advances in opto-fluidic assisted ramanassisted raman … · 2014. 12. 2. · – information on...

Advances in opto-fluidic assisted Ramanassisted Raman spectroscopy of liquids, gases and aerosolsgases and aerosols

Amr S. HelmyAmr S. Helmy

OutlineOutline

• Superiority of Raman analysis in comparison itsSuperiority of Raman analysis in comparison its counterparts

• Weakness of Raman in dilute solutions andWeakness of Raman in dilute solutions and gasses

• An effective method to enhancing the retrieved• An effective method to enhancing the retrieved Raman signal

• Examples from nano particle analysis• Examples from nano-particle analysis• Examples from bio-material analysis.• Summary

Amr S. Helmy @ U of T

Why Raman SpectroscopyWhy Raman Spectroscopy

• PL: limited information convoluted resultsPL: limited information, convoluted results• XRD, TEM: time consuming, unsuitable for in

situ monitoringsitu monitoring • Raman offers:

– Information on doping, stresses, composition, etc.– No sample preparation – real time analysis– Suitable for in situ monitoring

• Raman is extremely weak in solutionsRaman is extremely weak in solutionsAmr S. Helmy @ U of T

Conventional Raman Spectroscopy

Helmy Group Copyright

Limitation• Small Interaction Volume

P C ll ti Effi i• Poor Collection Efficiency

Helmy Group at U of T Protected © 2013


Photonic Bandgap Assisted Raman SpectroscopySpectroscopy

Induced and accumulatedaccumulatedRaman signals throughout the


throughout the ENTIRE length of the chip

SENSTIVITY IMPROVED BYIMPROVED BY

AT LEAST100 To 1000100 To 1000

TIMES!Helmy Group at U of T Protected © 2013


The root cause behind the enhancement

Inte

nsity 100 300 500

Length (cm)

Inte

nsity 100 300 500

Length (cm)

Nor

mal

ized

Nor

mal

ized

0 10 20 30

Length (cm)

HCPCF

0 20 40 60Length (cm)

TCT

J. App. Phys. 109, 113104 (2011)

Length (cm) Length (cm)

20 LP )1(2

20 LLcw eNAPI


The root cause behind the enhancement

Longer Fibers

J. App. Phys. 109, 113104 (2011)

Fingerprint Signal Enhancement increases with increasing fiber length!

A length of ~40 cm enhances signal by over 4000 times! Amr S. Helmy @ U of T

Advantages Compared to SERS/TERS

Enhancement on All Raman Modes

No Sample Preparation

Measures the Native State

Ultra Small Advanced FluidicUltra-Small Sampling Volume

Advanced Fluidic Functionality

Helmy Group at U of T Protected © 2013


Water



Water Fingerprint Comparison


Water



Water Fingerprint Comparison

Opto-fluidic fiber significantly enhances the water fingerprint!Fingerprint signal enhanced by ~ 90 times!Amr S. Helmy @ U of T

Examples from nanomaterial analysis.

14Amr S. Helmy @ U of T

Colloid Semiconductor Nanoparticles (NPs)

• Nanometer sized semiconductor crystal• Nanometer sized semiconductor crystal

– Surrounded with polymer ligands

– Solution based synthesis

• NP characteristics sensitive to synthesisNP characteristics sensitive to synthesis parameters

L k f i i i i h i i– Lack of in situ monitoring or characterization


Thermal Processing of CdTe NPs

• Anneal CdTe NPs in inert Argon• Anneal CdTe NPs in inert Argon

• Annealing temperatures from 200ºC to 600ºC, g p ,

with 100ºC intervals

• Maintain a constant 50ºC /s ramp rate

30 l ti• 30s anneal time

• Weigh and disperse in water after coolingWeigh and disperse in water after coolingAmr S. Helmy @ U of T

CdTe Nanoparticles with Varying Crystallinitiy

• No shift in PL peak wavelength up to 500ºC500ºC– Indicates no

change in NP sizechange in NP size• PL efficiency constant

b l 400ºCbelow 400ºC



• 3 assigned peaks:CdTe LO mode: 165 cm-1– CdTe LO mode: 165 cm 1

– Te-Te A1 mode: 125 cm-1

Te Te E mode: 142 cm-1– Te-Te E mode: 142 cm 1

• Te-Te modes represent defects inrepresent defects in crystal

• Annealing decreases defect peaks

Fingerprints obtained with 2 mg/mL, with only 5 nL of solution! 18



• Baseline removal

• Gaussian-Lorentzian

peak fit

• aRatio AmpTeTe / AmpCdTe

• Amplitude ratio reflects

crystalline quality




• Core is primarily of zincblende phase– 111, 220, 311 planes

• Shoulder at 29°Shoulder at 29– Wurzite?– Te inclusions or– Te inclusions or

defects?• Feature decreases withFeature decreases with

increased processing temperatures



Thermal Processing of CdTe NPs

• Raman spectroscopy provides insight to nanoscale changesnanoscale changes– Reduction of Te-Te bonds

Enhancement of core crystallinity– Enhancement of core crystallinity

– Corresponds to XRD results

S it bl f f t i it it i• Suitable for future in situ monitoring• RTA application to colloid NPs

– Improves core crystallinity

– Does not affect NP size

– Does not significantly affect fluorescenceAmr S. Helmy @ U of T

NPs Synthesized in Aqueous Environment

TGA

MPA

TG



Different Thiol ChainTGA

Different QD Properties

MPA

TGDifferent Molecular Interactions



1. How do the capping agents interact with the QD?Q

2. How is the QD interface like?3. Is the QD surface doped? If so, how much?

• Photoluminescence (PL)• Electroluminescence (EL)

C • UV-visible Spectroscopy (UV-vis)• Transmission Electron Microscope• X-ray Diffraction (XRD)

Current Characterization

T h i X ray Diffraction (XRD)• X-ray photoelectron Spectroscopy

(XPS)• Etc

Techniques

• Etc….Amr S. Helmy @ U of T

CdTe NP Spectra


Presence of CdTe Core and Te defects

1. CdTe Core (~160 cm-1)CdT LO d• CdTe LO mode

• Shifted from bulk CdTe crystal at 170 cm-1

• Presence of QDs

2 Te Defects (~122 cm-1)2. Te Defects ( 122 cm )• Te A1 mode (Te crystal

optical phonon mode)• P f T D f t• Presence of Te Defects

• Reduces PL efficiency


CdTe Core Crystallinity Comparison

3. Intensity Ratio (Te A1/ CdTe LO)

TGA TG MPA2.949 0.901 0.499

• Different ligand Different core crystallinity Different core crystallinity Different PL efficiency

QDs stabilized with MPA is most crystalline!


Presence of Interfacial Layer1. CdS Compound (~291 cm-1)

• CdS SO mode• Bonding between sulfur ions• Bonding between sulfur ions

and Cd ions• Presence of core-ligand

interaction2. CdS0.7Te0.3 Compound

(~261 cm-1)( )• Shifted from CdS LO mode

at 306 cm-1

• Formation of interfacial• Formation of interfacial layer around CdTe core

• Large sulfur content• Similar among the ligands


Carboxylate-Metal Interactions1. Carboxylate-Metal Complex (~1360 and ~1470 cm-1 )

• COO- symmetric stretching modes• Formation of carboxylate likely by bonding with Cd ions• Formation of carboxylate, likely by bonding with Cd ions • Presence of another core-ligand interaction


Carboxylate-Metal Complexes Formed2. Type of Complexes Formed

• TGA: Bridging bidentate, Chelating bidentate • MPA: Unidentate Chelating bidentateMPA: Unidentate, Chelating bidentate

Unidentate Bridging Bidentate Chelating Bidentate

3. Relative Amount of Complexes Formed• More carboxylate-metal complexes formed in MPA

νs(COO)1 / CdS 2SO νs(COO)2 / CdS 2SOTGA 0.205 (Bridging) 0.547 (Chelating)MPA 12.803 (Unidentate) 5.390 (Chelating)


Summary1. Raman spectroscopy using PCF

• Enhanced the detected Raman signal from aqueous th i d QDsynthesized QDs

• Allowed us to observed QD structures at the molecular level

2. Formations of the CdTe Core, Te defects and interfacial layer

• MPA-QD is most crystalline compared TGA and TG• Strong passivation by the Cd-S bonds

3. Type of interactions between the core and the capping agent

• Cd-S interactionCd S interaction• Carboxylate-core interaction


Examples from bio material analysis.

33Amr S. Helmy @ U of T

2 mM of DNA, Only 4 mW of Laser Power

DNA Fray Wire

Fingerprints shows hydrogen bonding specific in DNA Fray Wire!Fingerprints shows hydrogen bonding specific in DNA Fray Wire!

Typcially, > 500 mW of power are required to measure DNA fingerprints,


16uM of Streptavidin in PBS – Limit of Detection

Protein for Biomolecule Detections

Protein Concentration below 1 mM is typically dfifficult to detect !16 uM detected with 1.2 mW of power, and only 5 nL of

solution!

Protein Concentration below 1 mM is typically dfifficult to detect ! Amr S. Helmy @ U of T

Fingerprints of Blood Phantom

Wavelength: 633nmP 1 WPower: 1.7mWExposure Time: 10s

Optofluidic device enables fingerprints of blood phantom to be clearly determined!


Can this platform also work with SERS ?

• CTAB-coated gold nanorods were used as a SERS substrateSERS substrate.

• Transverse and longitudinal localized surface plasmon resonance wavelengths were locatedplasmon resonance wavelengths were located at 510 and 773 nm respectively.

• This SERS probe is used to• This SERS probe is used to– The dye Congo red is used to quantify the

enhancementenhancement

– Monitor the ligand exchange process


SERS Enhancement

Congo Red Dye(Biological stain)

Opt. Lett. 37, 680 (2012)

Fingerprint signal enhanced by over 1,000 times with nanoparticles incorporated into the optofluidic fiber!


SERS Enhancement

17

8

tens

ity

2 13

87

d

man

Int

15

12

11

55

b

c

Ram

a

b

Opt. Lett. 37, 680 (2012)500 1000 1500 2000

Wavenumber (cm-1)


Summary1. Raman spectroscopy using PCF

• Enhanced the detected Raman signal from aqueous th i d QDsynthesized QDs

• Allowed us to observed QD structures at the molecular level

2. Useful for nano-material characterization• Raman modes for NPs core, ligand and interface• Is able to convey structural information not conveyed by

PL

3. Of great utility for biomaterial characterization• DNA• ProteinsProteins• Blood phantoms• SERS can also be utilized in parallel


advances in opto-fluidic assisted ramanassisted raman … · 2014. 12. 2. · – information on...

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