KAWAI Ryoichi Ashida Lab.

1. Three-Dimensional Optical Controlof Individual Quantum DotsLiselotteJauffred, Andrew C. Richardson, and Lene B. OddershedeNano Lett. 2008, 10, 3376-3380 KAWAI Ryoichi Ashida Lab.

2. Contents • Abstract / Motivation • Introduction • What is Quantum Dots? • Radiation Force • Experiment / Results • Summary /Future work • My work /Future plan

3. Abstract / Motivation ３次元空間中で、低パワーでの赤外連続レーザー光による個々のCdSe-core量子ドットの光トラップ、および光操作が可能であることを示す。これにより、量子ドットが可視化だけでなく操作に利用することが可能となり、単一分子実験に非常に有益となる。さらに、我々は単一量子ドットに適用できる光誘起力の大きさ、個々の量子ドットの分極率の大きさの定量的な値を示す。 • Motivation: • Optically trapping a single QDs using a CW infrared laser at low power. • Deducing the strength of the optical trap and finding the magnitude of the optical force.

4. Introduction–Quantum dots (QDs) • Fluorescent semiconductor nanocrystals • Narrow emission spectrum …its wavelength is dependent on the size of QDs • Broad excitation spectrum • Fluorescence blinking…on/off Application: Markers to visualize biological systems (for instance, receptors in cell membranes, living embryos, and so on…) ⇧ QuantumDots (http://www.evidenttech.com/technology)

5. Introduction–Radiation Force Optical axis • Gradient force(勾配力) • Dissipative force(散逸力) • Scattering force(散乱力) • Absorption force(吸収力) Dissipative force (Scat.+Abs. force) Colloidal QD Trap region Gradient force Lens

6. Experimental set up / Sample_1 Ref: Andrew C. Richardson Development of optical trapping techniques for in vivo investigations

7. Experimental set up / Sample_2 set up Sample Quantum dots (Invitrogen) CdSe/ZnS(core-shell) -Water soluble -Emission wavelength: 655nm Quadrant photodiode ZnS shell Cover slips Colloidal QDs CdSe core shell 3µm Vacuum grease Oil immersion objective -NA=1.4, ×100 Nd:YVO₄ laser (5W(max) Spectra Physics Millenia,λ=1064[nm], TEM₀₀)

8. Results – the 1stexperiment (blue)…… 1 QD in the trap (red)…….. 2 QDs in the trap (purple)… 3 QDs in the trap (gray)……. 4 QDs in the trap Trapping only a single QD for at least 10 min. The full lines are Gaussian fits To the distributions.

9. Results – the 2nd experiment Before a QD is trapped After attaches the QD to a biotinylated surface Luminescence measurement The individuality of the QD in the optical trap A clear blinking behavior of the QD

10. Analysis Corner frequency / Trap stiffness_1 Harmonic force Trapped nanoparticle Langevin equation : polarization direction of the laser : optical axis Fourier transformation The power spectrum of the position The trap stiffness κ can be found.

11. Analysis Corner frequency / Trap stiffness_2 Fitting by Lorentzian function Trapped nanoparticle Power spectrum of the positions of a QD (1 lateral dimension) corner frequency: 180 Hz, , . @effective radius: 15nm : polarization : optical axis

12. Analysis Polarizability of one QD by σ : Standard deviation of the intensity distribution. …Gaussian beam ()

13. Analysis Polarizability of one QD by Clausius-Mossotti relation (for water at 1064 nm) The two different ways of finding the polarizability of a single QD.

14. Summary • Theysucceeded in three dimensional optical control of QDs using an infrared CW laser at low power. • They showed that only a single QD was in the trap. • They calculated the optical forces applicable on a trapped QD and the absolute polarization of it.

15. Future work They will address the issue of how the interaction with the electric field and QDs changes when changing the size of the QDs and the trapping laser wavelength.

16. Mywork / My futureplan I succeeded in trapping a single QD or some QDs in the air. This is photoluminescence spectrum of the trapped QD(s). Sample CdSe/ZnS Particle size: 6.3nm(average) emission central wavelength: 640nm