Thickness-shear Mode Acoustic Wave Research Articles

Surface Adsorption of the Cancer Biomarker Lysophosphatidic Acid in Serum Studied by Acoustic Wave Biosensor.

The thickness shear mode acoustic wave device is of interest for the sensing of biomarkers for diseases in various biological fluids, but suffers from the issue of non-specific adsorption of compounds other than those of interest to the electrode surface, thus affecting the device’s output. The aim of this present study was to determine the level of non-specific adsorption on gold electrodes from serum samples with added ovarian cancer biomarker lysophosphatidic acid in the presence of a surface anti-fouling layer. The latter was an oligoethylene molecule with thiol group for attachment to the electrode surface. It was found that the anti-fouling layer had a minimal effect on the level of both adsorption of components from serum and the marker. This result stands in sharp contrast to the analogous monolayer employed for anti-fouling reduction on silica.

Radiation-Activated Pre-Differentiated Retinal Tissue Monitored by Acoustic Wave Biosensor.

A thickness-shear mode acoustic wave biosensor operated within a flow-through system was used to examine the response of mouse retinal tissue to radiation. Control experiments conducted with respect to exposure of the bare gold electrodes of the device under various conditions of light intensity and bathing solution yielded reversible changes in resonant frequency (Fs) and motional resistance (Rm). The magnitude of transient changes was proportional to light intensity, but independent of solution type. These alterations in acoustic parameters were ascribed to acoustic coupling phenomena at the electrode-to-liquid interface. Pre-differentiated retina from mouse samples deposited on the thickness shear mode (TSM) electrode exposed to a high light intensity condition also exhibited reversible changes in both Fs and Rm, compared to control experiments involving a coating used to attach the tissue to the electrode. In this case, the radiation-instigated reversible responses for both acoustic parameters exhibited a reduction in magnitude. The changes are ascribed to the alteration in viscoelasticity of the retinal matrix on the TSM electrode surface. The precise biophysical mechanism responsible for the changes in Fs and Rm remains a challenge, given the complex make up of retinal tissue.

Measurement of Phase Changes in Live Crude Oil Using an Acoustic Wave Sensor: Asphaltene Instability Envelope

An experimental method is proposed for determining the asphaltene instability envelope of a crude oil or crude oil + antisolvent system under reservoir conditions by using a thickness shear mode acoustic wave sensor fully immersed in oil under pressure. The technique allows determining the upper asphaltene instability pressure by carrying out constant mass expansion experiments, whereas the lower asphaltene instability pressure can be determined during constant mass compression tests. The basis of the technique is presented, and measurements have been carried out in a bottomhole oil + CO2 system with various CO2 contents at reservoir temperature. Finally, the effect of temperature on the asphaltene instability envelope was studied on two systems with 45 and 55 mol % CO2.

Amplitude evolution equation and transient effects in piezoelectric crystal resonators

We study transient effects in AT-cut quartz plate thickness-shear mode acoustic wave resonators. Mindlin's equations for thin crystal plates are employed. Based on the relatively slow evolution of the vibration amplitude compared to the high-frequency thickness-shear vibration, a first-order differential equation governing the amplitude evolution is obtained. The equation allows simple and accurate solutions for transient processes in quartz resonators. A few numerical examples of resonator startup and turning off are given. The equation can be applied to other transient processes in crystal resonators such as driving voltage fluctuations and generalized to resonator-based acoustic wave sensors.

Label-free methods for probing the interaction of clioquinol with amyloid-β

The presence of amyloid-β (Aβ) fibrils is characteristic of Alzheimer's disease (AD), and the aggregation of these amyloidogenic proteins is a nucleation-dependent process. In this report, label-free methods based on surface plasmon resonance (SPR) and thickness shear mode acoustic wave sensors (TSM-AWS) were used to detect monomer elongation in real-time. The modulation of Aβ aggregation using a well-described flavonoid, clioquinol (CQ) was also observed. Established methods like fluorescence and electrochemistry were also employed to confirm the interaction of CQ with Aβ. Good correlation between the designed label-free methods creates a promising platform for the screening of novel amyloid inhibitors.

Thickness-shear vibration of an elastic plate carrying an array of rigid microbeams with consideration of couple stresses

We study thickness-shear vibration of an elastic plate carrying an array of rigid microbeams with their bottoms attached to the top surface of the plate. The beams undergo rigid-body translation and rotation when the plate is in thickness-shear motion. The plate is modeled by the couple-stress theory of elasticity to properly take into account both the shear forces and the bending moments at the bottoms of the beams. A equation that determines the resonant frequencies of the structure is derived. Analytical and numerical examinations of a few special cases of the general frequency equation reveal a few basic effects of the microbeams and the couple stress. The results are useful in measuring geometric/physical properties of the microbeams using plate thickness-shear mode acoustic wave sensors.

Synchronization of the circadian rhythm generator and the effects of glucagon on hypothalamic mouse neurons detected by acoustic wave propagation

A thickness shear mode acoustic wave sensor has been used to study the reaction of clonal, immortalized hypothalamic murine neurons in response to glucagon and serum shock in a label free, continuous and real time manner under physiological conditions. Two cell lines were examined; these were the mHypoE-38s and the mHypoE-46s. The technique possesses sufficient sensitivity to detect minor neuronal changes and is capable of discerning subtle differences in cellular behaviors under both stimuli. The kinetics and magnitude of the changes observed here are significantly different compared to those instigated upon causing depolarization, cytoskeletal modifications and surface-adhesion specific interaction alterations with the same cells. Interestingly, this technique has the sensitivity and capability of observing all such changes at the neuronal level without the necessity for invasive interrogation. Under the influence of glucagon, the neurons display both short- and long-term changes, in particular the resonant frequency shifts by -23 ± 8 Hz (n = 13, std. dev.) and the motional resistance decays at a rate of approximately 10 Ω h(-1) over a 2 hour interval. The effect of synchronizing the neurons prior to glucagon stimulation did not influence the cellular changes observed. The process of partial and full synchronization of the cells resulted in different responses. For full synchronization, the addition of the serum bolus triggered resonant frequency and motional resistance shifts of +75 Hz and +18.5 Ω respectively, which decayed back to baseline levels after 30 minutes. The duration of this decay closely matched the time required for full synchronization in a separate study. The changes observed for partial synchronization were significantly different from full synchronization as the baseline levels in both resonant frequency and motional resistance were not re-achieved indicative of the cell-sensor system detecting the difference between full and partial synchronization. Preliminary qualitative immunocytochemistry and RT-PCR studies on these cells support the results obtained with the TSM sensor for the glucagon receptor study.

Modulation of Acoustic Coupling by Photo-Oxidation of Self-Assembled Monolayers

A thickness-shear mode acoustic wave device operated in a flow-injection configuration has been used to study the effects of oxygen on thiol-based self-assembled monolayers at the liquid-sensor interface when exposed to UV light. The films were composed of dodecanethiol or undec-5-yne-1-thiol. Piezoelectric AT-cut quartz sensors with gold electrodes were submerged in thiol solutions with varying amounts of oxygen present in the solution by altering the amount of time that the solutions were exposed to nitrogen. Oxygen was also removed or incorporated into the system by sparging the liquid buffer used in the flow system with helium gas. When exposed to UV radiation, the device with thiol monolayers in place exhibited reversible changes in series renounces frequency and motional resistance only in the presence of oxygen. This result is ascribed to a photochemically induced oxidation of the sulfur moiety at the device-liquid interface. The response of the device under these conditions is governed by acoustic coupling phenomena and not mass effects. Finally, the in situ cross-linking of undec-5-yne-thiol does not result in any additional changes in response other than those indicated for dodecanethiol confirming that thickness viscoelastic changes at the monolayer level are not relevant to device response.

Interaction of cationic surfactants with DNA detected by spectroscopic and acoustic wave techniques

Interaction of the cationic surfactants benzalkonium chloride and 1-hexadecylpyridinium chloride, in the concentration range 0.1 microM to 1 mM with calf thymus DNA and with short 19-mer double-stranded DNA has been examined in solution using UV absorption and fluorescent spectroscopies and at the liquid-solution interface by thickness-shear mode acoustic wave sensor. Higher concentrations of surfactant resulted in an increase of UV absorption, and decrease of melting temperature and van't Hoff enthalpy of calf thymus DNA. Both surfactants induce fluorescence quenching of ethidium bromide which is also associated with intercalation of the molecules into the nucleic acid strand. The effect of the pyridinium compound is greater than for the other surfactant likely because of the lower size of polar head group in this molecule. With respect to acoustic wave detection at the device surface, for relatively low surfactant concentrations (below 100 microM), decreases of both series resonant frequency and motional resistance were observed. At higher surfactant concentration both parameters increased. These effects are attributed to acoustic coupling processes that occur at the device-film/liquid boundary.

Depolarization of surface-attached hypothalamic mouse neurons studied by acoustic wave (thickness shear mode) detector

Isolation of neurons from animal tissue is an important aspect of understanding basic biochemical processes such as the action of hormones and neurotransmitters. In the present work, the focus is on an effort to evaluate the utility of acoustic wave physics for the study of such cells. Immortalised hypothalamic neuronal cells from mouse embryos were cultured on the surface of the gold electrode of a 9.0 MHz thickness-shear mode acoustic wave sensor. These cells, which are clonal, are imposed on the surface of the device at a confluence in the range of 80-100%. The coated sensor is incorporated into a flow-injection configuration such that electrolytes can be introduced in order to examine their effects through measurement by network analysis. Both series resonance frequency, fs, and motional resistance, R(m), were measured in a number of experiments involving the injection of KCl and NaCl into the sensor-neuron system. The various responses to these electrolytes were interpreted in terms of changes in cellular structure associated with the depolarization process. The sensor-neuron system was found to elicit different responses to the addition of KCl and NaCl. Preliminary findings indicate that the TSM sensor does not purely measure changes in the membrane potential upon KCl addition. Typical changes in fs for 15 mM, 30 mM and 60 mM KCl additions were 54 +/- 15, 80 +/- 26 and 142 +/- 58 Hz (mean +/- standard deviation) respectively. Typical changes in R(m) for these KCl additions were 7 +/- 3, 13 +/- 4 and 23 +/- 6 Omega, respectively. These results were concluded after 17 runs at each concentration. Despite the large relative standard deviations, the dependence of f(s) and R(m) with respect to concentration was apparent. Controls performed by coating the TSM sensor with laminin or a cell attachment matrix showed no significant changes in either f(s) or R(m) for the same solutions tested on the sensor-neuron system.

Detection ofDNA damage: effect of thymidine glycol residues on the thermodynamic, substrate and interfacial acoustic properties of oligonucleotide duplexes

Thymidine glycol residues in DNA are biologically active oxidative molecular damage sites caused by ionizing radiation and other factors. One or two thymidine glycol residues were incorporated in 19- to 31-mer DNA fragments during automatic oligonucleotide synthesis. These oligonucleotide models were used to estimate the effect of oxidized thymidines on the thermodynamic, substrate and interfacial acoustic properties of DNA. UV-monitoring melting data revealed that modified residues in place of thymidines destabilize the DNA double helix by 8-22 degrees C, depending on the number of lesions, the length of oligonucleotide duplexes and their GC-content. The diminished hybridizing capacity of modified oligonucleotides is presumably due to the loss of aromaticity and elevated hydrophilicity of thymine glycol in comparison to the thymine base. According to circular dichroism (CD) data, the modified DNA duplexes retain B-form geometry, and the thymidine glycol residue introduces only local perturbations limited to the lesion site. The rate of DNA hydrolysis by restriction endonucleases R.MvaI, R.Bst2UI, R.MspR9I and R.Bme1390I is significantly decreased as the thymidine glycol is located in the central position of the double-stranded recognition sequences 5'-CC / WGG-3' (W = A, T) or 5'-CC / NGG-3' (N = A, T, G, C) adjacent to the cleavage site. On the other hand, the catalytic properties of enzymes R.Psp6I and R.BstSCI recognizing the similar sequence are not changed dramatically, since their cleavage site is separated from the point of modification by several base-pairs. Data obtained by gel-electrophoretic analysis of radioactive DNA substrates were confirmed by direct spectrophotometric assay developed by the authors. The effect of thymidine glycol was also observed on DNA hybridization at the surface of a thickness-shear mode acoustic wave device. A 1.9-fold decrease in the rate of duplex formation was noted for oligonucleotides carrying one or two thymidine glycol residues in relation to the unmodified analog.

TSM-AW Sensors Based on Miller XCOs for Microgravimetric Measurements in Liquid Media

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Up to now, the success of the design of quartz crystal-controlled oscillators (XCOs) based on high-stability classical configurations for uses as microgravimetric thickness-shear-mode acoustic-wave (TSM-AW) sensors in damping media has strongly depended on the ability and experience of the designer. The conditions of strong damping that quartz experiences imply the necessity to adapt the designs so that the oscillation stays in spite of the reduction of its quality factor. Despite all the efforts developed by various authors, a methodology of the design of electronic circuit oscillators for their use in damping media does not exist yet. This is due to the difficulty of the study of the oscillation condition and its possible optimization as a function of the application. In this paper, we propose a methodology to aid designers in developing TSM-AW sensors for high-resolution microgravimetrical applications in liquid media, such as detection of chemical species, biosensors for molecular recognition, etc. Approaches are presented to carry out sensor oscillators based on the Miller topology. </para>

Surface immobilisation and properties of smooth muscle cells monitored by on-line acoustic wave detector

The attachment of rat aortic smooth muscle cells to various surfaces has been monitored by a thickness shear mode acoustic wave device incorporated into an on-line configuration. Using the total injection analysis method, laminin and fibronectin were adsorbed to the device surface, to be followed by introduction of cells into the system. The results of these experiments in terms of frequency and motional resistance measurements were also compared with those for cell attachment to the bare gold electrode of the sensor. The responses of the surface-bound cells to the introduction of various ions, depolarisation events and damage subsequent to exposure to hydrogen peroxide were also observed. Morphological changes in the cells, as confirmed by scanning electron microscopy, are correlated with results of the acoustic wave measurements.

Thickness shear mode acoustic wave sensors for characterizing the viscoelastic properties of cell monolayer

The thickness shear mode (TSM) quartz crystal resonator attached with living cells has been shown to be an effective functional biosensing device to monitor the process of cell adhesion to a surface in real time. In this study, a multilayer acoustic wave sensor model including a quartz resonator substrate, a cell-substrate interfacial layer and a cell layer has been developed based on the state of cell adhesion to the quartz resonator substrate. In order to obtain comprehensive and detailed information on the resonator oscillation, the electrical admittance spectrum of the resonator sensor over a range of frequencies near resonance is measured by an impedance analyzer instead of only measuring the resonance frequency and motional resistance with an oscillator circuit. After cells are fully spread to form a monolayer on the surface, the admittance spectrum of the multilayer loaded acoustic wave sensor was recorded and used to extract the viscoelastic properties of the cell layer by fitting experimental spectrum curve with those obtained from the theoretical model through a curve-fitting algorithm. It is found that the viscoelastic properties of the cell layer are consistent with those measured by other techniques, indicating the quartz acoustic wave sensor can be used as a non-invasive device for characterizing the mechanical properties of cell layers.

Monitoring cell adhesion by using thickness shear mode acoustic wave sensors

The thickness shear mode (TSM) acoustic wave sensor attached with living cells has been shown to be an effective functional biosensing device to monitor the process of cell adhesion to a surface in real time. In this study, a multilayer sensor model that includes a quartz substrate, a cell–substrate interfacial layer and a cell layer was constructed based on the state of cell adhesion to the substrate. The dynamic process of cell adhesions as a function of cell seeding densities was monitored using the acoustic wave sensor. The mechanisms that are responsible for the frequency and resistance change are discussed according to the predictions of the acoustic wave sensor model. In addition, knowing that the actin cytoskeleton is important for cell adhesion, we investigated the motional resistance change caused by the disruption of actin cytoskeleton induced by fungal toxin cytochalasin D in the human skin fibroblasts. The results indicate that resistance changes are related to the disruption of actin cytoskeleton and dosage-dependent.

Characterization of polymer nanocomposite films using quartz thickness shear mode (TSM) acoustic wave sensor

Quartz thickness shear mode (TSM) resonator is adopted to characterize the viscoelastic properties of polymer nanocomposite thin films deposited on the resonators surface. The input electric admittance of multilayer loaded TSM acoustic wave resonator is first derived using transfer matrix method by taking into account the acoustic wave impedance of the polymeric layer. Nanocomposite thin films of multi-wall carbon nanotubes (MWCNTs) in copolymers of polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) are deposited on TSM resonators through spin-on coating processing. The electric impedance spectra of the unloaded and loaded acoustic wave resonators are measured experimentally, and a data fitting approach is applied to extract the properties of the polymer nanocomposites films. It has been found that the thickness of the polymer layer plays a very important role in the extraction of the viscoelastic properties of the films through data fitting. Viscoelastic properties of PVDF-TrFE/CNT nanocomposite thin films with CNT concentrations of 0%, 1% and 2% have been extracted by this method. The results indicate that under the current experimental conditions, for low CNT concentrations the reinforcement of the elastic shear modulus of polymer nanocomposite films is not significant.

Label-free detection of neuron–drug interactions using acoustic and Kelvin vibrational fields

Kelvin and acoustic fields of high-frequency have been employed in the non-invasive investigation of immortalized hypothalamic neurons, in order to assess their response to different concentrations of specific drugs, toxins, a stress-reducing hormone and neurotrophic factors. In an analytical systems biology approach, this work constitutes a first study of living neuron cultures by scanning Kelvin nanoprobe (SKN) and thickness shear mode (TSM) acoustic wave techniques. N-38 hypothalamic mouse neurons were immobilized on the gold electrode of 9 MHz TSM acoustic wave devices and gold-coated slides for study by SKN. The neurons were exposed to the neurochemicals betaseron, forskolin, TCAP, and cerebrolysin. Signals were collected with the TSM in real-time mode, and with the SKN in scanning and real-time modes, as the drugs were applied at biologically significant concentrations. With the TSM, for all drugs, some frequency and resistance shifts were in the same direction, contrary to normal functioning for this type of instrument. Possible mechanisms are presented to explain this behaviour. An oscillatory signal with periodicity of approximately 2 min was observed for some neuron-coated surfaces, where the amplitude of these oscillations was altered upon application of certain neurotrophic factors. These two new techniques present novel and non-invasive electrodeless methods for detecting changes at the cellular level caused by a variety of neuroactive compounds, without killing or destroying the neurons.

Ion, solvent and polymer dynamics in polyaniline conducting polymer films

We describe the application of a new model for the visualization of mobile species (ion and solvent) transfers accompanying redox switching of electroactive films. The system studied was polyaniline, for which the mobile species population changes were determined from redox-driven film mass changes using a thickness shear mode acoustic wave resonator. Acoustic admittance data were used to establish conditions under which the resonator frequency response could be interpreted gravimetrically. Charge and frequency changes accompanying the first redox transition of polyaniline films exposed to aqueous perchloric acid were then used to determine the film's ion and solvent populations. The data are best described by a mechanism in which the early stages of film oxidation are associated with proton transfer (exit) and the latter stages with perchlorate transfer (entry) to satisfy electroneutrality; solvent enters throughout film oxidation and exits throughout film reduction. The alternative of a single ion satisfying electroneutrality throughout would require the rather less likely situation of a non-monotonic solvent flux. Application of the model's diagnostic criteria indicates that the film solvent population is in equilibrium on the timescale of slow scan voltammetry, but shows thermodynamic non-idealities. Hysteresis in the film ion population signals failure of the redox state to maintain equilibrium with the applied potential.

DNA-duplexes containing abasic sites: correlation between thermostability and acoustic wave properties

Aldehydic apurinic or apyrimidinic sites that lack a nucleobase moiety are one of the most common forms of toxic lesions in DNA. In the present study, a close structural analog of such a site, the 2-(hydroxymethyl) tetrahydrofuranyl residue, was synthesized in order to act as a model for damaged nucleic acid probes. Prepared oligodeoxyribonucleotides containing one, two or three abasic sites were hybridized to complementary sequences immobilized on a gold surface using the neutravidin-biotin interaction for study by thickness shear mode acoustic wave detector. Measurement of the complex electrical impedance of an AT-cut quartz device with immobilized biotinylated nucleotide allowed the detection of changes of series resonance frequency, Deltafs, and motional resistance, Rm, associated with duplex formation. The changes as detected by the acoustic wave method correlated well with the thermostability of DNA duplexes in solution. With respect to the latter, UV-monitored melting curves indicate that both the number of sites and their localization in the double-stranded structure influence the amount by which a 19 b.p. duplex is destabilized. The presence of 3 abasic sites completely destabilized the DNA duplex.

Time−Temperature Superposition for Viscoelastic Properties of Regioregular Poly(3-hexylthiophene) Films

Shear moduli were determined for chemically polymerized and solvent cast regioregular poly(3-hexylthiophene) films, using thickness shear mode acoustic wave resonators. The results are strikingly different to those for electropolymerized regiorandom poly(3-hexylthiophene) films. The time scale of the measurement was varied directly by use of higher harmonics of the acoustic wave resonator and indirectly via temperature. The significant variations in shear modulus with effective time scale can be "normalized"onto a stress master relaxation curve by using the concept of time-temperature superposition; this is the first time this has been demonstrated for electroactive films. The shift factors required to effect this normalization do not follow the classical Williams-Landel-Ferry (WLF) equation developed for long-range backbone motions of bulk polymers. Instead, they follow an Arrhenius-like behavior, commonly used to describe secondary motions of polymer side-chains. The activation enthalpy associated with this is independent of applied potential, is the same as for as cast (undoped) films, and is similar to that for rotation about a carbon-carbon single bond. These all point to the hexyl side-chains as the origins of the observed phenomena, consistent with the "melting point" separating two temperature-dependent phases and with the different molecular packing arrangements that would necessarily apply to regioregular and regiorandom materials.