3D Dendritic Gold Nanostructures: Seeded Growth of Multi-Generation Fractal Architecture

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1 -Supporting Information- 3D Dendritic Gold Nanostructures: Seeded Growth of Multi-Generation Fractal Architecture Ming Pan, Shuangxi Xing, Ting Sun, Wenwen Zhou, Melinda Sindoro, Hui Hian Teo, Qingyu Yan, and Hongyu Chen * Division of Chemistry and Biological Chemistry and School of Materials Science and Engineering, Nanyang Technological University, Singapore hongyuchen@ntu.edu.sg Experimental section All solutions were prepared using ultra-pure water (resistivity > 18 MΩ cm -1 ). Aniline (99%, Alfa Aesar) were distilled before use and stored at 4 C. Hydrogen tetrachloroaurate(iii) (99.9%, Au 49% on metals basis, Alfa Aesar), sodium dodecylsulfate (SDS, 99.0%, Alfa Aesar), sodium citrate tribasic dihydrate (99.0%, Sigma), cetyl trimethylammonium bromide (CTAB, 99%, Sigma), L-ascorbic acid (99%, Sigma) and sodium borohydride (98%, Strem) were purchased and used without further purification. Copper specimen grids (300 mesh) with formvar support film (referred to as TEM grids in the text) were purchased from Beijing XXBR Technology Co. Transmission electron microscopy (TEM) images were collected using JEM-1400 (JEOL) operated at 100 ~ 120 kv. Ultraviolet-visible-near infrared (UV-vis-NIR) spectra were collected on a Shimadazu spectrophotometer. Raman spectra were collected from sample solutions in a cuvette (pathlength = 1.00 cm) using R-3000HR spectrometer (Raman Systems Inc.) with red LED laser ( λ = 785 nm). Preparation of TEM Samples. TEM grids were treated with oxygen plasma in a Harrick Plasma Cleaner/sterilizer for 45 s to improve the surface hydrophilicity. A sample solution was carefully dropped on the surface of a plastic Petri dish. The hydrophilic face of the TEM grid was then placed in contact with the sample solution. A filter paper was used to wick off the excess solution on the TEM grid which was then dried in air for 5 minutes. Syntheses of seed nanoparticles. Gold nanospheres were prepared by the citrate-reduction method following S1

2 previously reported procedures. 1 The size was tuned by varying amount of citrate added. The citrate-stabilized AuNPs used in our synthesis averaged 55 nm in diameter. The concentration of the as-synthesized sample is defined as C 1, which is estimated to be around 57 pm in number of particles. AuNRs with large aspect ratio were synthesized via seed mediated method reported previously. 2 The as-synthesized sample contain significant amount of nanospheres in addition to the AuNRs. The overall concentration is defined as C 2 in the following discussion. Synthesis of AuNP@PANI with different shell thickness. AuNP@PANI were synthesized by in situ polymerization of aniline on citrate-stabilized AuNPs. 3 The AuNP@PANI with 6 nm shells were synthesized following the literature procedures for the 1 st growth cycle. Briefly, AuNPs solution (4.5 ml) was concentrated to a total of 18 μl by centrifugation. After removal of supernatant, the isolated NPs were added to a solution that was made by pre-mixing aniline (2 mm, 1.5 ml) and SDS (40 mm, 300 μl). Then, the solution was vortexed for 5 s followed by addition of acidic (NH 4 ) 2 S 2 O 8 solution (2 mm in 10 mm HCl, 1.5 ml). The total volume of the final mixture was 3.3 ml, where [aniline] = 0.9 mm, [SDS] = 3.6 mm, [(NH 4 ) 2 S 2 O 8 ] = 0.9 mm and [HCl] = 4.5 mm. This reaction mixture was incubated at room temperature for 1 hr to give PANI shells of 6 nm. A similar reaction was carried out and the reaction mixture was incubated overnight to yield AuNP@PANI of 14 nm shell. These NPs were isolated by centrifugation and used as seeds for the 2 nd growth cycle. After incubation overnight, AuNP@PANI with 26 nm shells were prepared. Synthesis and purification of Au dendrimers. In a typical experiment (synthesis of G1 dedrimers from AuNPs), 1.5 ml as-synthesized AuNPs were concentrated to a total of 10 μl by centrifugation at 6000 rpm for 5 min. After removal of the supernatant, the isolated NPs were added to a solution that was made by pre-mixing aniline (, 0.1 M, for other dendrimers, refer to the tables below) and SDS (50 μl, 40 mm). Then the solution was vortexed for 5 s followed by addition of HAuCl 4 solution (, 0.6 mm, for other dendrimers, refer to the tables below). The total volume of the final mixture was 0.55 ml, where [aniline] = 68.2 mm, [SDS] = 3.6 mm, [HAuCl 4 ] = mm. After vortexing for 10 s, the reaction mixture was incubated at room temperature for 2 hr to ensure complete reduction of HAuCl 4. To isolate the G1 NPs, the reaction mixture (0.55 ml) was centrifuged twice at 4000 rpm for 5 min; the isolated NPs were dispersed in 0.55 ml of SDS solution (3.6 mm) to prevent further aggregation of the NPs in water. The purified seed, after being concentrated by centrifugation, could be used as seeds for multi-generation growth. The tables below show detailed conditions for the various types of Au dendrimers. S2

3 Seed aniline HAuCl 4 Product Citrate-AuNPs, 0.1 M, 0.6 mm, G1 1.5 ml, C 1 purified 100 μl, 2.73 C M, 0.6 mm, G2 purified 56 mm, 1 mm, G3 300 μl, C 1 Table 1: Synthetic details for the multi-generation growth from AuNPs. Seed aniline HAuCl 4 Product CTAB-AuNRs, 0.1 M, 0.6 mm, G1 purified, 1mL, C M, 0.6 mm, purified G2 100 μl, 1.82 C 2 56 mm, 1 mm, purified 300 μl, 0.33 C 2 G3 Table 2: Synthetic details for the multi-generation growth from AuNRs. S3

4 Seed aniline HAuCl 4 Product AuNPs@PANI (6nm Shell) 100 μl 0.1 M, 0.6 mm, Figure 2c AuNPs@PANI (26nm Shell) 100 μl 0.1 M, 0.6 mm, Figure 2d AuNRs 100 μl 0.1 M, 1 mm, Figure 3d AuNRs 100 μl 56 mm, 0.6 mm, Figure 3e Table 3: Synthetic details for the control experiments shown in Figure 2 and 3. Isolation of reaction intermediates. Reaction intermediates of dendrimers shown in Figure 3d and 3e were trapped 1 min after the initiation of the reactions by adding 20 mm 1-dodecanethiol in DMF solution (20 μl). The excess thiol-ended ligands coordinated to the Au surface, preventing further deposition of Au onto the seeds during the processes of centrifugation (about 15 min) and TEM sample preparation (about 5 min). References 1 G. Frens, Nat. Phys. Sci., 1973, 241, B. P. Khanal and E. R. Zubarev, J. Am. Chem. Soc., 2008, 130, S. Xing, L. H. Tan, M. Yang, M. Pan, Y. Lv, Q. H. Tang, Y. Yang and H. Chen, J. Mater. Chem., 2009, 19, S4

5 a b Figure S1. TEM images of the as-synthesized (a) AuNPs and (b) AuNRs that were used as seeds in our syntheses of Au dendrimers. S5

6 a b Figure S2. TEM images of typical failed products after the third generation growth, seeded from (a) AuNPs and (b) AuNRs, respectively. Without the controls as discussed in the main text, significant core growth and homogeneous nucleation of Au are the major problems in obtaining uniform-sized dendritic NPs with high surface area. S6

7 Figure S3. Raman spectra of solution mixture consists of AuNPs seed, aniline and SDS (blue) and the purified dendrimer intermediate 1 min after the initiation of the reaction by the addition of HAuCl 4 (red). S7

8 a b c d Figure S4. (a, b) TEM images of the G2 dendrimers by using AuNPs and AuNRs as seeds, respectively (Figure 1c and 1f). (c, d) TEM images of G2 dendrimers grown in a different batch (with higher concentration of G1 NPs as the seeds). S8

9 Figure S5. (a) TEM image (large-area view) of G3 dendrimers seeded from AuNPs. It is from a same batch of sample as that shown in Figure 1d. (b) TEM images of G3 dendrimers grown in a different batch (with higher concentration of G2 NPs as the seeds). S9

10 Figure S6. (a) A representative SEM image of typical G3 dendrimer shown in Figure S5-b; (b) magnified view of the selected region in a. These images indicate the 3-D structure of the dendrimers. S10

11 Supplementary Material (ESI) for Chemical Communications a1 a2 a3 b1 b2 b3 Figure S7. (a1-a3) TEM images of G3 dendrimers seeded from AuNRs, which were also shown in Figure 1g; (b1-b3) TEM images of a different batch of G3 products grown under conditions similar to that used in Figure 1g (with G2 NPs shown in Figure S4-c as the seeds). S11

12 a b c d Figure S8. TEM images of the AuNPs@PANI seeds with (a) 6 nm and (b) 26 nm shells, which were pre-fabricated by using (NH 4 ) 2 S 2 O 8 as oxidant (also shown in Figure 2a and 2b, respectively); (c, d) the resulting G1 nanostructures seeded from corresponding AuNPs@PANI seeds as indicated by the red arrows (also shown in Figure 2c and 2d, respectively). S12

13 a b c d Figure S9. TEM images of the reaction intermediates (a, b) isolated 1 min after the initiation of the reactions. The same batch of samples was incubated for 2 hrs; the products were the same as those shown in (c) Figure 3e and (d) 3d, respectively. S13

14 Figure S10: UV-vis-NIR spectra of AuNRs (black), dendritic rods in Figure 3e (red) and Figure 3d (blue). Compared to the original AuNRs, the resulting dendrimers showed broad absorption in near infrared region. Absorption peak around 420 nm indicated the presence of PANI. 3 S14