Miniature Sensors for Biological Warfare Agents using Fatty Acid ...

4. Results and Discussion
During the three years of this LDRD much has been learned about the devices
(micropyrolyzer, micro gas chromatographic (microGC) column, and the surface
acoustic wave (SAW) detector in the context of rapid biological agent detection.
The results have demonstrated that the micropyrolyzer is capable of performing
the desired pyrolysis reaction, that the microGC is capable of separating FAMEs,
and the SAW detector is capable of reversible response to low molecular weight
FAMEs. Each component is discussed separately.
4.1. Micropyrolysis
4.1.1. Device characteristics
The wide range of commercial pyrolysis instruments discussed in the Background
section of this document illustrate that there is no strict definition of pyrolysis that
defines temperature ramp rate or final temperature. The initial target here was
500°C in less than 1 second with sample load. Devices used in the course of this
work (shown in Figure 21) included deep reactive ion etched (DRIE, round) and
potassium hydroxide (KOH) etched devices (square). The platinum heater is not
visible on the KOH device.
A. B.
Figure 21: Scanning electron micrographs of micropyrolyzer devices A) DRIE and B) KOHetched.
Device membranes were more than capable of being heated adequately, both in
temperature (>500°C) and response time. Figure 22 shows the temperature
profile for a device with a FAME sample load. The upper limit measured in this
case is only about 270°C, however this was a limitation of the infrared camera
used to collect the data. It is clear that only a few milliseconds are required to
ramp from 80 to 270°C using only 130 mW of power (6.65V at 18.84 mA). A ramp
rate of approximately 70°C/ms was achieved. Additional IR camera analyses
demonstrated that both the round and rectangular micropyrolyzers exhibited a
significant temperature gradient from edge to center which was more pronounced
in the rectangular device. Variations in heating rates were observed dependent
upon presentation of sample load, the type of sample (e.g. fatty acids in methanol
versus straight canola oil), mass load, power level and sequence, and on
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