Supporting Information
Stable end-to-end assembly of gold nanorods directed by cyclic
disulfide-modified DNA
Zhiliang Zhang,1,a) Yongqiang Wen,2,b) Dan Zhao,2 Xueji Zhang 2
1
Research Center of Analysis and Test, Shandong Polytechnic University, Jinan 250353, China.
2
Research Center for Bioengineering & Sensing Technology, University of Science and Technology
Beijing, Beijing 100083, China
a)
Email: zhzhl@spu.edu.cn b) Email: wyq_wen @iccas.ac.cn
1. Materials and methods
1.1. Materials
Tetrachloroauric acid (HAuCl4), cetyltrimethyl ammonium bromide (CTAB), silver nitrate
(AgNO3), sodium borohydride (NaBH4), ascorbic acid and sodium dodecyl sulfate were
purchased from Aldrich. The gold nanorods (AuNRs) with an aspect ratio of 3 were
synthesized using a seed-mediated method.1 All buffers were prepared with ultra-pure MilliQ
water
(resistance
>
18
MΩ
cm-1).
1,2-dithiane-4-O-dimethoxytrityl-5-[(2-cyanoethyl)-N,N-diisopropyl]-phosphoramidite
(DTPA) was synthesized according to the literature procedures.2 The oligonucleotides were
specially designed and their DNA sequences used in the experiments were as followed:
3'-TCAGTCGTGCCATCCTTTTT-5'-(DTPA)3-5'-TTTTTAGTCAGCACGGTAGG-3'
3'-TCAGTCGTGCCATCCTTTTT-SH-5'
3'-GGATGGCACGACTGATTTTT-SH-5'
DTPA represent the cyclic disulfide-containing phosphate derivative;
1.2. Apparatus
The extinction spectra of AuNRs assembly were collected using a Hitachi U-4100
spectrophotometer. The assembly of the AuNRs was characterized by JEOL JEM-1011
transmission electron microscope (TEM) operated at 100 kV, and the samples were prepared
1
by dropping the solution onto carbon coated copper grids. The morphology of AuNRs was
investigated by Hitachi S-4800 scanning electron microscope (SEM).
2. Experimental section
2.1 The synthesis of DTPA molecule
Fig. S1. Synthetic approach to molecule DTPA.
DTPA molecule was synthesized as previously described by P. Liepold et al.2 All chemical
shifts were reported in parts per million (ppm), 1HNMR chemical shifts were referenced to
TMS (0 ppm) or residual CHCl3 (7.26 ppm). ESI mass spectra were recorded on a Bruker
Apex IV FTMS. Compound 1: 1H NMR (CDCl3, 300 MHz, ppm) δ 7.50-7.47 (d, J = 7.8 Hz,
2H), 7.40-7.16 (m, 7H), 6.86 -6.83 (d, J = 9.0 Hz, 4H), 3.80 (s, 6H), 3.44 (m, 2H), 2.90-2.73
(m, 4H). EI-MS: Calcd for C25H26O4S2: 454.1. Found: 454 (M+). Compound DTPA: 1H
NMR (CDCl3, 300 MHz, ppm) δ 7.56-7.53 (dd, J = 8.1 Hz, J = 2.7 Hz, 2H), 7.43-7.39 (m,
4H), 7.33-7.15 (m, 3H), 6.86-6.81 (m, 4H), 3.80 (d, J = 1.5 Hz, 6H), 3.74-3.64 (m, 2H),
3.60-3.45 (m, 2H), 3.11-3.07 (m, 2H), 2.75-2.68 (m, 4H), 2.65-2.54 (t, J = 6.6 Hz, 1H),
2.35-2.29 (t, J = 6.6 Hz, 1H), 1.18-0.96 (m, 12H). ESI-MS: Calcd for C34H43N2O5PS2: 654.2.
Found: 655.2 (M+H+), 677.2 (M+Na+).
2.2 The synthesis of AuNRs
The synthesis of AuNRs used in the assembly was carried out by using a seed-mediated
method.1 Firstly, a seed solution was prepared by mixing 0.5 mL HAuCl4 (0.01 M) and 19.5
mL CTAB (0.1 M) solution with 1.2 mL freshly prepared 0.01 M ice-old NaBH4 solution.
After 30min, this seed solution was used for the synthesis of AuNRs. Secondly, 1.0 mL
2
HAuCl4 (0.01 M), 19 mL CTAB (0.1 M) and 0.16 mL AgNO3 (0.01 M) were mixed with
0.12 mL 0.1 M ascorbic acid solution to prepared the grown solution. 32 μL seed solution
was added to above growth solution to initiate the growth of AuNRs. After 16 hours, the
solution of AuNRs was centrifuged several times at 13000 rpm for 15 min and was
redispersed in 0.01 M CTAB solution. The extinction spectra and SEM image in Fig. S2
indicated that this procedure gave AuNRs with an aspect ratio of 3 in high yield.
Fig. S2. (a) UV-Vis extinction spectra and (b) SEM image of the synthesized AuNRs with an
aspect ratio of 3
2.3 Assembly of DNA functionalized AuNRs
For preparation of AuNRs end-to-end assembly, 1.0 mL 2 nM AuNRs with the mean
aspect ratio of 3.0, was mixed with 100 μL 2 uM triple cyclic disulfide-derivated
double-stranded oligonucleotide. 100 μL 0.1 % SDS and 100 μL 0.1 M buffer solution of
sodium phosphate (pH=7.5) were added to the above solution. 25 μL 1 M NaCl was then
added into the solution for 4 times with 1h intervals between each salt addition. The
assembly of the AuNRs into chains was monitored continuously and characterized by
Hitachi U4100 spectrometer and JEOL JEM-1011 TEM.
2.4. Stability study of AuNRs assembly
The stability of the AuNRs assembly was evaluated by assessing the extinction spectra
changes in 50 mM phosphate buffer at different salt concentration at 40 ºC. The stability of
the AuNRs assembly was monitored by measuring the changes in the longitudinal plasmon
band absorbance using UV-Vis spectrometer at different time.
3
Fig. S3. UV-Vis extinction spectra changes of AuNRs assembly driven by triple cyclic
modified (a) and single thiol-modified (b) DNA in 50 mM phosphate buffer at various salt
concentrations: 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and1.0 M. All the data were obtained
after mixing the AuNRs assembly in the solution for 48 hours.
References
1
B. P. Khanal, E. R. Zubarev, Angew. Chem. Int. Edit., 46, 2195, (2007).
2
P. Liepold, T. Kratzmüller, N. Persike, M. Bandilla, M. Hinz, H. Wieder, H. Hillebrandt, E.
Ferrer, G. Hartwich, Anal. Bioanal. Chem., 391, 1759, (2008).
4