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Local enhanced fields in DNA
templated plasmonic molecules
Sbastien Bidault and Albert PolmanCenter for NanophotonicsFOM
Institute AMOLF
20nm
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Local fields in gold nanostructures
550nm 550nm
20Au
20
20
n=1.5 n=1.5Ienh
I
enh
Processes are increased between closely-packed particles and
lead
to SERS from single molecules. Can this be optimized by
relevantnanostructure engineering ??
Plasmon resonances in gold particles : high local fields
(SERS,sensing) and increase of radiative decay rates
(luminescenceenhancement)
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Optimizing nano-lenses and -antennas
Li, Stockman
& Bergman,PRL 2003
L. Rogobete etal, Opt. Lett.2007
Coupling particles ofdifferent sizes and invarious geometries
allowstuning of local enhanced
fields and polarizationdependence
Combining strong localfields and high scatteringcross-sections
leads tooptimized nanoantennas
Problems : reproducible
fabrication and placementof analyte or luminescentcenter
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Why DNA templated self-assembly ?
J. Zheng et al, Nanolett. 06
P. W. K. Rothemund, Nature 06
J. Seelig et al, Nanolett. 07
Are short interparticledistances possible ?
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Reproducible synthesis of close-packed NPs
Method: Programmed hybridization of DNA strands attached (C6
thiol)to passivated (BSPP) gold particles (A.P. Alivisatos et
al,Nature 1996, D. Zanchet et al, J. Phys. Chem. B 2002)
Head to tail orhead to headhybridizations
are possible
Au + HSSS
+
Analyte can be introduced by further modification of DNA
backbone:direct covalent binding or recognition site
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Electrophoretic purification
18
5
100bases~30nm
50bases~15nm
Electrophoretic separation of Au particles covalentlyattached to
known number of DNA molecules
1885
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Electrophoretic purification
8
8
8
100bases~30nm
50bases~
15nm
Electrophoretic separation of Au particles covalentlyattached to
known number of DNA molecules
185
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Head to tail example: dimer of 18nm gold
0 10 20 30 40 50 60 700
2
4
6
8
10
1214
16
18
18100bp~33nm
On ~500 particles:85% dimers10% single particles5% larger
aggregates %o
fdimers
Center to center distance (nm)
aggregates
52nm
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Head to head hybridization
Head to head hybridization brings interparticledistance down to
a few nanometers
100nm100nm75%
200nm
55%
5
8
5
8
5
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Plasmon mode coupling
Nanostructure size ~ /30: hybridization picture applicable
n=1.5
570nm
8 5
Eenh
n=1.5
530nm
8 5
Eenh
+-+ - + -+ -
+- +-
Longitudinal mode
Transverse mode
Energy
+-
+-
+
-
+
-
+ -+ -
+-+-
+-+-+-
85
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Using two DNA sequences
60%
Small interparticledistance (1nm)enables x40
fieldenhancement
n=1.5
18
600nm
8 5
Eenh100nm100nm
5
8
18
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Cooperative plasmon coupling
Eenh
Eenh
n=1.5570nm
n=1.5600nm
Cooperative couplingslightly increases field
enhancement (factor 2on intensity)
18 8 5
8 518 8
Eenh
n=1.5590nm
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400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
Opticald
ensity
Wavelength (nm)
35nm
Dimer
Trimer
Towards optical characterization
Extinction spectra in water
Groupings of 35nm Au NPsare obtained after surfaceligand
exchange (thio-PEGinstead of BSPP)
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500 1000 1500 2000 2500 30000
250
500
750
1000
1250
1500
CCDcounts/30s
W avenumber (cm-1
)
Preliminary results of SERS measurements
Confocal SERS spectra of 460MW thiolatedPEG on Au with 532nm
illumination
500 1000 1500 2000 2500 30000
250
500
750
CCDCounts/3
0s
W avenumber (cm-1
)
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Conclusions and perspectives
DNA hybridization allows nanometer-scale distances between
goldparticles of different sizes
Plasmon mode coupling in free-standing nanostructure:plasmonic
molecule with intensity enhancement reaching 3
orders of magnitude
Enhancement of Raman scatteringis being investigated
Synthesis of nanostructures with aRaman scatterer on the
hot-spot isunder way
SCy3
k l d
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Acknowledgements
Synthesis
Ron ZuckermannMelike Firat
Shelley ClaridgeSassan SheikholeslamiPaul Alivisatos
TEM measurements
Hans Meeldijk
