at a longer distance than the van der Waals forces would predict. The strong adhesion was reflected in the friction forces as a nonlinear relationship between load and friction and a large friction response at zero applied load. Indirect evidence of adsorption to the hydrophilic silica surface was also observed in this case, and QCM studies were performed to confirm the adsorption of material to both surfaces.

    © 2007 Published by Elsevier Inc.

  • Review of Scientific Instruments 78, 083110 (2007) System for in situ studies of atmospheric corrosion of metal films using soft x-ray spectroscopy and quartz crystal microbalanceJ. Forsberg, L.-C. Duda, A. Olsson, T. Schmitt, J. Andersson, J. Nordgren, J. Hedberg, C. Leygraf, T. Aastrup, D. Wallinder, and J.-H. Guo

    We present a versatile chamber (“atmospheric corrosion cell”) for soft x-ray absorption/emission spectroscopy of metal surfaces in a corrosive atmosphere allowing novel in situ electronic structure studies. Synchrotron x rays passing through a thin window separating the corrosion cell interior from a beamline vacuum chamber probe a metal film deposited on a quartz crystal microbalance (QCM) or on the inside of the window.We present some initial results on chloride induced corrosion of iron surfaces in humidified synthetic air. By simultaneous recording of QCM signal and soft x-ray emission from the corroding sample, correlation between mass changes and variations in spectral features is facilitated.

    © 2007 American Institute of Physics.

  • Sensors and Actuators B 123 (2007) 21–26 Quartz crystal microbalance biosensor design II. Simulation of sample transportMats Jönsson, Henrik Anderson, Ulf Lindberg, and Teodor Aastrup

    The influence of flow cell geometry on sample dispersion in a quartz crystal microbalance (QCM) biosensor system was investigated. A circular and a rectangular flow cell and corresponding sensor electrodes were studied experimentally and modelled using a coupled Navier–Stokes and convection–diffusion model. Finite element simulations showed that dispersion phenomena in a flow cell can be significantly reduced with the rectangular flow cell compared to a circular system. Experimental results from measurement of the time-dependent viscosity change of a model sample indicate that the sample delivery system has a predominant effect on the dispersion of the whole sensor system. Consequently, improvement of the sensor flow cell should be accompanied with improvement of the sample delivery system. With reference to kinetic studies of biological interactions, the current dispersion should have little effect on the results for studies of interaction pairs with relatively slow to normal binding rates such as antibody–antigen interactions. Incentive for further development of the flow cell and sample delivery system exists primarily for applications with high reaction rates such as for certain receptor ligand interactions.

    © 2007 Elsevier B.V. All rights reserved.

  • Sensors and Actuators B 123 (2007) 27–34 Quartz crystal microbalance sensor design I. Experimental study of sensor response and performanceHenrik Anderson, Mats Jönsson, Lars Vestling, Ulf Lindberg, and Teodor Aastrup

    This paper investigates a novel quartz crystal microbalance (QCM) biosensor with a small and rectangular flow cell along with a correspondingly shaped crystal electrode. The sensor was evaluated with impedance analysis and compared to standard circular sensor crystals and sensor crystals with small circular electrodes. Comparative QCM measurements on an antibody–antigen interaction system were carried out on the rectangular and standard circular sensor systems. Impedance analysis and subsequent data extraction of the three different sensor crystals showed that the smaller sensors had significantly higher Q-values in air, but that liquid load on the electrodes lowered the Q-values radically for all crystals. Under liquid load, Q-values for the standard circular and the rectangular sensors were similar whereas the Q-value for the small circular sensor was 50% higher. QCM experiments showed that the QCM system with rectangular crystal electrodes was fully functional in a liquid environment. The rectangular system showed higher and more rapid responses for series of antibody injections, albeit at a higher noise level than the standard system. The study elucidates a significant potential for improvement of sensor performance by optimising the sensor electrode size and shape together with the flow cell geometry.

    © 2007 Elsevier B.V. All rights reserved.

  • Analytica Chimica Acta 536 (2005) 191–196 Molecularly imprinted polymer thin films on quartz crystal microbalance using a surface bound photo-radical initiatorTheeraphon Piacham, Åsa Josell, Hans Arwin, Virapong Prachayasittikul, Lei Ye

    The present work aims to study preparation of thin MIP films on a gold-coated QCM resonator in a well-controlled and reproducible manner. A surface-bound photo-radical initiator was used to furnish an imprinting polymerization in a dilute solution of template, functional monomer and crosslinker. Prior to polymerization, the photo-initiator was covalently coupled to a self-assembled monolayer of carboxyl terminated alkanethiol on a gold surface. With this approach we were able to control the thickness of the MIP film to be below 50nm, where the selective recognition of target analytes can be easily detected by the underlying quartz crystal resonator. When used in a flow injection analysis system, the assembled QCM sensor generated a large frequency change (>30 Hz) upon encountering a small amount of analyte (0.19 mM). The sensor had a very short response time (<1 min), and displayed certain chiral selectivity towards the original template, (S)-propranolol at a concentration higher than 0.38mM in aqueous solution.

    © 2004 Elsevier B.V. All rights reserved.