Post on 11-May-2015
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Providing Chemical Information When & Where You Need It
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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
www.rta.biz
Detection of DEHP, Melamine & Pesticides in Liquid and Solid Field Samples
by SERS
Challenge: food contamination & adulteration
Providing Chemical Information When & Where You Need It
• 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
Challenge: minimize pesticide contamination
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Food and Drug Administration Pesticide Program
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%
Challenge: Detect Residues in Food & Feed
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Residues in Food Baby Food Feed (2003)
DDT carbaryl malathionchlorpyrifos-methyl chlorpyrifos-methyl chlorpyrifos-methylmalathion malathion chlorpyrifos endosulfan permethrin methoxychlordieldrin ethylenethiourea tribufoschlorpyrifos endosulfan pirimiphos-methylchlorpropham chlorpyrifos diazonpermethrin iprodione ethoxyquiniprodione thiabendazole ethionchlordane dimethoate gardona
Requirements 0.1 to 50 ppm.
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
Providing Chemical Information When & Where You Need It
The Solution: SERSSpecificity: 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.
Raman: Pure
SERS: 1 mg/mL
Melamine
hνTransmitted
Absorbed
Scattered
Rayleigh
Raman
HH
H H
H H
Raman
How it works: Raman
(IR)
Laser light directed at a chemical generates Raman light.
o hνvib
hνvib
hνo hνscat
vib0
vib1
virt
hνscat
Light Chemical
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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.
Chemical contribution can provide additional 103
enhancement
Single Molecule Detection: requires 1012 -1014 Enhancement
Surface-enhanced Raman Spectroscopy
Dispersive Raman
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Laser
Grating
CCD
Filter
Sample
Bin Columns
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).
500 750 1000 1250 1500 1750Raman Shift (cm-1)
O
3+ NH CH
2
_
CH
COPhenylalanine
Ram
an In
tens
ity
RTA’s SERSID - Trace Chemical Analyzer
Patents: 6623977, 6943031, 6943032, 7312088, 7393691, 7393692, 7462492, 7462493, 7713914
2010
Metal Particle
Sol-Gel Matrix
AdsorbedMolecules
Moleculesin Solution
Laser
RamanScattering
2001: Simple SERS Sample Vials
2001
1 10
2004: SERS-Active Capillary
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Extraction and Pre-Concentration
RTA’s SERS Sampling Systems
2003: SERS Microplate
High Throughput Screening
10-3M
10-5M
10-8M(~10 ppb)
102
104
107
Concentration EnhancementFactor
Commercial SERS Substrates: Benzenthiol
Analysis: methyl parathion
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Normal Raman
Surface-Enhanced Raman
Normal Raman
Surface-Enhanced Raman
Analysis: Fonofos
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Normal Raman
Surface-Enhanced Raman
Normal Raman
Surface-Enhanced Raman
Sensitivity: 10 ppb
75 mW of 785 nm1 min
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Standard Method: 1-2 hours
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Blank Sample: 1 ppm pesticide
1100g sample + 200 mL 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 ml4b SPE: C-18 SPE: C-184c add CH2Cl2/CH3OH add CH2Cl2/CH3OH test eluant
5a evap to 5 ml evap to 5 ml5b SPE: amino-propyl SPE: amino-propyl5c add CH2Cl2/CH3OH add CH2Cl2/CH3OH test eluant
6a evap to 5 ml evap to 5 ml6b SPE: carbon-black SPE: carbon-black6c 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
3 times
Method: 10-minute analysis
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sma
SGPlug
SGPlug
50 ppb Chlorpyrifos-methylin Solvent,in Orange Juice
400 800 1200 1600Wavenumbers (cm-1)
OJ Blank
Food Contamination: Pesticides
Ag-SG
Sens & Instrumen Food Qual, 4, 101-107 (2010)
Swab Test: carbaryl on an apple
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1 Spray
4 Measure
2 Swab 3 Extract
Analysis: SERS of carbaryl on apple
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Raman Spectra of Baby Milk Formula
785 nm Laser
1064 nm Laser
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1% Melamine in Baby Milk Formula
1% in Formula
Pure Formula
Difference spectrum
Pure Melamine
Melamine: NR & SERS -785
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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.
Melamine: SERS at 785 nm
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FA) 1mg/mLB) 100 microg/mLC) 10 microg/mLD) 1 microg/mL (1 ppm)
All spectra were taken at 80mW, 1min.
Spectroscopy: April 2011, Applied Spectroscopy: May 2011
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SERS of Melamine
0.5 PPM(X20)
5 PPM
Pure MelamineSimple SERS Sample Vial
Glass Luminescence
SERS of Melamine
0.5 PPM in Solvent(X20)
5 PPM in Solvent
250 PPM extracted from Baby Formula
Simple SERS Sample Vial
Glass Luminescence
Applications of Vibrational Spectroscopy in Food Science, Wiley, 2010, p.663
Food Contamination: Melamine
400 800 1200 1600Wavenumbers (cm-1)
0.5 ppm in solvent
glass bkg
5 ppm in solvent
250 ppm in Baby Formula
Ag-SG
Applications of Vibrational Spectroscopy in Food Science, Wiley, 2010, p.663
Challenge: DEHP- Toxic Plasticizer
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Bis(2-ethylhexyl)phthalate
June 2011: roughly 900 products have been recalled from nearly
40,000 Taiwanese retailers
Multiple, Fast Sample Analysis:96-Well SERS-Active Plate
We develop SERS Sample Systems for You
SERSLibrary
50Food
Contaminants &
Adulterants
SERSID – Trace Chemical Analyzer
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