michael – kotula anthrax slides - case closed what really
TRANSCRIPT
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Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
Joseph R. Michael and Paul G. Kotula
Materials Characterization Department 1822Sandia National Laboratories, Albuquerque, NM 87185
Elemental Microanalysis of Bacillus Anthracis Spores from the Amerithrax
Case
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Outline
Tools for elemental microanalysis
Spectral imaging
Microanalysis of Leahy and NYP with SEM
Microanalysis of Leahy, NYP and Daschle with STEM and TOF-SIMS
Are the letter powders unique with respect to elemental signatures?
Summary
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Signature Statistics
•Signals from Individual Spores
•Variability between fields of view
•Variability within bulk material
1 μm
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Comparison of SEM and STEM
SEM – scanning electron microscope
STEM – scanning transmission electron microscope
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Comparison of SEM and STEM
SEM•Imaging – 0.6 nm currently•Microanalysis – about 1 μm•Elements – limited to >Be •Diffraction for crystallography•No sample preparation may be required
•STEM•High Resolution Imaging – 0.2 nm•Microanalysis – 1-2 nm spatial resolution
•Elements – limited to >Be •Diffraction for crystallography•Electron transparent (thin) samples
Volume excited~ 1 μm3
Volume excited~ 10-8 μm3
100 nm
1 nm 1 nm
SEM STEMIn this study we make use of the characteristic x-rays generated by the electron/sample interactions.
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1 μm
Automated Spectral-Image Analysis: Why?
STEM image of spores
• How do you comprehensively survey the chemistry of large sample areas?
• Point analyses can be subjective– where to take them from and how many.
• 2D distributions of chemical phases are needed but simple mapping alone is not the answer. Mapping has potential artifacts and requires fore-knowledge.
1
2
3
‘Chemical component images’ are needed–a spectrum from each component and an image describing where in the microstructure it’s found
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0 2 4 6 8 100
0.1
0.2
0.3
0.4
0.5 Ti
What are x-ray spectral images?
xy
energypixel
X-ray spectrum: chemical information from sample Spectral Image Data Set
X-ray Signal
Focused Electron
Probe
What do we do with all that data?Typically 10’s of millions of pieces of data
Thin foil or bulk sample
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energy
yx
= ++*
W-M
W-L
* CoNiCo-L
Ni-L
*Sn-L
0 5 10 15
Spectrum imaging
• Rapid decomposition of huge data sets• Unbiased—no input guesses needed• Elemental associations shown• Ability to find “needle in haystack”
Spectrum imaging for elemental forensic signatures
Statistical Analysis ToolsFocused electron probe
Distribution of elemental x-ray signals
Red = CRed = C--supportsupportGreen = aluminaGreen = aluminaBlue = Blue = FeCoFeCoCyan = CaCyan = Ca--SS--SiSi--OOBlack = shadowed supportBlack = shadowed support
Keenan, M. R., and Kotula, P. G.,(2003) Apparatus and System for Multivariate Spectral Analysis., US Patent #6584413. (filing date June 1, 2001).
Keenan, M. R., and Kotula, P. G.,(2004) Method of Multivariate Spectral Analysis., US Patent #6675106. (filing date June 1, 2001)
Kotula, P. G., Keenan, M. R., Michael, J. R. (2003), “Automated Analysis of SEM X-ray Spectral Images: A Powerful New Microanalysis Tool, Microscopy and Microanalysis; Feb. 2003; vol.9, no.1, pp.1-17.
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Preparation of samples for STEM or SEMSample fixation/ inactivation
Gamma irradiation (4Mrad) or
1 %Osmium tetroxide (1 hour) or
Glutaraldehyde (96 hours)
Rinse in Millonig’s buffer
Dry powder sample
Dry powder sample
SEMAccess sample and dust on stub in disposable glove bag
Image sample either uncoated (variable pressure SEM) or after conducive coating
Access sample and mount on stub in disposable glove bag
Mount sample in FIB and ion mill thin sample from spore(s)
Move thin sample to carbon film on TEM Grid
Dehydration
(30% ethanol) 50% ethanol 70% ethanol 90% ethanol 100% ethanol 100% propylene oxide
Embedding1:1 propylene oxide:resin100% resinPlace in mold with fresh resin and cure (oven) overnight
Section and collect on TEM grid
Stain
Uranyl Acetate Lead citrate
(S)TEM
(S)TEM
Performed at USAMRIID or NBFAC
Performed at Sandia National Laboratories
Dry powder sample(S)TEM
Access sample and dust on TEM grid in disposable glove bag
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Bacillus Thuringiensis treated with Silica nano- particles for flow improvements
0
100 0
200 0
300 0
400 0
500 0
600 0
700 0
0 1 2 3 4 5
Cou
nts
Energy (kV)
Si
P Ca
O
C
MgSecondary electron image of SiO nano-particles on Bt spores.
EDS acquired at 10 kV
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Si-O
Mg-P0 1.00 2.00 3.00 4.00 5.00
0
0.050.1
0.150.2
0.250.3
0.350.4
0.450.5
0 10 20 30 40 0 1.00 2.00 3.00 4.00 5.000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 5 10 15 20
100 μm
keV
Si
O
C
0 1.00 2.00 3.00 4.00 5.000
0.02
0.04
0.06
0.08
0.1
0.12 P
Cl K
Ca
0 10 20 30
keV0 1.00 2.00 3.00 4.00 5.00
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0 10 20 30
P
Mg
Cl KNa
O
Substrate
Ca-P
Spores
SEM – Spectral images of weaponized surrogate material
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SEM of Leahy and New York Post MaterialN
ew Y
ork
Post
le
tter m
ater
ial
Leah
y le
tter
mat
eria
l
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0
500
1000
1500
2000
2500
0 1 2 3 4 5 6
Inte
nsity
(cou
nts)
Energy (kV)
0
500
1000
1500
2000
2500
3000
3500
0 1 2 3 4 5 6
C
OCaSi P SNaMg
Leahy letter material
New York Post materialC
O
CaSiSNaMg P
20 kV15 kV5 kV
Inte
nsity
(cou
nts)
1 2 43Energy (keV)
CaP
Si
MgS
S
New York Post material
Lower voltages produce more surface elemental information.
Very small amount of Si detected at 5 kV therefore Si is locate away from the spore surface.
Si = 1.2 - 2.3 wt% ±50%
Ca =3.1 - 6.5 wt% ±50%
Si = 1.2 - 1.5 wt% ±50%
Ca =2.7 – 3.1 wt% ±50%
5 kV= 300 nm
15 kV = 2100 nm
20 kV= 3300 nm
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Bulk EDS Spectrum from Edgewood Report*Bacillus subtilis var. niger spores grown in Casein Digest (CD) Medium (no indication that an anti-foam agent was added).
*L. F. Carey, D. C. St. Amant and M. A. Guelta, Production of Bacillus spores as a simulant for biological warfare agents, Edgewood Chemical Biological Center,ECBE-TR-372, April 2004.
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SEM Image of Leahy material
0 2.00 4.00 6.000
0.2
0.4
0.6
0.8
1
1.2
0 2.00 4.00 6.000
0.02
0.04
0.06
0.08
0.1
0 5 10 150 5 10 15
10 μm
C
keV keV
CaP
Si
S
O
NaMg
10 μm
Spore material Support material
SEM – Spectral images of Leahy spore material
Spectral Image components of Leahy material
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Summary of SEM Observations of spore materials
Microanalysis in the SEM shows that Si is present in the Leahy and New York Post materials.
But- microanalysis of bulk samples in the SEM lacks sufficient spatial resolution to show where the Si is located with respect to the spores.
Low kV shows Si is mostly on the interior of the spores.
Microanalysis in the SEM is can be made quantitative.
But not from samples like the powder attack materials.
Spectral imaging with component analysis provides some useful information.
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Comparison of SEM and STEM
SEM•Imaging – 0.6 nm currently•Microanalysis – about 1 μm•Elements – limited to >Be •Diffraction for crystallography•Instrumentation is expensive•No sample preparation may be required
•STEM•High Resolution Imaging – 0.2 nm•Microanalysis – 1-2 nm spatial resolution
•Elements – limited to >Be •Diffraction for crystallography• Instrumentation is really expensive•Electron transparent (thin) samples
Volume excited~ 1 μm3
Volume excited~ 10-8 μm3
100 nm
1 nm 1 nm
SEM STEMIn this study we make use of the characteristic x-rays generated by the electron/sample interactions.
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Preparation of samples for STEM or SEMSample fixation/ inactivation
Gamma irradiation (4Mrad) or
1 %Osmium tetroxide (1 hour) or
Glutaraldehyde (96 hours)
Rinse in Millonig’s buffer
Dry powder sample
Dry powder sample
SEMAccess sample and dust on stub in disposable glove bag
Image sample either uncoated (variable pressure SEM) or after conducive coating
Access sample and mount on stub in disposable glove bag
Mount sample in FIB and ion mill thin sample from spore(s)
Move thin sample to carbon film on TEM Grid
Dehydration
(30% ethanol) 50% ethanol 70% ethanol 90% ethanol 100% ethanol 100% propylene oxide
Embedding1:1 propylene oxide:resin100% resinPlace in mold with fresh resin and cure (oven) overnight
Section and collect on TEM grid
Stain
Uranyl Acetate Lead citrate
(S)TEM
(S)TEM
Performed at USAMRIID or NBFAC
Performed at Sandia National Laboratories
Dry powder sample(S)TEM
Access sample and dust on TEM grid in disposable glove bag
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Weaponized Bt Surrogate
Bright Field TEM image
Spore
Si-Onanoparticles
1 μm
Annular Dark Field STEM image
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• Fluidized agent has silica nano-particles • Ca-phosphate nano-particles present• Na, Ca and Cl associated with spore body
Spectrum imaging for elemental forensic signatures
See: L. N. Brewer, J. A. Ohlhausen, P. G. Kotula and J. R. Michael, Forensic imaging of bioagents by X-ray and TOF- SIMS hyperspectral imaging”, Forensic Science International, vol. 179, 2008, 98-106.
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Weaponized SurrogateAutomated x-ray spectral image analysis
keV0 2.00 4.00 6.00
0
2
4
6
8
200 600 1000
SiO
Cl
Si-O particles are found on the exosporium
1 μm
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0 5.00 10.000
0.05
0.1
0.15
0.2
0 5.00 10.000
0.05
0.1
0.15
0.2
0.25
0.3
20 40 60 80 100 0 20 40 60 80
Fe
SiO
Pb
U
Ni
OsOs
500 nm
Si-O is on the spore coat and not the exosporium
Elements from stain overlap other possible elemental signals
STEM microanalysis of Daschle letter material
Fixed, stained and ultramicrotomed section
keV keV
STEM ADF
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SI5
0 5.00 10.000
0.05
0.1
0.15
0.2
0.25
0.3
0 5.00 10.000
0.05
0.1
0.15
0.2
0 20 4010 20 30 40
keV
Si
O
PbU
Ni
Pb
OsU
Ni
Os
250 nm
Red = StainPb, U, C …Green = Coating Si, O…Blue = Carbon in spore and supportSpore
Carbon in support media
100 nm
Exosporium
Fe
STEM microanalysis of Leahy letter material
Fixed,stained and ultramicrotomed section
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Focused Ion-Beam (FIB) Tool/ Scanning Electron Microscope (SEM)
FIB/SEM
Electron sourceAcceleratorScan coilsLens
Sample
Ga+Sou
rce
Ion columnElectron column
FIB allows unfixed/unstained site-specific TEM specimens to be prepared even of single spores
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FIB Specimen Preparation
SEM of clump of spores.
Ion image of TEM specimen
SEM of TEM specimen ready to be extracted
<100nmthick STEM
sample
Region of TEM sample
Can also prepare specimens from isolated spores
STEM image
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STEM Annular Dark- Field Image of spores in cross-section
5 μm
sporespore
spore spore
Pt from FIB
Cross-section sample made with FIB through irradiated, unfixed, unstained spores.
Leahy Letter FIB Cross-section
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Leahy Letter FIB Cross-section – FIB prepared section
0 2.00 4.00 6.000
0.1
0.2
0.3
0.4
0 2.00 4.00 6.000
0.05
0.1
0.15
0.2
0 20 40 600 10 20 30
Si
O
Fe
Ca
K
P
MgNa
O
500 nm
3.00 4.00 5.00 6.00 7.000
0.005
0.01
0.015
0.02
Sn
keV
keV
keV
Sn FeAdditional chemistry, Sn, revealed
in the absence of fixative and heavy metal stains
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00.10.20.30.40.50.60.70.80.91
10µm
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 2000
5
10
15
Mass / Charge
110 120 1300.0
0.1
0.2
0.3
0.4
0.5
Si
KGa
Fe
SiOHCa
Sn
Sn
Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS)
Ga+ ion sputtering was used to remove surface of spore.
Layer that contains Si and O also has trace amounts of Sn and Fe
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0 2.00 4.00 6.000
0.1
0.2
0.3
0.4
0.5
0 2.00 4.00 6.000
0.1
0.2
0.3
0.4
0.5
0 2.00 4.00 6.000
0.2
0.4
0.6
0.8
1
1.2
1.40 10 20
0 10 20 30
20 40 60 80
Sn
Si
OC
C
NSO
Ca
keV
keV
0 2.00 4.000
0.02
0.04
0.06
0.08
0.1Si
P S
OC
Al
Fe
Sn
500 nm
keV
P
C
O
KNaMg
New York Post Material – FIB prepared section
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ADF STEM image
0 2.00 4.00 6.000
0.1
0.2
0.3
0.4
0 5 10 15
0 2.00 4.00 6.000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2.00 4.00 6.000
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0 10 20 30
5 10 15 20 25
Ca
PK
O
C
S
C
O
Si
O
C
S Sn
keV
keV
1 μm
Fe
NaMg
New York Post Material – FIB prepared section
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0 2.00 4.000
0.02
0.04
0.06
0.08
0.1
1.00 2.00 3.00
0
0.05
0.1
0.15
0.2
0 10 20 30
0 20 40
OSi
keV
P + Os
ClCa
Vegetative cell with endospore.
Spore coat incorporates Si and O (Sn, Fe) within sporulating mother cell.
1 μm
New York Post Microtomed, Unstained Section
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0 2.00 4.00 6.000
0.1
0.2
0.3
0.4
0.5
20 40 60 80
Sn
Si
OC
keV
Fe
0 2.00 4.00 6.000
0.1
0.2
0.3
0.4
0 20 40 60
Si
O
FeSn0 5.00 10.00
0
0.05
0.1
0.15
0.2
0.25
0.3
0 20 40 60 80
Fe
SiO
keV
Daschle Material
New York Post Material
Leahy Material
Leahy, New York Post and Daschle are indistinguishable
Spore coats on Leahy and New York Post samples are indistinguishable (both contain Si, Fe and Sn. Daschle appears the same (Si and Fe present, Sn is obscured by other elements in stain). Material from the Daschle letter was not made available for FIB sectioning.
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Importance of Spore Count
• 10 spores per sample is not sufficient for a reasonable comparison
• 100 spores is both experimentally achievable and allow for reasonable comparison, but comparisons of spore count near 50% will lack real comparison power
• 1000 spores allow precise comparisons but was experimentally unreasonable (~10 days and 10 TEM samples of analysis per bulk sample) until late development of new EDS detector for STEM in SEM.
X Number of spores with a particular chemical featuren Total number of spores analyzed
(Fraction of spores showing a certain chemical make-up)
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Sample # Analyzed # with SiO %SPS02.266 124 97 76SPS02.057 111 73 66SPS02.088 141 91 65
040255-1 level 2 163 42 26040255-1 level 5 161 17 11040255-1 level 8 172 50 29
040030-2 level 2 94 6 6040030-2 level 5 118 0 0040030-2 level 8 113 7 6
040089-1 level 2 98 0 0040089-1 level 5 115 0 0040089-1 level 8 91 0 0
Leahy
Daschle
NYP
Analysis of fraction of spores with Si and O signature
RMR-1029RMR-1029RMR-1029
RMR-1030RMR-1030RMR-1030
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
500 nm
Si-O image
Bacillus anthracis Ames which was grown in shaker flasks at USAMRIID using Leighton-Doi media.
Sample 1030
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STEM images and Si and O component images of two samples of 040255
Note variability in number of spores with Si and O elemental signature.
BA Ames grown via fermentation (Dugway) using Leighton-Doi media
0 1 2 3 4 5 6 7 8 9 10
Energy (keV)
SiO
Ni grid
Si and O spectral component from spores
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Sample # Analyzed # with SiO %NBFAC.071102.0001.
0221.00021051 197 18.7
NBFAC.071102.0001. 0228.0002
982 86 8.8
NBFAC.071102.0001. 0232.0002
986 40 4.4
NBFAC.071102.0001. 0230.0002
476 7 1.5
NBFAC.071102.0001. 0235.0002
989 12 1.2
Analysis of fraction of spores with Si and O signature
Sample was described as “evidence”, no further description given by FBI.
Analyzed using STEM in SEM technique
Si in the spore coat – new detector not sensitive to oxygen, STEM used to verify presence of oxygen
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Red= Si, Green = Ca-P, Blue, Cl-SSEM defines field of view for spectral image acquisition
MSA identifies three chemical signatures
Si-containing spore coat
From this it is possible to count x and n
STEM in SEM of unstained, microtomed section
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Background
Coat
Cortex
Core
Previous studies have shown Si on the coat*
*Johnstone, K. et al., Location of metal ions on Bacillus megaterium spores by high-resolution electron probe x-ray microanalysis, FEMS microbiology Letters, vol. 7, 1980, p 97-101.
Modifed CCY medium containing: MgCl2 6H2O, MnCl2 4H2O, FeCl3 6H2O, ZnCl2, CaCl2 6H2O, KH2PO4, K2HPO4, glutamine, acid casein hydrolysate, enzymatic casein hydrolysate, enzymatic yeast extract and glycerol.
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M. Stewart et al., Journ. Bact., July 1980, p. 481- 491
Bacillus cereus
Si
PCa
darkfield
Analysis of samples from a previous study
0 0.1 0.2 0.3 0.4 0.5 0.6
0 1 2 3 4 5 6 7 8 9 10
OSi
Ni grid
Inte
nsity
Energy (keV)
Grown in modified liquid G media, no anti-foam used
Mg
Si
P
S
Ca
Mn
Cu from grid
Author’s noted: “considerable variation in Si content both within and between different spore preparations,… unlikely to be due entirely to contamination.”
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Conclusions
The NYP, Leahy and Daschle materials are indistinguishable elementally at the spore level.
NYP, Leahy and Daschle materials all have similar fraction of spores with Si-O in spore coat
Si-O signature found on endospores in New York Post sample
The letter powders are not unique with respect to Si and O elemental signatures. Examples from the literature and from samples grown for this study.
SEM and STEM have proven useful for spore characterization