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C. T. Yuan , P. T. Tai, P. Yu, D. H. Lee, H. C. Ko, J. Huang, J. Tang*

Single-Molecule Fluorescence Blinking and Ultrafast Dynamics in Semiconductor and Metal Nanomaterials. Single-QD fluorescence images. 1. Single-molecule detection. (2) 2. Introduction to single colloidal QDs. (4) 3. Fluorescence blinking in semiconductor nanostructures. (8)

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C. T. Yuan , P. T. Tai, P. Yu, D. H. Lee, H. C. Ko, J. Huang, J. Tang*

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  1. Single-Molecule Fluorescence Blinking and Ultrafast Dynamics in Semiconductor and Metal Nanomaterials 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) C. T. Yuan, P. T. Tai, P. Yu, D. H. Lee, H. C. Ko, J. Huang, J. Tang* Single-QD fluorescence time traces Colloidal CdSe/ZnS QDs Fluorescent gold NCs

  2. 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

  3. Why Single-Molecule Detection in Nanomaterials? Time-dependent dynamical fluctuation (intensity, lifetime) Sample Heterogeneity (size, shape, local surface) Time Phys. Rev. Lett. 88, 077402 (2002)

  4. Potential applications based on SMDProtein folding/unfolding dynamics • Fluorescent labels for SMD • Nontoxic • Small • Biocompatible

  5. Roger Tsien, Nobel Prize in Chemistry in 2008Green fluorescent protein

  6. Colloidal Semiconductor CdSe QDs

  7. Colloidal semiconductor QDs Glove box Excellent fluorescence properties 1. Photostability 2. Broad absorption band 3. Narrow emission band 4. Emission tunability 5. Bio-compatibility

  8. Photo-stability and multi-colors labeling 3T3 cells Nature materials 4, 435, 2005 QDs AlexaFluor 488 Human epithelial cells Nature biotechnology 22, 969, 2004

  9. Fluorescence blinking in single CdSe QDs Binning-threshold methods On-time Off-time • 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 Off states, charged QDs On states, neutral QDs • How the electron is rejected and returned from QDs and traps • Power-law distributions • Timescales (ms~min) Surface, substrates

  10. Auger Processes • Long-range Coulomb interactions. • Efficient in 0D QDs due to lack of momentum conservation. • Time-scales of ~ps, depending on size, shape. Fluorescence blinking dark states Complication for achieving the lasing regime

  11. Nature Physics, 4, 519 (2008)

  12. Diffusion Controlled Electron Transfer (DCET) models dark state (charged QDs) Future work Present work Previous work Bright state (neutral QDs) Auger process Photon emission Tang and Marcus, Phys. Rev. Lett. 95, 107401 (2005)

  13. 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

  14. 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.

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

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

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

  18. Fluorescence Time Traces and Intensity Distribution for Immobilized QDs

  19. Fluorescence lifetime

  20. Nontoxic, Water-soluble, Tiny, Fluorescent Gold Nanoclusters

  21. Three regimes for gold NPs Nanoparticle (scattering light) bulk Nanocluster (fluorescence) R<2 nm, electron Fermi-wavelength R~50 nm, electron mean free path R>>λ

  22. 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)

  23. History of Fluorescence from Gold Materials Robert M. Dickson • Encapsulating Au clusters • by PMAMA dendrimers • QYs~50%

  24. Size, 30*300 nm • Similar behavior to SPR • Orientation dependent emission

  25. 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

  26. Optical Properties of Ensemble Au NCs • No surface plasmon resonance features. • Broad band emission.

  27. Fluorescence properties of single gold NCs Incomplete shape : photobleaching phenomenon blinking behavior Single-step photobleaching Streaky pattern : blinking behavior

  28. On/off-time distribution • Power-law distribution for on/off-times • Power-law exponents for on/off-times are 2, 1.8, respectively

  29. Fluorescence Lifetime Image Microscopy (FLIM)

  30. 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.

  31. Ultrafast Dynamics in Metal NPs

  32. 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)

  33. Relative surface energy: γ111< γ100 < γ110 A B Thin film Prism Sphere Rod Disc Triangular pyramid 2014/9/18 33

  34. Silver Nanoprisms A B H = 31.4 nm, T = 8.5 nm H = 31.6 nm, T = 7.8 nm C H = 31.4 nm, T = 8.5 nm 2014/9/18 34

  35. 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).

  36. Thank you for your attention

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