advances in opto-fluidic assisted ramanassisted raman … · 2014. 12. 2. · – information on...
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Advances in opto-fluidic assisted Ramanassisted Raman spectroscopy of liquids, gases and aerosolsgases and aerosols
Amr S. HelmyAmr S. Helmy
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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
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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
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Conventional Raman Spectroscopy
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Limitation• Small Interaction Volume
P C ll ti Effi i• Poor Collection Efficiency
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Photonic Bandgap Assisted Raman SpectroscopySpectroscopy
Induced and accumulatedaccumulatedRaman signals throughout the
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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
Amr S. Helmy @ U of T
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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
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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
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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
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Water
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Water Fingerprint Comparison
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Water
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Water Fingerprint Comparison
Opto-fluidic fiber significantly enhances the water fingerprint!Fingerprint signal enhanced by ~ 90 times!Amr S. Helmy @ U of T
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Examples from nanomaterial analysis.
14Amr S. Helmy @ U of T
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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
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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
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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
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CdTe Nanoparticles with Varying Crystallinitiy
• 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
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CdTe Nanoparticles with Varying Crystallinitiy
• Baseline removal
• Gaussian-Lorentzian
peak fit
• aRatio AmpTeTe / AmpCdTe
• Amplitude ratio reflects
crystalline quality
Fingerprints obtained with 2 mg/mL, with only 5 nL of solution! 19
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CdTe Nanoparticles with Varying Crystallinitiy
• Baseline removal
• Gaussian-Lorentzian
peak fit
• aRatio AmpTeTe / AmpCdTe
• Amplitude ratio reflects
crystalline quality
Fingerprints obtained with 2 mg/mL, with only 5 nL of solution! 20
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CdTe Nanoparticles with Varying Crystallinitiy
• 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
Fingerprints obtained with 2 mg/mL, with only 5 nL of solution! 21
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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
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NPs Synthesized in Aqueous Environment
TGA
MPA
TG
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NPs Synthesized in Aqueous Environment
Different Thiol ChainTGA
Different QD Properties
MPA
TGDifferent Molecular Interactions
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NPs Synthesized in Aqueous Environment
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
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CdTe NP Spectra
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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
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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!
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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
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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
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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)
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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
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Examples from bio material analysis.
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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,
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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
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Fingerprints of Blood Phantom
Wavelength: 633nmP 1 WPower: 1.7mWExposure Time: 10s
Optofluidic device enables fingerprints of blood phantom to be clearly determined!
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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
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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!
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SERS Enhancement
17
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man
Int
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11
55
b
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Ram
a
b
Opt. Lett. 37, 680 (2012)500 1000 1500 2000
Wavenumber (cm-1)
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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
Amr S. Helmy @ U of T