1. Securing Our Nations Water Supplies:
Detecting Poisons by SERS
Frank Inscore, Chetan Shende, Atanu Sengupta,
and Stuart Farquharson
Support:
EPA: EP-D-05-034, EP-D-06-084
www.rta.biz
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2. Challenge: specific, fast, sensitive
• Specificity – identify chemical agents & hydrolysis products
• No False Positives!
• Speed – monitor poisoned water (batch & continuous)
• 10 min or less
• Sensitivity – Requirements to protect
• CN – 6 mg/L (6 ppm)
• HD - 100 microg/L (100 ppb) TDG
• Nerve - 5 microg/L (5 ppb) MPA
Part-per-billion is challenging!
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3. Analysis: CWA Hydrolysis Products
H2 O
HCN H3 O+ + CN-
H2 O TDG
2 HCl +
HD S S
Cl Cl HO OH
O
O H2 O
DIASH + P
O H2 O N EMPA ethanol + O OH
HS P
VX P N O OH MPA
O S
HO H2 O
EtOH + EA2192 DIASH + MPA
P N
O S
O N H2 O O N H2 O O N
GA P HCN + EDMAPA ethanol +
O P P DMAPA
C N O OH O OH
H2 O
O H2 O O
HF + IMPA 2-propanol + MPA
GB P P
O F O OH
H2 O H2 O
GD O HF + O PMPA 2-pinacolyl + MPA
P P
O F O OH
H2 O
H2 O
O O CMPA cyclohexanol + MPA
GF HF +
P P
O F O OH
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4. Approach: Surface-enhanced Raman Spectroscopy
When a molecule is within
a plasmon field, hν
the efficiency of Raman scattering Ag
can increase by 1 million times! H N
H
O N
Sub part-per million detection H
P
O NS
H
N
N
N
H
becomes possible. VX
Chemical contribution
Plasmon Field
can provide additional 103 enhancement Surface-Enhanced
Raman Photon
Single Molecule Detection: requires 1012 -1014
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5. SERS-Active Substrates
benzenethiol
10-3M
10-5M
10-8M
(~10 ppb)
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6. Approach: RTA SERS Sampling Systems
2001: Simple SERS Sample Vials
Molecules Sol-Gel Matrix
Raman
in Solution
Scattering
2001
Laser
Adsorbed
Molecules Metal Particle
2004: SERS-Active Capillary
1 10
More suited to extract and pre-concentrate
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7. 2007: Functionalized Sol-Gel SERS Capillary
PC
OTC unreduced reduced
Std SERS vials
2nd generation
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8. RTA’s Portable Raman Analyzer
1064 nm
Advantages:
• No sample preparation
• Simple integration via fiber optics
• Remote analysis, multi-component
25 pounds • Complete spectral coverage
water tight • Wavelength stability
• Confident spectral subtraction
• and library search/match
785 nm • Real-time, On-demand analysis
• Long term stability
• Temperature and vibration immune
• Shock resistant
SERS-Active Capillary
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9. Potassium Cyanide: IR, NR, SERS
Infrared (solid)
CO2
Raman (saturated 2080 cm-1
solution, 1W, 10 min)
SERS (1 mg/ml water 2140 cm-1
100 mW, 1-min)
Wavenumbers (∆cm-1)
Enhancement Factor ~ 3x106
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10. SERS: cyanide
2003 (Vial) 2005 (Capillary) 2007 (F-Cap)
PPM PPB PPT
100 100 10000
10 10 100
1 1 1
100 mW 785 nm, 1-min
SERS is Non-linear (Langmuir function)
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11. Thiodiglycol (TDG): SERS & NR
SERS:
1 mg/mL, 1.5-min
100 mW 785 nm
Raman:
neat solution, 5-min
300 mW 785 nm
Enhancement Factor = 2x105
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12. SERS: Thiodiglycol
2005 (Capillary) 2007 (F-Cap)
PPM
1
10
PPB
10
100
1000
100 mW 785 nm, 1-min
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13. SERS: MPA
SERS:
0.1 mg/mL, 1-min,
100 mw 785 nm 756 C
PC
P
Raman:
1000 mg/mL, 5-min,
300 mw 785 nm
Enhancement Factor = 8x105
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14. SERS: Methyl Phosphonic Acid
2003 (Vial) 2007 (F-Cap)
P-C
760 PPM PPB
1000 1000
100 100
10 10
100 mW 785 nm, 1-min
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15. SERS: Methyl Phosphonic Acid
0.075
SERS
MPA
0.05
Peak height
ppb
0.025
1000
0
500 0 100 200 300 400 500 600 700 800 900 1000
Concentration (ppb)
250
125
25 ppb
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17. SERS: Alkyl Phosphonic Acids
1 ppm
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18. SERS: 10 parts-per-billion
IpMPA
PMPA
CMPA
EMPA
DIASH
80 mW, 785 nm, 1-min
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19. SERS: 10 parts-per-billion
CEMS
CEES
HEES
40 mW, 785 nm, 30-sec
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20. SERS: 10 parts-per-billion
Fonofos
Chlorobenzoic
Acid
Sunset Yellow
80 mW, 785 nm, 1-min
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21. Summary: specific, fast, sensitive
• Specificity – identify chemical agents & hydrolysis products
• No False Positives!
• Speed – monitor poisoned water (batch)
• 10 min or less – 1 minute
• Sensitivity – Requirements Lowest Measured Concentration!
• CN – 6 mg/L (6 ppm) CN – 1 ng/L (1 ppt!)
• HD - 100 microg/L (100 ppb) TDG - 10 microg/L (10 ppb)
• Nerve - 5 microg/L (5 ppb) MPA - 10 microg/L (10 ppb)
“pH dependence MPA, DPA, CN by SERS”, SPIE, 5269, 117-125 (2004)
“SERS Analyzer for Monitoring Chemical Agents and Their Hydrolysis
Products”, IJHSE, 102-111 (2007)
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22. Continuous Monitoring
1) Preliminary lab
Measurements Fiber Optic
cable
10 ppb CN! to instrument
3) Interface design
to sample
extraction line
SERS-active
capillary
1/8” Tygon opening to
tubing pass light
5”
FO Probe
2) 10 ppb food dye hole to pass
& Mount
for water mounting
screw
supply tests threaded for
1.5”
device
1.5”
attachment
SERS-Capillary
Interface Block
3”
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23. Future Work: NeSSI &Real-World Sampling
Parker-Hannifin Swagelok
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24. NeSSI &Real-World Sampling
3-Way 3-Way Surface Ex- Surface 3-Way Surface SERS Surface
Valve Valve Connection tractor Connection Valve Connection Sensor Connection
Regulated
Water
Sample MeOH Pump Waste
Bottle Bottle
Load Sample Into Extractor (5 min)
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25. NeSSI &Real-World Sampling
3-Way 3-Way Surface Ex- Surface 3-Way Surface SERS Surface
Valve Valve Connection tractor Connection Valve Connection Sensor Connection
Regulated
Water
Sample MeOH Pump Waste
Bottle Bottle
Load Sample Into SERS Capillary (10 sec)
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26. NeSSI &Real-World Sampling
3-Way 3-Way Surface Ex- Surface 3-Way Surface SERS Surface
Valve Valve Connection tractor Connection Valve Connection Sensor Connection
Regulated
Water
Sample MeOH Pump Waste
Bottle Bottle
Measure SERS
Load Next Sample Into Extractor (5 min)
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27. In Progress
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