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Quartz crystal microbalance study of endothelial cell number dependent differences in initial adhesion and steady-state behavior: evidence for cell-cell cooperativity in initial adhesion and spreading.

The quartz crystal microbalance (QCM) technique has been applied to the real time monitoring of endothelial cell (EC) adhesion and spreading on the QCM gold surface. We previously showed that the measured QCM Deltaf and DeltaR shifts were due to cells adhering to the gold crystal surface, requiring proteolytic enzyme treatment to be removed from the surface, in order for the Deltaf and DeltaR shifts to return to zero. In the present report, we demonstrate the quantitative dependence and saturation of the measured Deltaf and DeltaR shifts on the number of firmly attached ECs as measured by electronic counting of the cells. We demonstrate through a light microscope simulation experiment that the different Deltaf and DeltaR regions of the QCM temporal response curve correspond to the incident ECs contacting the surface, followed by their adhesion and spreading, which reflect cellular mass distribution and cytoskeletal viscoelasticity changes. Also, we demonstrate that the dose response curve of Deltaf and DeltaR values versus attached EC number is more sensitive and possesses less scatter for the hydrophilically treated surface compared to the native gold surface of the QCM. For both surfaces, a Deltaf and DeltaR versus trypsinized, attached EC number plot 1 h post-seeding exhibits a sigmoid curve shape whereas a similar plot 24 h post-seeding exhibits a hyperbolic curve shape. This number dependence suggests cell-cell cooperativity in the initial cell adhesion and spreading processes. These QCM data and our interpretation are corroborated by differences in cell appearance and spreading behavior we observed for ECs in a light microscope fluorescence simulation experiment of the cell density effect. For a stably attached EC monolayer at 24 h post-addition, steady-state Deltaf and DeltaR values are higher and exhibit saturation behavior for both the hydrophilically treated gold surface as compared to the untreated surface. The steady-state 24 h Deltaf and DeltaR values of stably attached ECs are shifted from the 1 h attached ECs. The 24 h values are characteristic of a more energy-dissipative structure. This is consistent with the time-dependent elaboration of surface contacts in anchorage-dependent ECs via the attachment of intregrins to underlying extracellular matrix. It is also in agreement with the known energy dissipation function of the ECs that cover the interior of blood vessels and are exposed to continuous pulsatile blood flow.

Animals↗
PubMed2001

Effect of solvation on induce-fit molecular recognition in supercritical fluid to organic crystals immobilized on a quartz crystal microbalance.

The inclusion behavior of guest molecules to a solid apohost of an orthogonal anthracene-bis(resorcinol)tetraol (1) was investigated in supercritical carbon dioxide (scCO(2)) by using a 9 MHz quartz-crystal microbalance (QCM). Compound 1 forms crystals composed of molecular-sheet bound together by an extensive hydrogen-bonded network. The selective binding of gaseous ethyl acetate to the apohost-immobilized QCM in scCO(2) was observed, and the inclusion amount of ethyl acetate showed a drastic increase above a threshold concentration, [Guest](th) = 0.08 M, and the apparent Gibbs' free energy for the binding was DeltaG(app) = -1.3 kcal mol(-1). Similar selective bindings of ethyl acetate or ethanol had been observed in the gas phase and in water: [Guest](th) = 0.002 M with DeltaG(app) = -3.5 kcal mol(-1) and [Guest](th) = 0.5 M with DeltaG(app) = -0.41 kcal mol(-1), respectively. These values obtained in scCO(2) were intermediate between those in the gas and water phases. Since various physical properties (viscosity, density, polarity, diffusion constant, and solvation) of supercritical fluid are known to be intermediate between gas and liquid, these values clearly reflect the solvation behavior of guest molecules. Thus, the lower solvation of guest molecules indicates the lower threshold concentration and the larger binding energy in the following order: in air > in scCO(2) > in water.

Journal Article↗
PubMed2003

Molecular dynamics simulation of an electric field driven dipolar molecular rotor attached to a quartz glass surface.

Molecular dynamics simulations of the response of a dipolar azimuthal 3-chloroprop-1-ynyl rotor mounted on the surface of quartz glass to a rotating electric field were performed. The rotor motion was classified as synchronous, asynchronous, random, or hindered, based on the value of the average lag of the rotor behind the field and a comparison of the intrinsic rotational barrier V(b) with kT. A phase diagram of rotor behavior was deduced at 10, 300, and 500 K as a function of field strength and frequency. A simple model for the rotor motion was developed, containing the driving force, the temperature, the height of the torsional barrier, and the friction constant of the rotor. Defining E(bo) to be the electric field strength necessary to get rotational response from the rotor ("breakoff field") and mu to be the rotor dipole moment component in the plane of rotation, we find that E(bo) is frequency independent when 2 microE(bo) is less than either V(b) or kT (the driving force needs to overcome the more important of the two, the intrinsic barrier or random thermal motion). At higher frequencies, E(bo) is a quadratic function of the frequency and the driving force fights friction, which is dictated by intramolecular vibrational redistribution (IVR) from the pumped rotational mode to all others. Fitting the simple model to simulation data, we derived a friction constant of 0.26 ps eV x (nu - 0.5)/THz between 500 and 1000 GHz.

Journal Article↗
PubMed2004

Kinetic studies of AMP-dependent phosphorolysis of amylopectin catalyzed by phosphorylase b on a 27 MHz quartz-crystal microbalance.

Catalytic cleavage reactions of phosphorylase b were monitored directly on an amylopectin-immobilized 27 MHz quartz-crystal microbalance (QCM). When the inactivated phosphorylase b was injected into a phosphate buffer solution of amylopectin-immobilized QCM (method A), the binding of the enzyme to amylopectin was observed as a frequency decrease (mass increase). Then, when AMP (adenosine monophosphate) was added to activate the enzyme, the frequency gradually increased (mass decreased) due to the phosphorolysis of amylopectin in the presence of phosphates as buffers. When the AMP-activated phosphorylase b was employed (method B), the continuous reaction was observed which includes both the mass increase due to the enzyme binding to amylopectin at first and then the following mass decrease due to the phosphorolysis by the AMP-activated enzyme. All kinetic parameters for the enzyme binding to the substrate (binding and dissociation rate constants, k(on) and k(off), and dissociation constant, K(d)), the AMP binding to the enzyme as activator (K(AMP)), the catalytic rate constant (k(cat)) were obtained from curve fittings of time-courses of frequency (mass) changes. The obtained kinetic parameters were compared with those from Michaelis-Menten kinetics.

Adenosine Monophosphate↗
PubMed2006

In situ adsorption studies of a 14-amino acid leucine-lysine peptide onto hydrophobic polystyrene and hydrophilic silica surfaces using quartz crystal microbalance, atomic force microscopy, and sum frequency generation vibrational spectroscopy.

The adsorption of a 14-amino acid amphiphilic peptide, LK14, which is composed of leucine (L, nonpolar) and lysine (K, charged), on hydrophobic polystyrene (PS) and hydrophilic silica (SiO2) was investigated in situ by quartz crystal microbalance (QCM), atomic force microscopy (AFM), and sum frequency generation (SFG) vibrational spectroscopy. The LK14 peptide, adsorbed from a pH 7.4 phosphate-buffered saline (PBS) solution, displayed very different coverage, surface roughness and friction, topography, and surface-induced orientation when adsorbed onto PS versus SiO2 surfaces. Real-time QCM adsorption data revealed that the peptide adsorbed onto hydrophobic PS through a fast (t < 2 min) process, while a much slower (t > 30 min) multistep adsorption and rearrangement occurred on the hydrophilic SiO2. AFM measurements showed different surface morphologies and friction coefficients for LK14 adsorbed on the two surfaces. Surface-specific SFG spectra indicate very different ordering of the adsorbed peptide on hydrophobic PS as compared to hydrophilic SiO2. At the LK14 solution/PS interface, CH resonances corresponding to the hydrophobic leucine side chains are evident. Conversely, only NH modes are observed at the peptide solution/SiO2 interface, indicating a different average molecular orientation on this hydrophilic surface. The surface-dependent difference in the molecular-scale peptide interaction at the solution/hydrophobic solid versus solution/hydrophilic solid interfaces (measured by SFG) is manifested as significantly different macromolecular-level adsorption properties on the two surfaces (determined via AFM and QCM experiments).

Adsorption↗
PubMed2005

Density functional energetics of alpha-quartz for calibration of SiO2 interatomic potentials.

All-electron, Gaussian basis density functional theory (DFT) total energies for alpha-quartz were generated on a substantial grid of points for eventual use in a first-principles check of calibration of a widely used effective interionic potential for SiO2. Unlike a previous all-electron, Gaussian basis calculation, we do not find a weak double minimum with respect to cell volume. Rather there is a weak double minimum with respect to internal cell parameters that is at the margins of numerical precision and, hence, may only be the signal of a very flat potential surface. The results show typical dependence on the choice of approximate DFT functional and differ from experimental values enough that both aspects may be problematic for parametrization of potentials.

Journal Article↗
PubMed2005

Electrosynthesis of Cu-Se films on copper electrodes in alkaline media: a voltammetric, electrochemical quartz crystal microbalance and I/t transient study.

The electroformation of Cu-Se phases, obtained by selenizing a thin film of copper deposited on the quartz/gold electrode system, was studied with an electrochemical quartz crystal microbalance (EQCM) and by cyclic voltammetry (CV) in an alkaline solution (0.05 M Na(2)B(4)O(7)) containing selenide ion. Potentiodynamic parameters showed that the formation of the initial Cu-Se phases (Cu(2-x)Se/Cu(3)Se(2)) is ruled by an irreversible diffusion controlled mechanism, where a first electron transfer is the rate-determining step. A CV study was also performed with a bulk copper electrode in 1 M NaOH solution containing selenide ion. The deconvolution of the anodic and cathodic I/E profiles corresponding to the electroformation and electroreduction of the Cu-Se film formed allowed us to establish that, depending on the anodic potential limit of the potentiodynamic scan, the Cu-Se phases formed were either a mixture of Cu(2)(-x)Se/Cu(3)Se(2) or Cu(2-x)Se/Cu(3)Se(2)/CuSe. An EQCM study showed that, during the initial stage of Cu-Se phase electroformation, water molecules were released from the electrode. In advanced stages of the process, when the electrode was completely covered by Cu-Se compounds, selenide anions were adsorbed on the formed phase. When the anodic potential limit was extended to -0.2 V, copper oxide compounds were formed. The analysis of the cathodic charge related to Cu-Se phase electroreduction and Energy Dispersive X-ray Spectroscopy (EDXS) analysis confirmed that when the anodic limit was -0.8 V, a mixture of different Cu-Se phases was formed. A I/t transient study performed with a bulk copper electrode in alkaline solution containing selenide established that the nucleation and growth mechanism (NGM) of the Cu-Se phases takes place through an initial bidimensional-instantaneous nucleation (IN2D), followed by four bidimensional-progressive nucleations (PN2D). These results and atomic force microscopy (AFM) experiences supported that the growth of the Cu-Se films occurs through a layer-by-layer mechanism.

Journal Article↗
PubMed2006

Mechanisms of oscillations and formation of nano-scale layered structures in induced co-deposition of some iron-group alloys (Ni-P, Ni-W, and Co-W), studied by an in situ electrochemical quartz crystal microbalance technique.

We have investigated mechanisms of oscillations and formation of nano-scale layered structures in induced co-deposition of some iron-group alloys (Ni-P, Ni-W, and Co-W) that have unique properties and are widely used in industries. Detailed in situ electrochemical quartz crystal microbalance (EQCM) experiments have revealed that the electrodeposition (induced co-deposition) of the alloys has negative differential resistances (NDRs), from which the oscillations and the layer-structure formation arise. The NDRs, however, cannot necessarily be seen in current-potential curves owing to overlap of hydrogen evolution current, indicating that the oscillations are of a hidden-NDR (H-NDR) type. The EQCM experiments have also shown that electrolyte components (such as H2PO2- and WO4(2-)) or related species are adsorbed at the electrode (deposit) surface and act as a promoter for the co-deposition reaction and that the NDRs arise from desorption of the adsorbed promoter. Interestingly, the adsorbed promoter is drawn into the deposition reaction itself, thus resulting in the alloy deposits. This mechanism was supported by in situ EQCM investigations of the oscillation as well as Auger electron spectroscopic (AES) analyses of deposits formed during the oscillation. The present work has for the first time clarified a general mechanism for the induced co-deposition reactions of some industrially important iron-group alloys (Ni-P, Ni-W, and Co-W).

Journal Article↗
PubMed2006

Confocal Raman observation of the efflorescence/deliquescence processes of individual NaNO3 particles on quartz.

Confocal Raman spectroscopy was used to study the structural changes of bulk NaNO3 solutions with molar water-to-solute ratios (WSRs) of 54.0-12.3 and NaNO3 droplets (10-100 microm) with WSRs of 9.5-1.0 on a quartz substrate. Upon reduction of the WSR, a blue shift of the symmetric stretching band (nu(1)(NO3-)) from approximately 1048 to approximately 1058 cm(-1) was observed in the confocal Raman spectra with high signal-to-noise ratios. Accordingly, the full width at half-height of the nu(1)(NO3-) band increased from approximately 8.4 cm-1 for the dilute solution (WSR = 54.0) to approximately 15.6 cm-1 for the extremely supersaturated droplet (WSR = 1.0), suggesting the formation of contact ion pairs with different structures. For the O-H stretching band, the ratio of weak hydrogen-bonding components to strong ones, i.e., I(3488)/I(3256), increased from approximately 1.2 at WSR = 54.0 to approximately 7.3 at WSR = 1.0, indicating that the strong hydrogen bonds were heavily destroyed between water molecules especially in the supersaturated droplets. In the humidifying process, two hygroscopic behaviors were observed depending on the morphology of solid NaNO3 particles. No surface water was detected for a solid NaNO3 particle with rhombohedral shape at relative humidities (RHs) below 86%. When the RH increased from 86% to 93%, it suddenly absorbed water and turned into a solution droplet. For a maple-leaf-shaped NaNO3 particle with a rough surface, however, a trace of residual water originally remained on the rough surface even at very low RH according to its Raman spectrum. Its initial water uptake from the ambient occurred at approximately 70% RH. The small amount of initially adsorbed water induced surface rearrangement of the maple-leaf-shaped particle. A further increase of RH made the particle gradually turn into a regular solid core swathed in a solution layer. Eventually, it completely deliquesced in the RH region of 86-93%, similar to the case of the NaNO3 particle with rhombohedral shape.

Journal Article↗
PubMed2006

Adsorption of polymeric micelles and vesicles on a surface investigated by quartz crystal microbalance.

Polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) diblock copolymers either with or without thiol end groups, depending on the relative length of the two blocks, form micelles or vesicles in water. The adsorption of such micelles or vesicles on a gold surface from aqueous solution was investigated in situ at 20 degrees C by use of a quartz crystal microbalance with dissipation monitoring (QCM-D). The changes in frequency (Deltaf) and dissipation (DeltaD) revealed that the micelles and vesicles without thiol groups were intact with some deformation when they were deposited on the surface. On the other hand, the micelles and vesicles with thiol groups at the end of PNIPAM blocks would transform into trilayers due to the strong interaction between thiols and gold surface.

Journal Article↗
PubMed2004

Quartz crystal microbalance (QCM) in high-pressure carbon dioxide (CO2): experimental aspects of QCM theory and CO2 adsorption.

The quartz crystal microbalance (QCM) technique has been developed into a powerful tool for the study of solid-fluid interfaces. This study focuses on the applications of QCM in high-pressure carbon dioxide (CO2) systems. Frequency responses of six QCM crystals with different electrode materials (silver or gold) and roughness values were determined in helium, nitrogen, and carbon dioxide at 35-40 degrees C and at elevated pressures up to 3200 psi. The goal is to experimentally examine the applicability of the traditional QCM theory in high-pressure systems and determine the adsorption of CO2 on the metal surfaces. A new QCM calculation approach was formulated to consider the surface roughness contribution to the frequency shift. It was found that the frequency-roughness correlation factor, Cr, in the new model was critical to the accurate calculation of mass changes on the crystal surface. Experiments and calculations demonstrated that the adsorption (or condensation) of gaseous and supercritical CO2 onto the silver and gold surfaces was as high as 3.6 microg cm(-2) at 40 degrees C when the CO2 densities are lower than 0.85 g cm(-3). The utilization of QCM crystals with different roughness in determining the adsorption of CO2 is also discussed.

Journal Article↗
PubMed2004

Application of the quartz crystal microbalance to the evaporation of colloidal suspension droplets.

An investigation into the evaporation of sessile droplets of latex and clay particle suspensions is presented in this work. The quartz crystal microbalance (QCM) has been used to study the interfacial phenomena during the drying process of these droplets. Characteristic changes of the crystal oscillating frequency and crystal resistance (damping of the oscillating energy) have been observed and related to the different stages of the evaporation process. Measurements have been made for latex particle sizes from 1.9 to 10 microm and for rough and polished crystals using drops from 0.3 to 1.5 microL. The behavior of the QCM is shown to depend strongly on the size of particles present and on the morphology of the crystal surface. One of the most striking features is a drastic damping of the oscillation energy and corresponding rise in frequency observed during the final stages of evaporation, particularly for the clay suspensions.

Journal Article↗
PubMed2004

Nanoscale high-frequency contact mechanics using an AFM tip and a quartz crystal resonator.

The transmission of high-frequency shear stress through a microscopic contact between an AFM tip and an oscillating quartz plate was measured as a function of vertical pressure, amplitude, and surface properties by monitoring the MHz component of the tip's deflection. For dry surfaces, the transmission of shear stress is proportional to the vertical load across the contact. This provides a measure of the forces of adhesion between the substrate and the tip. When stretching soft polymeric fibers created by pulling on the surface of a pressure sensitive adhesive, the transmitted shear stress decreased linearly with extension over the entire range of pulling. This contrasts with the static adhesive force, which remained about constant until it discontinuously dropped at the point of rupture.

Journal Article↗
PubMed2005

Reentrant behavior of poly(N-isopropylacrylamide) brushes in water-methanol mixtures investigated with a quartz crystal microbalance.

The solvent composition induced reentrant behavior of poly(N-isopropylacrylamide) (PNIPAM) chains grafted on a SiO2 surface in water-methanol mixtures was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) at 20 degrees C. The frequency and energy dissipation responses showed that the grafted PNIPAM chains sharply collapse when the methanol content (x(m)) reaches approximately 17 mol %. In the range 17-50 mol %, the grafted chains remain in a collapsed state. Further increase of the methanol content leads to an abrupt reswelling of the collapsed chains at x(m) > approximately 50 mol %. The sharp reentrant swelling-to-collapse-to-swelling transition was attributed to the water-methanol complexation instead of the preferential adsorption effect. Our results also suggest that the water-methanol complexation is not induced by hydrophobic interaction but by hydrogen bonding.

Journal Article↗
PubMed2005

Surface plasmon resonance spectroscopy and quartz crystal microbalance study of streptavidin film structure effects on biotinylated DNA assembly and target DNA hybridization.

Surface plasmon resonance (SPR) spectroscopy is employed for the study of biotinylated DNA assembly on streptavidin modified gold surfaces for target DNA hybridization. Two immobilization strategies are involved for constructing streptavidin films, namely, (1) physical adsorption on biotin-containing thiol treated surfaces through biotin-streptavidin links and (2) covalent attachment to 11-mercaptoundecanoic acid (MUA) treated surfaces through amine coupling. To understand the structural properties of the streptavidin films, a quartz crystal microbalance with energy dissipation monitoring (QCM-D) is used to monitor the streptavidin immobilization procedures. The simultaneously measured frequency (Deltaf) and dissipation factor (DeltaD) changes, together with the SPR angle shifts (Deltatheta), suggest that the streptavidin film assembled on the biotin-containing surface is highly rigid with a well-ordered structure while the streptavidin film formed through amine coupling is highly dissipative and less structured. The subsequent biotinylated DNA (biotin-DNA) assembly and target hybridization results show that the streptavidin film structure has distinct effects on the biotin-DNA binding amount. On the streptavidin matrix, not only the probe DNA density but also the strand orientation mediated by the streptavidin films has distinct effects on hybridization efficiency. Particularly, the molecularly ordered streptavidin films formed on the biotin-containing surfaces ensure a well-ordered DNA assembly, which in turn allows for a higher efficiency in target DNA capture and for a higher sensitivity in the hybridization analysis when compared to the biotin-DNA assembled on the less structured streptavidin films formed through amine coupling.

Base Sequence↗
PubMed2004

Effects of laterally heterogeneous slip on the resonance properties of quartz crystals immersed in liquids.

A formalism is presented which predicts the influence of laterally heterogeneous slip (for instance, induced by nanoscopic air bubbles) on the shift of the resonance frequency and bandwidth of quartz crystal resonators immersed in liquids. The lateral heterogeneities are decomposed into their Fourier components. The distribution of slip lengths provides a boundary condition, giving rise to a small, secondary flow field. The mean stress exerted by this secondary field induces a shift in resonance frequency and bandwidth. If the slip length is much smaller than the penetration depth of the shear waves and smaller than the lateral correlation length, one finds that the effects of the heterogeneities scale as n(3/2), with n being the overtone order. The frequency, f, and half-band-half-width, Gamma, decrease by the same amount. These calculations match experimental results obtained with a gold-coated resonator in contact with various hydrophilic liquids.

Journal Article↗