Electronic Supporting Information
Unique self-assembly properties of a bridge-shaped protein dimer with quantum dots
Jianhao Wang1, 2, * · Pengju Jiang1, * · Liqian Gao2 · Yongsheng Yu2 · Yao Lu2· Lin Qiu1 · Cheli Wang1 · Jiang
Xia 2
1
School of Pharmaceutical Engineering and Life Science, Changzhou University, Changzhou, Jiangsu, China,
213164
2
Department of Chemistry, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
* These authors contributed equally to this work.
Correspondence: jiangxia@cuhk.edu.hk
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EXPERIMENTAL SECTION
Preparation of oil-soluble CdSe/ZnS core-shell QDs
Core-shell QDs (CdSe/ZnS) were synthesized using a two-step method according to previous reports (Peng et al.
2001; Qu et al. 2001). Briefly, 7 g TOPO and 3 g HDA were mixed and heated in a 50 mL three-neck flask for
solvent under vacuum. Then 0.125 g cadmium acetate (Cd(Ac) 2) was added in the solutions. After the mixture
was heated to 310 °C, the heater was removed. And the stock solution of TOP/Se prepared by dissolving 0.2 g
selenium in 5 g of TOP was injected quickly into the reaction solution under vigorous stirring, resulting in
nucleation of CdSe nanocrystals. The synthesis of the shell of CdSe QDs is briefly described as the following. 6
g TOPO, 2 g HDA and 0.2 g Zn(Ac)2 were mixed in three-necked flask. Then as-prepared TOPO-capped CdSe
nanocrystals in chloroform was added to the mixture and the temperature was increased to the desired
temperature quickly. The desired stock solution of TOP/S prepared by adding 0.1 mL (TMS) 2S to 3 mL TOP
was added at 1 mL/min. In the following 2 h, the temperature was maintained at 90 °C to keep the inorganic
epitaxial growth of the shell to proceed on the surface of the core. QDs with emission wavelength (612 nm)
were synthesized.
Preparation of GSH stabilized QDs
GSH stabilized QDs were synthesized based on the previously reported procedures of the exchange of TOPO on
the surface of as-synthesized QDs by GSH (Freeman et al. 2010). QDs were dissolved in chloroform, to which a
100 μL GSH solution (containing 0.142 g GSH and 40 mg KOH in 2 ml methanol) was added followed by
vigorous shaking. After the addition of 1.5 ml NaOH aqueous solution (1 mM), the top aqueous layer was
separated and precipitated with NaCl and methanol to remove excess GSH. The resulting QDs were dissolved in
500 μL borate buffer (pH 8.5, 10 mM). The concentration of QDs was measured based on the previously
reported method (Yu et al. 2003). The transmission electron microscopy (TEM) images of QDs were obtained
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using a transmission electron microscope (Tecnai G2 20, FEI, Netherlands). For hydrodynamic diameter
analyses, the size distribution of QD and QDs-(SpeA)8 were determined by a Nano ZS90 (Malvern, UK)
according to a dynamic light scattering (DLS) technique at 25 ºC.
Protein sequence of SpeA
The concentration of SpeA was determined by UV spectrophotometry at 280 nm using the absorption coefficient
factor 27810 cm-1 M-1 as calculated from the contents of tyrosine, tryptophan, and cysteine in the SpeA
sequence.
HMDPDPSQLHRSSLVKNLQNIYFLYEGDPVTHENVKSVDQLLSHDLIYNVSGPNYDKLKTELKNQEMA
TLFKDKNVDIYGVEYYHLCYLCENAERSACIYGGVTNHEGNHLEIPKKIVVKVSIDGIQSLSFDIETNKK
MVTAQELDYKVRKYLTDNKQLYTNGPSKYETGYIKFIPKNKESFWFDFFPEPEFTQSKYLMIYKDNETL
DSNTSQIEVYLTTK (without N-terminal His-Tag).
Fig. S1. LC-MS of SpeA.
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Fig. S2. TEM images of QDs.
(A)
(B)
Fig. S3. DLS analysis of QDs (with an average diameter of 7.5 nm) (A) and QD-(SpeA)8 (with an average
diameter of 11.6 nm) (B).
References
Freeman R, Finder T, Gill R, Willner L (2010) Probing protein kinase (CK2) and alkaline phosphatase with
CdSe/ZnS quantum dots. Nano Lett 10:2192–2196
Peng Z A, Peng X (2001) Formation of high-quality CdTe, CdSe, and CdS nanocrystals using CdO as precursor.
J Am Chem Soc 123:183–184
Qu L, Peng Z A, Peng X (2001) Alternative routes toward high quality CdSe nanocrystals. Nano Lett 1 333–337
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Yu W W, Qu L, Guo W, Peng X (2003) Experimental Determination of the Extinction Coefficient of CdTe,
CdSe, and CdS Nanocrystals. Chem Mater 15:2854–2860
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