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New Developments in Raman Spectroscopic Analysis Mike Kayat B&W Tek, Inc 19 Shea Way Newark, DE 19713 United States of America +1 302 368 7824 [email protected] 1

New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 [email protected] 1. Overview 2 Raman spectroscopy is now

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Page 1: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

New Developments in Raman Spectroscopic Analysis

Mike Kayat

B&W Tek, Inc19 Shea WayNewark, DE 19713United States of America+1 302 368 7824

[email protected]

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Page 2: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

Overview

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Raman spectroscopy is now an established and evolving scientific method for analyzing molecular compounds and crystalline solids

There have been some recent new developments where the Raman technique has been enhanced to increase the inherently low emissions

These new approaches include: Coherent anti-Stokes Raman spectroscopy (CARS) Surface enhanced Raman spectroscopy (SERS) Surface enhanced resonance Raman spectroscopy (SERRS) Spatially offset Raman spectroscopy (SORS)

A review of these new Raman spectroscopy enhancements will be presented, together with several practical application areas, including: Biomedical Forensics Security

o Counterfeit goodso Explosiveso Narcotics identification.

Page 3: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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Raman Scattering –

The Raman effect comprises a very small fraction, about 1 in 107 of the

incident photons.

Page 4: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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Raman Scattering –

Raman Shifto Independent of laser outputo Excitation wavelength is

determined by analytical and sample needs (avoid Fluorescence interference)

Raman Intensityo Depends on laser wavelength o The larger the excitation

wavelengths the lower Raman peak counts (at same power output)

Page 5: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – Resonance Raman Scattering (RRS)

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Raman shift is constant

• UV: resonance enhanced, R<F, photo damage, low penetration

• Visible: Raman -4, fluorescence overlaps with Raman signal

• NIR: low fluorescence, deep penetration, Raman -4

Raman scattering Resonance Raman scatteringNo overtones Overtones More modes in spectrum Same modes are selectively

enhancedNo electronic information Electronic informationWeak scattering Strong scattering

Page 6: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – UV RRS Example

RRS response of various carotenoid solutions under 488-nm excitation, shown as a function of increasing concentrations: β-carotene zeaxanthin Lutein lycopene

The response is linear up to ~5 μg/mL, which is a carotenoid concentration exceeding that found in human skin

Slight variations in the slopes for each carotenoid solution are in very good agreement with their respective excitation efficiencies.

RRS responses in the spectral vicinity of the C==C stretching frequency, measured for various antioxidants as a function of concentration in ethanol under identical excitation and detection conditions

Page 7: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – UV RRS Example

System measures carotenoid levels in the skin (β-carotene)

Skin carotenoids correlate significantly to serum carotenoid levels

The significant correlation between skin biopsy-levels of carotenoids and serum carotenoid levels eliminates the need for routine skin removal

Highly significant correlation between serum total carotenoids and skin carotenoids as assessed by Raman Spectroscopy

Use UV RRS as a method to assess skin carotenoid status as an indication of broad-spectrum antioxidant status, without the inconvenience of skin and blood samples

Page 8: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – SERS

SERS absorbs molecules onto a rough gold or silver surface and provides 103 to 107

amplification of the Raman signal

In addition, the use of gold or silver in this technique removes any interference from fluorescence for Vis-NIR wavelengths

Effects depend on size, morphology, and composition of gold and silver nanoparticles

Occurs due to the presence of a metal surface near the scattering molecule and contains two components; (1) electromagnetic and (2) chemical - electromagnetic enhancements due to the excitation of a surface plasmonwhich generates a strong, localized, secondary field, that Raman scatters from the molecules together with the incident field

Source: Renishaw

PRaman = NRaman.σRaman.ILaser

PSERS = NSERS.σSERS.ILaser.|FLaser|2.|FStokes|2 

Page 9: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – SERS Fabrication – Colloidal

SERS 10 ppm benzenethiol in methanol

Raman neat benzenethiol

SERS-active plates ~1-mm thick coating of silver (Ag)-doped sol-gel chemistry on glass bottoms with ~ 100–200 μL of each analyte in solution was added to individual SERS-active wells for analysis.

SERS 100 ppm and 5 wt% herring sperm fragments in water

Raman 100 ppm and 5 wt% herring sperm fragments in water

Can be used for explosives, chemical warfare agents, pharmaceuticals, and biological compounds

Page 10: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – SERS Examples

Page 11: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – SERS Examples

Page 12: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – Portable SERS-based System Yeast bacteria

TrycyclazoleMelamine

Substrate is a Si wafer of 5 mm X 5 mm with nanostructures glued on a standard microscope glass slide (3 inch by 1 inch)

100-500 ppb to 10-100 ppm detection levels

Page 13: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – Portable SERS-based System Substrate

Example detection limits

Source: Nanova

Page 14: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – Portable SERS-based System

Portable Analyzer is based on SERS

Capable of identifying hazardous materials at the ~ O(100 ppb)

Can precisely measure the Raman spectra of materials

The analysis algorithms in the embedded computer provide fast identification of samples.

Can be used for rapid detection of:o explosiveso chemical warfare agentso contraband narcoticso toxic industrial chemicalso food contaminants

Page 15: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – SERRS

SERS and Resonance Raman Spectroscopy (RRS) have been combined to produce surface enhanced resonance Raman scattering (SERRS)

This combines the signal enhancement of both RRS and SERS and the SERS's avoidance of fluorescence to produce ultra-sharp spectrographs

To date, SERRS has proven to be extremely useful in DNA detection

Page 16: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – SORS

Source: Rutherford Appleton Labs, UK

Use the diffuse component of scattered light

Measure Raman spectra from sublayers

Page 17: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – SORS Application

SORS used for screening of liquids, aerosols and gels (LAGs)

Can screen substances inside non-metallic containers such as plastic and glass bottles

SORS is typically successful through opaque plastic and colored glass

Page 18: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – CARS

CARS spectroscopy eliminates the effects of fluorescence

Combines two high intensity, pulsed lasers beams (pico-second or femto-second) to create a single high energy beam

Difference in frequency is the same as the target Raman mode of the sample

Raman spectra can be detected over background fluorescence

This system also has the advantage of being able to determine a molecule's chirality

CARS has a big disadvantage it cannot distinguish between small equally sized molecules

Still at early research stage, very expensive

Two laser beams with frequencies v1 and v2 (v1 > v2) interact coherently, and because of the wave mixing, produce strong scattered light of frequency 2v1 - v2

If the frequency difference between two lasers v1 - v2 is equal to the frequency vm of a Raman-active mode then a strong light of frequency v1 + vm is emitted.

Page 19: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – CARS Example

CARS has been used for monitoring the temperature of hot gases and flames

CARS has been utilized as a method for non-invasive imaging of lipids in biological samples, both in vivo and in vitro

Page 20: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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New Raman Methods – Advantages of SERS and SERRS

Sensitivity – similar or better than fluorescence

Selectivity – many peaks, minimal interference

Simplicity – only one excitation wavelength required

Multiplexing – different labels per well, easy to identify by PCA

Stability – highly stable reagents, not light sensitive

Shelf life & repeatability – advances in reusable substrates for specific targeted applications

Enable use of handheld Raman instruments for trace identification

Page 21: New developments in Raman spectroscopic analysis · New Developments in Raman Spectroscopic Analysis Mike Kayat ... 368 7824 mikek@bwtek.com 1. Overview 2 Raman spectroscopy is now

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Contact Information

Michael Kayat, Ph.D.Vice PresidentB&W Tek, Inc19 Shea WayNewark, DE 19713USA

+1 302 368 7824

[email protected]