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The quartz crystal monitor (QCM) is a common sensor platform based on the room temperature compensated pure shear mode (PSM) of thickness field excited (TFE) AT-cut quartz. However, with electrodes on both crystal faces, TFE only allows sensing of mechanical property changes. Lateral field excitation (LFE), where both electrodes are on a single face, enables the detection of both mechanical and electrical changes, potentially leading to higher sensitivity. As lithium tantalate (LT) has an LFE PSM and piezoelectric coupling several times greater than that of quartz, LFE LT was chosen as a possible replacement for TFE quartz. A theoretical search of all LT cuts identified those exhibiting a room temperature compensated PSM. A set of orientations ranging from (YXwl) 0°/-85° to 0°/-90° was chosen for experimental verification. The temperature response of each sample was shown to be parabolic, with a roughly linear relationship between crystal cut angle and temperature inflection point/turnaround temperature. Specifically, the (YXwl) 0°/-87° cut with a turnaround temperature at 26.4°C demonstrates that a room temperature PSM in LT can be excited via LFE. Future work focusing on the development of an LT sensing platform could profoundly impact sensor systems in agriculture, homeland security, global warming, and medical applications.
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Lateral field excited quartz crystal microbalances for biosensing applications
The most common bulk acoustic wave device used in biosensing applications is the quartz crystal microbalance (QCM), in which a resonant pure shear acoustic wave is excited via electrodes on both major faces of a thin AT-cut quartz plate. For biosensing, the QCM is used to detect the capture of a target by a target-capture film. The sensitivity of the QCM is typically based solely on the detection of mechanical property changes, as electrical property change detection is limited by the electrode on its sensing surface. A modification of the QCM called the lateral field excited (LFE) QCM (LFE-QCM) has been developed with a bare sensing surface as both electrodes are now on a single face of the quartz plate. Compared to the QCM, the LFE-QCM exhibits significantly higher sensitivity to both electrical and mechanical property changes. This paper presents theoretical and experimental aspects of LFE-QCMs. In particular, the presence and strength of the usual and newfound LFE-QCM modes depend on the electrical properties of the film and/or sensing environment. This work also presents examples of experimental setups for measuring the response of an LFE-QCM, followed by results of LFE-QCMs used to detect liquid electrical and mechanical properties, chemical targets, and biological targets. Finally, details are given about the attachment of various target-capture films to the LFE-QCM surface to capture biomarkers associated with diseases such as cancer.
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- PAR ID:
- 10589252
- Publisher / Repository:
- American Vacuum Society
- Date Published:
- Journal Name:
- Biointerphases
- Volume:
- 15
- Issue:
- 3
- ISSN:
- 1934-8630
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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