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A novel setup was recently developed, combining quartz crystal microbalance with dissipation monitoring (QCM-D) 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 SLB and transiently adsorbed vesicles, (C) binding of a hydrated peptide on a functionalized SLB, and (D) streptavidin coupling to a biotinylated SLB, 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.

The thermal stability of hydroxyalkanethiolate self-assessed monolayers (SAM) on gold can be improved by introducing an amide group in the vicinity of the thermal group. The study reveals that lateral hydrogen bonding, introduced via amide groups, is a convenient way to improve the thermal stability of alkanthiolate SAMs.

Research has been conducted on the oligo(ethylene glycol)-terminated alkanethiol amides. The synthesis of the these amides and analogous esters has been conducted via attaching hydrophobic tails at the far end of the hexa(ethylene glycol) chains and the results are discussed.

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 [epsilon]-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, [DELTA]f) 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, [DELTA]D), 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, [DELTA]D 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. 10.1021/ac1016419

An example is provided on how lipid transfer is used to form lipid layers with striking new features with respect to stability. The results have provided evidence for lipid transfer between the initial POEPC supported lipid bilayer (SLB) and D31-POPS vesicles in solution and the reassembled SLB has a major asymmetry between the two leaflets.

A comparative study of the self-assembly and phase behavior of seven different oligo(ethylene glycol) (OEG)-terminated alkanethiols on polycrystalline gold surfaces is presented. The results from contact angle goniometry, null ellipsometry, and infrared reflection, absorption spectroscopy (IRAS) indicate that the intermolecular interactions can be partly used to control the conformation and order of the OEG portion of the self-assembled monolayers (SAMs).

The phase behavior of oligo(ethylene glycol) self assembled monolayers using temperature programmed infrared reflection adsorption spectroscopy are explored. The oligomer conformation is marginally affected upon increasing the temperature to 75 degree Celsius, displaying the dominating all-trans phase.