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

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released chemical energy warms the surrounding environment to a degree that
depends on the energy released in the exothermic reaction, which is characteristic of
the particular chemistry and the amount of reactants. The heating is then dependent on
the glucose concentration.
Figure 12 shows these devices. They are
made by MEMS techniques involving the
processes of using patterning by
exposure to light through a mask
(photolithography), metal deposition by
evaporation, and sputter etching. The
result is the fabrication of sensors in
large arrays with many identical sensors
on a single substrate. The figure is a
photomicrograph of a part of a wafer
production run with nine identical
devices. Each one of the devices is less
than 1 mm in size and would be cut
apart and used independently. The
darker rectangular areas at the top of
each device are the electrical bonding
pads where wires attach to the device
to readout its electrical response.
Figure 13 shows the basic process in the
sensor operation. The sensor is planar
and composed of a layered structure
consisting of an enzyme gel and a
·--· ·--·
·--
·--· ·--· ·--·
Figure 12. Photomicrograph 3 x 3 Array of
Thermoelectric Glucose Sensors Constructed by
Towe et al. at ASU
thermoelectric temperature sensor. Glucose from the local medium naturally diffuses to
the gel and the temperature sensor underlies a thin film of enzyme gel that contains
the glucose oxidase. A second enzyme called catalase is used to secondarily break
down hydrogen peroxide produced by the first reaction.
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