Post on 05-Feb-2018
Plasmonic Metal NanoparticleFunctionalization forSelective Sensing ofPersistent Pollutants
by SERSLuca Guerrini
Instituto de Estructura de la Materia. CSIC. Serrano, 121. 28006-Madrid. Spain.
SERS roundtable 2007, Poltersdorf, Germany
OUTLINESERS: looking for Hot Spots (HS)Metal Colloids: best active SERS substrateMetal-Adsorbate interactionsDetection of molecules (PAHs) with low
affinity toward the metal surface: Functionalization
Host Molecules:– Calixarenes– Viologen Dications– Alkyl Diamines
Conclusions
Nanostructures for spectroscopy
Enhancement of Spectroscopic Signal
10-28 cm2/mol
10-22 cm2/mol
10-18 cm2/mol
SERSRaman
No Metal Metal as substrate
Cross-section
Surface-enhanced Spectroscopy: Mechanisms
Electromagnetic Mechanism
Charge Transfer Mechanism
SERS, SEIRA, SEF
SERS
E0 (ω0) Sphere: A=1/3 Eint
E0 3E0 Eint = ⎯⎯⎯⎯⎯⎯ ≅ ⎯⎯⎯
1 + ( ε - 1 ) A ε + 2
Edip (ωR) ESC (ωR)
(1) Electromagnetic Mechanism
A: Depolarisation constant depending on nanoparticle size and shape
ε : Dielectric constant ε(ω) = Re[ε(ω)] + Im[ε(ω)]iRe[ε(ω)] ≈ -2 ⇒ Plasmon ResonanceIm[ε(ω)] → 0 ⇒ Minimum Resistivity
Metals: Ag, Au, Cu
d
Localization of electromagneticfield on Interparticle
JUNCTIONSHOT SPOTS
2nm
25nm
80% SERS signal from 0.64% of molecules adsorbed(Le Ru et al. J.Chem.Phys. 125, 204701(2006))
(2) Charge Transfer Mechanism(chemical mechanism)
Otto wrote: “without the EM mechanism there would be no signal, but the chemical mechanism determines what is observed”
NO O
Ag, Au, Cu
• Distortion of the electronic cloud of theadsorbate new molecule or surface complex
• First layer effect
Characteristics of the phenomenon (EM mechanism and CT mechanism)
High sensitivity: cross section increases (EF up to 1014 SMD).Short range effect (>10nm, no SERS effect) .Quenching FluorescenceNew selection rules (EDIP(ω0) has tangential and normal components with different enhancements. Molecule adsorbed with specific orientation with respect to the surface) .
OUTLINESSERS: looking for Hot Spots (HS)Metal Colloids: best active SERS substrateMetal-Adsorbate interactionsDetection of molecules (PAHs) with low
affinity toward the metal surface: Funtcionalization
Host Molecules:– Dithio Calixarenes– Viologen Dications– Alkyl Diamines
Conclusions
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-- -
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Obtention: Nucleation
CHEMICAL REDUCTION
Mp+ + Red → M0 + Prod
Red: NaBH4, Na3Cit, NH2OH, NH2NH2
Nucleation:
nM0 → Mn
mMn → Mn*m
Metal Colloids as SERS substrate
• Easy to prepare, broad plasmon resonance in the visible-near IR Region, high stability…
• Empirical knowledge: highly aggregated colloids as the best substrate for obtaining good SERS signals
• Each preparation leads to a distinct distribution
(MACRO): AVERAGE SERS (Semi)Quantitative Analysis• statistical average SERS spectra from an ensemble of scatterers• relatively low Raman enhancement factors (up to ~106)• normally stable and reproducible spectra
(MICRO): ULTRASENSITIVE SERS Trace Detection (SMD)• SERS from highly localized nanoscale interstitial sites in nanostructures • Raman enhancement factors >1010
• fluctuations on reaching submonolayer coverage
Slide glass
(MACRO): AVERAGE SERS (Semi)Quantitative Analysis• statistical average SERS spectra from an ensemble of scatterers• relatively low Raman enhancement factors (up to ~106)• normally stable and reproducible spectra
(MICRO): ULTRASENSITIVE SERS Trace Detection (SMD)• SERS from highly localized nanoscale interstitial sites in nanostructures • Raman enhancement factors >1010
• fluctuations on reaching submonolayer coverage
Slide glass
OUTLINESSERS: looking for Hot Spots (HS)Metal Colloids: best active SERS substrateMetal-Adsorbate interactionsDetection of molecules (PAHs) with low
affinity toward the metal surface: Funtcionalization
Host Molecules:– Dithio Calixarenes– Viologen Dications– Alkyl Diamines
Conclusions
In wet systems the diffusion of the adsorbate from the bulk to the NP surface is needed.
(Ag-O) OXYGEN-containing Adsorbatesi.e. Benzoic Acids, Catechol
(Ag-N) NITROGEN-containing Adsorbatesi.e. Pyridine
(Ag-S) SULFUR-containing Adsorbatesi.e. Thiols and Dithiocarbamates
(Ag-X) X= halogen i.e R6G
Metal NP-Adsorbate Interactions
Many other molecules are not able to approach the NP surface due to their poor affinity to the metal
PAHs are a group of pollutants with condensed benzene rings formed during the incomplete combustion of coal, oil, and gas or other organic substances such as tobacco or charbroiled meat. Many of them have been reported to be strong carcinogens.
PYRENE (PYR)
POLYCYCLIC AROMATIC HYDROCARBONS
OUTLINESSERS: looking for Hot Spots (HS)Metal Colloids: best active SERS substrateMetal-Adsorbate interactionsDetection of molecules (PAHs) with low
affinity toward the metal surface:Functionalization
Host Molecules:– Dithiocarbamate Calixarenes– Viologen Dications– (Alkyl Diamines)
Conclusions
Functionalization
=
• Good adherence on the metal• High affinity to bind the analyte• No bands overlapping • Inter or Intra-molecular CAVITY
Conditions to be fulfilled by the host molecule:
Calixarenes
OO
OO
OO
OO
HH
Calixarenes (CXs) are synthetic cyclooligomers:• "cup-like" shape• capable of size-selective molecular encapsulation. • by changing the chemical groups of the upper
and/or lower rim, it is possible to modifytheir affinity toward the guest and themetal surface.
Pyrene
Triphe
nilen
e
Anthrac
ene
Benzo
[c]ph
enan
trene
Chrise
ne
Rubice
ne
Dibenz
oanth
racen
e
Corone
ne
SER
S In
tens
ity
1500 1000 500
SERS of Pyrene (10-4 M)
Solid Pyrene
CalixarenesCalixarenes (CXs) are synthetic cyclooligomers:
• "cup-like" shape• capable of size-selective molecular encapsulation. • by changing the chemical groups of the upper
and/or lower rim, it is possible to modifytheir affinity toward the guest and themetal surface.
Pyrene
Triphe
nilen
e
Anthrac
ene
Benzo
[c]ph
enan
trene
Chrise
ne
Rubice
ne
Dibenz
oanth
racen
e
Corone
ne
SER
S In
tens
ity
1500 1000 500
SERS of Pyrene (10-4 M)
Solid Pyrene
OO
NH
OO
HH
SHS
N H
SHS 5 6 7 8 9 10
SER
S in
tens
ity o
f PA
Hs
-log[PAHs]
PYRENE BENZO[C]PHENANTHRENE
CORONENE TRIPHENYLENE
Functionalization
=
• Good adherence on the metal• High affinity to bind the analyte• No bands overlapping • Inter or Intra-molecular CAVITY
Conditions to be fulfilled by the host molecule:
• BIFUNCTIONAL COMPOUNDSPromoting the organization of the metal NPs intocontrolled architectures (inducing HS formation)attract analytes to the region of the so-formed HS
VIOLOGEN DICATIONS (VGD)N
N
CH3
CH3
N
N
N
N
CH3
CH3
+
+
+
+
+
+
DQ2+
MV2+ LG2+
• Disubstituted-4,4’-bipyridilium dication• Bifunctionality• Strong Electron-acceptors charge
transfer interactions with charge donors
1550 1600 1650
1624
1627
1585
1584
1608
1578
1613
Wavenumbers (cm-1)
N
NCH3
H3C
(+)
(+)
N
N(+)
(+)
= Cl-
solid LG
SERS LG 10-6M
solid DQ
SERS DQ 10-4M
Two bands in the 1550-1650 cm-1 regionare sensitive to the dication structure:
1550 1600 1650
Wavenumbers (cm-1)
VIOLOGEN DICATIONS (VGD)N
N
CH3
CH3
N
N
N
N
CH3
CH3
+
+
+
+
+
+
DQ2+
MV2+ LG2+
• Disubstituted-4,4’-bipyridilium dication• Bifunctionality• Strong Electron-acceptors charge
transfer interactions with charge donors
1550 1600 1650
1624
1627
1585
1584
1608
1578
1613
Wavenumbers (cm-1)
N
NCH3
H3C
(+)
(+)
N
N(+)
(+)
= Cl-
solid LG
SERS LG 10-6M
solid DQ
SERS DQ 10-4M
LG high tendency to form CT complexes both in solid state and adsorbed on AgNP
DQ high tendency to form CT complexes just when adsorbed on AgNP
MV CT transition seems not to take place both in solid state and adsorbed on AgNP
VIOLOGEN DICATIONS (VGD)N
N
CH3
CH3
N
N
N
N
CH3
CH3
+
+
+
+
+
+
DQ2+
MV2+ LG2+
• Disubstituted-4,4’-bipyridilium dication• Bifunctionality• Strong Electron-acceptors charge
transfer interactions with charge donors
1550 1600 1650
1624
1627
1585
1584
1608
1578
1613
Wavenumbers (cm-1)
N
NCH3
H3C
(+)
(+)
N
N(+)
(+)
= Cl-
solid LG
SERS LG 10-6M
solid DQ
SERS DQ 10-4M
VDG interact with the Ag surfacethrough the formation of a CT complexwith the adsorbed chloride.
LG is the best candidate to formjunctions between NPS.
400 600 800 1000 1200 1400 1600
LG 10-6M
SER
S in
tens
ity
wavenumber (cm-1)
SERS DETECTION OF PYRENE
LG 10-6MPYR 10-6M
difference spectra
Solid PYR
• Changes in relative intensities of Raman bands of PYR (590cm-1)
• Rotation of the acridine rings
1200 1250 1300
SER
S In
tens
ity
LG(1191)
LG(1280)
PYR
Wavenumber (cm-1)
H
H
δ(C-H)
N
N(+)
CH3
(+)
CH3
ν(C-C)ir
LG-PYR interaction takes place through a CT complex
N
N
CH3
H3C(+)
(+)
Upwards view of PYR interaction
LG – PYR INTERACTION
+
N
N
CH3
H3C(+)
(+)
+
PYR 10-6M: SERS intensity variation at different [VGD]
LIMIT OF DETECTION:LG 10-6M, DQ 10-4M, MV 10-6M
6 7 8 9 10
I 590
of P
YR
6 7 8 9 10
-log [PYR]
1064nm
785nm
514nm
3 4 5 6 7 8 9 10
I 590 o
f PY
R3 4 5 6 7 8 9 10
MV2+
DQ2+
LUC2+
-log[VGD]
1064nm
785nm
514nm
MICRO SERS:~ 100 molecules of PYR
6 7 8 9
SER
S in
tens
ity o
f PA
Hs
-log[PAHs]
DQ 10-4M PYR LG 10-6M PYR
DQ 10-4M BcP LG 10-6M BcP
6 7 8 9
SE
RS
inte
nsity
of P
AH
s
-log[PAHs]
DQ 10-4M PYR LG 10-6M PYR
DQ 10-4M BcP LG 10-6M BcP
785nm
HH
H
H
H
HHH
H
H
H
H
HH
HH
HH
H
HH
H
HH
H
HHH
PYRENE BENZO[C]PHENANTHRENE
N
NCH3
H3C
(+)
(+
pyrene
400 500 600 700 800 900 1000
plas
mon
abs
orba
nce
wavelenght (nm)
Absorption Spectra
AgNPLG 10-6M
400 600 800 1000 1200 1400 1600
difference spectra
PYR 10-6MLG 10-6M
PYR 10-5M
SER
S in
tens
ity
wavenumbers (cm-1)
SERS Spectra
HS FORMATION BY VGD
400 500 600 700 800 900 1000
370-390
800-1000
500-600
Plas
mon
Abs
orba
nce
Wavelength (nm)
UV-Vis Spectroscopy
50 nm
500 nm
SEM AFM
370-390assigned to non aggregated NPs
and/or transversal plamons in associated NPs chains
500-600may corresponds to the gaps
between two NPs (Käll et al. J. Raman Spectr. 2006, 36, 510)
800-1000assigned to larger aggregates or
multimers
DIFFERENCE ABSORPTION SPECTRA
HS FORMATION BY VGD
400 500 600 700 800 900 1000
370-390
800-1000
500-600
Plas
mon
Abs
orba
nce
Wavelength (nm)
UV-Vis Spectroscopy (500-600) DIMER ADS. BANDTo understand the formation of HS by VGD we have followed the dimer absorption band, whose position depends on:• the VGD structure• the concentration (DQ)
DIFFERENCE ABSORPTION SPECTRA
480 560 640
556
540 590
N
NCH3
H3C
(+)
(+)
-N
NCH3
H3C
(+)
(+)
d2 < d1
N
N
d1
N
N
d2
LG 10-6 M
DQ 10-4 M
DQ 10-5 M
DQ 10-6 M
Good agreement with the changes that the v(Ag-Cl) band undergoes in SERS spectra
nm
3 4 5 6 7 8 9 100,0
0,5
1,0No
rmal
ized
Abs
orba
nce
(a. u
.) AgNPs/LG AgNPs/DQ
-log[VGD]
0,0
0,5
1,0
3 4 5 6 7 8 9 10
LucigeninDiquatMethyl VIologen
3 4 5 6 7 8 9 10-log[VGD]
SER
S In
tens
ity o
f VG
D
I 590 o
f PY
RNo
rmal
ized
Abs
orba
nce
(a. u
.) AgNPs/LG AgNPs/DQ
-log[VGD] Plasmon absorbance intensity of AgNPs dimers in the 500-600 nm region at different VGD concentrations
Intensity of the 590 cm-1 band of PYR 10-6M at different VGD concentrations
Intensity of the SERS spectra measured for the main band of LG, DQ and MV at different VGD concentrations
N
NCH3
H3C
(+)
(+
pyrene
• assignment of the plasmon band to the interparticle junctions in dimers
• the VGD are mainly placed in these junctions
• the main part of the pollutant is attracted in these junctions to render a huge SERS signal
The lower SERS effectiveness observed for MV is presumably related to the different adsorption mechanism on metallic surfaces.
0,0
0,5
1,0
3 4 5 6 7 8 9 10
LucigeninDiquatMethyl VIologen
3 4 5 6 7 8 9 10-log[VGD]
SER
S In
tens
ity o
f VG
D
I 590 o
f PY
RNo
rmal
ized
Abs
orba
nce
(a. u
.) AgNPs/LG AgNPs/DQ
-log[VGD]
CONCLUSIONSEfficiency of VG dications in the formation of highly sensitiveHS localized at junctions between Ag NPs. • VGD act as:
builders of sensitive areas of giant EM fieldenhancement
hosts to selectively interact with pollutant takingadvantage of the formation of intermolecular cavities(PYR detection down to a few molecules!).
• A new approach in the design of functionalized NPs for thedetection of target molecule having low affinity toward the metal surface
Alkyl Diamines as hosts forChlorinated Pesticides
CSIC: Consejo Superior de Investigaciones CientíficasInstituto de Estructura de la Materia.
Santiago Sánchez-Cortés
José Vicente García Ramos
Concepción Domingo
Acknowledgements • We acknowledge project FIS2004-00108 from Dirección General de Investigación,
Ministerio de Educación y Ciencia and Comunidad Autonoma de Madrid project number S-0505/TIC/0191 MICROSERES for financial support.
• Luca Guerrini acknowledges an I3P fellowship from CSIC.
Thank you for your
attention