Direct Measurement Of Interaction Forces Research Articles

Direct measurements of interaction forces of bovine serum albumin and lysozyme with stainless steel by atomic force microscopy

The adsorption of proteins on metal surfaces is important in various fields of engineering and science. Thus, it is necessary to understand the very complex phenomena of interactions between proteins and metal surfaces. In this study, we directly measured the interactions between proteins and stainless steel (SS) surfaces, the most common metal in engineering, by atomic force microscopy (AFM). Bovine serum albumin (BSA) and lysozyme (LSZ) were chemically attached to the tip of an AFM probe, and the interaction forces between the probe tip and the SS substrate were measured. The approaching forces between the proteins and metal surfaces were dominated by electrostatic double-layer and steric repulsion. However, the dependence of adhesion force on pH was not totally consistent with the approaching forces for both proteins. The adhesion of BSA to the SS surface was strongest in mildly acidic solutions, whereas that of LSZ was almost independent of pH. This result indicates that local interactions between the functional groups of proteins and SS, particularly the interactions between carboxyl and hydroxyl groups, are significant. The dependence of the adhesion forces on the contact time reveals that the mechanical properties (hardness) of proteins also have a significant effect on their adhesion on surfaces.

Direct measurement of interaction force between hydrophilic silica surfaces in triblock copolymer solutions with salt by atomic force microscopy

Triblock copolymers composed of polyethylene oxide (PEO) and polypropylene oxide (PPO) are used in various fields as nonionic surfactants. In this study, we measured interaction forces between untreated hydrophilic silica surfaces in solutions with two typical triblock copolymers, Pluronic P123 (PEO20PPO70PEO20) and F127 (PEO99PPO65PEO99), in the presence of 1 mM and 500 mM NaCl using atomic force microscopy (AFM). In solutions at the copolymer concentration of 1 µM, which is below the critical micelle concentration (CMC), the measured interaction forces were monotonically repulsive in the presence of 1 mM NaCl, which suggested the brush-like conformation of copolymers on the surfaces. When the concentration of NaCl was increased to 500 mM, interaction forces became attractive, which indicated the bridging of adsorbed polymers onto surfaces, the strength of which varied depending on the affinity and adsorption density of copolymers. The interactions at the copolymer concentration of 1 mM, which were above the CMC of both copolymers, were steric repulsions between adsorbed micelles on the surfaces with 1 mM of NaCl. For 500 mM of NaCl, an attractive jump after a steric repulsion was observed only in the force curve for P123, which inferred that the displacement of micelles from the surfaces was presumably due to a decrease in the strength of adsorption caused by the dehydration of EO groups. These results indicated that the length of the EO group considerably affected the interactions.

A feasibility study on direct measurements of interaction forces between carbon fiber surfaces and other substances

AbstractMechanical properties of carbon fiber (CF) reinforced plastic composites are influenced by physicochemical interactions between CF surfaces and matrix polymers. Poor interfacial adhesion between CF surfaces and matrix polymer molecules caused by inertness of graphitic carbon still remains to be solved. Deeper comprehension of the interfacial properties would promote advancement of technologies enhancing the physicochemical interactions. Versatile methods for evaluation of CF surface properties along with interactions at the CF/polymer interface are required. In the present paper, we propose a method to measure interaction forces between CF surfaces and other substances with the aid of atomic force microscope (AFM). Small CF chips were mounted on AFM cantilevers to measure forces between the CF chip surfaces and other materials. Interaction forces between CF chips with/without ultraviolet generated ozone (UV‐ozone) treatment and epoxy precursor molecules were monitored. It has been widely accepted that the UV‐ozone treated CF surfaces exhibit superior affinity to organic molecules. Results of the interaction force measurements were consistent with the knowledge. This is the first paper reporting direct measurement of interaction forces between CF surfaces and other substances.

Flotation intensification of low-rank coal using a new compound collector

Traditional non-polar oil collectors cannot achieve high recovery of low-rank coal because of the presence of oxygen-containing groups at coal surface. In this study, a new mixture of fossil oil and oxygen containing compound (FO) was used to enhance low-rank coal flotation compared with that using traditional collector, diesel oil. The oil droplet-particle detachment, induction-time, stability of the bubble-particle aggregate, attachment angle test and chemical force microscopy (CFM) were selected to further analyze the strengthening mechanism of collectors. The results show that higher yield was obtained using FO than that using diesel. Compared with diesel, FO was easier to adhere and spread on coal surface. The shorter induction time, higher amplitude and bigger attachment angle in presence of FO indicated that the FO treatment enabled the particles to much easily adhere to bubble. CFM provided a new insight into intensification mechanism of collector by the direct measurement of interaction force.

Direct measurement of interaction force between solid surface and air bubble: Relationship between interaction force and contact angle

Estimating the hydrophobicity of a solid surface is important for flotation process. Measuring the contact angle or interaction force between air bubbles and a solid surface has been widely used for evaluating the hydrophobicity of surfaces. However, the correlation between the contact angle and interaction force was not be fully explained because contact angle was measured on a macroscale surface and interaction force was measured on a microscale surface (ranging nm2 – μm2) using atomic force microscopy. In this study, we directly measured the macroscale surface – air bubble interaction force in terms of attachment force and detachment energy. We then correlated our measured attachment force and detachment energy values with the static contact angle of specimen surface. The attachment force (Fa) and detachment energy in phase 2 (E2) represented the hydrophobicity of specimen surface. And Fa and Ed in phase 2 were found to have an exponential relationship until 90° of the surface contact angle.

Direct measurement of interaction forces between a yeast cell and a microbubble using atomic force microscopy

The removal of adhered cells on surfaces is an important issue in every industrial process. Although bubbles are increasingly being considered for use in cleaning technology due to their positive properties, the cleaning effects of using bubbles and their mechanisms related to interaction forces remain poorly understood. Atomic force microscopy (AFM) is capable of nanoscale force resolution and has been increasingly applied to measure the interaction forces targeting bubbles or biological surfaces. However, few studies have reported on the quantitative measurement of interaction forces between a single microbial cell and a hydrophobic bubble surface. In this study, we attempted to conduct direct measurement of the interaction forces between a yeast cell and a microbubble (MB) using AFM. We demonstrated that the strong adhesive force is attributed to the capillary and hydrophobic forces between a yeast cell and a MB. This force was found to be larger than that between a yeast cell and a stainless-steel substrate. These findings provide useful information for various applications using MBs, including cleaning technology for industrial processes.

Direct Measurement of Interaction Forces between Surfaces in Liquids Using Atomic Force Microscopy

The stability of particle suspensions, which is important in numerous industrial processes, is generally dominated by the interaction forces between the suspended particles. Understanding the interaction forces between surfaces in liquids is therefore fundamentally important in order to evaluate and control how particulates, including fluid droplets in emulsions and air bubbles in foams, behave in various systems. The invention of the surface force apparatus (SFA) enabled the direct measurement of interaction forces in liquids with molecular level resolution and it has led to remarkable progress in understanding surface forces in detail. Following the SFA, the application of atomic force microscopy (AFM) to force measurement has further extended the possibility of force measurements to a broad field of research, mainly due to the range of materials that can be employed. This review provides an overview of developments in the investigation of interaction forces between surfaces using AFM. The properties of various interaction forces, important in particle technology, revealed by the studies using AFM are described in detail.

Direct Measurement of Interaction Force in the Oil by AFM

Direct Measurement of Interaction Force in the Oil by AFM

A Lyapunov Stable Controller for Bilateral Haptic Teleoperation of Single-Rod Hydraulic Actuators Subjected to Base Disturbance

In this paper, a control scheme is developed and evaluated for stable bilateral haptic teleoperation of a single-rod hydraulic actuator subjected to base disturbance. The proposed controller, based on Lyapunov stability technique, is capable of reducing position errors at master and slave sides, and provides a feel of the contact force between the actuator and the task environment to the operator without a need for direct measurement. The controller requires only the measurements of the actuator line pressures and displacements of the master and slave. The system stability is insensitive to the uncertainties of the physical parameters and of the measurement of the base point motion. Stability of the proposed controller incorporating hydraulic nonlinearities and operator dynamics with an estimated upper value for the base disturbance is analytically proven. Simulation studies validate that the proposed control system is stable while interacting with a task environment. Experimental results demonstrate the effectiveness of control scheme in maintaining stability, while having good position tracking by the hydraulic actuator as well as providing a haptic feel to the operator without direct measurement of interaction force, while the hydraulic actuator is subjected to base disturbance.

Direct measurement of interaction forces between a platinum dichloride complex and DNA molecules.

The interaction forces between a platinum dichloride complex and DNA molecules have been studied using atomic force microscopy (AFM). The platinum dichloride complex, di-dimethylsulfoxide-dichloroplatinum (II) (Pt(DMSO)2Cl2), was immobilized on an AFM probe by coordinating the platinum to two amino groups to form a complex similar to Pt(en)Cl2, which is structurally similar to cisplatin. The retraction forces were measured between the platinum complex and DNA molecules immobilized on mica plates using force curve measurements. The histogram of the retraction force for λ-DNA showed several peaks; the unit retraction force was estimated to be 130 pN for a pulling rate of 60nm/s. The retraction forces were also measured separately for four single-base DNA oligomers (adenine, guanine, thymine, and cytosine). Retraction forces were frequently observed in the force curves for the DNA oligomers of guanine and adenine. For the guanine DNA oligomer, the most frequent retraction force was slightly lower than but very similar to the retraction force for λ-DNA. A higher retraction force was obtained for the adenine DNA oligomer than for the guanine oligomer. This result is consistent with a higher retraction activation energy of adenine with the Pt complex being than that of guanine because the kinetic rate constant for retraction correlates to exp(FΔx - ΔE) where ΔE is an activation energy, F is an applied force, and Δx is a displacement of distance.

Direct measurement of interaction forces between bovine serum albumin and poly(ethylene oxide) in water and electrolyte solutions.

The net interaction between a probe tip coated with bovine serum albumin (BSA) protein and a flat substrate coated with poly(ethylene oxide) (PEO) polymer was measured directly on approach in water and electrolyte solutions using AFM. The approach force curve between the two surfaces was monotonically repulsive in water and in electrolyte solutions. At pH ~5, slightly above the isoelectric point (pI) of BSA, and at large distances, the force was dominated by electrostatic repulsion between the oxygen atoms of the incoming protein with those belonging to the ether groups of PEO. Such repulsive force and range decreased in NaCl. Under physiological conditions, pH 6, BSA is definitely charged and the electrostatic repulsion with ether groups in PEO appears at larger separation distances. Interestingly, at pH 4, below the pI of BSA, the repulsion decreased because of an attractive, although weak, electrostatic force that appeared between the ether groups in PEO and the positively charged amino groups of BSA. However, for all solution conditions, once compression of PEO begun, the net repulsion was always dominated by short-range polymeric steric repulsion and repulsive enthalpy penalties for breaking PEO-water bonds. Results suggest that PEO in mushroom conformation may also be effective in reducing biofouling.

Direct measurement of interaction forces between charged multilamellar vesicles†.

Depletion-attraction induced adhesion of two giant (∼ 40 μm), charged multilamellar vesicles is studied using a new Cantilevered-Capillary Force Apparatus, developed in this laboratory. The specific goal of this work is to investigate the role of dynamics in the adhesion and de-adhesion processes when the vesicles come together or are pulled apart at a constant velocity. Hydrodynamic effects are found to play an important role in the adhesion and separation of vesicles at the velocities that are studied. Specifically, a period of hydrodynamically controlled drainage of the thin film between vesicles is observed prior to adhesion, and it is shown that the force required to separate a pair of tensed, adhering vesicles increases with increasing separation velocity and membrane tension. It is also shown that the work done to separate the vesicles increases with separation velocity, but exhibits a maximum as the membrane tension is varied.

Direct Measurement of Interaction Forces between Adsorbed Polymer Layers

Abstract The interaction forces between adsorbed layers of two graft copolymers were directly measured using surface force apparatus and atomic force microscopy. Two types of graft copolymers that were adsorbed on hydrophobic surfaces were used: (i) a graft copolymer consisting of poly(methyl methacrylate)/poly(methacrylic acid) backbone (the B chain) on which several poly(ethylene oxide) chains are grafted (to be referred to as PMMA/PEOn) and (ii) a graft copolymer consisting of inulin (linear polyfructose with degree of polymerization greater than 23) (the A chain) on which several C12 chains are grafted (INUTEC SP1). In the first case, adsorbed layers of the graft copolymer were obtained on mica sheets and the interaction forces were measured using the surface force apparatus. In the second case, the interaction forces were measured using atomic force microscopy (AFM). For this purpose, a hydrophobically modified glass sphere was attached to the tip of the cantilever of the AFM and the glass plate was also made hydrophobic. Both the sphere and the glass plate contained an adsorbed layer of INUTEC SP1. The curves of energy E(D) versus distance D for the graft copolymer of PMMA/PEOn between mica surfaces bearing the graft copolymer could be used to estimate the interaction energy between flat surfaces, by using Derjaguin approximation for cross cylinders. The results were compared with the theoretical calculations using de Gennes scaling theory. The agreement between experimental results and theoretical calculations was satisfactory. The same graft copolymer was used in latex dispersions, and the high frequency modulus G′∝ was measured as a function of the volume fraction φ of the dispersion. This high-frequency modulus could be related to the potential of mean force. In this way, one could compare the results obtained from rheology and those obtained from direct measurement of interaction forces. In the AFM method, the interaction forces are measured in the contact area between two surfaces, i.e., the surfaces of a spherical glass particle and a glass plate. The glass spheres and plates were hydrophobized using dichlorodimethylsilane. Results were obtained for adsorbed layers of INUTEC SP1 in water and in the presence of various concentrations of Na2SO4 (0.3, 0.8, 1.0, and 1.5 mol dm−3). All results showed a rapid increase in force with a decrease in the separation distance, and the forces were repulsive up to the highest Na2SO4 concentration. This explains the high stability of dispersions when using INUTEC SP1 as the stabilizer.

Interaction Forces between BSA Adsorbed Layer on Amino-Thiolated Gold Surfaces

Direct measurement of interaction forces between bovine serum albumin (BSA) adsorbed layers on amino-thiolated gold surfaces has been carried out using colloidal probe atomic force microscopy (AFM). The substrate was prepared via self-assembly of 2-aminoethanethiol on gold in aqueous media. In the absence of BSA, an electric double layer interaction was observed, resulting from protonation of the primary amine groups on the gold surface. Similar electric double layer repulsions were seen in the presence of BSA over a whole range of BSA concentration investigated. These repulsive interactions were found to be dependent on the BSA concentration, that is, the magnitude of the repulsion increases with the BSA concentration. This phenomenon is attributed to the difference in the adsorbed amount of BSA on the amino-thiolated gold surface, which was confirmed using a 27 MHz quartz crystal microbalance (QCM).

Non-Contact to Contact Transition: Direct Measurements ofInteraction Forces between a Solid Probe and a Planar Air–WaterInterface

The interaction force between a solid probe and a planar air–waterinterface is measured by using an atomic force microscope. It isdemonstrated that during the approach of the probe to the air–waterinterface, the force curves decline all the time due to the van derWaals attraction and induces a stable profile of water surface raised.When the tip approaches very close to the water surface, force curvesjump suddenly, reflecting the complex behaviour of the unstable watersurface. With a theoretical analysis we conclude that before the tiptouches water surface, two water profiles appear, one stable and theother unstable. Then, with further approaching, the tip touches watersurface and the non-contact to contact transition occurs.

Sensor for direct measurement of interaction forces in probe microscopy

We introduce a sensor for direct measurement of tip-sample interaction forces in probe microscopy. The sensor uses a micromachined membrane structure built on a transparent substrate with an integrated diffraction grating for optical interferometric detection, and a built-in electrostatic actuator. To demonstrate our concept for this sensor, we measured the force curves between an atomic force microscope (AFM) cantilever tip and a micromachined aluminum sensor membrane built on a quartz substrate. We also measured transient interaction forces exerted on the sensor membrane during each cycle of the vibrating AFM cantilever. These agree well with the temporal response of the sensor to a short force pulse applied by our integrated electrostatic actuator. With the addition of an integrated tip, this structure may be used for scanning probe microscopy with a bandwidth limited by the membrane dynamics.

原子間力顕微鏡による水溶液中での固体微粒子‐気泡間相互作用力の直接測定

Interaction forces between a bubble and a particle are critical for various industrial processes that handle colloidal dispersions, especially for froth flotation. Therefore, it is fundamentally important to understand the surface force between a bubble and a particle to control froth flotation process effectively. In this study, we conducted direct measurements of interaction forces between a spherical solid particle (silica and iron oxide) and a small air bubble in aqueous electrolyte using atomic force microscope (AFM). Interaction forces were measured between the particle attached on the top of AFM probe and air bubble generated on the flat surface. The forces between the silica and the bubble were repulsive over the wide range of the conditions of present experiments. The origin of the force was considered to be electrostatic force. In the case of iron oxide-air bubble system, the interaction forces were attractive when the pH was lower than isoelectric point (iep) of the ion oxide, while the forces were repulsive when the pH exceeded the iep. The attractive forces were stronger and longer-ranged than the force predicted by heterocoagulation theory. It was found that these interaction forces could explain batch column flotation results with nitrogen gas bubbles qualitatively.

Interaction Forces on α-Alumina Surfaces with Coadsorption of Anionic/Nonionic Surfactant Mixtures

Direct measurement of interaction forces between α-alumina surfaces with coadsorbed anionic sodium dodecyl sulfate (SDS) and nonionic hexaoxyethylenedodecyl ether (C12E6) at pH 3.5 is carried out by colloidal probe atomic force microscopy. The strength of interaction forces is found to be dependent on the initial SDS concentrations, whereas the addition of C12E6 alone causes negligible effects on the interaction. This is due to the absence of attractive interactions between C12E6 molecules and α-alumina. On the other hand, the interaction forces are remarkably different for the simultaneous addition of the two surfactants. At lower C12E6 concentrations the observed repulsion induced by the electric double layer is larger than that in the corresponding single SDS solution, suggesting the stronger SDS adsorption as a consequence of the reduction of the electrostatic repulsion between the ionic headgroups of SDS admicelles. By the further addition of C12E6 a steric stabilizing force is detected from the separation of approximately 5 nm. This is attributed to the formation of a closely packed adlayer comparing with the case of the single SDS admicelles. The effects of sequential addition of C12E6 to the α-alumina preadsorbed hydrophobically with SDS are also investigated to understand the complex phenomena that occur at the interface.

Direct measurement of interaction forces between a single bacterium and a flat plate

A technique for precisely measuring the equilibrium and viscous interaction forces between a single bacterium and a flat surface as functions of separation distance is described. A single-beam gradient optical trap was used to micromanipulate the bacterium against a flat surface while evanescent wave light scattering was used to measure separation distances. Calibrating the optical trap far from the surface allowed the trapped bacterium to be used as a force probe. Equilibrium force–distance profiles were determined by measuring the deflection of the cell from the center of the optical trap at various trap positions. Simultaneously, viscous forces were determined by measuring the relaxation time for the fluctuating bacterium. Absolute distances were determined using a best-fit approximation to the theoretical prediction for the hindered mobility of a diffusing sphere near a wall. Using this approach, forces in the range from 0.01 to 4 pN were measured at near-nanometer resolution between Staphylococcus aureus and glass that was bare or coated with adsorbed protein.

Direct Force Measurements between α-Alumina Surfaces with Adsorption of Anionic Surfactant/Polymer Mixtures

Direct measurements of interaction forces between α-alumina surfaces with coadsorbed anionic surfactant sodium dodecyl sulfate (SDS) and anionic polyelectrolyte poly(sodium 4-styrenesulfonate) (PSS) at pH 3.5 are carried out by colloidal probe atomic force microscopy. It is found that in aqueous PSS solutions the interaction forces are dependent on the initial PSS concentration. At low PSS concentration the electrostatic repulsion initially present is neutralized, resulting in a weak attraction between the surfaces, while as the concentration is increased further, repulsive forces reappear due to the additional adsorption of PSS on the surface. The adsorbed PSS adopts a relatively flat conformation at all PSS concentrations investigated. On the other hand, the interaction forces are dramatically different for the simultaneous addition of SDS and PSS: the force profile for the coaddition comes progressively close to that for the addition of SDS alone with increasing SDS concentration. This is attributed to the fact that SDS plays a key role for the coadsorption of SDS and PSS over a high SDS concentration region. The dispersion stability and ζ potential of α-alumina suspensions are evaluated for comparison with the resultant forces, and a good correlation is obtained between them. The effects of sequential addition of SDS and PSS are also investigated.