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The sequential hybridization of a534 base pair DNA concatemerlayer was monitored by QCM-D and SPR, and the QCM-D data were analyzedby Voigt viscoelastic models. The results show that Voigt-based modelinggives a good description of the experimental data but only if shearviscosity and elasticity are allowed to depend on the shear frequency.The derived layer thickness, shear viscosity and elasticity of thegrowing film give a representation of the DNA film in agreement withknown bulk properties of DNA, and reveal a maximum in film viscositywhen the molecules in the layer contain 75 base pairs. The experimentaldata during construction of a 3084 bp DNA concatemer layer were comparedto predictions of the QCM-D response of a 1 μm thick film ofrod-like polymers. A predicted nonmonotonous variation of dissipationwith frequency (added mass) is in qualitative agreement with the experiments,but with a quantitative disagreement which likely reflects that theflexibility of such long DNA molecules is not included in the model. [ABSTRACT FROM AUTHOR]

A novel setup was recently developed, combining quartz crystal microbalance with dissipation monitoring (QCMD) and optical reflectometry for measurements on one and the same surface of, for example, biomolecular adlayers and interactions (Wang et al. Rev. Sci. Instr. 2008, 79 075107).. This combination was chosen on the basis of prior experience of using QCM-D and optical techniques in separate instruments, which showed both the advantage of employing multiple techniques and the disadvantage of not working with the same surface and (flow) cell. The new instrument provides, for example, information about associated water and structural changes of the adlayers that would often pass unnoticed or be hard to interpret or quantify using either technique alone. The triple response instrument (QCM.D frequency and dissipation and reflectometry) is here applied to four model systems: (A) formation of supported lipid bilayers (SLBs), (B) lipid exchange between a SIB and transiently adsorbed vesicles, (C) binding of a hydrated peptide on a functionalized SIB, and (D) streptavidin coupling to a biotinylated SIB, followed by attachment of biotinylated vesicles. The results demonstrate three major advantages of the combination instrument: (i) much faster data collection because the experiments are done on one surface for all signals, (ii) a common time axis and the same relative importance of surface kinetics and mass transport because the same liquid sample and the same transport conditions apply, and (iii) new features are discovered about the studied system that would be difficult to unravel in separate instruments. [ABSTRACT FROM AUTHOR]

We have developed an instrument for surface interaction studies, which combines a newly invented four detector optical reflectometry setup with quartz crystal microbalance with dissipation (QCM-D) monitoring. The design is such that data from both techniques can be obtained simultaneously on the same sensor surface, with the same signal-to-noise ratio and time resolution, as for the individual techniques. In addition, synchronized information about structural transformations, molecular mass, and the hydration of thin films on solid surfaces can be obtained on the same specimen, as validated by monitoring the formation of supported lipid bilayers on a silica-coated QCM sensor surface. We emphasize that the optical (molecular) mass can be separated from the acoustic mass including hydrodynamically coupled solvent, which means, in turn, that the amount of solvent sensed by the QCM-D technique can be dynamically resolved during adsorption processes. In addition, the advantage/necessity to use four, compared to two, detector reflectometry is emphasized. [ABSTRACT FROM AUTHOR]

Abstract: An electrodeless quartz crystal microbalance with dissipation monitoring (QCM-D) setup is used to monitor the formation of supported lipid bilayers (SLBs) on bare quartz crystal sensor surfaces. The kinetic behavior of the formation of a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) SLB on SiO2 surfaces is discussed and compared for three cases: (i) a standard SiO2 film deposited onto the gold electrode of a quartz crystal, (ii) an electrodeless quartz crystal with a sputter-coated SiO2 film, and (iii) an uncoated electrodeless quartz crystal sensor surface. We demonstrate, supported by imaging the SLB on an uncoated electrodeless surface using atomic force microscopy (AFM), that a defect-free, completely covering bilayer is formed in all three cases. Differences in the kinetics of the SLB formation on the different sensor surfaces are attributed to differences in surface roughness. The latter assumption is supported by imaging the different surfaces using AFM. We show furthermore that electrodeless quartz crystal sensors can be used not only for the formation of neutral SLBs but also for positively and negatively charged SLBs. Based on our results we propose electrodeless QCM-D to be a valuable technique for lipid bilayer and related applications providing several advantages compared to electrode-coated surfaces like optical transparency, longer lifetime, and reduced costs. [ABSTRACT FROM AUTHOR]

Plasminogen is a precursor to the fibrinolytic enzyme plasmin and is known to undergo large conformational changes when subjected to low molecular lysine analogues such as tranexamic acid (TA) or e-amino-n-caproic acid (EACA). Here, we demonstrate how well-controlled surface immobilization of biotinylated plasminogen allows for monitoring of the interaction between TA and EACA with plasminogen. The interaction was studied by the quartz crystal microbalance with dissipation monitoring (QCM-D) technique as well as by surface plasmon resonance (SPR) based sensing. QCM-D measures changes in acoustically coupled mass (by detection of changes in the resonance frequency of the crystal, Δf) and is sensitive to changes in mass adsorbed on the sensor surface including how liquid medium is associated with this material. Through the dissipation factor (i.e., changes in the energy dissipation of the crystal oscillation, ΔD), QCM-D is also sensitive to the viscoelastic properties of material adsorbed to the sensor surface. Upon binding of TA or EACA, changes in the plasminogen structure were recorded as distinct, although small, ΔD responses which were used to determine affinity constants. By comparing native and truncated plasminogen, we conclude that the observed dissipation shifts were caused by conformational changes in the proteins leading to changes in the viscoelastic properties of the protein layer on the surface. These results demonstrate a novel application of the QCM-D technique, paving the way for a whole new approach to screening of this target for novel lead structures. [ABSTRACT FROM AUTHOR]

The article discusses a study of lipid transfer from vesicles in the in situ preparation and modification of supported lipid bilayers (SLBs). The study used the combination of quartz crystal microbalance with dissipation (QCM-D) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) to characterize SLB formation and quality of bilayers. It states that the approach used to create a stabilized lipid monolayer on TiO2 is potential method for asymmetric SLBs preparation.