TECHNOLOGY DIGEST - Draper Laboratory

B. anthracis spores. This would be beneficial as it would
allow distinction between B. subtilis or other spores from
B. anthracis. Additionally, we further demonstrate the ability
of the DMS to detect chemical weapon agent simulants.
Pyrolysis was used as the sample introduction method for
the DMS, which uses thermal energy to break apart chemical
bonds. [45] The fragmentation of the sample will be
characteristic of the relative strengths of the bonds in the
original molecule. The maximum known detectable particle
size for the DMS is about 500 Daltons (0.5 kDa) based
on previous results (data not shown). We tested several
pyrolysis methods to ensure that the spores were broken
down sufficiently for detection by the DMS. Based on the
SDS-PAGE results shown, the spores were fragmented
completely at temperatures above 650°C. However, it is
important to note that the spores were also completely
fragmented at the lower temperature 550°C when this
temperature was held for 10 s. The fragmentation thus
seems to be dependent not only on temperature, but also
on the time at which this temperature is held. This allows
flexibility in determining an optimal pyrolysis condition to
use for DMS analysis. The knowledge of various pyrolysis
conditions that ensure adequate fragmentation for DMS
analysis is important not only for these experiments, but
for any field setups in the future that use pyrolysis as a
sample introduction method.
We examined the response of the DMS to pyrolyzed
spores. We chose to use a lower pyrolysis temperature and
extend it over a longer period of time in an attempt to
ensure fragmentation of the spores to particles well under
the detection limit of the gel, but also without complete
destruction of any characteristics of these molecular fragments.
The DMS spectra shown in Figure 4 demonstrate the ability
of the DMS to distinguish the spores from the sterile
water in which they are suspended. Significant peaks are
marked with numbers 1-5. Peaks 1, 3, and 4 appear to be
correlated with the presence of spores and could potentially
mark the presence of specific biomarkers. In fact, it
seems that these peaks may also be concentration-dependent,
as their magnitude appears to increase proportionally
to the number of spores present in the sample. The spectra
for the spores can be distinguished from that of the
water in which they were resuspended.
We also demonstrate the use of the DMS for chemical
weapons agents. MS was used as a simulant nerve agent.
The DMS produces a clear spectrum for MS at concentration
levels as low as 45 ppt, as shown in Figures 5a and 5b.
Another compound, DMMP, was used as a simulant blister
agent. A unique DMS spectrum is obtained for this compound
when compared with the one obtained for MS.
When a mixture of these two compounds was analyzed, the
resultant spectrum showed features of both compounds.
38
Detection of Biological and Chemical Agents Using Differential Mobility Spectrometry (DMS) Technology
This experiment shows that the specificity of the DMS
enables the detection of multiple chemical warfare agents
simultaneously.
CONCLUSIONS
In view of the growing concern over terrorism, there is a
need for a sensor that can detect trace amounts of chemical
or biological warfare agents to minimize the potential
impact of such a release on the public. Such a sensor
would aid the government in the defense against chemical
and biowarfare attacks; an early alert to such an attack
could save many lives. It would also aid the public health
sector in the treatment of biowarfare victims by speeding
diagnosis based on the identification of the particular
agent delivered. To service both industries, such a sensor
must be portable, inexpensive, sensitive, and able to detect
multiple biological or chemical agents.
Draper Laboratory has designed a sensor that fits these
characteristics, the DMS. Sionex Corporation is a Draper
spin-off company created to commercialize and market
this new device. The DMS has several advantages over
other types of detectors. It is small, extremely sensitive,
and relatively inexpensive. Not only are conventional ion
mobility spectrometers much larger and more expensive,
they also operate with short pulses of ions. In comparison,
the DMS analyzes continuously-introduced ions with
nearly 100% of the “tuned” ions reaching the detector.
Also, as the electric fields required to filter the ions are on
the order of 10,000 V/cm, the DMS actually benefits from
miniaturization; by reducing the gap dimensions to the
order of 500 µm, the voltages required for ion filtering are
easily achievable. Mass spectrometers are larger and more
expensive. They also require an inert environment for
detection, whereas the DMS operates at atmospheric pressure.
A portable hand-held DMS unit is already a reality
and further miniaturization is possible.
We have demonstrated the utility of the DMS to detect
potential biological and chemical warfare agents. The DMS
is a sensitive, hand-held device that can detect multiple
biological and chemical agents, even in the presence of
interferents. Furthermore, these devices can be manufactured
using mass production techniques, significantly
lowering their cost. The DMS identified a unique, repeatable
spectrum for B. subtilis spores, used as a surrogate for
B. anthracis spores. The concentrations shown here as
being detected easily are very low for the reagentless and
fast (less than 5 min) class of sensors. Even at such low
concentrations, the spores can be distinguished from the
water in which they are resuspended. This sensor with the
detection capacity currently shown could be used initially
as a trigger device, where a warning would be given if a
signal that looks similar to that resulting from the presence
of spores is discovered. In the future, however, if we can
show the ability to detect lower concentrations than