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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

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Detection of DEHP, Melamine & Pesticides in Liquid and Solid Field Samples

by SERS

Challenge: food contamination & adulteration

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• 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

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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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