Simultaneous Quartz Crystal Microbalance Research Articles

The Interaction between Anesthetic Isoflurane and Model-Biomembrane Monolayer Using Simultaneous Quartz Crystal Microbalance (QCM) and Quartz Crystal Impedance (QCI) Methods.

The interaction between anesthetic Isoflurane (Iso) and model-biomembrane on the water surface has been investigated using quartz crystal microbalance (QCM) and quartz crystal impedance (QCI) methods. The model-biomembranes used were dipalmitoyl phosphatidyl choline (DPPC), DPPC-palmitic acid (PA) mixture (DPPC:PA = 8:2), DPPC-Alamethicin (Al) mixture (DPPC:Al = 39:1), and DPPC-β-Lactoglobulin (βLG) mixture (DPPC:βLG = 139:1) monolayers, respectively. The quartz crystal oscillator (QCO) was attached horizontally to each monolayer, and QCM and QCI measurements were performed simultaneously. It was found that Iso hydrate physisorbed on each monolayer/water interface from QCM and changed those interfacial viscosities from QCI. With an increase in Iso concentration, pure DPPC, DPPC-PA mixed, and DPPC-Al mixed monolayers showed a two-step process of Iso hydrate on both physisorption and viscosity, whereas it was a one-step for the DPPC-βLG mixed monolayer. The viscosity change in the DPPC-βLG mixed monolayer with the physisorption of Iso hydrate was much larger than that of other monolayers, in spite of the one-step process. From these results, the action mechanism of anesthetics and their relevance to the expression of anesthesia were discussed, based on the "release of interfacial hydrated water" hypothesis on the membrane/water interface.

High-speed nanoscale tribology enabled by combined QCM/AFM

Forming a fundamental understanding of tribological processes on the atomic scale has the potential to revolutionize the control of friction and wear in macroscopic mechanical systems. On the other hand, methods such as atomic force microscopy (AFM) that provide nanoscale spatial resolution are severely limited in terms of scanning speed when compared with macroscopic mechanical processes, leading to a “speed gap” between fundamental and applied tribology that spans several orders of magnitude. Here, we propose a new method combining AFM experiments with simultaneous quartz crystal microbalance (QCM) measurements for high-speed nanoscale tribology. In particular, scanning speed and vibration amplitude are controlled by QCM whereas normal loads are controlled by AFM. Complementary data are simultaneously recorded in the form of nanoscale, two-dimensional maps of frequency shifts and lateral forces provided by the QCM and AFM, respectively. Proof-of-principle results are presented on a gold-coated QCM sensor surface patterned with a graphene array, whereby stick and partial slip regimes are observed as a function of sliding speed.

Morphology of surfactant mixtures at solid/liquid interfaces: High-speed AFM observation

We characterized time-dependent morphological changes in cationic monomeric/gemini surfactant mixtures adsorbed on silica using high-speed atomic force microscopy (HS-AFM). The gemini surfactant employed in this study was 1,2-bis(dodecyldimethylammonio)ethane dibromide (12-2-12). This surfactant was mixed with a monomeric surfactant, hexadecyltrimethylammonium bromide (HTAB), in the presence of a background electrolyte. The HS-AFM measurements revealed that wormlike surface aggregates that formed in an HTAB solution transformed into a bilayer within a few hundred seconds after the HTAB solution was replaced by an HTAB + 12-2-12 mixed solution. This morphological change was reversed within a few hundred seconds after this solution was replaced by the initial HTAB solution. These time-dependent morphological changes were supported by simultaneous quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry measurements. The energy dissipation, monitored by QCM-D, changed reversibly in response to the solution exchanges.

Structural Investigation of a Self-Cross-Linked Chitosan/Alginate Dialdehyde Multilayered Film with in Situ QCM-D and Spectroscopic Ellipsometry.

A chitosan/alginate dialdehyde multilayered film was fabricated using the layer-by-layer assembly method. Besides electrostatic interaction that promotes alternate adsorption of the oppositely charged polyelectrolytes, the Schiff base reaction between the amine groups on chitosan and the aldehyde groups on alginate dialdehyde provides a covalently cross-linked film, which after reduction by sodium cyanoborohydride is stable under both acidic and alkaline conditions. Moreover, the cross-linked film is responsive to changes in pH and addition of multivalent salts. The structural properties of the multilayered film such as thickness, refractive index, and water content were examined using simultaneous quartz crystal microbalance with dissipation monitoring and spectroscopic ellipsometry.

Friction and adhesion control between adsorbed layers of polyelectrolyte brush-grafted nanoparticles via pH-triggered bridging interactions

HypothesisAdsorption of polyelectrolyte brush-grafted nanoparticles (BGNPs) produces a heterogeneous interface with sub-monolayer surface coverage resulting from lateral electrostatic repulsions that limit packing. As a result, the interaction forces between opposing BGNP layers include an adhesive cross-surface BGNP-substrate bridging force that depends on the interparticle spacing, particle size, and strength of electrostatic interactions. We hypothesize that BGNPs with pH-responsive, annealed polyelectrolyte brushes can undergo controlled changes in surface area coverage through post-adsorption swelling or de-swelling into non-equilibrium layer conformations and that such changes in surface coverage can switch off or switch on particle intercalation, bridging attractions, and enhanced energy dissipation upon sliding. This work aims to characterize the nature of surface forces in heterogeneous BGNP adsorbed layers and to utilize pH-sensitive bridging forces as a mechanism to tune friction and adhesion. ExperimentsColloidal probe atomic force microscopy (CP-AFM) is used to measure normal and lateral forces between negatively charged silica surfaces with adsorbed pH-responsive cationic BGNPs. The BGNPs are poly(2-dimethylaminoethyl methacrylate) brush-grafted silica nanoparticles. Adhesion force and friction analysis is complemented by simultaneous quartz-crystal microbalance and ellipsometry measurements under conditions that render the particles strongly charged and swollen (acidic) or weakly charged and de-swollen (basic). FindingsAdsorbed BGNPs can be swollen or de-swollen via pH rinses, enabling direct control of surface coverage and bridging interactions. Transitions from adhesive bridging contacts with high friction to non-adhesive contacts with low friction forces occur when adsorbed BGNP layers are switched from a de-swollen/weakly charged state to a swollen/highly charged state. The ability to controllably shift the character of normal and lateral forces via coverage-mediated bridging interactions is a unique feature of adsorbed nanoparticulate brush constructs and highlights their potential to condition surfaces with additional functionality compared to dense, planar homopolymer brushes.

The retention of liquid by columnar nanostructured surfaces during quartz crystal microbalance measurements and the effects of adsorption thereon

HypothesisA surface comprising spatially coherent columnar nanostructures is expected to retain intercolumnar liquid during a quartz crystal microbalance measurement due to the surface structure. Part of the liquid retained by the nanostructures may then be displaced by adsorbate. ExperimentsSlanted columnar nanostructure thin films were designed to vary in height but remain structurally similar, fabricated by glancing angle deposition, and characterized by generalized ellipsometry. A frequency overtone analysis, introduced here, was applied to analyze quartz crystal microbalance data for the exchange of isotope liquids over the nanostructured surfaces and determine the areal inertial mass of structure-retained liquid. The adsorption of cetyltrimethylammonium bromide onto nanostructures was investigated by simultaneous quartz crystal microbalance and generalized ellipsometry measurements. FindingsThe areal inertial mass of structure-retained liquid varies linearly with nanostructure height. The proportionality constant is a function of the surface topography and agrees with the generalized ellipsometry-determined nanostructure film porosity, implying that nearly all intercolumnar liquid is retained. We report that for adsorption processes within porous nanostructured films, the quartz crystal microbalance is sensitive not to the combined areal inertial mass of adsorbate and retained liquid but rather to the density difference between adsorbate and liquid due to the volume exchange within the nanostructure film.

Solvent-assisted lipid bilayer formation on silicon dioxide and gold.

Planar lipid bilayers on solid supports mimic the fundamental structure of biological membranes and can be investigated using a wide range of surface-sensitive techniques. Despite these advantages, planar bilayer fabrication is challenging, and there are no simple universal methods to form such bilayers on diverse material substrates. One of the novel methods recently proposed and proven to form a planar bilayer on silicon dioxide involves lipid deposition in organic solvent and solvent exchange to influence the phase of adsorbed lipids. To scrutinize the specifics of this solvent-assisted lipid bilayer (SALB) formation method and clarify the limits of its applicability, we have developed a simplified, continuous solvent-exchange version to form planar bilayers on silicon dioxide, gold, and alkanethiol-coated gold (in the latter case, a lipid monolayer is formed to yield a hybrid bilayer) and varied the type of organic solvent and rate of solvent exchange. By tracking the SALB formation process with simultaneous quartz crystal microbalance-dissipation (QCM-D) and ellipsometry, it was determined that the acoustic, optical, and hydration masses along with the acoustic and optical thicknesses, measured at the end of the process, are comparable to those observed by employing conventional fabrication methods (e.g., vesicle fusion). As shown by QCM-D measurements, the obtained planar bilayers are highly resistant to protein adsorption, and several, but not all, water-miscible organic solvents could be successfully used in the SALB procedure, with isopropanol yielding particularly high-quality bilayers. In addition, fluorescence recovery after photobleaching (FRAP) measurements demonstrated that the coefficient of lateral lipid diffusion in the fabricated bilayers corresponds to that measured earlier in the planar bilayers formed by vesicle fusion. With increasing rate of solvent exchange, it was also observed that the bilayer became incomplete and a phenomenological model was developed in order to explain this feature. The results obtained allowed us to clarify and discriminate likely steps of the SALB formation process as well as determine the corresponding influence of organic solvent type and flow conditions on these steps. Taken together, the findings demonstrate that the SALB formation method can be adapted to a continuous solvent-exchange procedure that is technically minimal, quick, and efficient to form planar bilayers on solid supports.

Electrochemically addressed cross-links in polyelectrolyte multilayers: cyclic duravoltammetry.

In situ nanoindentation was performed on a multilayer of poly(acrylic acid) and a high molecular weight, pendant chain polyviologen under controlled electrochemical potential. The modulus of the thin film of polyelectrolyte complex was reversibly modulated, by about an order of magnitude, upon changing the state of charge within the material using the electrochemically active and addressable viologen repeat units. The applied potential, under aqueous conditions, is believed to control the extent of cross-link formation. Simultaneous quartz crystal microbalance measurements revealed the flux of ions into or out of the multilayer during redox cycling. Apparent film modulus also depends on the identity of the last layer.

Attenuated Total Reflection Fourier Transform Infrared Spectroscopy to Investigate Water Uptake and Phase Transitions in Atmospherically Relevant Particles

In this study, attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy is used to investigate water uptake and phase transitions for atmospherically relevant particles. Changes in the ATR-FT-IR spectra of NaCl, NH(4) NO(3), (NH(4))(2)SO(4), Ca(NO(3))(2), and SiO(2) as a function of relative humidity (RH) are presented and discussed. For these various particles, water can (1) become adsorbed on the particle surface; and/or (2) become absorbed in the particle structure to form a hydrate salt; and/or (3) become absorbed by the particle to form a liquid solution. Spectral features and analyses that distinguish these various processes are discussed. For the salts that do undergo a solid to liquid phase transition (deliquescence), excellent agreement is found between the measurements made here with ATR-FT-IR spectroscopy, a relatively simple, inexpensive, and readily available analytical tool, compared to more expensive, elaborate aerosol flow reactor systems using tandem differential mobility analyzers. In addition, for particles that adsorb water, we show here the utility of coupling ATR-FT-IR measurements with simultaneous quartz crystal microbalance (QCM) measurements. This coupling allows for the quantification of the amount of water associated with the particle as a function of relative humidity (f(RH)) along with the spectroscopic data.

Analysis of Desiccation and Vitrification Characteristics of Carbohydrate Films by Shear-Wave Resonators

Desiccated state preservation of mammalian cells and tissues in the presence of carbohydrates has started to show promise in the last two decades. Certain carbohydrates play a major role in preservation by reducing molecular mobility in the desiccated state. In this communication, the feasibility of utilizing shear-wave resonators to collect real-time molecular mobility information during desiccation and vitrification of carbohydrate based thin films was demonstrated. Simultaneous quartz crystal microbalance experimentation and optical imaging were utilized to determine the conditions for thin film formation and the vitrification kinetics of certain carbohydrate solutions of biological importance. Using the technique presented here, it was possible to gain insight into the vitrification characteristics of carbohydrate solutions establishing the basics for future research with quantitative analysis of film properties and experimentation with live mammalian cells.

Simultaneous Surface Plasmon Resonance and Quartz Crystal Microbalance with Dissipation Monitoring Measurements of Biomolecular Adsorption Events Involving Structural Transformations and Variations in Coupled Water

Simultaneous quartz crystal microbalance with dissipation monitoring (QCM-D) and surface plasmon resonance (SPR) measurements are used to analyze the surface kinetics of two biomacromolecular systems, one lipid and one protein based, undergoing surface-induced conformational changes. First we establish a theoretical platform, which allows quantitative analysis of the combined SPR and QCM-D data. With this theoretical base, new information can be extracted, not obtainable with either technique alone. As an example we demonstrate how time-resolved measurements with these two techniques in combination--yielding three independent measured quantities--add new information about (i) kinetics, i.e. number of adsorbed molecules per unit area versus time, and (ii) temporal variation in the mass fraction of coupled water versus coverage. In particular, it is demonstrated for the first time, how the kinetics of the process during which adsorbed vesicles are spontaneously transformed into a supported phospholipid bilayer (SPB) on SiO(2) can be quantitatively separated into its two dominating states: adsorbed vesicles and supported planar bilayer patches. In addition, the relevance of dynamically coupled water for interpretation and modeling of the QCM-D response during bilayer formation is discussed and further illustrated with a second model system: streptavidin adsorption on a biotin-modified SPB. A very strong coverage dependence in the number of water molecules per protein sensed by the QCM is demonstrated, with strong implications for the use of QCM as a tool for quantitative determination of protein mass uptake kinetics.

Simultaneous quartz crystal microbalance impedance and electrochemical impedance measurements. Investigation into the degradation of thin polymer films.

The reproducible degradation of thin polymer films in the presence of an analyte or a reaction product of an analyte has potential applications in the development of highly sensitive, disposable biosensors. In this study, a novel combination of quartz crystal microbalance (QCM) and electrochemical impedance spectroscopy (EIS) has been developed to monitor the degradation of thin polymer films. Unlike a conventional QCM, the instrument described here allows rapid in situ measurement of quartz crystal impedance spectra. Simultaneously, classical electrochemical impedance spectra are measured in situ, affording the polymer film capacitance and bulk resistance. The combination of QCM impedance and classical EIS provides a wealth of information about the process of degradation of thin polymer films such as mass variation, swelling, delamination, viscoelasticity, and pore formation. Three different systems have been analyzed with this experimental setup; in two of the systems, polymer degradation was promoted by hydrolytic enzymes, and in the third one by a pH change. The results obtained show that the degradation of these three systems follows very different mechanisms. It is also underlined how the complementary information obtained by the two techniques allows a detailed description of the dissolution process.

Visual evoked potential measure of texture discrimination in infants: A longitudinal study

A surface comprising spatially coherent columnar nanostructures is expected to retain intercolumnar liquid during a quartz crystal microbalance measurement due to the surface structure. Part of the liquid retained by the nanostructures may then be displaced by adsorbate.Slanted columnar nanostructure thin films were designed to vary in height but remain structurally similar, fabricated by glancing angle deposition, and characterized by generalized ellipsometry. A frequency overtone analysis, introduced here, was applied to analyze quartz crystal microbalance data for the exchange of isotope liquids over the nanostructured surfaces and determine the areal inertial mass of structure-retained liquid. The adsorption of cetyltrimethylammonium bromide onto nanostructures was investigated by simultaneous quartz crystal microbalance and generalized ellipsometry measurements.The areal inertial mass of structure-retained liquid varies linearly with nanostructure height. The proportionality constant is a function of the surface topography and agrees with the generalized ellipsometry-determined nanostructure film porosity, implying that nearly all intercolumnar liquid is retained. We report that for adsorption processes within porous nanostructured films, the quartz crystal microbalance is sensitive not to the combined areal inertial mass of adsorbate and retained liquid but rather to the density difference between adsorbate and liquid due to the volume exchange within the nanostructure film.

Liposome and phospholipid adsorption on a platinum surface studied in a flow cell designed for simultaneous quartz crystal microbalance and ellipsometry measurements

A flow cell was designed for simultaneous mass measurements with a quartz crystal microbalance and ellipsometry and was used for studying the adsorption processes of different liposomes, prepared from phospholipids and cholesterol, on both bare and lipid monolayer-covered platinum surfaces. Ellipsometric and gravimetric data were collected during recirculation of liposomes in 0.15 M NaCl. Experiments with ATP-containing liposomes with subsequent lysis were also performed. The results are discussed in terms of both intact liposome adhesion and intact liposome adhesion in combination with planar bilayer formation.

Simultaneous ellipsometric and microgravimetric measurements during the electrochemical growth of polyaniline

We describe an experimental system for simultaneous quartz crystal microbalance (QCM) and ellipsometric measurements performed in situ during the growth of a thin film on an electrode surface. The film studied is grown on a Pt electrode sputtered onto a quartz crystal, which serves as the microbalance. The quartz crystal is positioned in a semicylindrical cell equipped with glass windows, allowing continuous optical probing of the electrode surface. The automatic elllipsometer readings are taken simultaneously with the QCM measurements. The information obtained from the two techniques is complementary: the QCM measures the overall mass increase during film growth, whereas the ellipsometer measures the optical properties of the film and its thickness. From such combined simultaneous measurements, the apparent density of the film can be derived. We describe here results of such combined measurements performed during the anodic growth of polyaniline in aqueous acid solutions showing substantial variations in film density as a function of electrochemical growth conditions.