Graduation Year

2009

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Chemical and Biomedical Engineering

Major Professor

Venkat R. Bhethanabotla, Ph.D.

Co-Major Professor

John T. Wolan, Ph.D.

Committee Member

Vinay K. Gupta, Ph.D.

Committee Member

Patricia Kruk, Ph.D.

Committee Member

Rajan Sen, Ph.D.

Keywords

Acoustic Streaming, Device Design, Biofouling Elimination, Focused SAW, Orthogonal SAW, Micro-Cavities

Abstract

Surface acoustic wave (SAW) devices find uses in a plethora of applications including

but not limited to chemical, biological sensing, and microfluidic actuation. The primary aim of

this dissertation is to develop a SAW biosensor, capable of simultaneous detection of target

biomarkers in fluid media at concentrations of picogram/ml to nanogram/ml levels and removal

of non-specific proteins from sensor surface using the process of acoustic streaming, for potential

chemical sensing, medical, and clinical diagnostic applications. The focus is on the development

of three dimensional finite element structural and fluid-structure interaction models to study wave

propagation and acoustic actuation of fluids in a SAW biosensor. This work represents a

significant improvement in understanding fluid flow over SAW devices, over the currently

available continuum model of Nyborg. The developed methodology includes use of a novel

substrate, namely, Langasite coupled with various combinations of novel multidirectional

interdigital transducer (IDT) configurations such as orthogonal, focused IDTs as well as sensor

surface modifications, such as micro-cavities. The current approach exploits the capability of the

anisotropic piezoelectric crystal to launch waves of different characteristics in different

directions, which can be put to the multiple uses including but not limited to sensing via

shear

horizontal waves and biofouling elimination via

Rayleigh wave induced acoustic streaming.

Orthogonal IDTs gives rise to constructive interference, thereby enhancing the magnitudes of

device displacements and fluid velocities. The net effect is an increase in device sensitivity and

acoustic streaming intensity. The use of micro-cavities in the delay path provides a synergistic

effect, thereby further enhancing the device sensitivity and streaming intensity. Focused IDTs are

found to enhance the device displacements and fluid velocities, while focusing the device

displacements and fluid motion at the device focal point, thereby enhancing the SAW device

biosensing performance. The work presented in this dissertation has widespread and immediate

use for enhancing sensor sensitivity and analyte discrimination capabilities as well as biofouling

removal in medical diagnostic applications of SAW sensors. This work also has a broad relevance

to the sensing of multiple biomarkers in medical applications as well as other technologies

utilizing these devices such as microfluidic actuation.

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