Simultaneous measurement of the maximum oscillation amplitude and the transient decay time constant of the QCM reveals stiffness changes of the adlayer

An Adaptive Measurement System for the Simultaneous Evaluation of Frequency Shift and Series Resistance of QCM in Liquid

In this paper, a novel measurement system based on Quartz Crystal Microbalances is presented. The proposed solution was conceived specifically to overcome the measurement problems related to Quartz Crystal Microbalance (QCM) applications in dielectric liquids where the Q-factor of the resonant system is severely reduced with respect to in-gas applications. The QCM is placed in a Meacham oscillator embedding an amplifier with adjustable gain, an automatic strategy for gain tuning allows for maintaining the oscillator frequency close to the series resonance frequency of the quartz, which is related in a simple way with the physical parameters of interest. The proposed system can be used to monitor simultaneously both the series resonant frequency and the equivalent electromechanical resistance of the quartz. The feasibility and the performance of the proposed method are proven by means of measurements obtained with a prototype based on a 10-MHz AT-cut quartz.

Load Impedance of Immersed Layers on the Quartz Crystal Microbalance: A Comparison with Colloidal Suspensions of Spheres

The analytical theories derived here for the acoustic load impedance measured by a quartz crystal microbalance (QCM), due to the presence of layers of different types (rigid, elastic, and viscous) immersed in a fluid, display generic properties, such as "vanishing mass" and positive frequency shifts, which have been observed in QCM experiments with soft-matter systems. These phenomena seem to contradict the well-known Sauerbrey relation at the heart of many QCM measurements, but here, we show that they arise as a natural consequence of hydrodynamics. We compare our one-dimensional immersed plate theory with three-dimensional simulations of rigid and flexible submicron-sized suspended spheres and with experimental results for adsorbed micron-sized colloids, which yield a "negative acoustic mass". The parallel behavior unveiled indicates that the QCM response is highly sensitive to hydrodynamics, even for adsorbed colloids. Our conclusions call for a revision of existing theories based on adhesion forces and elastic stiffness at contact, which should, in most cases, include hydrodynamics.

On the Measurement of Energy Dissipation of Adhered Cells with the Quartz Microbalance with Dissipation Monitoring

We previously reported the finding of a linear correlation between the change of energy dissipation (Δ D) of adhered cells measured with the quartz crystal microbalance with dissipation monitoring (QCM-D) and the level of focal adhesions of the cells. To account for this correlation, we have developed a theoretical framework for assessing the Δ D-response of adhered cells. We rationalized that the mechanical energy of an oscillating QCM-D sensor coupled with a cell monolayer is dissipated through three main processes: the interfacial friction through the dynamic restructuring (formation and rupture) of cell-extracellular matrix (ECM) bonds, the interfacial viscous damping by the liquid trapped between the QCM-D sensor and the basal membrane of the cell layer, and the intracellular viscous damping through the viscous slip between the cytoplasm and stress fibers as well as among stress fibers themselves. Our modeling study shows that the interfacial viscous damping by the trapped liquid is the primary process for energy dissipation during the early stage of the cell adhesion, whereas the dynamic restructuring of cell-ECM bonds becomes more prevalent during the later stage of the cell adhesion. Our modeling study also establishes a positive linear correlation between the Δ D-response and the level of cell adhesion quantified with the number of cell-ECM bonds, which corroborates our previous experimental finding. This correlation with a wide well-defined linear dynamic range provides a much needed theoretical validation of the dissipation monitoring function of the QCM-D as a powerful quantitative analytical tool for cell study.

The quartz crystal microbalance: a new tool for the investigation of the bioadhesion of diatoms to surfaces of differing surface energies

Diatoms are a major component of the biofoul layer found on modern low-surface-energy, 'foul release' coatings. While diatoms adhere more strongly to hydrophobic, as opposed to hydrophilic, surfaces, surprisingly little is known of the chemical composition of their adhesives. Even less is known about the underlying processes that characterize the interaction between the adhesive and a given surface, including those of differing wettability. Using the quartz crystal microbalance with dissipation monitoring (QCM-D), we examined differences in the viscoelastic properties of the extracellular adhesives produced by the marine diatoms Amphora coffeaeformis Cleve and Craspedostauros australis Cox interacting with surfaces of differing wettability; 11-mercaptoundecanoic acid (MUA) that is hydrophilic and 1-undecanethiol (UDT) that is hydrophobic. While the overall delta f/delta D ratios were slightly different, the trends were the same for both diatom species, with the layer secreted upon UDT to be more viscoelastic and far more consistent over several experiments, compared to that on MUA which was less viscoelastic and demonstrated far more variability between experiments. While the nature of the parameter shifts for C. australis were the same for both surfaces, A. coffeaeformis cells settling upon UDT illustrated significant positive f and D shifts during the initial stages of cell settlement and adhesion to the surface. Further experiments revealed the parameter shifts to occur only during the initial adhesion of cells upon the pristine virgin UDT surface. The mechanism behind these parameter responses was isolated to the actin-myosin/adhesion complex (AC), using the myosin inhibitor 2,3-butanedione 2-monoxime (BDM) to remove the cells ability to 'pull' on adhesive strands emanating from the cell raphe. The observations made herein have revealed that adhesives secreted by fouling diatoms differ significantly in their interaction with surfaces depending on their wettability, as well as illustrating the unique mechanics behind the adhesion of A. coffeaeformis upon hydrophobic surfaces, a mechanism that may contribute significantly to the cells success in colonizing hydrophobic surfaces.

Monitoring cell adhesion by piezoresonators: impact of increasing oscillation amplitudes

In recent years, the quartz crystal microbalance (QCM) has been established as a sensitive analytical tool to monitor the attachment and spreading of mammalian cells to in vitro surfaces. Due to its superior time resolution, the device is capable of reading even subtle differences in cell adhesion kinetics. However, thickness shear mode piezoresonators, which are the core component of the QCM approach, can be used not only as a sensor but also as an actuator when the oscillation amplitude of the crystal is increased so that molecular recognition at the solid-liquid interface is disturbed. In this study, we have addressed the impact of elevated lateral oscillation amplitudes on the adhesion kinetics of three mammalian cell lines. We used AT-cut piezoresonators with a fundamental resonance frequency of 5 MHz, and the analytical readout was performed by impedance analysis. Formation of stable cell-substrate contacts is retarded or entirely blocked when the lateral oscillation amplitude (in the center of the resonator) exceeds values higher than 20 nm. Shear oscillations of similar amplitude were, however, not sufficient to displace attached cells from the surface. Moreover, the experimental data prove that the normal QCM readout with oscillation amplitudes smaller than 1 nm is, indeed, non-invasive with respect to mammalian cells.

A survey of the 2001 to 2005 quartz crystal microbalance biosensor literature: applications of acoustic physics to the analysis of biomolecular interactions

The widespread exploitation of biosensors in the analysis of molecular recognition has its origins in the mid-1990s following the release of commercial systems based on surface plasmon resonance (SPR). More recently, platforms based on piezoelectric acoustic sensors (principally 'bulk acoustic wave' (BAW), 'thickness shear mode' (TSM) sensors or 'quartz crystal microbalances' (QCM)), have been released that are driving the publication of a large number of papers analysing binding specificities, affinities, kinetics and conformational changes associated with a molecular recognition event. This article highlights salient theoretical and practical aspects of the technologies that underpin acoustic analysis, then reviews exemplary papers in key application areas involving small molecular weight ligands, carbohydrates, proteins, nucleic acids, viruses, bacteria, cells and lipidic and polymeric interfaces. Key differentiators between optical and acoustic sensing modalities are also reviewed.

Utilizing QCM-D To Characterize the Adhesive Mucilage Secreted by Two Marine Diatom Species in-Situ and in Real-Time

The quartz crystal microbalance with dissipation monitoring (QCM-D) was used to monitor the deposition of adhesive extracellular polymeric substances (EPS) employed by the marine biofouling diatoms Craspedostauros australis Cox and Amphora coffeaeformis Cleve during initial adhesion and subsequent motility. Upon injection into the QCM chamber, initial negative frequency (f) shifts and positive dissipation (D) shifts were measured that correlated to cells impacting and adhering to the QCM sensor surface. Following this "initial adhesion" response, f continued to decrease while D increased logarithmically. Rather than the result of any cell morphological alterations at the substrate surface, the shifts were correlated to the time-dependent deposition of EPS upon the substrate surface as a result of cellular motility, or gliding. Experiments utilizing comparable cell concentrations of the diatom species C. australis and A. coffeaeformis revealed significant differences between the parameter responses recorded, where A. coffeaeformis produced Deltaf and DeltaD values of -32 Hz and 6.6, and C. australis produced values of -82 Hz and 42, respectively, after 20 h post-inoculation. The viscoelastic properties of the adhered EPS adlayer from both species were examined via a Deltaf/DeltaD plot, providing reproducible signature "ratio" values for each species that likely correlate to differences in EPS interactions with the substrate that may be associated directly to differences in the fouling potential of the two species. There is a distinct lack of knowledge regarding the chemical nature of the adhesive polymers engaged, and few quantitative techniques are applicable to the study of diatom EPS. We propose that QCM-D may be a useful tool in identifying differences in the EPS employed by diatoms of different fouling potential.