Application of Shear Horizontal Surface Acoustic Wave (SH-SAW) Immunosensor in Point-of-Care Diagnosis.

Point-of-care testing (POCT), also known as on-site or near-patient testing, has been exploding in the last 20 years. A favorable POCT device requires minimal sample handling (e.g., finger-prick samples, but plasma for analysis), minimal sample volume (e.g., one drop of blood), and very fast results. Shear horizontal surface acoustic wave (SH-SAW) biosensors have attracted a lot of attention as one of the effective solutions to complete whole blood measurements in less than 3 min, while providing a low-cost and small-sized device. This review provides an overview of the SH-SAW biosensor system that has been successfully commercialized for medical use. Three unique features of the system are a disposable test cartridge with an SH-SAW sensor chip, a mass-produced bio-coating, and a palm-sized reader. This paper first discusses the characteristics and performance of the SH-SAW sensor system. Subsequently, the method of cross-linking biomaterials and the analysis of SH-SAW real-time signals are investigated, and the detection range and detection limit are presented.

Evaluation of Shear Horizontal Surface Acoustic Wave Biosensors Using "Layer Parameter" Obtained from Sensor Responses during Immunoreaction.

Shear horizontal surface acoustic wave (SH-SAW) biosensors measure the reaction of capture antibodies immobilized on the sensing surface to capture test molecules (antigens) by using the change in SH-SAW propagation characteristics. SH-SAW displacement exists not only on the SH-SAW propagating surface, but also partially penetrates the specimen liquid to a certain depth, which is determined by the liquid properties of the specimen and the operating frequency of the SH-SAW. This phenomenon is called viscosity penetration. In previous studies, the effect of viscosity penetration was not considered in the measurement of SH-SAW biosensors, and the mass or viscosity change caused by the specific binding of capture antibodies to the target antigen was mainly used for the measurement. However, by considering the effect of viscosity penetration, it was found that the antigen-antibody reaction could be measured and the detection characteristics of the biosensor could be improved. Therefore, this study aims to evaluate the detection properties of SH-SAW biosensors in the surface height direction by investigating the relationship between molecular dimensions and SH-SAW propagation characteristics, which are pseudo-changed by varying the diameter of gold nanoparticles. For the evaluation, we introduced a layer parameter defined by the ratio of the SH-SAW amplitude change to the SH-SAW velocity change caused by the antigen-antibody reaction. We found a correlation between the layer parameter and pseudo-varied molecular dimensions. The results suggest that SH-SAW does not only measure the mass and viscosity but can also measure the size of the molecule to be detected. This shows that SH-SAW biosensors can be used for advanced functionality.

The Peculiarities of the Acoustic Waves of Zero-Order Focusing in Lithium Niobate Plate.

In this research, beam focusing in lithium niobate plate was studied for fundamental anti-symmetric (A0) and symmetric (S0) Lamb waves, and the shear-horizontal (SH0) wave of zero-order. Using the finite element method, appropriate configuration of the interdigital transducer with arc-like electrodes was modeled accounting for the anisotropy of the slowness curves and dispersion of the modes in the plate. Profiles of the focalized acoustic beams generated by the proposed transducer were theoretically analyzed. Based on the result of the analysis, relevant delay lines were fabricated and transfer functions (insertion loss) of the line were measured for SH0 wave in YX-lithium niobate plate. Using an electron scanning microscope, distribution of the electric fields of the same wave were visualized. The results of this study may be useful for hybrid devices and sensors combining nano and acoustoelectronic principles.

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.

Inkjet Printing of Plate Acoustic Wave Devices.

In the paper, the results of production of Ag inkjet printed interdigital transducers to the acoustic delay line based on Y-cut X-propagation direction of lithium niobate plate for the frequency range from 1 to 14 MHz are presented. Additionally, morphological, structural, and electro-physical characteristics of the obtained electrodes were investigated. Mathematical modeling of the excitation of acoustic waves by these electrode structures was carried out. Comparison of the theoretical results with experimental ones showed their qualitative and quantitative coincidences. It was shown that conventional inkjet printing can replace the complex photolithographic method for production of interdigital transducers for acoustic delay lines working up to 14 MHz. The resulting electrode structures make it possible to efficiently excite acoustic waves with a high value of electromechanical coupling coefficient in piezoelectric plates.

Feasibility Study on Shear Horizontal Surface Acoustic Wave Sensors for Engine Oil Evaluation.

On site monitoring of engine oil is required. The features of a shear horizontal surface acoustic wave (SH-SAW) sensor include simultaneous detection of mechanical and electrical properties of liquids (such as viscosity, relative permittivity, and conductivity) and loaded mass on the sensor surface. In this paper, the used engine oil extracted from a motorbike was measured using the SH-SAW sensor. The degradation factors of the used engine oil were experimentally discussed. Especially, the influences of the particles in the engine oil, heating effect, and water contained in the engine oil were considered by comparing the differences between new and used engine oils. The results indicate that the influence of the water contained in the engine oil is the primary cause of the degradation of the used engine oil.

Rayleigh SAW-Assisted SH-SAW Immunosensor on X-Cut 148-Y LiTaO3.

In this paper, we describe a shear horizontal surface acoustic wave (SH-SAW) immunosensor that utilizes induce agitation by a Rayleigh SAW (R-SAW) on an X-cut 148-Y LiTaO3 substrate. On this substrate, SH-SAWs and R-SAWs with different frequencies can be effectively generated at an interdigital transducer (IDT). First, to consider the power flow angles of SH-SAWs and R-SAWs on this substrate, the 360-MHz delay lines with six different tilt angles were designed and fabricated. From the experiments, an optimal power flow angle of 9° for the SH-SAW on this substrate is obtained. Second, in order to consider the immunoreactions of the SH-SAW immunosensors, a delay line with a tilt angle of 9° was designed and fabricated on this substrate. The delay line, which can generate two SAWs, namely, a 100-MHz SH-SAW and an 88.8-MHz R-SAW, has a propagation area covered with antigens of human serum albumin between transmitting and receiving IDTs. The immunoreactions caused by antigen-antibody binding events on the surface of the delay line were investigated on the basis of the velocity changes of the SH-SAWs for sensing with and without the assistance of an R-SAW. As a result, it was confirmed that the SH-SAW velocity changes due to antigen-antibody reactions can be markedly increased by the assistance of R-SAW agitation.

Molecular characteristics and physiological functions of major royal jelly protein 1 oligomer.

Royal jelly contains numerous components, including proteins. Major royal jelly protein (MRJP) 1 is the most abundant protein among the soluble royal jelly proteins. In its physiological state, MRJP 1 exists as a monomer and/or oligomer. This study focuses the molecular characteristics and functions of MRJP 1 oligomer. MRJP 1 oligomer purified using HPLC techniques was subjected to the following analyses. The molecular weight of MRJP 1 oligomer was found to be 290 kDa using blue native-PAGE. MRJP 1 oligomer was separated into 55 and 5 kDa spots on 2-D blue native/SDS-PAGE. The 55 kDa protein was identified as MRJP 1 monomer by proteome analysis, whereas the 5 kDa protein was identified as Apisimin by N-terminal amino acid sequencing, and this protein may function as a subunit-joining protein within MRJP 1 oligomer. We also found that the oligomeric form included noncovalent bonds and was stable under heat treatment at 56 degrees C. Furthermore, MRJP 1 oligomer dose dependently enhanced and sustained cell proliferation in the human lymphoid cell line Jurkat. In conclusion, MRJP 1 oligomer is a heat-resistant protein comprising MRJP 1 monomer and Apisimin, and has cell proliferation activity. These findings will contribute to further studies analyzing the effects of MRJP 1 in humans.

Liquid heating effects by SAW streaming on the piezoelectric substrate.

When a liquid is placed on a surface acoustic wave (SAW) propagation surface, a longitudinal wave is radiated into the liquid, and the liquid begins to vibrate stream, jet, and atomize. This phenomenon is known as SAW streaming. In this paper, we describe experimental results concerning the temperature of a thin liquid layer during SAW generation. The results reveal that the temperature of the liquid is a function of the SAW amplitude, which is determined by the applied voltage. This means that the liquid temperature can be controlled by the applied voltage. We conclude that a novel microliquid heating system can be realized using the SAW device.

On-line monitoring of polymer deposition for tailoring the waveguide characteristics of love-wave biosensors.

The Love-wave sensor is an acoustic sensing device which is particularly suitable for sensing in a liquid environment. The superior characteristics of the device are achieved by the use of an acoustic waveguide, consisting of a thin layer deposited on the surface of the substrate material. The exact thickness and material properties of the layer will not only determine sensitivity and sensing performance of the resulting device but can also be adjusted to generate higher-order Love modes. Thus, to obtain a sensing device with the desired specifications, precise control over the process of waveguide deposition is required. This has been realized by implementation of a vapor deposition polymerization system where the transmission curve (amplitude vs frequency) of one of the sensing devices is continuously monitored during deposition. As soon as the desired device specifications are reached, the deposition can be interrupted immediately. From the recorded transmission curves, information about the sensitivity of the device can be deduced, and the formation of higher-order Love modes can be visualized. The system has been used to produce biosensors based on various Love modes. It is shown that sensors operated on higher-order Love modes have a high mass sensitivity which, together with their excellent shielding properties, makes them advantageous for biosensing in conducting buffer solutions.