Plate Mode Sensors Research Articles

Performance optimization of plate-mode sensors with bi-layered structure

The acoustic characteristics of plate-mode sensors with bi-layered structures composed of a piezoelectric film and a non-piezoelectric substrate are studied by numerical calculations using the transfer matrix method. Performances of the sensors can be evaluated based on the theoretical calculations of the dispersion curves, electromechanical coupling coefficients and sensitivities of the plate-mode sensors with a bi-layered structure. In order to obtain the optimized operating conditions of the sensors, the operating mode, frequency and the ratios of thickness of piezoelectric film to that of the substrate are evaluated when the sensors are applied in gas and/or liquid conditions.

Theoretical mass sensitivity of Love wave and layer guided acoustic plate mode sensors

A model for the mass sensitivity of Love wave and layer guided shear horizontal acoustic plate mode (SH–APM) sensors is developed by considering the propagation of shear horizontally polarized acoustic waves in a three layer system. A dispersion equation is derived for this three layer system and this is shown to contain the dispersion equation for the two layer system of the substrate and the guiding layer plus a term involving the third layer, which is regarded as a perturbing mass layer. This equation is valid for an arbitrary thickness perturbing mass layer. The perturbation, Δν, of the wave speed for the two-layer system by a thin third layer of density, ρp and thickness Δh is shown to be equal to the mass per unit area multiplied by a function dependent only on the properties of the substrate and the guiding layer, and the operating frequency of the sensor. The independence of the function from the properties of the third layer means that the mass sensitivity of the bare, two-layer, sensor operated about any thickness of the guiding layer can be deduced from the slope of the numerically or experimentally determined dispersion curve. Formulas are also derived for a Love wave on an infinite thickness substrate describing the change in mass sensitivity due to a change in frequency. The consequences of the various formulas for mass sensing applications are illustrated using numerical calculations with parameters describing a (rigid) poly(methylmethacrylate) wave-guiding layer on a finite thickness quartz substrate. These calculations demonstrate that a layer-guided SH–APM can have a mass sensitivity comparable to, or higher, than that of Love waves propagating on the same substrate. The increase in mass sensitivity of the layer guided SH–APMs over previously studied SH–APM sensors is of significance, particularly for liquid sensing applications. The relevance of the dispersion curve to experiments using higher frequencies or frequency hopping and to experiments using thick guiding layers is discussed.

A concentration dependent study of acoustic plate mode immunosensor response using antigen/antibody systems with different binding ability

Acoustic plate mode sensors have been used to monitor immunochemical reactions as a function of antigen concentration. In the studies, antibodies were covalently linked to the gold-coated sensing surface via mercaptoethanol, aminosilane, and glutaraldehyde. Two antigen/antibody model systems that differ in their ability to mutually bind one another have been used. For sensor operation at about 150 MHz, a detection limit of approximately 0.5 microg/ml was obtained in both cases. No significant difference between the two systems was found for the value of the binding constants. They amount to about 1.10(8) 1/mole and fall well into the range of binding constants reported for homogeneous immunoassays. A comparison of the sensor response obtained for the two model systems shows that about 70% of the immobilized antibodies are active.

Detection of non-specific protein adsorption at artificial surfaces by the use of acoustic plate mode sensors

The interaction of proteins with artificial surfaces is important to many medical and biochemical applications. Such examples involve the incorporation of catheters and prostheses as well as the non-specific adsorption of pharmacological proteins at the walls of a container, which may drastically reduce their activity. A fast analytical tool capable of determining the specific adsorption characteristics at these surfaces would, therefore, support technological progress. Contrary to traditional immunoassay, acoustic wave-based sensors allow an on-line and direct detection of label-free proteins, thus saving time and providing the oppurtunity to monitor the kinetics of the binding process. In this study, Cr/Au-coated acoustic plate mode (APM) sensors have been used to investigate the interaction of immunoglobulin G (IgG) and fibrinogen with differently terminated self-assembled monolayers (SAMs) of thiols. By this method, both the low affinity of hexa(ethylene glycol)-terminated (HS(CH2)11(OCH2CH2)6OH) alkanethiol SAMs and the high affinity of methyl-terminated (HS(CH2)11CH3) surfaces towards protein adsorption were confirmed. It was found that the amount of bound proteins depends on the pH of the solution. At low pH values, protein binding to methyl-terminated surfaces is drastically reduced. The adsorption characteristics of fibrinogen at methyl-terminated surfaces are explained by a kinetic model which involves the initial binding of native proteins and a subsequent unfolding process. Complete regeneration of the sensor element is achieved by the use of sodium dodecylsulfate.

Multifrequency evaluation of different immunosorbents on acoustic plate mode sensors.

Previous studies of acoustic plate modes on ZX-LiNbO3 have indicated that practical mass-sensitive immunosensors can be implemented by using devices with higher frequencies of operation and/or by improving techniques for the immobilization of antibodies. However, it is also known from these studies that the viscoelastic properties of aminosilane films, used for the covalent immobilization of antibodies on the crystal surface, cannot be ignored in the sensor response. In the present work, in an attempt to study the effect of viscoelasticity of the binding film, three different films with different viscoelasticity and binding capacities, an aminosilane, a dextran, and a poly-(etherurethane)-based immunosorbent (XP-5), were prepared on the sensor surface for the immobilization of antibodies. Immunochemical reactions were monitored by the acoustic plate mode sensor at three different frequencies, thus allowing the direct observation of the frequency dependence of mass sensitivity with different films. Depending on the type of immunosorbent, the sensitivity at the third harmonic was enhanced by a factor of 2-5 with respect to the fundamental response. A third acoustic mode at a closely spaced frequency to the third harmonic yielded lower sensitivity values, which indicates that sensitivity depends not only on the frequency of device operation but also on particle displacement amplitude and components of the selected wave. Since antigen binding capacities of the different immunosorbents were determined independently by a modified ELISA test, sensor responses can also be correlated to the immunosorbent structure, and hence the viscoelastic properties. A dual delay line configuration was used which compensates for second-order effects such as temperature variations and nonspecific adsorption.

Acoustic Plate Mode Sensor for Immunochemical Reactions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAcoustic Plate Mode Sensor for Immunochemical ReactionsR. Dahint, M. Grunze, F. Josse, and J. RenkenCite this: Anal. Chem. 1994, 66, 18, 2888–2892Publication Date (Print):September 15, 1994Publication History Published online1 May 2002Published inissue 15 September 1994https://doi.org/10.1021/ac00090a015RIGHTS & PERMISSIONSArticle Views116Altmetric-Citations36LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (524 KB) Get e-Alerts Get e-Alerts

Observation of liquid-solid phase transitions using a shear horizontal acoustic plate mode sensor

We present a method for characterizing liquid-solid phase transitions by using an acoustic shear horizontal (SH) plate mode sensor. The sensor consists of a Y-cut quartz plate provided with suitable interdigital transducers on the lower surface. To study the temporal evolution of a phase transition, the liquid is deposited in a thin layer on the upper surface and the SH mode attenuation is observed as a function of time during a programed temperature change. With this sensor the theoretical time resolution is about 1 μs. Experimental results are presented for the liquid-solid transition for deionized water, tap water, and 90%/10% mixture of tap water and ethanol, measured with an instrument time resolution of 50 ms.

Monitoring photo-polymerization of thin films using SH acoustic plate mode sensors

Abstract The use of shear-horizontal (SH) acoustic plate mode (APM) devices to monitor the cross-linking of polymer films in real time has been demonstrated. The SH-APM, which is excited and detected in a thinned quartz plate by interdigital transducers patterned on the surface, has displacement in the plane of the surface and normal to the direction of mode propagation. Because APM propagation velocity is affected by the shear stiffness (but not the bulk modulus) of a thin film in contact with the device surface, the APM acts as a sensitive probe of this film property. Using an APM sensor, the changes in shear modulus which accompany the photocross-linking of a negative photoresist polymer film were monitored as a function of time and of the wavelength of the cross-linking radiation.

Liquid-solid phase transition detection with acoustic plate mode sensors: Application to icing of surfaces

Abstract An acoustic plate mode (APM) device operating at 158 MHz has been used to monitor liquid-to-solid phase transitions. Shear-horizontal plate modes propagating in a quartz plate probe the phase of a medium in contact with the plate. When liquid contacts the device, viscous damping of the APM is the dominant means of energy transfer, with the resulting APM attenuation serving as a measure of liquid viscosity. When the liquid freezes, acoustic energy is mechanically coupled from the plate into the adjacent solid, leading to a dramatic increase in APM propagation loss. Because effective coupling of acoustic energy from the plate into the adjacent medium depends on continuity of shear displacement across the solid/ solid interface, the magnitude of the propagation loss is an indication of the intimacy of contact between the solid and the APM surface. Possible applications of this sensor include a monitor for airplane wing icing.