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

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concentration of glucose) and thus causes a change in one of these fundamental
quantities. Electrical sensors can be inherently small and so we have a combination
device with biology and electrical sensing in a small and compact form.
When compared to much larger bench top machines, microscale configurations of
sensors usually have a superior performance because they are less prone to various
interferences such as power-line noise and they have much shorter diffusion distances
for sensed molecules. Some physical quantities such as micro-degrees of temperature
change are much easier to measure over small distances.
BioMEMS Implantable Sensors
Biosensors placed inside the body, or in-vivo, measure biological parameters such as
blood pH, oxygen, carbon dioxide, and blood glucose. (Blood pH is a measure of the
acidity of the blood.) These parameters are the most important in medicine since these
are all independent blood chemistries that give a moment-to-moment insight into the
physiological state of a living being.
Since the early days of the space program NASA has been interested in ways of
noninvasively monitoring these blood parameters in astronauts for the instant
assessment of their physiological condition. Until recently, blood withdrawal was the
only accurate and reliable way to obtain such information. Indwelling sensors that use
needle penetrations are now available but still have trouble with accuracy and
longevity.
The military has also been interested in the assessment of the state of readiness of a
soldier which is reflected in his blood chemistry. An exhausted solider will show a highly
acidic blood pH (less than about 7.3). Remote electronic readout of biosensor
information of a soldier to a central command center is presently the stuff of science
fiction movies but reflects real desires of the military.
Figure 7 shows a photo of a pH sensor (which measures concentration of hydrogen
ions). It is designed as a needle for tissue insertion or placement at the end of a
catheter for introduction into the blood stream. The pointed tip is inserted into the
medium to be measured, and the electrical signal and power supply are connected to
the device at the gold film contacts at the base.
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