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

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Figure 15. Thermopile Glucose Sensor (left} With Functional Illustration (right} are Made Using
Photolithographic Techniques. This larger device is about 8 mm in length but has approximately 50 micron
minimum geometries. (Towe et al.)
At ASU the glucose sensor has been constructed on a thin mylar plastic substrate and
so can be curved into a cylinder to form a small tube. This tube is then sensitive to
glucose concentrations on its outside exposure to the blood stream. Figure 16 shows a
photograph and an illustration of a glucose sensor implemented in the form of a
catheter. The electrical output signal is routed by wires down the length of the catheter
for a remote readout. The device was implanted in a pig over a short duration and the
decrease in blood glucose concentrations in response to administration of insulin were
recorded and are shown in the right hand panel of Figure 16.
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Figure 16. Photograph and Illustration of the Thermopile Glucose Sensor in a Catheter. Its configuration
is shown (left) and its response in detecting changes 1n blood glucose in a pig as a result of insulin administration
to the animal. (ASU research.) Towe et al.
This glucose sensor approach has been found to have limitations in stability when
introduced into tissue or blood. Primarily the problems, as with many sensors, arise
from the system chemistry and not as much from the electronic portion of the sensor.
The glucose oxidase enzyme slowly decays over time and thus the sensor sensitivity
and calibration drifts making it eventually unusable.
These problems have no easy solution. Investigators have been working with various
forms of blood chemistry sensors for forty years or more. Microfabricated
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