1. Detection of DEHP, Melamine & Pesticides in
Liquid and Solid Field Samples
by SERS
RTA SERS Team: Stuart Farquharson (CEO), Frank Inscore (R&D Director),
Chetan Shende & Atanu Sengupta (Senior Research Chemists),
Hermes Huang (Application Scientist)
• The Need/Challenges
• Basic SERS Theory
• SERS Sampling Devices
• Applications
• Illegal Drugs in Saliva/Surfaces
• Poisons in Food
• Explosives on Surfaces
We have
www.rta.biz a Booth
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2. Challenge: food contamination & adulteration
• Need pesticides to meet food demand
• 3 Million tons of contaminated fruits &
vegetables reaches the US market/yr
• Intentional adulteration/substitution - $
• Melamine – 50,000 hospitalizations
• DEHP – replace palm oil as clouding
agent in food
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3. Challenge: minimize pesticide contamination
Modern agriculture depends on pesticides to protect crops
and to produce the quantity and quality of food demanded by
today's society.
Foods Animal Feeds
Domestic Import Domestic Import
With Residues 34.5% 29.6% 40.8% 45.9%
Exceeding Guidance 0.8% 4.3% 1.6% 6.7%
Food and Drug Administration Pesticide Program
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4. Challenge: Detect Residues in Food & Feed
Residues in Food Baby Food Feed (2003)
DDT carbaryl malathion
chlorpyrifos-methyl chlorpyrifos-methyl chlorpyrifos-methyl
malathion malathion chlorpyrifos
endosulfan permethrin methoxychlor
dieldrin ethylenethiourea tribufos
chlorpyrifos endosulfan pirimiphos-methyl
chlorpropham chlorpyrifos diazon
permethrin iprodione ethoxyquin
iprodione thiabendazole ethion
chlordane dimethoate gardona
Requirements 0.1 to 50 ppm.
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5. The Need & Challenges
Various Agencies require a field-usable analyzer to identify
trace contaminants & adulterants in food.
The analyzer must typically provide the following:
• Specificity – Identify and discriminate the chemical from others
(No False Positives!)
• Sensitivity – Detect ~10-8 M or less (e.g. 25 ppb cocaine)
• Reproducibility – Accurate and Repeatable
(No False Negatives!)
• Speed – Analysis within 10 minutes
• Field Usable – Battery Operated and Rugged
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6. The Solution: SERS
Specificity: Every chemical produces a unique Raman spectrum
allowing unequivocal identification.
Sensitivity: Silver and gold nanoparticles increase Raman signals by
1 million times or more allowing 10-8M (ppb) detection.
Melamine
SERS: 1 mg/mL
Raman: Pure
7. How it works: Raman
Light Chemical
virt
H H Transmitted
hνo
H H hνvib
Absorbed (IR) hνo hνscat
H H
Raman
Raman
Scattered
hνscat vib1
Rayleigh hνvib
vib0
Laser light directed at a chemical generates Raman light.
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8. Surface-enhanced Raman Spectroscopy
When a molecule is within
a plasmon field,
the efficiency of Raman scattering
can increase by 1 million times!
Sub part-per million detection
becomes possible.
Single Molecule Detection: Chemical contribution
requires 1012 -1014 Enhancement can provide additional 103
enhancement
9. Dispersive
Sample Raman
Grating
Phenylalanine O
_
C O
Raman Intensity
+
Filter H3N CH
CH 2
Laser
CCD
500 750 1000 1250 1500 1750
Bin Columns Raman Shift (cm-1)
Limitations: 1) fluorescence, 2) unequal resolution, 3) x-axis
instability (laser shifting and expanding optics (temperature)
will shift spectrum across CCD face like an accordion).
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11. RTA’s SERS Sampling Systems
2001: Simple SERS Sample Vials
Molecules Sol-Gel Matrix
Raman
in Solution
Scattering
2001
Laser
Adsorbed
Molecules Metal Particle
2003: SERS Microplate
2004: SERS-Active Capillary
1 10
Extraction and Pre-Concentration
High Throughput Screening
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13. Analysis: methyl parathion
Normal Raman
Normal Raman
Surface-Enhanced Raman
Surface-Enhanced Raman
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14. Analysis: Fonofos
Normal Raman
Normal Raman
Surface-Enhanced Raman
Surface-Enhanced Raman
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16. Standard Method: 1-2 hours
Blank Sample: 1 ppm pesticide
100g sample + 200 mL
1 CH3CN 50% add 50 microg pesticide test
50% 100%
2 10g NaCl 10g NaCl test organic layer
3 Centrifuge Centrifuge test eluant
4a evap to 5 ml evap to 5 ml
4b SPE: C-18 SPE: C-18
4c add CH2Cl2/CH3OH add CH2Cl2/CH3OH test eluant
5a evap to 5 ml evap to 5 ml
3 times 5b SPE: amino-propyl SPE: amino-propyl
5c add CH2Cl2/CH3OH add CH2Cl2/CH3OH test eluant
6a evap to 5 ml evap to 5 ml
6b SPE: carbon-black SPE: carbon-black
6c add CH3CN/Toluene add CH3CN/Toulene test eluant
7a evap to 5 ml evap to 5 ml
7b 1 microL in GC-FID 1 microL in GC-FID compare
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18. Food Contamination: Pesticides
50 ppb Chlorpyrifos-methyl
in Solvent, Ag-SG
in Orange Juice
OJ Blank
400 800 1200 1600
Wavenumbers (cm-1)
Sens & Instrumen Food Qual, 4, 101-107 (2010)
19. Swab Test: carbaryl on an apple
1 Spray
2 Swab 3 Extract
4 Measure
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20. Analysis: SERS of carbaryl on apple
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21. Raman Spectra of Baby Milk Formula
785 nm Laser
1064 nm Laser
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22. 1% Melamine in Baby Milk Formula
1% in Formula
Pure Formula
Difference spectrum
Pure Melamine
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23. Melamine: NR & SERS -785
A) SERS spectrum of 1mg/mL melamine in water (80mW, 1 min.)
B) Raman spectrum of pure melamine (200mW, 5 min).
The enhancement factor is approximately 100,000.
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24. Melamine: SERS at 785 nm
FA) 1mg/mL
B) 100 microg/mL
C) 10 microg/mL
D) 1 microg/mL (1 ppm)
All spectra were taken at 80mW, 1min.
Spectroscopy: April 2011, Applied Spectroscopy: May 2011
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25. SERS of Melamine
0.5 PPM
(X20) Glass
Luminescence
5 PPM
Simple SERS
Pure Melamine Sample Vial
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26. SERS of Melamine
0.5 PPM in Solvent
(X20) Glass
Luminescence
5 PPM in Solvent
250 PPM extracted Simple SERS
from Baby Formula Sample Vial
Applications of Vibrational Spectroscopy in Food Science, Wiley, 2010, p.663
27. Food Contamination: Melamine
0.5 ppm in solvent
glass bkg
Ag-SG
5 ppm in solvent
250 ppm in Baby Formula
400 800 1200 1600
Wavenumbers (cm-1)
Applications of Vibrational Spectroscopy in Food Science, Wiley, 2010, p.663
28. Challenge: DEHP- Toxic Plasticizer
June 2011: roughly 900 products
have been recalled from nearly
40,000 Taiwanese retailers
Bis(2-ethylhexyl)phthalate
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29. Multiple, Fast Sample Analysis:
96-Well SERS-Active Plate
We develop SERS Sample Systems for You
