Modeling and simulation of a biosensor
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II. Technical background
Surface acoustic wave (SAW) devices are of great interest
for chemical and biochemical sensing applications. They can
be used for determining the concentration of a certain compound
in a liquid or gaseous environment.
All acoustic wave devices and sensors use a piezoelectric material to generate the acoustic wave. Applying an appropriate electrical field to a piezoelectric material creates a mechanical stress. Piezoelectric acoustic wave sensors apply an oscillating electric field to create a mechanical wave, which propagates through the substrate and is then converted back to an electric field for measurement.
When used as a biosensor, the acoustic surface is coated with a biosensing layer selective to the analyte and then exposed to a solution containing the analyte. The binding of the selective molecules to the analyte molecules results in an increase in mass that causes a phase shift in the electric signal which is measured by the sensor.
For sensing in liquids, shear horizontal (SH)-polarized wave modes are most attractive as they do not radiate energy into the fluid. To increase sensitivity, the surface of a piezoelectric substrate is overlaid by a thin isotropic guiding layer in which the shear velocity is less than the shear velocity in the substrate. Such devices are known as Love-wave acoustic sensors. They are supposed to be used for the specific detection of biological analytes such as antibodies/antigens, enzymes and hormones.
The triplet "Biosensor" at caesar is developing a Love wave acoustic
sensor that uses highly selective nucleic acids, known as aptamers,
to specifically bind to target molecules. The design and characterization
of the biosensor is supported in the Modeling and Simulation Group.
