Single-Molecule Fluorescence Blinking and Ult rafast 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 1.0 0 5 10 15 20 25 30 35 40 In te n s ity (C o u n ts/m s) T im e (s) ingle-QD fluorescence images Single-QD fluorescence time traces Colloidal CdSe/ZnS QDs Fluorescent gold NCs
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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,
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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
5
10
15
20
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30
35
40
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
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
5
10
15
20
25
30
35
40
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.
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
150
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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3
4
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7
8
G()
Lag time (ms)
CdSe/ZnS QDs QDs+triangular Ag NPs
1E-3 0.01 0.1 1 10 100 10000
1
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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
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8
G()
Lag time (s)
QDs+Ag for former-half part QDs+Ag for later-half part