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

2.1.2. Portable Biological Detectors
Methods that have been adapted to portable systems can be divided into three
types: liquid based, pyrolysis based, and optical based.
2.1.2.1. Liquid Based Detection
Liquid based detection of pathogens relies on antibody-based or immunochemical
assay chemistries. Antibody (Ab) based detectors are the best performing
technology to date for high sensitivity/specificity detection and identification of BW
agents. There are two detectors of this type that have been fielded, the Interim
Biological Agent Detector (IBAD) and the Biological Detector, a component of
Biological Integrated Detection System (BIDS). These detectors rely on the
fluorescent signal of an Ab/fluorescent tag/BW agent complex for identification.
Specific antibodies must be developed for each agent and existing devices have
demonstrated systems that can detect 4-8 agents. Simultaneous coverage of the
full spectrum of BW threats is limited by the development of effective antibodies
and the possibility that developed antibodies will not detect engineered BW
agents. The high specificity that can be achieved via antibody-based detection is
balanced by the limited robustness of biological systems which are susceptible to
fouling and have finite lifetimes and regenerability. Reaction times for
identification range from 15 minutes (BIDS) to 45 minutes (IBAD).
Also, false positive results may be generated by non-specific binding to materials
in the sample stream or by unforeseen cross-reactivity with sample materials, and
the Ab-coated surface has limited regenerability once a positive sample is
encountered.
2.1.2.2. Pyrolysis Based Detection
There are portable instruments being fielded and/or developed for biological
detection, based on pyrolysis of the collected aerosol sample. None are
autonomous (can be battery operated).
One instrument called the "Block II CBMS", uses pyrolysis / methylation to create
detectable species from biologicals [29, 43]. The system, however, weighs
approximately 130 lbs. and uses on the order of 500 W (average) power for
operation, including aerosol collection, pyrolysis and mass spectrometric analysis.
Pyrolysis is performed at 550°C for 16 seconds in a quartz tube. The slow
pyrolysis causes transport effects where all fatty acids do not arrive at the detector
simultaneously, complicating identification. The instrument has been
demonstrated in field trials and can detect biological aerosol concentrations less
than 50 agent containing particles per liter of air (APCLA). They state that "there
is no significant interference from other cellular products of the thermolysismethylation",
although they do see diketopiperizines when they pyrolyze albumin.
Another instrument uses pyrolysis (but without methylation) coupled with an IMS
detector [44, 45]. A laptop computer was required, however, for the signal
processing and the instrument weighed approximately 30 lbs. (without the aerosol
collector). The instrument performed well in biological aerosol trials, but
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