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) Single-QD fluorescence images Single-QD fluorescence time tracesColloidal 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~10 11 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, (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 AlexaFluor 488 QDs 3T3 cells Human epithelial cells Nature materials 4, 435, 2005 Nature biotechnology 22, 969, 2004

Fluorescence blinking in single CdSe QDs 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 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

Nature Physics, 4, 519 (2008)

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, (2005) Previous workPresent workFuture work

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) Laplace transformation F(t)=G(t)/G(0)-1

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.

Interaction between single QDs and Ag NPs Energy transfer. Plasmonic effects. 100 nm

Fluorescence Lifetime Correlation Spectroscopy (FLCS) Fluorescence quenching for individual QDs (uniform quenching). Improvement of photo-stability.

Fluorescence decay profiles Brightness per QDs (FCS) Measured lifetimes (TCSPC) No significant effect on radiative decay rates. Enhancing nonradiative decay rates.

Fluorescence Time Traces and Intensity Distribution for Immobilized QDs

Fluorescence lifetime

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 bulk Nanoparticle (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, (2004) Absorption~R 3 Scattering~R 6 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 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

Fluorescence Lifetime Image Microscopy (FLIM)

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

( fs ( sec) ~ ps ( sec) mm (10 -6 m) ~ cm (10 -2 m) Pump-Probe Techniques – to achieve ~fs resolution

RodDiscTriangular pyramid Thin filmPrismSphere A B 2015/10/3133 Relative surface energy: γ 111 < γ 100 < γ 110

A B C H = 31.4 nm, T = 8.5 nm H = 31.6 nm, T = 7.8 nm Silver Nanoprisms 2015/10/3134

References Y. C. Yeh, C. T. Yuan, C. C. kang, P. T. Chou, J. ang, Appl. Phys. Lett. 93, (2008). P. Yu, J. Tang, S. H. Lin, J. Phys. Chem. C 112, (2008). J. Tang, Y. C. Yeh, P. T. Tai, Chem. Phys. Lett. 463, 134 (2008). J. Tang, J. Chem. Phys. 129, (2008). C. T. Yuan et al, Appl. Phys. Lett. 92, (2008). D. H. Lee, J. Tang, J. Phys. Chem. C 112, (2008). J. Tang, Chem. Phys. Lett. 458, 363 (2008). J. Tang, J. Chem. Phys. 128, (2008). J. Tang, Appl. Phys. Lett. 92, (2008).

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