single-molecule fluorescence blinking and ultrafast dynamics in semiconductor and metal...
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Single-Molecule Fluorescence Blinking and Ultrafast Dynamics in Semiconductor and Metal Nanomaterials
C. T. Yuan, P. T. Tai, P. Yu, D. H. Lee, H. C. Ko, J. Huang, J. Tang*
1. Single-molecule detection. (2)2. Introduction to single colloidal QDs. (4)3. Fluorescence blinking in semiconductor nanostructures. (8)4. Fluorescence properties of noble metal nanoclusters. (8)5. Ultrafast dynamics in metal nanomaterials. (3)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00
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10
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Inte
nsit
y (
Co
un
ts/m
s)
Time (s)
Single-QD fluorescence images
Single-QD fluorescence time traces Colloidal CdSe/ZnS QDs Fluorescent gold NCs
Why Single-Molecule Detection?
Ensemble measurementsLaser volume~10-6 L
Sample concentration~10-6 MolarTotal measured particles~1011
Single-Molecule DetectionOnly one target is probed at a time
Why Single-Molecule Detection in Nanomaterials?
Sample Heterogeneity (size, shape, local surface)
Time-dependent dynamical fluctuation(intensity, lifetime)
Time
Phys. Rev. Lett. 88, 077402 (2002)
Potential applications based on SMD Protein folding/unfolding dynamics
• Fluorescent labels for SMD• Nontoxic• Small• Biocompatible
Roger Tsien, Nobel Prize in Chemistry in 2008Green fluorescent protein
Colloidal Semiconductor CdSe QDs
Colloidal semiconductor QDs
Glove box
Excellent fluorescence properties1. Photostability2. Broad absorption band 3. Narrow emission band 4. Emission tunability5. Bio-compatibility
Photo-stability and multi-colors labeling
AlexaFluor 488
QDs
3T3 cells
Human epithelial cells
Nature materials 4, 435, 2005
Nature biotechnology 22, 969, 2004
Fluorescence blinking in single CdSe QDs
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00
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Inte
nsit
y (
Co
un
ts/m
s)
Time (s)
100 1000 10000
0.01
0.1
1
Nor
mal
ized
eve
nts
On time (ms)
• Single molecules, polymers, Si, PbSe, CdTe NCs……• On the timescales of ms to minutes.• Power-law distribution for on/off-times.• Power-law exponent, 1.1~2.• Modified by surface and environments
On-time
Off-time
tPvs
tAP
AtP
AtP
log.log
logloglog
loglog
On states, neutral QDs Off states, charged QDs
• How the electron is rejected and returned from QDs and traps• Power-law distributions• Timescales (ms~min)
Surface, substrates
Binning-threshold methods
Auger Processes• Long-range Coulomb interactions.• Efficient in 0D QDs due to lack of momentum conservation.• Time-scales of ~ps, depending on size, shape.
Complication for achieving the lasing regime
Fluorescence blinking dark states
radAuger
Nature Physics, 4, 519 (2008)0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
0
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In
ten
sity
(C
ou
nts/m
s)
Time (s)
Diffusion Controlled Electron Transfer (DCET) models
Bright state (neutral QDs)
dark state (charged QDs)
Auger process
Photon emission
Tang and Marcus, Phys. Rev. Lett. 95, 107401 (2005)
Previous workPresent workFuture work
,if)(exp~)(
if~)(
2/2
2/
cc
cc
ttttttP
tttttP
Γ
Power-law behavior with extended time ranges by autocorrelation function analysis
2)(
)()()(
tI
tItIG
Disadvantages for conventional binning-threshold methods-Time resolution is limited by bin sizes (~10 ms).-Bin size is limited by SN ratio.-Pre-defined threshold is affected by human subjectivity.
,)()(1
11
)(21
1
sgsgsssG
,)()(1)(
212
1
sgsgssF
.if~)(
if~)(
2/
2
cc
cc
tttttF
tttttF
The main purpose is to find out the relationship between P(t) and G(t)
Laplace transformation
F(t)=G(t)/G(0)-1
Relationship between power-law blinking statistics P(t) and autocorrelation functions G(t)
63.1 ,37.02
22
m
m
• No requirements of selecting bin times and threshold.• Microsecond time resolution can be achieved.
Interaction between single QDs and Ag NPs
• Energy transfer.• Plasmonic effects.
300 400 500 600 700 800 900 10000.0
0.5
1.0
Spherical particles Triangular prism
Nor
mal
ized
abs
orpt
ion
(a.u
.)
Wavelength (nm)
100 nm
620 640 660 680 700 720 740 760 7800
50
100
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C
ou
nts
/10
ms
Observation time (s)
CdSe/ZnS QDs QDs+triangular Ag NPs
1E-3 0.01 0.1 1 10 100 10000
1
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G()
Lag time (ms)
CdSe/ZnS QDs QDs+triangular Ag NPs
1E-3 0.01 0.1 1 10 100 10000
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8
G()
Lag time (ms)
QDs for former-half part QDs for later-half part
1E-3 0.01 0.1 1 10 100 10000
1
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5
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7
8
G()
Lag time (s)
QDs+Ag for former-half part QDs+Ag for later-half part
Fluorescence Lifetime Correlation Spectroscopy (FLCS)
• Fluorescence quenching for individual QDs (uniform quenching).• Improvement of photo-stability.
])exp(1
1[)1()1(1
)(
blinking QDsdiffusion 3D
)]exp(1
1[)1()1(1
)(
blinking statetriplet diffusion 3D
)1()1(1
)(
diffusion 3D
2/120
201
2/120
201
2/120
201
tdd
tdd
dd
T
T
z
r
NG
T
T
z
r
NG
z
r
NG
11~
8.2~
4~)(
)(
AgQDs
QDs
QDs
Ag
AgQDs
QDs
F
F
N
N
QYs
QYs
Fluorescence decay profiles
0 10 20 30 400.01
0.1
1
Nor
mal
ized
inte
nsit
y (a
.u.)
Decay time (ns)
QDs QDs coupled triangular Ag
AgQDsQDs
AgQDs
QDs
AgQDs
QDs
AgQDs
QDs
AgQDs
QDs
AgQDs
QDs
flrnrr
r
kk
F
F
k
k
F
F
kkk
kF
~
10~,11~
Brightness per QDs(FCS)
Measured lifetimes(TCSPC)
• No significant effect on radiative decay rates.• Enhancing nonradiative decay rates.
5 10 15 20 25 30
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Cou
nts/
10 m
s
Observation time (s)
CdSe/ZnS QDs CdSe/ZnS QDs+triangular Ag NPs
Fluorescence Time Traces and Intensity Distribution for Immobilized QDs
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Cou
nts/
10
ms
Normalized events
Fluorescence lifetime
0 50 100 150
1E-3
0.01
0.1
1 CdSe/ZnS QDs CdSe/ZnS QDs+triangular Ag NPs
Nor
mal
ized
inte
nsit
y (a
.u.)
Decay time (ns)
5 10 15 20 250.0
0.2
0.4
0.6
0.8
1.0
Nor
mal
ized
eve
nts
Lifetime (ns)
Nontoxic, Water-soluble, Tiny, Fluorescent Gold Nanoclusters
Three regimes for gold NPs
R>>λ R~50 nm, electron mean free path
R<2 nm, electron Fermi-wavelength
bulkNanoparticle (scattering light)
Nanocluster (fluorescence)
Why fluorescent gold nanoclusters?
• CdSe QDs, toxic precursor• Gold NPs, scattering signal is too weak for <10 nm particles
Fluorescent, nontoxic, nanometer-sized materials gold nanoclusters
Dickson et al, Phys. Rev. Lett. 93, 077402 (2004)
Absorption~R3
Scattering~R6
useless
Robert M. Dickson
• Encapsulating Au clusters by PMAMA dendrimers• QYs~50%
History of Fluorescence from Gold Materials
• Size, 30*300 nm• Similar behavior to SPR• Orientation dependent emission
Synthesis and Characterization of Gold NCs
• NP fragmentation (6 nm-2 nm).• DHLA ligands for water soluble.• QYs~1 %.• Good colloidal stability.
Collaborator: Prof. Chang, in CYCU
Optical Properties of Ensemble Au NCs
• No surface plasmon resonance features.• Broad band emission.
Fluorescence properties of single gold NCs
0 100
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Co
un
ts/b
in
Observation time (s)
Single Au NCs10 ms bin time
0 1 2 3 4 50
5
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C
ounts
/ms
Observation time (s)
blinking behavior
Single-step photobleaching
Incomplete shape : photobleaching phenomenon
Streaky pattern : blinking behavior
On/off-time distribution
• Power-law distribution for on/off-times• Power-law exponents for on/off-times are 2, 1.8, respectively
1 10
0.01
0.1
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Nor
mal
ized
eve
nts
On-time duration (ms)
1 10
0.01
0.1
1
Nor
mal
ized
eve
nts
Off-time duration (ms)
1 2 3 4 5 6
100
1000
10000
E
vent
s
On-time duration (ms)
Fluorescence Lifetime Image Microscopy (FLIM)
-2 0 2 4 6 8 10 12 140.01
0.1
1
Nor
mal
ized
inte
nsit
y (a
.u.)
Decay time (ns)
Single NCs ns
Specific labeling and nonspecific uptake
• Human hepatoma cells for specific labeling.• Streptavidin-biotin pairs.• Human aortic endothelial cells for nonspecific uptake.
Scale bar : 50 micron
Ultrafast Dynamics in Metal NPs
(http:www.nims.go.jp)
fs (10-15 sec) ~ ps (10-12 sec)
mm (10-6 m) ~ cm (10-2 m)
Pump-Probe Techniques – to achieve ~fs resolution
Rod Disc Triangularpyramid
Thin film Prism Sphere
A
B
112/04/21 33
Relative surface energy: γ111 < γ100 < γ110
0 20 40 60 80
Res
idua
ls (no
rmal
ized
)
Delay Time / ps
Resi
duals
(norm
aliz
ed)
Oscillation component zN(t)-z
1(t), 0.04
0 2 4 6 8
Resi
duals
(nor
mal
ized)
Delay Time / ps
A B
C
H = 31.4 nm, T = 8.5 nm
H = 31.4 nm, T = 8.5 nm
H = 31.6 nm, T = 7.8 nm
Silver Nanoprisms
112/04/21 34
References
• Y. C. Yeh, C. T. Yuan, C. C. kang, P. T. Chou, J. ang, Appl. Phys. Lett. 93, 223110 (2008).
• P. Yu, J. Tang, S. H. Lin, J. Phys. Chem. C 112, 17133 (2008).
• J. Tang, Y. C. Yeh, P. T. Tai, Chem. Phys. Lett. 463, 134 (2008).
• J. Tang, J. Chem. Phys. 129, 084709 (2008).
• C. T. Yuan et al, Appl. Phys. Lett. 92, 183108 (2008).
• D. H. Lee, J. Tang, J. Phys. Chem. C 112, 15665 (2008).
• J. Tang, Chem. Phys. Lett. 458, 363 (2008).
• J. Tang, J. Chem. Phys. 128, 164702 (2008).
• J. Tang, Appl. Phys. Lett. 92, 011901 (2008).
Thank you for your attention