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*
Single-QD fluorescence images
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)
40
Intensity (Counts/ms)
35
30
25
20
15
10
5
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Time (s)
Single-QD fluorescence time traces
Colloidal CdSe/ZnS QDs
Fluorescent gold NCs
Why Single-Molecule Detection?
Ensemble measurements
Laser volume~10-6 L
Sample concentration~10-6 Molar
Total measured particles~1011
Single-Molecule Detection
Only 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 2008
Green fluorescent protein
Colloidal Semiconductor CdSe QDs
Colloidal semiconductor QDs
Glove box
Excellent fluorescence properties
1. Photostability
2. Broad absorption band
3. Narrow emission band
4. Emission tunability
5. Bio-compatibility
Photo-stability and multi-colors labeling
3T3 cells
Nature materials 4, 435, 2005
QDs
AlexaFluor 488
Human epithelial cells
Nature biotechnology 22, 969, 2004
Fluorescence blinking in single CdSe QDs
Binning-threshold methods
P  At 
40
On-time
log P  log At 
log P  log A   log t
30
25
20
log Pvs. log t  
Off-time
15
10
5
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1
Time (s)
• 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
Normalized events
Intensity (Counts/ms)
35
0.1
0.01
100
1000
10000
On time (ms)
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
Auger Processes
• Long-range Coulomb interactions.
• Efficient in 0D QDs due to lack of momentum conservation.
• Time-scales of ~ps, depending on size, shape.
 Auger   rad
Fluorescence blinking dark states
Complication for achieving the lasing regime
40
Intensity (Counts/ms)
35
30
25
20
15
10
5
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Time (s)
0.7
0.8
0.9
1.0
Nature Physics, 4, 519 (2008)
Diffusion Controlled Electron Transfer (DCET) models
P(t ) ~ t tc 
  /2
P(t ) ~ t tc 
2   / 2
dark state (charged QDs)
if t  tc
exp ( Γt ) if t  tc ,
Future work Present work Previous work
Bright state (neutral QDs)
Auger process
Photon emission
Tang and Marcus, Phys. Rev. Lett. 95, 107401 (2005)
Power-law behavior with extended time ranges
by autocorrelation function analysis
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.
The main purpose is to find out the relationship between P(t) and G(t)
G ( ) 
I (t )  I (t   )
I (t )
2
Laplace transformation
1
1
G ( s)  1 
s  s 1  g1 ( s)  g 2 ( s)


,


F(t)=G(t)/G(0)-1
F ( s) 
1
,
s 2 1  g 1 ( s)  g 2 ( s)


F (t ) ~ t tc  2
if t  tc
F (t ) ~ t tc   / 2
if t  t c .
Relationship between power-law blinking statistics P(t)
and autocorrelation functions G(t)
• No requirements of selecting bin times and threshold.
• Microsecond time resolution can be achieved.
m  2

2

2
 0.37, m  1.63
Interaction between single QDs and Ag NPs
100 nm
Normalized absorption (a.u.)
Spherical particles
• Energy transfer.
• Plasmonic effects.
Triangular prism
1.0
0.5
0.0
300
400
500
600
700
Wavelength (nm)
800
900
1000
Fluorescence Lifetime Correlation Spectroscopy (FLCS)
3D diffusion
G ( ) 
r 2
1

(1  ) 1 (1  20 ) 1/ 2
N
d
z 0 d
3D diffusion  triplet state blinking
G ( ) 
r 2
1

T

(1  ) 1 (1  20 ) 1/ 2 [1 
exp(  )]
N
d
z 0 d
1 T
t
3D diffusion  QDs blinking
G ( ) 
r 2
1

T

(1  ) 1 (1  20 ) 1/ 2 [1 
exp(  )  ]
N
d
z 0 d
1 T
t
8
CdSe/ZnS QDs
QDs+triangular Ag NPs
7
G()
(QYs ) QDs Ag
5
4
3
N Ag
N QDs
F
F
6
150
~4
CdSe/ZnS QDs
QDs+triangular Ag NPs
~ 2 .8
QDs for former-half part
QDs for later-half part
7
100
G()
(QYs ) QDs
Counts/10 ms
6
8
5
4
3
2
50
1
QDs
0
~ 11
620
640
660
680
700
720
740
760
0
1E-3
780
0.01
0.1
1
10
100
1000
Observation time (s)
QDs Ag
Lag time (ms)
8
2
QDs+Ag for former-half part
QDs+Ag for later-half part
7
6
0
1E-3
G()
1
5
4
3
0.01
0.1
1
10
100
1000
Lag time (ms)
• Fluorescence quenching for individual QDs (uniform quenching).
• Improvement of photo-stability.
2
1
0
1E-3
0.01
0.1
1
Lag time (s)
10
100
1000
Fluorescence decay profiles
Brightness per QDs
(FCS)
Normalized intensity (a.u.)
1
kr
F
 k r   fl
k r  k nr
QDs
QDs coupled triangular Ag
FQDs
FQDs Ag
0.1
FQDs
FQDs Ag
0.01
0
10
20
Decay time (ns)
30
Measured lifetimes
(TCSPC)
40

kQDs

 QDs
kQDs Ag  QDs Ag
~ 11,
 QDs
 QDs Ag
~ 10
kQDs ~ kQDs Ag
• No significant effect on radiative decay rates.
• Enhancing nonradiative decay rates.
Fluorescence Time Traces and Intensity Distribution for Immobilized QDs
CdSe/ZnS QDs
CdSe/ZnS QDs+triangular Ag NPs
200
Counts/ 10 ms
Counts/10 ms
200
150
100
150
100
50
50
0
0
5
10
15
20
Observation time (s)
25
30
0.0
0.2
0.4
0.6
Normalized events
0.8
1.0
Fluorescence lifetime
CdSe/ZnS QDs
CdSe/ZnS QDs+triangular Ag NPs
0.1
1.0
Normalized events
Normalized intensity (a.u.)
1
0.01
0.8
0.6
0.4
0.2
1E-3
0
50
100
Decay time (ns)
150
0.0
5
10
15
Lifetime (ns)
20
25
Nontoxic, Water-soluble, Tiny, Fluorescent Gold Nanoclusters
Three regimes for gold NPs
Nanoparticle (scattering light)
bulk
Nanocluster (fluorescence)
R<2 nm, electron Fermi-wavelength
R>>λ
R~50 nm, electron mean free path
Why fluorescent gold nanoclusters?
• CdSe QDs, toxic precursor
• Gold NPs, scattering signal is too weak
for <10 nm particles
Absorption~R3
Fluorescent, nontoxic, nanometer-sized materials
gold nanoclusters
Scattering~R6
useless
Dickson et al, Phys. Rev. Lett. 93, 077402 (2004)
History of Fluorescence from Gold Materials
Robert M. Dickson
• Encapsulating Au clusters
by PMAMA dendrimers
• QYs~50%
• 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
Incomplete shape : photobleaching phenomenon
blinking behavior
30
Single Au NCs
10 ms bin time
25
Counts/bin
20
15
Single-step photobleaching
10
5
0
0
10
Observation time (s)
30
25
Counts/ms
20
15
10
5
Streaky pattern : blinking behavior
0
0
1
2
3
Observation time (s)
4
5
On/off-time distribution

1

1
10000
1000
0.1
100
1
2
3
4
On-time duration (ms)
5
6
Normalized events
Events
Normalized events

0.1
0.01
0.01
1
10
On-time duration (ms)
1
10
Off-time duration (ms)
• Power-law distribution for on/off-times
• Power-law exponents for on/off-times are 2, 1.8, respectively
Fluorescence Lifetime Image Microscopy (FLIM)
1
Single NCs
Normalized intensity (a.u.)
ns
0.1
0.01
-2
0
2
4
6
8
Decay time (ns)
10
12
14
Specific labeling and nonspecific uptake
Scale bar : 50 micron
• Human hepatoma cells
for specific labeling.
• Streptavidin-biotin pairs.
• Human aortic endothelial cells
for nonspecific uptake.
Ultrafast Dynamics in Metal NPs
Pump-Probe Techniques – to achieve ~fs resolution
fs (10-15 sec) ~ ps (10-12 sec)
mm (10-6 m) ~ cm (10-2 m)
(http:www.nims.go.jp)
Relative surface energy: γ111 < γ100 < γ110
A
B
2016/3/23
Thin film
Prism
Sphere
Rod
Disc
Triangular
pyramid
33
Silver Nanoprisms
A
B
Oscillation component
H = 31.4 nm, T = 8.5 nm
0
20
40
60
80
C
Residuals (normalized)
Residuals (normalized)
zN(t)-z1(t), 0.04
H = 31.6 nm, T = 7.8 nm
Residuals (normalized)
Delay Time / ps
H = 31.4 nm, T = 8.5 nm
0
2016/3/23
2
4
6
Delay Time / ps
8
34
References
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•
•
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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