Defense Intelligence Reference Document Biosensors And A Survey Of The Present Field

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Thus the trend has been to employ
MEMS technology to reduce the size of
the cantilever beams to microscopic
proportions. In such cases, even the
mass of cells or virus particles can be
measured. Figure 35 shows a
microcantilever system that is on the
order of one micron in width and 10
microns in length. This cantilever beam
was used as a mass detector, with
sensitivity to a single vaccinia virus
particle (vaccinia virus forms the basis of
the smallpox vaccine).
Biomolecular sensors with the ability to
"multiplex," or to detect a large number
of different molecular species at the
same time, are being developed for
cancer diagnostics and therapy
monitoring.
Figure 35. Scanning Electron Micrograph Showing a
Cantilever Beam With a Single Vaccinia Virus
Particle
The secret to good performance is finding a coating that has a high sensitivity for a
specific material of interest. Antibodies are often used as coatings since they can be
tailored to bind to many different molecules. Even so, there are often problems of
antibody shelf-life and they are not perfectly specific and so experience interference
from other chemicals in the test sample.
Figure 36 illustrates the affinity coating. Antibodies for different proteins are coated
onto different micro-cantilever beams, making each beam a sensor.
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0
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Figure 36. Antibodies Attached to a Cantilever Array Create Different Specificities to Substances in
Blood That are Indicative of Cancer
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