Supporting Information

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1 Supporting Information Wiley-VCH Weinheim, Germany

2 Stepwise Directing Nanocrystals to Self-Assemble at Water/Oil Interfaces Jing Wang, Dayang Wang, Nelli S. Sobal, Michael Giersig, Ming Jiang, and Helmuth Möhwald Max Planck Institute of Colloids and Interfaces, D-14424, Potsdam, Germany, Department of Macromolecular Science, Fudan University, , Shanghai, P. R. China, and Center of Advanced European Studies and Research, D-53175, Bonn, Germany Experimental details 1. Preparation of NCs. 6 nm CoPt 3 capped with HDA and ACA were synthesized as described elsewhere. 1 6 nm and 17 nm Fe 3 O 4 NCs stabilized with oleic acid and oleylamine were prepared based on the method reported by Sun et al. 2 6 nm Ag NCs stabilized by oleic acid were synthesized by thermal reduction of silver trifluoroacetate in isoamyl ether in the presence of oleic acid nm citrate stabilized Au NCs were obtained by using the Frens method Synthesis of SH-β-CD. (Mono-6-(p-tolylsulfonyl)-β-cyclodextrin) (TsCD) was first synthesized as described elsewhere 5. MALDI-TOF on THAP matrix (M-OTs + Na + ) m/z calcd for C 49 H 76 NaO 37 S (M - OTs +Na + ) , measured Afterwards, 250 mg TsCD and 300 µl 1,6-hexadithiol in 25 ml aqueous solution of Na 2 CO 3, containing 20% ethanol, were mixed together and stirred at 50 o C under Ar atmosphere for 48 h. After removal of the insoluble material by filtration, the filtrate was stored for further use. 3. Ligand exchange of Fe 3 O 4 NCs with ACA

3 ACA was capped on Fe 3 O 4 NCs via a ligand exchange. Typically, 15 mg Fe 3 O 4 NCs were incubated in 5mL toluene solution of ACA for 2 d. The ACA concentrations were varied from 2, 10 to 20 mg/ml to control the capping amount of ACA on the Fe 3 O 4 NCs. Excess ACA is removed by washing with methanol. The number of ACA per NC was varied from 62, 128, and 199, analyzed by 1 H-NMR spectroscopy. Herein CDCl 3 with TMS as internal standard was used as solvent and Fe 3 O 4 NCs were entirely decomposed by DCl (37%) prior to performance of 1 H-NMR spectroscopy. To simplify the calculation, only the terminated groups of oleic acid or oleylamine are considered when calculating the projection area of long chain ligands onto NCs surface, and the space due to oleyl groups leaving are supposed to be occupied by ACA molecules. References: 1. E. Shevchenko, D. Talapin, A. Rogach, A. Kornowski, M. Haase, H. Weller, J. Am. Chem. Soc. 2002, 124, S. Sun, H. Zeng, D. Robinson, S. Raoux, P. Rice, S. Wang, G. Li, J. Am. Chem. Soc. 2004, 126, Y. Wang, J. Wong, X. Teng, X. Lin, H. Yang, Nano Lett. 2003, 3, G. Frens, Nature-Phys. Sci. 1973, 241, R. Petter, J. Salek, C. Sikorski, G. Kumaravel, F. Lin, J. Am. Chem. Soc. 1990, 112,

4 Figure S1. Photograph of a toluene solution of 6 nm CoPt 3 NCs in contact with water. Fe 3 O 4 -S3 -CH 3,3H Oleylamine or Oleic acid -CH 3,12H TMS Fe 3 O 4 -S2 Fe 3 O 4 -S1 Fe 3 O 4 -original ppm Figure S2. 1 H NMR spectra of the solutions obtained by decomposion of original Fe 3 O 4 NCs and those partially capped with ACA. 1 H-NMR spectra were recorded with a Bruker DMX 400 spectrometer. Fe 3 O 4 NCs were washed with equal volume of methanol and redispersed in CDCl 3 with TMS(0.1%, w/v) as internal standard. The NCs were entirely decomposed by DCl (37%) prior to performance of 1 H-NMR spectroscopy.

5 Absorbance HPCD 19 mm 10 mm 5 mm 1 mm 0.1 mm 0.01 mm 0 mm wavelength(nm) Absorbance HPCD 19 mm 10 mm 5 mm 1 mm 0.1 mm 0.01 mm 0 mm wavelength(nm) Figure S3. The absorption spectra of 6 nm Fe 3 O 4 NCs capped with 128 (upper) and 199 ACAs per particle (lower) in the toluene phase as a function of the concentration of HPCD in water. After mixing 1 ml toluene, containing 0.3 mg Fe 3 O 4 NCs, with 1 ml HPCD aqueous solution by 5 min shaking, 0.8 ml organic aliquots were taken for UV-Vis absorption measurements.

6 a b Figure S4. TEM pictures of the thin films of 6 nm CoPt 3 NCs self-assemble at the water/oil interface in the presence of β-cd in water (1 mm), obtained directly at room temperature (a) and after heating at 70 o C for 20 min (b). The insets are the corresponding photographs. Figure S5. Confocal fluorescence micrograph of emulsion droplets obtained via selfassembly of 6 nm Fe 3 O 4 NCs at the water/toluene interface, driven by the presence of 1 mm β-cd in water. In the aqueous phase, 2.8 nm aqueous CdTe NCs are dissolved in order to highlight the aqueous phase under irradiation. Confocal fluorescence micrographs were obtained with a Leica TCS NT inverted confocal system (Leica, Germany).

7 Figure S6. TEM image of the monolayer of 6 nm CoPt 3 NCs self-assembled at the water/toluene interface in the presence of NH 2 -β-cds in water. a b Figure S7. TEM pictures of broken areas in 6 nm Ag/6 nm Fe 3 O 4 NC bilayer films (a) and 6 nm Ag/6 nm Fe 3 O 4 /12 nm Au NC trilayer films (b), derived from stepwise selfassembly at the water/oil interface in the presence of SH-β-CD in water. The different layers are marked by numbers. a b Figure S8. (a) Photograph and (b) TEM image of the thin film obtained by consecutive self-assembly of 6 nm CoPt 3 and 12 nm Au NCs at the water/toluene

8 interface. NH 2 -β-cd is used for interfacial self-assembly. The interface is highlighted by the arrow. a b c Figure S9. (a) Scanning TEM micrograph of a 6 nm Ag/6 nm Fe 3 O 4 /12 nm Au trilayer (shown in Figure S7b) and (b) its corresponding EDX mapping image obtained by e Kα(Red), Ag Lα(Green) and Au Lα(Blue). Scanning TEM and EDX mapping were performed by a LEO 922A transmission electron microscope. (c) EDX spectrum of the trilayer film transferred on a silicon wafer from the water/toluene interface. The element weight compositions is C 44.79%, O 15.03%, Si 37.25%, Fe

9 0.18%, Ag 0.78%, and Au 1.96%. EDX was conducted using a Philips XL30 scanning electron microscope. Figure S10. AFM analysis of the heights of 6 nm Ag/ 6 nm Fe 3 O 4 /12 nm Au NC trilayer films, derived from stepwise interfacial self-assembly. Their thickness is in the range of nm. AFM was performed by a Dimension 3100 AFM (Digital Instruments, CA).

10 Figure S11. Upper panel: photographs of accumulation of 6 nm Fe 3 O 4 NCs monolayers self-assembled at the water/toluene interface (left) and the bilayers composed of 6 nm CoPt 3 and 12 nm Au NCs (right) by using a magnet. Lower panel: photographs of accumulation of the bilayers composed of 6 nm Fe 3 O 4 and 6 nm Ag NCs (left) and the trilayer of 6 nm Fe 3 O 4, 6 nm Ag and 12 nm Au NCs (right) by using a magnet.