Shear Horizontal Surface Acoustic Wave Device Research Articles

New Advances in Rapid Pretreatment for Small Dense LDL Cholesterol Measurement Using Shear Horizontal Surface Acoustic Wave (SH-SAW) Technology.

Atherosclerosis is an inflammatory disease of the arteries associated with alterations in lipid and other metabolism and is a major cause of cardiovascular disease (CVD). LDL consists of several subclasses with different sizes, densities, and physicochemical compositions. Small dense LDL (sd-LDL) is a subclass of LDL. There is growing evidence that sd-LDL-C is associated with CVD risk, metabolic dysregulation, and several pathophysiological processes. In this study, we present a straightforward membrane device filtration method that can be performed with simple laboratory methods to directly determine sd-LDL in serum without the need for specialized equipment. The method consists of three steps: first, the precipitation of lipoproteins with magnesium harpin; second, the collection of effluent from a 100 nm filter; and third, the quantification of sd-LDL-ApoB in the effluent with an SH-SAW biosensor. There was a good correlation between ApoB values obtained using the centrifugation (y = 1.0411x + 12.96, r = 0.82, n = 20) and filtration (y = 1.0633x + 15.13, r = 0.88, n = 20) methods and commercially available sd-LDL-C assay values. In addition to the filtrate method, there was also a close correlation between sd-LDL-C and ELISA assay values (y = 1.0483x - 4489, r = 0.88, n = 20). The filtration treatment method also showed a high correlation with LDL subfractions and NMR spectra ApoB measurements (y = 2.4846x + 4.637, r = 0.89, n = 20). The presence of sd-LDL-ApoB in the effluent was also confirmed by ELISA assay. These results suggest that this filtration method is a simple and promising pretreatment for use with the SH-SAW biosensor as a rapid in vitro diagnostic (IVD) method for predicting sd-LDL concentrations. Overall, we propose a very sensitive and specific SH-SAW biosensor with the ApoB antibody in its sensitive region to monitor sd-LDL levels by employing a simple delay-time phase shifted SH-SAW device. In conclusion, based on the demonstration of our study, the SH-SAW biosensor could be a strong candidate for the future measurement of sd-LDL.

Thin-film lithium niobate-on-insulator (LNOI) shear horizontal surface acoustic wave resonators

This work investigates the design methodology to obtain large electromechanical coupling factor () and high quality factor (Q) of shear-horizontal surface acoustic wave (SH-SAW) resonators based on the thin-film lithium niobate-on-insulator (LNOI) technology. The guided SH wave can be excited through interdigital transducers and propagate at the very surface of the material stackings. Such a guided SH wave in LN/SiO2 double layer structure is expected to offer high by confining the elastic strain energy in the piezoelectric thin film. To capture the optimum design window for high-performance LNOI SH-SAW devices, the impact of electrode material and its thickness on the dispersive characteristics are intensively investigated by finite element method (FEM). In this study, various one-port resonators with wavelengths from 2.8 μm to 8 μm were fabricated on a LNOI wafer with LN and SiO2 thickness of 0.7 and 2 μm, respectively. The 100 nm thick gold film was chosen as the electrode of the devices, which demonstrate a similar dispersive behavior to the FEM simulation with small discrepancy. Among the measurement results over several tested samples, a high- of 25.5% and Q of 960 was recorded at a resonance frequency of 581 MHz (FOM = = 245), revealing great potential for the application of wide-band frequency selection in telecommunications.

Multifunctional and Sensitivity Enhancement of Hybrid Acoustoplasmonic Sensors Fabricated on 36XY-LiTaO3 with Gold Nanoparticles for the Detection of Permittivity, Conductivity, and the Refractive Index.

Integration of high-sensitivity sensors with multiple sensing performance for the environmental detection of permittivity (εr), conductivity (σ), and the refractive index (n) is required to support Societies 5.0. However, there are still many sensors with low sensitivity that stand alone. A shear-horizontal surface acoustic wave (SH-SAW) sensor is usually used because of its high-sensitivity performance in detecting electrical properties. Moreover, localized surface plasmon resonance (LSPR) sensors show remarkable optical side capability. Here, we have successfully combined these advantages with an additional benefit of sensitivity enhancement. We propose a hybrid acoustoplasmonic sensor generated by integrating SH-SAW and LSPR devices to simultaneously detect εr, σ, and n. The SH-SAW sensor was fabricated on a 36XY-LiTaO3 substrate using a developed interdigital transducer. Then, the LSPR sensor was implemented by the deposition of gold nanoparticles (AuNPs) on the propagation surfaces of the SH-SAW sensor. Fascinatingly, the AuNPs not only generate the LSPR effect but also enhance the SH-SAW sensor sensitivity. Comprehensive investigations were performed with atomic force microscopy imaging, CST software used for plasmonic E-field simulation, and hybrid sensing evaluation. Moreover, the SH-SAW sensitivity enhancement achieved using AuNPs was verified by frequency-domain and time-domain measurements. Thus, the SH-SAW sensor with AuNPs has a wide εr detection range (25-85), sensing capabilities for ultrasmall σ (0.00528-0.02504 S/m), and high sensitivity for n detection (45.5-201.9 nm/RIU). The cross-sectional effects were also evaluated. The effect of the LSPR device on the SH-SAW device was examined by turning the light OFF or ON (hereafter OFF/ON). The impact of the SH-SAW device on the LSPR device was investigated by turning the sine signal OFF/ON. We found that the SH-SAW sensor was not impacted by light. Interestingly, the presence of the SH-SAW sensor affects the positions of the AuNPs, which consistently generates a small blueshift in the LSPR effect. However, insignificant variation was noted in independent performances. In general, the SH-SAW sensor with AuNPs shows multifunctional independent characteristics and high-sensitivity performance, making it suitable for a chemical environment, with the possibility of integration with a wireless network.

Obtaining Chemical Selectivity from a Single, Nonselective Sensing Film: Two-Stage Adaptive Estimation Scheme with Multiparameter Measurement to Quantify Mixture Components and Interferents.

A new approach is reported to detect and quantify the members of a group of small-aromatic-molecule target analytes: benzene, toluene, ethylbenzene, and xylenes (BTEX), dissolved in water, in the presence of interferents, using only the data collected from a single polymer-coated SH-SAW (shear horizontal surface acoustic wave) device and a two-stage adaptive estimation scheme. This technique is composed of exponentially weighted recursive least-squares estimation (EW-RLSE) and a bank of Kalman filters (BKFs) and does not require any prior knowledge of the initial concentration range of the target analytes. The proposed approach utilizes the transient sensor response to sorption and/or desorption of the analytes as well as the error range associated with the response time constants to provide more information about the analyte-specific interactions with the polymer film. The approach assumes that the sensor response to contaminated groundwater is a linear combination of the responses to the single target analytes, the interferents that interact with the selected polymer sensor coatings, and measurement noise. The proposed technique was tested using actual sensor responses to contaminated groundwater samples containing multiple BTEX compounds with concentrations ranging from 10 to 2000 parts per billion, as well as common interferents including ethanol, 1,2,4-trimethylbenzene, naphthalene, n-heptane, and MTBE (methyl tert-butyl ether). Estimated concentration values, accurate to ±10% for benzene/toluene and ±15% for ethylbenzene/xylenes, are obtained in near-real time. The utilization of sorption and/or desorption data enables detection and quantification of BTEX compounds with improved accuracy, high tolerance to measurement noise, and improved chemical selectivity.

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.

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...

Detection of cellular damage by hydrogen peroxide using SV40-T2 cells on shear horizontal surface acoustic wave (SH-SAW) sensor

The rat lung epithelial cell line SV40-T2 was used to develop a cellular biosensing system to assay for environmental toxicants. The novel approach on which this system is based involves direct attachment of cultured rat or human cells onto a cell-adhesive matrix on the device through which shear horizontal surface acoustic waves (SH-SAW) are transmitted using 50MHz SAW resonator. This novel design enables sensitive monitoring of changes of the electrophysical characteristics of cells, such as their conductivity and relative permittivity. A time-dependent change of phase of SAW and change of insertion loss (change of amplitude) were observed when the cells were treated with 0.5 or 1.0mM H2O2. The change of insertion loss was biphasic, with an early phase (1–3h) and a late phase (3–6h). The late phase coincided with the destruction of cell–cell tight junctions detected by measurement of the transepithelial electrical resistance and paracellular permeability; in contrast, the early phase coincided with the destruction of intracellular actin filaments by H2O2. The early-phase effect of H2O2 on phase shift may be attributable to the change of intracellular permittivity by a change of cellular polarity. Immunofluorescence microscopy showed the disappearance of zonula occludens protein 1 from the region of cell–cell contact. These results suggest the correlation between the change of insertion loss as an SAW parameter and the destruction of tight junctions of the cells on the SH-SAW device in the late phase.

Modeling Development of a High-Sensitivity <i>Escherichia</i> <i>coli</i> O157:H7 Detection Based on SH SAW Sensor

Surface acoustic waves based devices were initially developed for the telecommunication purpose such as signal filters and resonators. The acoustic energy is strongly confined on the surface of the surface acoustic waves (SAW) based devices and consequent their ultra-sensitivity to the surface perturbation. This has made SAW permits the highly sensitive detection of utterly diminutive charges on the surface. Hence, SAW based devices have been modified to be sensors. Food contamination has become critical issue and sensitive detection devices are needed urgently as small amount of harmful bacterial pathogens such as Escherichia coli (E.coli) O157:H7with the dose fewer than 100 organisms in food products or water is enough to cause serious gastrointestinal illness to human. Therefore, ultra-high sensitive, label free biosensors have been designed in this research for the low concentration E.coli detection. After the saturated development in telecommunication filed, SAW sensors were developed for gas detections and have been moving towards biological detections recently. Shear horizontal surface acoustic wave (SHSAW), one of the SAW based types is most suitable for the liquid based application as it has the advantage of acoustic energy is not being radiated into liquid. Therefore, SHSAW device has the potential to provide high-performance sensing platform in this research. There have been a lot of complicated theoretical models for the SAW devices development since 1960 as signal filters and resonators such as from delta function model, equivalent circuit model, to the current SAW models such as coupling-of-modes (COM) model, P-matrix model and finite element analysis (FEA) model. However, SHSAW device in this research is not meant for signal filter or resonators but used for surface sensing purpose, therefore the simplicity method of the modeling is presented in the paper for the E.coli detection sensor development.

Signal change of surface acoustic wave (SAW) caused by H2O2 damage to SV40-T2 cells cultivated on SH-SAW sensor

We developed a cellular biosensing system based on the direct assembly of rat- or human-cultured cells onto a shear horizontal-surface acoustic wave (SH-SAW) device. This novel design enables the sensitive monitoring of changes in physical cell-characteristics, such as viscosity or density inside the cells. In our system, the change of phase of SAW and insertion loss was observed to be time-dependent when the rat lung epithelial cells were treated with 1.0mM H2O2. Immunofluorescence microscopy showed the disappearance of the zonula occludens protein from the cell–cell contact region. Furthermore, the transepithelial electrical resistance of the cells gradually decreased owing to this treatment. These results suggest the correlation between the change of SH-SAW phase, the insertion loss of the SH-SAW parameter, and the destruction of the tight junction of the cells on SH-SAW devices.

Improved SHSAW transduction efficiency using grating and uniform electrode guiding

Pure shear-horizontal surface acoustic wave (SHSAW) devices have been increasingly considered for liquidphase and biosensing applications because of their ability to operate under liquid-loaded conditions and intrinsic sensitivity to mass, stiffness, viscosity, and electrical perturbations occurring at the device/fluid interface. Typically, the SHSAW is weakly guided by a free surface boundary condition (BC) or may not even exist for some materials and orientations, such as the quartz ST-90° orientation considered in this work. For a surrounding free surface BC, the interdigital transducer (IDT) typically generates strong shear-horizontal bulk acoustic waves (SHBAWs) relative to SHSAW. For that reason, guiding structures, e.g., dense and/or thick electrodes in periodic or uniform configurations, are incorporated into the design and placed between IDTs in delay-line devices to increase the ratio of transduced SHSAW power to IDT input power, ηSHSAW. The degree of ηSHSAW improvement depends on the thickness, composition, and geometry of the guiding structure. In previous work, the authors evaluated ηSHSAW using hybrid finite and boundary element method (FEM/BEM) models, but were limited to cases of stress-free or finite-thickness-grating surrounding surfaces. This work extends the analysis to the important boundary condition case of uniform finite-thickness electrode guiding, which is typically employed in liquid-phase and biosensor applications. To integrate the uniform electrode guiding structure with the SHSAW device analysis, a combined finite-length uniform electrode structure followed by an additional quarter-wavelength electrode was considered. In this work, it is shown that adjusting the quarter-wavelength electrode's film thickness and length allows cancellation of the SHSAW reflection from the edge discontinuity. As a result, the finite-length uniform guiding electrode can be treated as if it extends to infinity, and ηSHSAW can be easily obtained. In addition, the finite thickness of all electrodes is considered in the calculations. To verify the model, an IDT with uniform guiding electrodes was simulated and compared with the experimental results of a fabricated and tested device. The simulations predict SHSAW excitation directivity of 9 dB by the IDT, which is experimentally confirmed to within 0.8 dB.

Detergents sensing system based on SH-SAW devices

We report on the design and characterization of a novel analytical sensing system for the detection and discrimination of various detergents. Our sensor system could play a key role in the development of more efficient and environmentally-friendly washing machines by enabling the measurement of residual detergents. The sensing device comprises of a dual shear horizontal surface acoustic wave (SH-SAW) resonator device housed in a poly- dimethylsiloxane (PDMS) microfluidic chamber. Unmetalized and electrically shorted device configurations were used to analyze synthetic samples of liquid detergents of different concentrations. The sensor system correctly classified all three detergents without the need for an additional biological or chemical coating.

High velocity shear horizontal surface acoustic wave modes of interdigital transducer/(100) AlN/(111) diamond

In this research, shear horizontal (SH) surface acoustic wave (SAW) modes of interdigital transducer (IDT)/(100) AlN/(111) diamond propagated along the y-axis were theoretically analyzed and they exhibited excellent SH SAW properties. This is special for mode 0 where the K2 curve shows a maximum value (1.27%) at h/λ=0.28 and the velocity is 7496 m/s. The research results provide a predictable and theoretical basis for further application on high velocity SH SAW devices.

Improvement of Detection System for a Fast-Scanning and Phase-Sensitive Laser Probe for Surface Acoustic Wave Devices in 2 GHz Range

This paper describes recent advance in the detection system for the fast-scanning and phase-sensitive laser probing system for surface acoustic wave (SAW) devices operating in a 2 GHz range. Electric and electro-optic components were examined, and high sensitivity and high signal–noise ratio were achieved in a 2 GHz range without reducing the signal bandwidth. The developed detection system was installed to the laser probe system, and its performance was demonstrated by the SAW field visualisation of a shear-horizontal SAW device operating in a 2 GHz range.

Taste sensors utilizing high-frequency SH-SAW devices

Recent interest in the development of taste sensors has been motivated by their potential application in the food and beverage industries as well as environmental monitoring. This paper describes the development of novel high-frequency dual delay line and two-port resonator shear-horizontal surface acoustic wave (SH-SAW) microsensors for liquid analysis. The acoustic devices have been designed to function without the need for analyte-specific coatings and to operate at the wireless ISM frequency of 433 MHz; the sensors are small, robust and are built on a piezoelectric substrate (36° YX LiTaO 3). Liquid samples are introduced to the active sensing area via a microfluidic cell that has been fabricated using microstereolithography (MSL) and then attached to the SH-SAW sensor substrate. A low cost flow system has been developed and integrated with the sensor housing to create a fully automated measurement system. Tests have been performed on aqueous solutions with different tastants representing not only the four basic tastes of saltiness, sweetness, sourness, and bitterness but also of umami and metallic. Results show that good discrimination between the different taste samples is possible using both delay-line and resonator type piezoelectric devices.

Development of practical surface acoustic wave liquid sensing system and its application for measurement of Japanese tea

In this paper, we report on the development of a practical compact and stable sensing system with a shear horizontal surface acoustic wave (SH-SAW) sensor for liquid. First, the oscillation circuits for the liquid-phase sensor based on the SH-SAW device is discussed. Two sensor outputs, i.e., frequency and amplitude, are required for evaluating the liquid properties. To monitor the amplitude, an automatic gain control amplifier (AGC amp) is utilized in the oscillation circuit. The developed sensing system has a low standard deviation of noise that is less than the temperature coefficient of the frequency of the dual SH-SAW sensor and from which the detection limit is estimated. The dynamic range of the developed SH-SAW sensing system is also estimated. The system is applied for the measurement of Japanese tea. The results indicate that the slight differences among teas can be detected by the SH-SAW liquid sensing system.

New Application of Shear Horizontal Surface Acoustic Wave Sensors to Identifying Fruit Juices

The objective of this paper is to present a new application of shear horizontal surface acoustic wave (SH-SAW) devices on 36° rotated Y-cut X-propagating LiTaO3 for a sensing system that can identify liquid samples, such as fruit juices. Theoretical sensor sensitivity for acoustoelectric interaction with a liquid loaded on the SAW propagation surface was derived and confirmed with experimental results. The results strongly suggested that by employing SH-SAW devices with different center frequencies the sensor can recognize many liquid samples without a film coated on the substrate surface. In the experiment, the sensing system which identifies fruit juices was fabricated using three SH-SAW devices with center frequencies of 30, 50, and 100 MHz. Identification of samples, eleven kinds of fruit juices, was achieved by classification in principal component analysis and discriminant analysis. Since the SH-SAW sensor without a coating film has intrinsically good reproducibility and stability, it is effective for identification and quality control of liquid samples.