Shear Horizontal Surface Research Articles

Vertical jetting induced by shear horizontal leaky surface acoustic wave on 36° Y-X LiTaO3

Shear horizontal surface acoustic waves (SH-SAWs) have been regarded as good candidates for liquid sensing applications but are inefficient in fluid manipulation due to a minimal fluid coupling between the fluid and acoustic waves. However, in this letter, a vertical jetting function was realized using the SH-SAW generated from a 36° Y-X LiTaO3 SAW device. The jetting of the droplet induced by the SH-SAWs was observed nearly along the vertical direction, and the aspect ratio of the liquid beam is proportional to the applied power before breaking up, which is dramatically different from those generated from the conventional Rayleigh SAWs. By conducting theoretical simulation and experimental investigation on the SH-SAWs systematically, we concluded that the wave/energy pressure dissipated into the sessile droplets causes this vertical ejection on the device surface.

Rapid cell separation with minimal manipulation for autologous cell therapies

The ability to isolate specific, viable cell populations from mixed ensembles with minimal manipulation and within intra-operative time would provide significant advantages for autologous, cell-based therapies in regenerative medicine. Current cell-enrichment technologies are either slow, lack specificity and/or require labelling. Thus a rapid, label-free separation technology that does not affect cell functionality, viability or phenotype is highly desirable. Here, we demonstrate separation of viable from non-viable human stromal cells using remote dielectrophoresis, in which an electric field is coupled into a microfluidic channel using shear-horizontal surface acoustic waves, producing an array of virtual electrodes within the channel. This allows high-throughput dielectrophoretic cell separation in high conductivity, physiological-like fluids, overcoming the limitations of conventional dielectrophoresis. We demonstrate viable/non-viable separation efficacy of >98% in pre-purified mesenchymal stromal cells, extracted from human dental pulp, with no adverse effects on cell viability, or on their subsequent osteogenic capabilities.

The Rotation Effect on Shear Horizontal Surface Wave in a Piezoelectric Semi-Space Covered by a Semiconductor Film

In this study, a mathematical model of the rotation effect on Shear Horizontally wave (SH-wave) propagation in a piezoelectric semi-space covered by a semiconductor film is investigated. The semiconducting layer is rotating with a constant angular velocity and the interface between the piezoelectric substrate and the semiconductor layer is imperfectly bonded. Furthermore, the surfaces of the bilayer system assumed free of traction and electrically shorted or open. The governing equations of the dynamical displacement and electrical potential function under the effect of rotation are driven by solving the coupled electromechanical field equations of the piezoelectric half-space and the semiconductor film. In addition, the exact frequency equations of SH waves are derived. Next, the numerical examples are considered to clarify the effects of rotation and electromagnetic boundary conditions for the different values of the film thickness and wave number on the dispersion behaviors. Finally, the effect of rotation on the frequency equation is investigated in detail for piezoelectric material PZT-5H and the semiconductor silicon. The obtained results provide a predictable and theoretical basis for applications of piezoelectric and semiconductor structures to surface acoustic wave equipments.

Highly Sensitive Escherichia coli Shear Horizontal Surface Acoustic Wave Biosensor with Silicon Dioxide Nanostructures

In this study, a shear horizontal surface acoustic wave (SHSAW) was used for Escherichia coli (E. coli) detection. E. coli O157:H7 serotype, a dangerous strain among 225 E. coli unique serotypes was chosen as test sample. A few cells of this bacterium are able to cause young children to be most vulnerable to serious complications. Presence of higher than 1 cfu E. coli O157:H7 in 25 g of food has been considered as a dangerous level. The SHSAW biosensor was fabricated on 640 YX LiNbO3 substrate. Five different interdigital transducers (IDT) parameters (Fig. 1(a)-1(e)) SHSAW were fabricated to compare the mass loading sensitivity before advancing to the bio sensing application: four of them were 32 μm pitch size (with the average of synchronous frequency, f0 = 144.303 MHz) and one was 12 μm pitch size (with f0 = 384.948 MHz). All of the four 32 μm pitch sizes were with different combination of delay line length (3.904 mm and 7.296 mm) and aperture size (1.376 mm and 2.464 mm). As for the 12 μm pitch size device, it was with 2.1 mm delay line length and 0.72 mm aperture size. Eventually, 12 μm pitch size device was selected for oligonucleotides detection and its mass loading sensitivity was 1558.04 MHz/ (mg/mm2), 4.8-fold higher than the most sensitivity one in 32 μm pitch size).Its sensitivity was enhanced by depositing 130 nm thin layer of SiO2 nanostructures with particle size less than 70 nm (Fig. 1(f)-1(g)). The nanostructures act both as a waveguide as well as the surface physical modification of the sensor prior to biomolecule immobilization. For this work, a specific DNA sequence from E. coli O157:H7 having 22 mers as an amine-terminated probe ssDNA was immobilized on the thin film sensing area through chemical functionalization [(CHO-(CH2)3-CHO) and (APTES; NH2-(CH2)3-Si(OC2H5)3]. The high-performance of sensor was shown with the oligonucleotide target and attained the sensitivity of 0.6439 nM/ 0.1 kHz and detection limit was down to 1.8 femtomolar (1.8 x 10-15 M). Further evidence was provided by specificity analysis using single mismatched and complementary oligonucleotide sequences.

Highly Sensitive SH-SAW Resonator with SiO2 trenches for Biosensing Application

The paper presents three dimensional finite element simulation of a sensitive shear-horizontal surface acoustic wave device for biosensing application. The resonator consisting of 36°-YX LiTaO3 substrate with SiO2 trenches generates a shear-horizontal standing wave. Eigenmode study and frequency response are used to calculate displacements, admittance and electromechanical coupling coefficient of the device. For a given mode, the coupling coefficient of the device increases with trench height to a maximum of about 7% and then starts to decrease till next higher order mode becomes dominant. The trenches not only serve as guiding layer to keep the energy of the wave at the surface but also cause coupled resonance leading to increase in resonance frequency and average stress at the contact area between trench and substrate. Mass loading of resonator is simulated by applying the equivalent surface mass density of double stranded DNA of length 50 base pairs uniformly over the surface area of trenches. Close to the resonant height of trenches, mass loading causes a large frequency shift making the device a highly sensitive biosensing platform.

Investigation of Polymer-Plasticizer Blends as SH-SAW Sensor Coatings for Detection of Benzene in Water with High Sensitivity and Long-Term Stability.

We report the first-ever direct detection of benzene in water at concentrations below 100 ppb (parts per billion) using acoustic wave (specifically, shear-horizontal surface acoustic wave, SH-SAW) sensors with plasticized polymer coatings. Two polymers and two plasticizers were studied as materials for sensor coatings. For each polymer-plasticizer combination, the influence of the mixing ratio of the blend on the sensitivity to benzene was measured and compared to commercially available polymers that were used for BTEX (benzene, toluene, ethylbenzene, and xylene) detection in previous work. After optimizing the coating parameters, the highest sensitivity and lowest detection limit for benzene were found for a 1.25 μm thick sensor coating of 17.5%-by-weight diisooctyl azelate-polystyrene on the tested acoustic wave device. The calculated detection limit was 45 ppb, with actual sensor responses to concentrations down to 65 ppb measured directly. Among the sensor coatings that showed good sensitivity to benzene, the best long-term stability was found for a 1.0 μm thick coating of 23% diisononyl cyclohexane-1,2-dicarboxylate-polystyrene, which was studied here because it is known to show no detectable leaching in water. The present work demonstrates that, by varying type of plasticizer, mixing ratio, and coating thickness, the mechanical and chemical properties of the coatings can be conveniently tailored to maximize analyte sorption and partial chemical selectivity for a given class of analytes as well as to minimize acoustic-wave attenuation in contact with an aqueous phase at the operating frequency of the sensor device.

Shear-horizontal surface acoustic wave characteristics of a (110) ZnO/SiO2/Si multilayer structure

Shear-horizontal (SH) surface acoustic wave (SAW) propagation characteristics in IDT/(110)ZnO/SiO2/Si multilayered structure were theoretically investigated using 3-dimensions (3D) finite element analysis (FEA). X-ray diffraction result shows that the prepared ZnO films have preferred (110) orientation with its c-axis parallel to the substrate. 3D FEA results and the out of plane vibration experiment confirmed that SH-SAW was successfully excited in the multilayered structure. The phase velocities Vp, electromechanical coupling coefficients K2, and temperature coefficient of frequency (TCF) dispersion properties of mode 0 were studied considering various thicknesses of ZnO and SiO2 thin films, which were verified by experiments. SiO2 film with a positive TCF not only compensate the negative TCF of the (110) ZnO but also enhance the K2. A large K2 of 3.37 and nearly zero TCF of −0.1 ppm/°C was achieved in SH-SAW device based on IDT/(110)ZnO(2 μm)/SiO2(1 μm)/Si multilayer structure, which is promising for high sensitive and temperature stable bio-sensing application.

Highly sensitive Escherichia coli shear horizontal surface acoustic wave biosensor with silicon dioxide nanostructures

Surface acoustic wave mediated transductions have been widely used in the sensors and actuators applications. In this study, a shear horizontal surface acoustic wave (SHSAW) was used for the detection of food pathogenic Escherichia coli O157:H7 (E.coli O157:H7), a dangerous strain among 225 E. coli unique serotypes. A few cells of this bacterium are able to cause young children to be most vulnerable to serious complications. Presence of higher than 1cfu E.coli O157:H7 in 25g of food has been considered as a dangerous level. The SHSAW biosensor was fabricated on 64° YX LiNbO3 substrate. Its sensitivity was enhanced by depositing 130.5nm thin layer of SiO2 nanostructures with particle size lesser than 70nm. The nanostructures act both as a waveguide as well as a physical surface modification of the sensor prior to biomolecular immobilization. A specific DNA sequence from E. coli O157:H7 having 22 mers as an amine-terminated probe ssDNA was immobilized on the thin film sensing area through chemical functionalization [(CHO-(CH2)3-CHO) and APTES; NH2-(CH2)3-Si(OC2H5)3]. The high-performance of sensor was shown with the specific oligonucleotide target and attained the sensitivity of 0.6439nM/0.1kHz and detection limit was down to 1.8femto-molar (1.8×10−15M). Further evidence was provided by specificity analysis using single mismatched and complementary oligonucleotide sequences.

Determining biosensing modes in SH-SAW device using 3D finite element analysis

Surface acoustic wave (SAW) sensors are electromechanical devices that exploit the piezoelectric effect to induce elastic (acoustic) waves which are sensitive to small perturbations: for example specific binding and recognition of disease biomarkers. Shear horizontal surface acoustic waves (SH-SAWs) are particularly suited to biosample analysis as the wave is not completely radiated and lost into the liquid medium (e.g., blood, saliva) as is the case, for example, in a device implementing Rayleigh waves. Here, using 3D finite element analysis (FEA) the nature of waves launched on a particular quartz device is investigated with respect to the cut of the quartz, the addition of gold guiding layers, and the addition of other linear elastic materials of contrasting acoustic properties. It is demonstrated that 3D FEA analysis showing the device's frequency shift with added guiding layer height reveals a proportional relationship in agreement with the Sauerbrey equation from perturbation theory. It is directly shown, given certain device parameters and a gold guiding layer, that shear horizontally polarized waves are launched on the surface with a dominant mode frequency around 250MHz. This would be an appropriate biosensing mode in Point of Care (POC) testing for the particular properties of certain disease biomarkers delivered via a liquid medium.

Rayleigh and Wood anomalies in the diffraction of acoustic waves from the periodically corrugated surface of an elastic medium

By the use of the Rayleigh method we have calculated the angular dependence of the reflectivity and the efficiencies of several other diffracted orders when the periodically corrugated surface of an isotropic elastic medium is illuminated by a volume acoustic wave of shear horizontal polarization. These dependencies display the signatures of Rayleigh and Wood anomalies, usually associated with the diffraction of light from a metallic grating. The Rayleigh anomalies occur at angles of incidence at which a diffracted order appears or disappears; the Wood anomalies here are caused by the excitation of the shear horizontal surface acoustic waves supported by the periodically corrugated surface of an isotropic elastic medium. The dispersion curves of these waves in both the nonradiative and radiative regions of the frequency-wavenumber plane are calculated, and used in predicting the angles of incidence at which the Wood anomalies are expected to occur.

Shear horizontal surface acoustic waves in a magneto-electro-elastic system

AbstractPropagation of shear horizontal surface acoustic waves (SHSAWs) within a functionally graded magneto-electro-elastic (FGMEE) half-space was previously presented (Shodja HM, Eskandari S, Eskandari M. J. Eng. Math. 2015, 1–18) In contrast, the current paper considers propagation of SHSAWs in a medium consisting of an FGMEE layer perfectly bonded to a homogeneous MEE substrate. When the FGMEE layer is described by some special inhomogeneity functions – all the MEE properties have the same variation in depth which may or may not be identical to that of the density – we obtain the exact closed-form solution for the MEE fields. Additionally, certain special inhomogeneity functions with monotonically decreasing bulk shear wave velocity in depth are considered, and the associated boundary value problem is solved using power series solution. This problem in the limit as the layer thickness goes to infinity collapses to an FGMEE half-space with decreasing bulk shear wave velocity in depth. It is shown that in such a medium SHSAW does not propagate. Using power series solution we can afford to consider some FGMEE layers of practical importance, where the composition of the MEE obeys a prescribed volume fraction variation. The dispersive behavior of SHSAWs in the presence of such layers is also examined.

Surface Acoustic Waves (SAW)-Based Biosensing for Quantification of Cell Growth in 2D and 3D Cultures.

Detection and quantification of cell viability and growth in two-dimensional (2D) and three-dimensional (3D) cell cultures commonly involve harvesting of cells and therefore requires a parallel set-up of several replicates for time-lapse or dose–response studies. Thus, developing a non-invasive and touch-free detection of cell growth in longitudinal studies of 3D tumor spheroid cultures or of stem cell regeneration remains a major unmet need. Since surface acoustic waves (SAWs) permit mass loading-based biosensing and have been touted due to their many advantages including low cost, small size and ease of assembly, we examined the potential of SAW-biosensing to detect and quantify cell growth. Herein, we demonstrate that a shear horizontal-surface acoustic waves (SH-SAW) device comprising two pairs of resonators consisting of interdigital transducers and reflecting fingers can be used to quantify mass loading by the cells in suspension as well as within a 3D cell culture platform. A 3D COMSOL model was built to simulate the mass loading response of increasing concentrations of cells in suspension in the polydimethylsiloxane (PDMS) well in order to predict the characteristics and optimize the design of the SH-SAW biosensor. The simulated relative frequency shift from the two oscillatory circuit systems (one of which functions as control) were found to be concordant to experimental data generated with RAW264.7 macrophage and A549 cancer cells. In addition, results showed that SAW measurements per se did not affect viability of cells. Further, SH-SAW biosensing was applied to A549 cells cultured on a 3D electrospun nanofiber scaffold that generate tumor spheroids (tumoroids) and the results showed the device's ability to detect changes in tumor spheroid growth over the course of eight days. Taken together, these results demonstrate the use of SH-SAW device for detection and quantification of cell growth changes over time in 2D suspension cultures and in 3D cell culture models, which may have potential applications in both longitudinal 3D cell cultures in cancer biology and in regenerative medicine.

A Shear horizontal surface acoustic wave biosensor for a rapid and specific detection of d-serine

d-serine is an amino acid that has an important role in the regulation of N-methyl-d-aspartate (NMDA) signalling in the central nervous system. In fact, it acts as an endogenous co-agonist molecule for the NMDA receptor activation. Since an abnormal body level of d-amino acids is usually associated to different neurological diseases, it appears evident that it is of high interest to develop a fast and specific biosensor for the determination of d-serine.In this work, we report on the design and development of a surface acoustic wave (SAW) biosensor to detect the level of d-serine. The SAW-biosensor is based on the utilization of an inactivated form of the d-serine dehydratase isolated from Saccharomyces cerevisiae, a biomolecule that is able to specifically bind d-serine. In particular, we produced a PLP-reduced d-serine dehydratase biomolecule that was still able to bind d-serine and not to transform it into the product. The binding event between the “inactivated” d-serine dehydratase and d-serine was monitored by SAW delay-lines.

Detection and Quantification of Aromatic Hydrocarbon Compounds in Water Using SH-SAW Sensors and Estimation-Theory-Based Signal Processing

This work investigates a sensor system for direct groundwater monitoring, capable of aqueous-phase measurement of aromatic hydrocarbons at low concentrations (about 100 parts per billion (ppb)). The system is designed to speciate and quantify benzene, toluene, and ethylbenzene/xylenes (BTEX) in the presence of potential interferents. The system makes use of polymer-coated shear-horizontal surface acoustic wave devices and a signal processing method based on estimation theory, specifically a bank of extended Kalman filters (EKFs). This approach permits estimation of BTEX concentrations even from noisy data, well before the sensor response reaches equilibrium. To utilize estimation theory, an analytical model for the sensor response to step-changes, starting from clean water, to mixtures of multiple analytes is first formulated that makes use of both equilibrium frequency shifts and response times (for individual analyte), the latter being specific for each combination of coated device and analyte. The mode...

Finite element simulation of Love wave resonator for DNA detection

The paper presents 3D finite element simulation of a Love wave resonator using coupled resonance with ZnO nanorods for biosensing application. The variation in mode shape, phase velocity, and coupling coefficient with rotation angle for a Y-cut LiTaO3 crystal is reported. At rotation angle of 36° the leaky SAW is transformed into a perfect shear horizontal surface wave with high coupling coefficient. Mass sensitivity and electromechanical coupling coefficient of Love wave resonator are calculated for different guiding layer materials (ZnO, SiO2 and PMMA) of varying thickness. The mass sensitivity provided by PMMA is about 15 times that of SiO2 layer but coupling coefficient falls rapidly as its thickness increases, offering a narrow range of thickness of the guiding layer. Simulations are performed for ZnO nanorods of varying height (300–1800 nm) present over 315.605 MHz Love wave resonator having 4.7 μm thick SiO2 waveguide layer. The addition of double stranded DNA is simulated by applying its equivalent surface mass density on the sensor surface. Coupled resonance occurs when the resonance frequency of ZnO nanorods is close to the device operating frequency and causes frequency shift of about 10.5 MHz which is about 20 times greater than the value obtained in the absence of coupled resonance. Love wave device with resonant nanostructures operating in coupled resonance is a promising candidate for designing highly sensitive biosensor.

Shear horizontal surface acoustic waves in functionally graded magneto-electro-elastic half-space

The propagation of shear horizontal surface acoustic waves (SHSAWs) in an inhomogeneous magneto-electro-elastic (MEE) half-space with 6-mm symmetry is studied. By virtue of both the direct approach and Stroh-formalism, the dispersion relations corresponding to two general cases of material properties variation are obtained. In the first case, it is assumed that all material properties involving the MEE properties and density vary similarly in depth, whereas, the second case considers identical variation for the MEE properties, which differs from the variation of the density. The non-dispersive SHSAW velocities pertinent to the homogeneous MEE media are obtained under eight different surface electromagnetic boundary conditions as the limiting cases of the current study. The dispersion curves corresponding to eleven inhomogeneity profiles of practical importance are presented in an effective dimensionless format, and the effects of different types of inhomogeneity functions describing the composition of the functionally graded magneto-electro-elastic (FGMEE) half-space on the dispersion relation are discussed.

In-House Development of Shear Horizontal Acoustic Waves Based Sensitive Sensors for Bacterial Pathogens Detection

Surface acoustic wave can be generated at the free surface of an elastic solid. Interdigital transducers (IDTs) are fabricated on the piezoelectric substrate surface that will act as electrical input and output port. When appropriate AC voltage stimulus is applied to the input transducer, surface acoustic wave will be produced. The output or receiving port will detect the incident surface acoustic wave and convert it back to a suitably filtered electrical once. For this property, surface acoustic based devices were initially developed for the telecommunication purpose such as signal filters and resonators. SAW based devices have been modified to be sensors later on from for gas detections and have been moving towards biological detections recently for its ultra-sensitivity to surface perturbation. The main component of this device is the IDTs. Recently, there are several methods to produce IDTs; Ultra-Violet (UV), deep UV lithography, Electron beam (e-beam) lithography and X-ray lithography. Although, these methods can produce very fine and accurate electrodes in term of submicron size but the costs are extremely expensive. Thus, this paper will discuss the conventional CMOS method which is much more economical to produce the applicable IDTs for the bacterial pathogens sensing purpose. Shear horizontal surface acoustic wave (SHSAW), one of the SAW based types is used in this paper as it is most suitable for the liquid based application as it has the advantage of acoustic energy is not being radiated into liquid.

Effect of viscoelastic film for shear horizontal surface acoustic wave on quartz

A numerical analysis for the mass loading sensitivity of shear horizontal surface acoustic wave (SH-SAW) immunoassay biosensors on quartz has already been studied. However, the mass loading analysis is insufficient to explain the actual biosensor performance. To understand the SH-SAW biosensor performance, we analyze the effect of a viscoelastic film on SH-SAW biosensors. In this paper, a numerical analysis using a simple viscoelastic model for the SH-SAW biosensors is presented. In the theoretical model, the bioreaction layer on the SH-SAW biosensors can be treated as a viscoelastic film. The velocity changes of the 250 MHz SH-SAWs on quartz substrates, which are covered with bovine serum albumin (BSA) layers of different thicknesses, were measured and compared with the theoretical results obtained using the proposed viscoelastic model. Good agreement of the velocity changes of SH-SAWs versus changes in the viscoelastic film thickness between theoretical and experimental results was obtained.

Shear-horizontal surface waves in a half-space of piezoelectric semiconductors

We study the propagation of shear-horizontal waves near the surface of a piezoelectric semiconductor half-space of crystals of class 6 mm with the presence of a biasing electric field in the propagation direction. The three-dimensional equations of linear piezoelectric semiconductors are used. A transcendental equation that determines the dispersion relation is obtained and solved numerically. Results show that the semiconduction affects the wave speed and causes wave dispersion as well as attenuation, and that the waves can be amplified by the biasing electric field.

Acousto-Optic Diffraction by Shear Horizontal Surface Acoustic Waves in 36° Rotated Y-Cut X-Propagation Lithium Tantalate

Acousto-Optic Di raction by Shear Horizontal Surface Acoustic Waves in 36◦ Rotated Y -Cut X-Propagation Lithium Tantalate R. Rimeika, D. ƒiplys and M. Shur Department of Radiophysics, Vilnius University, Vilnius, Lithuania ECSE, and PAPA, Rensselaer Polytechnic Institute, Troy, NY, USA We have investigated the acousto-optic di raction by shear horizontal surface acoustic waves in 36◦ rotated Y -cut X-propagation lithium tantalate (LiTaO3) crystals. The measurements were performed at the optical wavelength 633 nm of He Ne laser and acoustic wavelengths of 50 60 μm. The anisotropic di raction with the light polarization rotation in the transmission mode was observed. The measured and calculated values of the light incidence angle corresponding to the strongest di raction di ered signi cantly. A narrow strip of a thin metal lm deposited on the crystal surface drastically a ected the light di raction. We attribute these e ects to the conversion processes between the shear horizontal leaky surface acoustic wave and shear horizontal surface skimming bulk wave.