The Integrated Detection of Hazardous Materials
David S. Koltick
Center for Sensing Science and Technology
Purdue University, West Lafayette, Indiana 47907
Abstract. The goal of this research effort is to combine a number of high quality detection techniques together in order to
identify hazardous materials. These techniques include (1) elemental analysis for hazardous materials using neutron
interrogation and gamma ray spectrum analysis techniques as well as associated a-particle imaging techniques, (2) ion mobility
using new miniaturized instrumentation in simple ion trap instruments, (3) point-of-need chemical analysis systems for analyses
in aqueous systems using antibody arrays on micro-chips, (4) micro-sensors using advanced scanning probe microscope (SPM)
technique on gold and silicon surfaces coated with antibodies and antigen in both dry and aqueous environments. The
combination of several of these techniques into a single decision process gives broad response capability with a reduction in
false signals.
INTRODUCTION
The detection of hazardous materials has become
critical in the present terrorist threat environment. The
spectrum of possible threats range from biological and
chemical warfare agents, to explosive and radiological
materials and even simply mechanical threats such as
knives and guns. This broad range of threats cannot be
sensed with a single technology or discipline.
Because of this we have established the Center for
Sensing Science and Technology (CSST) at Purdue
University[1]. The Center has 10 tasks or groups that
are focused on specialized areas which contribute to
the Integrated Detection of Hazardous Materials
(IDHM) Program. This paper will discuss only 3 of the
focus areas as an illustration of the Center's approach.
NEUTRON INTERROGATION
A common problem is to protect a building, ship or
other area using a portal inspection system. A gun or
conventional bomb in luggage can be identified by
forming an x-ray shadow image of the object, due to
the device's unique mechanical form. However, as an
example, for chemical warfare threats there is no
unique physical form to search for. These agents work
directly on the functioning of the human body. If the
agent is in a sealed container, it must be identified by
its chemical composition, without opening the
container. However, the problem is made more
complex because the allowed interrogation time is
limited to about 10 seconds, if large numbers of
containers are to be examined.
Neutron interrogation technology is an excellent
candidate technology to solve this problem. A striking
feature of chemical compounds is that their elemental
composition as a function of density gives an
identifying fingerprint, allowing separation of a large
number of substances[2,3]. While a combination of
elements does not mean that a substance under
investigation has a particular chemical composition,
and while this method alone cannot differentiate a
simple mixture from a true chemical compound, it can
be used as a powerful sorting technique. Typically, H,
C, N and O ratios are studied. More importantly,
chemical agents contain additional markers such as F,
Cl, P, As and S that can provide an additional tag,
allowing a second level of checks that further help to
differentiate a sample of concern from ordinary
materials. If a sample can be shown to contain a
certain mix of elements in ratios similar to those of
chemical agents as well as specific elemental markers,
there is a good chance that this sample should be
CP680, Application of Accelerators in Research and Industry: 17th Int'l. Conference, edited by J. L. Duggan and I. L. Morgan
© 2003 American Institute of Physics 0-7354-0149-7/03/$20.00
835
handled in a specific manner and further tests would
handled in a specific manner and further tests would
be highly recommended.
be highly recommended.
available in systems which attempt to gain decision
available in systems which attempt to gain decision
speed by using large area detectors with poorer
speed by using large area detectors with poorer
resolution. Because the gamma ray spectrum is so
resolution. Because the gamma ray spectrum is so
sharp, strong uninteresting signals do not over power
sharp, strong uninteresting signals do not over power
and wash out more subtle effects. This means that
and wash out more subtle effects. This means that
small quantities of threat materials can be searched for
small quantities of threat materials can be searched for
in
shorterperiods
periodsofoftime.
time.
in shorter
To accomplish this analysis, neutrons produced by
To accomplish this analysis, neutrons produced by
an associated particle neutron generator with a flux up
an associated particle neutron generator with a flux up
toto1010^8neutrons
per second is used to excite a sample.
neutrons per second is used to excite a sample.
AAtotal
flux
of
on aa
total flux of approximately
approximately 10^
109 neutrons
neutrons on
luggage-sized
container
is
sufficient
to
produce
luggage-sized container is sufficient to produce
enough
enoughy-ray
γ-rayradiation
radiation that
that elemental
elemental tags
tags for
for many
many
chemical
agents
can
be
identified.
Common
chemical agents can be identified. Common materials
materials
and
and chemical
chemical agents
agents can
can be
be differentiated
differentiated by
by aa
comparison
of
the
elemental
content
at
a
second
step.
comparison of the elemental content at a second step.
The system
system also
alsocontains
containstwo
twocalibration
calibrationmonitors
monitors
The
on
each
side
of
the
container
used
to
normalize
on each side of the container used to normalize thethe
comparison of
of the
the scan
scan toto pre-stored
pre-stored background
background
comparison
9 9
spectra.
A
scan
would
consist
of
approximately
spectra. A scan would consist of approximately 1010
neutrons passing
passingthrough
throughthe
thecontainer.
container.
neutrons
J Reference
rS Neutron
A system
systemdiagram
diagramisisshown
shownininFigure
Figure2.2.
A
Accelerator Head _ I I Monitor
Associated Alpha
(end view)
Particle Detector
HPGe
Gamma
Detector
HPGe
Gamma
Detector
Shielding
Continuous
Conveyor
Neutron
Monitor
Figure1.1.An
Anassociated
associatedparticle
particle neutron
neutron generator
generator based
Figure
based
sealedcontainer
containerscanning
scanningsystem.
system.
sealed
Figure
x- xFigure2.2. Integrated
Integratedscanning
scanningsystem
systememploying
employingboth
both
ray
and
neutron
interrogation
techniques.
ray and neutron interrogation techniques.
Thepower
powerofofthis
this technique
technique isis that
that neutrons
neutrons are
The
are aa
penetratingradiation
radiationthat
thatcan
can pass
pass through
through material
material to
penetrating
to
induce nuclei
nuclei toto emit
emit y-ray
γ-ray radiation
radiation that
that is
induce
is
characteristicofofthat
that element,
element. y-ray
γ-ray radiation
radiation is
is also
characteristic
also
penetrating. InInthis
thisway,
way,information
information on
on the
the elemental
elemental
penetrating.
content
of
the
container
can
be
found.
The
generator
content of the container can be found. The generator
can be used in a number of different ways to search for
can be used in a number of different ways to search for
chemical agents. By pulsing the neutron generator,
chemical agents. By pulsing the neutron generator,
three different nuclear signals, neutron scattering,
three different nuclear signals, neutron scattering,
neutron capture and neutron activation can be
neutron capture and neutron activation can be
observed and measured. This mode gives an overall
observed
and measured. This mode gives an overall
view of the sealed container. If not satisfied with the
view
of
the
sealed
container.
If not particle
satisfiedmode
with can
the
results of this
mode,
the associated
results
of
this
mode,
the
associated
particle
mode
can
then do a second level imaging scan using fast
then
do a This
secondtechnique
level imaging
neutrons.
will bescan
overusing
laid fast
on
neutrons.
This
technique
will
be
over
laid
information gained using x-ray techniques in order on
to
information
usingofx-ray
techniques
in agents.
order to
increase thegained
confidence
detecting
chemical
increase the confidence of detecting chemical agents.
Interrogation
InterrogationofofLiquids
LiquidsororPowders
Powdersinin
Small
SmallSealed
SealedContainers
Containers
A
A key
key element
elementshown
shownininthe
theFigure
Figure2 2schematic
schematicis is
the ability to scan small or large bottles by neutron
the ability to scan small or large bottles by neutron
interrogation. If a threat is suspected in the container
interrogation. If a threat is suspected in the container
and appears to be a small object, it can be removed
and appears to be a small object, it can be removed
and examined in a similar manner with a dedicated
and examined in a similar manner with a dedicated
bottle scanning system. Because of the smaller size of
bottle
scanning system. Because of the smaller size of
the container, it is very difficult to mask or hide
the
container,
it is in
verythisdifficult
mask or The
hide
hazardous materials
reducedto volume.
hazardous
materials
in
this
reduced
volume.
The
neutrons and gamma rays easily penetrate the
neutrons
and
gamma
rays
easily
penetrate
container walls, including metallic containers, so thatthe
container
walls, including
metallicMost
containers,
that
the
wall thickness
is irrelevant.
liquids sothat
the
wall
thickness
is
irrelevant.
Most
liquids
that
people carry such as perfume, drinks, toiletries, and
peoplewill
carry
as perfume,
drinks,
and
other
givesuch
a strong
deuterium
signaltoiletries,
due to the
other
will
give
a
strong
deuterium
signal
due
to
capture of neutrons on the hydrogen in the water.the
capture ofmany
neutrons
on agents
the hydrogen
in elements
the water.
However,
chemical
contain the
However,
F,
P, As, S,many
and Cl.chemical agents contain the elements
Proposed Scanner
Proposed Scanner
Figure 1 shows the proposed system for the scanner
Figure 1 shows
the proposed
systemshielded
for the scanner
consisting
of 2 Germanium
detectors
from a
consisting
of 2 Germanium
detectors
shieldedarefrom
neutron generator.
Germanium
detectors
useda
neutron
detectors
aretoused
becausegenerator.
the decisionGermanium
time is directly
related
the
because
decisionBut
time
is directly
the
detectorthe
resolution.
more
than this,related
spectraltolines
becomeresolution.
available But
for more
identification
are lines
not
detector
than this, that
spectral
become available for identification that are not
F, P, As, S, and Cl.
Because the elemental tags include an uncommon
Because
tags ratio,
includethese
an uncommon
material
and the
an elemental
odd Hydrogen
materials
material
anda an
odd Hydrogen
ratio,
materials
should
have
false-positive
rate that
willthese
be small.
If
the
positive
level rate
is set
a 3 If
should
have adetection
false-positive
that to
willrequire
be small.
the positive detection level is set to require a 3
836
spectrometry is often the answer. Unfortunately,
spectrometry
Unfortunately, most
most
mass spectrometers are large and delicate lab-based
lab-based
instruments.
standard deviation
deviation signal
signal above
above background
background for
for aa
standard
positiveresult
resultthen
then the
the false-positive
false-positive rate
rate will
will be
be at
at the
positive
0.4% level.
level. AA recheck
recheck would
would consist
consist of
of simply
simply
0.4%
passing the
the container
container back
back through
through the
the system.
system. This
passing
would reduce
reduce the
the false-positive
false-positive ratio
ratio down
down to
to 22 cases
cases
would
100,000 ordinary
ordinary samples,
samples, aa very
very acceptable
acceptable rate.
rate.
inin 100,000
Other positive
positive signals
signals might
might include
include odd
odd liquids
liquids that
that
Other
would require
require further
further investigation.
investigation. For
For example,
example, aa
would
containerfull
full of
of phosphorus
phosphorus would
would be
be of
of interest
interest even
even
container
wouldnot
notbe
beused
usedas
asaachemical
chemical agent.
agent.
ififititwould
TO
TI
m
:t|
We have developed a miniature mass spectrometer,
spectrometer,
shown
shown in Figure 4, that is portable and rugged,
rugged, yet
yet
capable of all the sophisticated experiments
experiments of
of a
conventional,
larger,
laboratory-based
mass
laboratory-based
mass
spectrometer.
Previous
research
in
this
lab
on
spectrometer. Previous research in this lab on the
the
fundamentals of
of ion
ion traps[7,8,9]
traps[7,8,9] have
fundamentals
have allowed
allowed for
for the
the
simplification and
and construction
construction of
simplification
of aa miniaturized
miniaturized CIT,
CIT,
the
heart
of
this
instrument
[10].
the heart of this instrument[10].
;»
lull tiriie (s&6)
Figure 4.
4. Miniature
Miniature cylindrical
cylindrical mass
Figure
mass spectrometer.
spectrometer.
FIGURE3.3. Confidence
Confidence level
level verse
verse search
search time
time to
to detect
detect aa
FIGURE
SarinSimulant,
Simulant,based
basedon
ondata.
data.
Sarin
This
second-generation
miniature
mass
This
second-generation
miniature
mass
spectrometer
consists
of
a
cylindrical
ion
trap
(CIT)
spectrometer consists of a cylindrical ion trap (CIT)
mass analzyer
analzyer (r
(r0 =
= 2.5
2.5 mm),
mass
mm), an
an off-axis
off-axis conversion
conversion
o
dynode
and
electron
multiplier
for
dynode and electron multiplier for ion
ion detection,
detection, aa
custom-vacuum manifold,
manifold, miniature
custom-vacuum
miniature vacuum
vacuum pumps
pumps
(Alcatel
turbo
pump,
KNF
Neuberger
(Alcatel turbo pump, KNF Neuberger diaphragm
diaphragm
backing pump),
pump), data
data acquisition
backing
acquisition and
and control
control
electronics,
embedded
PC
computer,
battery
electronics, embedded PC computer, battery pack
pack and
and
flat panel
panel video
video display.
display. The
flat
The total
total instrument
instrument package
package
is 28x70x18cm and weighs 20kg. Power consumption
is 28x70x18cm and weighs 20kg. Power consumption
is 150 W. Performance of this instrument has been
is 150 W. Performance of this instrument has been
characterized, with special emphasis on MS/MS
characterized, with special emphasis on MS/MS
experiments. The upper mass limit of the instrument
experiments. The upper mass limit of the instrument
(RF drive frequency 2 MHz, 1000 V . ) is mass/charge
(RF drive frequency 2 MHz, 1000 V00-pp ) is mass/charge
ratio (m/z) ~ 260. Ions are generated by electron
ratio (m/z) ~ 260. Ions are generated by electron
ionization (Rh filament, 50 juA emission current)
ionization (Rh filament, 50 µA emission current)
within the CIT. These ions are trapped, mass selected
within the CIT. These ions are trapped, mass selected
and manipulated using the normal ion trap operations
and manipulated using the normal ion trap operations
available in instruments capable of resonance ejection
available in instruments capable of resonance ejection
(q = 0.7, v ject = 700 kHz) and excitation. These
(qzz = 0.7, νeeject
= 700 kHz) and excitation. These
capabilities allow tandem and higher stage mass
capabilities allow tandem and higher stage mass
spectrometry experiments.
spectrometry experiments.
MASS SPECTROMETER
SPECTROMETER
MASS
Whileneutron
neutron interrogation
interrogation of
of containers
containers can
can be
be an
an
While
effective
approach
to
detecting
chemical
agents
in
effective approach to detecting chemical agents in aa
sealed containers
containers before
before their
their introduction
introduction into
into the
the
sealed
environment,
it
is
extremely
important
to
detect
an
environment, it is extremely important to detect an
agent
is
in
the
air.
The
IDHM
project
has
focused
on
agent is in the air. The IDHM project has focused on
the development of a prototype portable mass
the development of a prototype portable mass
spectrometer capable of detecting trace organic species
spectrometer capable of detecting trace organic species
in complex mixtures, such as untreated air. This
in complex mixtures, such as untreated air. This
fieldable instrument, which is capable of operating on
fieldable instrument, which is capable of operating on
battery power, has been carried into the field, and after
battery power, has been carried into the field, and after
transportation can be ready for analysis in less than 10
transportation can be ready for analysis in less than 10
minutes.
A typical demonstration shows that this
minutes.
A typical demonstration shows that this
extremely sensitive instrument can reliably detect the
extremely sensitive instrument can reliably detect the
CW simulant methyl salicylate in the presence of the
CW simulant methyl salicylate in the presence of the
many other organic compounds present in ordinary
many other organic compounds present in ordinary
urban air (exhaust, hydrocarbons, perfumes, etc). This
urban air (exhaust, hydrocarbons, perfumes, etc). This
is the result of the superior selectivity and specificity
is the result of the superior selectivity and specificity
of the instrument.
of the instrument.
The high sensitivity and wide applicability of mass
The high sensitivity and wide applicability of mass
spectrometry is desired in many situations in which
spectrometry is desired in many situations in which
direct analysis of samples is the ultimate goal. Many
direct
analysis
of samples
is thetheultimate
goal. Many
of these
situations
require
identification
and
ofquantification
these situations
require
the
identification
and
of chemical species in real time from
quantification
of chemical
species
in real
time from
complex mixtures,
a daunting
challenge
in which
mass
complex mixtures, a daunting challenge in which mass
Optimization of these devices has shown that CITs
Optimization of these devices has shown that CITs
are capable of producing comparable data to full size
are capable of producing comparable data to full size
laboratory instruments while requiring less voltage and
laboratory
instruments while
requiring
voltage
and
power. Miniaturization
of the
ion trapless
itself
allowed
power.
Miniaturization
of
the
ion
trap
itself
allowed
for a reduction in the size of the electronics as well as
for
reduction
in the size
of the electronics
as well
as
the avacuum
components
required
for its operation.
The
the
vacuum
components
required
for
its
operation.
The
aim of our research is to develop instrumentation and
aim of our research is to develop instrumentation and
837
methods based on mass spectrometry to monitor trace
methods
on massinspectrometry
to monitor
trace
levels
of based
compounds
air at sub-toxic
levels,
levels
of
compounds
in
air
at
sub-toxic
levels,
including chemical warfare agents (parts per billion
warfare agents
per billion
andincluding
parts chemical
per trillion),
very (parts
rapidly,
very
and
parts
per
trillion),
very
rapidly,
very
reliably—without false alarms—and in the field.
reliably—without false alarms—and in the field.
These instruments are directly applicable to
These instruments are directly applicable to
environmental and medical analysis, as well as
environmental and medical analysis, as well as
homeland security. We have tested this instrument in
homeland security. We have tested this instrument in
the lab and in battery-powered mode, in the field; the
the lab and in battery-powered mode, in the field; the
detection limit for the CW simulant methyl salicylate
detection limit for the CW simulant methyl salicylate
is 1is picogram.
1 picogram.
The longer term thrust of this effort is to develop
The longer
terma thrust
of this
effort system
is to develop
protocols
to allow
prototype
readout
that is
protocols
to
allow
a
prototype
readout
system
that is
compatible with the ultimate use of bio-sensitive
compatible in
with
the ultimate
usedetector.
of bio-sensitive
micro-chips
a hand-held
remote
Prototype
micro-chips in a hand-held remote detector. Prototype
tests have indicated the efficacy of this approach to a
tests have indicated the efficacy of this approach to a
2- and 3-element micro-chip. We believe the
2- and 3-element micro-chip. We believe the
successful specification and demonstration of such a
successful specification and demonstration of such a
multiple array micro-chip system will find wide
multiple array micro-chip system will find wide
applicability for the detection of proteins and
applicability for the detection of proteins and
bacterium
bacterium in
in the
the environment.
environment.
BIO-DETECTION
BIO-DETECTION
The
Thedetection
detection ofof biological
biological threats
threats are
are very
very
difficult.
One
approach
that
is
being
taken
is
difficult. One approach that is being taken isdevoted
devoted
to to
thethe
development
developmentofofmicro-systems
micro-systemsfor
forthe
thedetection
detection
of ofbiological
warfare
agents
and
hazardous
biological warfare agents and hazardousmaterials
materials
using
usingantibody
antibodyarrays
arraysononmicro-chips,
micro-chips, inin aqueous
aqueous
environments.
environments.The
Thedevelopment
developmentofofthis
thisability
abilityininan
an
aqueous
aqueoussystem
systemhowever
howeverdoes
doesnot
notlimit
limitit’s
it's use
use for
for
airborne
airbornethreats.
threats. Passing
Passingairairthrough
througha asimple
simple fine
fine
mist
mistspray,
spray,collecting
collectingit itand
andthen
thenpassing
passingititover
over the
the
bio-chip
will
allow
bio-chip
will
allowforforsuch
sucha asensitivity.
sensitivity.
Duringthethepast
pasttwo
twoyears[13,14],
years[13,14], work
work has
has be
be
During
systematically
and
successfully
completed
focused
on
systematically and successfully completed focused on
three
components
a bio-micro-chipsystem.
system.The
Thefirst
first
three
components
ofofa bio-micro-chip
designand
andfabrication
fabricationofofa abasic
basicassay
assayprotocol
protocol
is is
thethe
design
systemcapable
capableofofdetecting
detecting both
both antibodies
antibodies and
and
system
bacterium. This
This system
system consists
consists ofof patterning
patterning
bacterium.
appropriateantibodies
antibodiesonto
ontofunctionalized
functionalized substrates
substrates
appropriate
usingPDMS
PDMSstamp
stamppads.
pads. ToTopattern
patternprotein
proteinon
onthe
the
using
surface
a technique
developedbybyWhitesdies
Whitesdieselelal.
al.was
was
surface
a technique
developed
used[15]. Figure
Figure 5 5 shows
shows a a scanning
scanning probe
probe
used[15].
microscope
image
of
a
cross-reaction
study
between
microscope image of a cross-reaction study between E.E.
Coli antibodies
antibodies after
after incubation
incubation inin a a solution
solution
Coli
containing
E.
Coli
bacteria.
The
high
selectivity
containing E. Coli bacteria. The high selectivity ofofE.E.
Coli
selectivelypatterned
patternedregions
regionsofofantibody
antibodyisis
Coli
to to
thetheselectively
clearly visible in this image.
clearly visible in this image.
Figure 5.
5. An
An scanning
scanning probe microscope
Figure
microscope image
image of
of aa
microarray fabricated
fabricated to detect
microarray
detect E.
E. coli
coli 0157:H7.
0157:H7. The
The
stamped anti-body
anti-body region is approximately
stamped
approximately 5x5
5x5 micron.
micron.The
The
bacteria isis clear
clear detected.
detected.
bacteria
CONCLUSION
CONCLUSION
We have
have presented
presented aa few
We
few of
of the
the efforts
efforts now
nowbeing
being
pursued
under
the
Integrated
Detection
of
Hazardous
pursued under the Integrated Detection of Hazardous
Materials Program
Program within
within the
Materials
the Center
Center for
for Sensing
Sensing
Science and Technology at Purdue University. While
Science and Technology at Purdue University. While
each of the individual systems is fully capable of threat
each of the individual systems is fully capable of threat
detection for specific threats, together they can
detection for specific threats, together they can
function to greatly reduce the threat from chemical and
function to greatly reduce the threat from chemical and
biological agents. The neutron system has the
biological
The neutron
the
potential toagents.
detect chemical
threat atsystem
a portalhas
before
potential
to
detect
chemical
threat
at
a
portal
before
deployment while the mass spectrometer and microdeployment
while
theinmass
spectrometer
and microchip arrays can
serve
the role
as point detectors
and
chip
arrays
can
serve
in
the
role
as
point
detectors
and
have the potential to detect chemical and biological
have
the
potential
to
detect
chemical
and
biological
threats both airborne and in aqueous environments.
threats both airborne and in aqueous environments.
The second effort has been the incorporation of a
The second effort has been the incorporation of a
preliminary fractionation system to clean up samples
preliminary fractionation system to clean up samples
before exposure to the micro-chips. At present, this
before exposure to the micro-chips. At present, this
system consists of micro-fluidic flow channels.
system consists of micro-fluidic flow channels.
Finally we are developing the expansion of a single
Finally detector
we are developing
channel
to a 2x2 or the
3x3 expansion
assay array.of a single
channel detector to a 2x2 or 3x3 assay array.
838
9. Wells, J. M.; Badman, E. R.; Cooks, R. G., A Quadrupole
Ion Trap of Cylindrical Geometry Operated in the Mass
Selective Instability Mode, Anal. Chem., 1998, 70, 438444.
ACKNOWLEDGMENTS
I would like to thank S. Howel, R. Reifenberger, G.
Cooks, R. Noll, J. Cooper, R. Koltick and Y. Kirn for
help developing this paper. I would like to thank the
Navsea, Crane Division for their support of this work.
10. Patterson, G. E.; Guymon, A. J.; Riter, L. S.; Everly, M.;
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Direct Analysis of Volatile Organic Compounds in
Human Breath using a Miniaturized Cylindrical Ion Trap
Mass Spectrometer with a Membrane Inlet, Rapid
Commun. Mass Spectrom., 2002, submitted.
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