ChemComm
Communication
four more times. This protocol was to ensure removal of any DBCO modified CNT and versatile water-soluble azide modified
non-covalently bound AuNP. The successful synthesis and AuNP. This I-SPAAC reaction was fast and effective, leading to
purification of the covalent SWCNT–AuNP hybrid was con- CNT homogeneously covered with small AuNP and to a robust
firmed by XPS and TEM. The XPS spectrum of SWCNT–AuNP and stable hybrid material thanks to the covalent bond that
(Fig. S10c, ESI†) shows the appearance of the peaks from Au at links the two nano-partners. Importantly, due to the nature of
84 eV (4f), 334–353 eV (4d), 547–643 eV (4p), and 762 eV (4s), the AuNP ligands these hybrid materials are easily dispersed in
and from S at 162.9 eV (2p) and 228 eV (2s). The high-resolution aqueous environment to aid in use for a variety of applications
carbon 1s spectrum (Fig. 1a, right) shows a marked increase of as varied as gas sensors, catalysts, and as structural compo-
the component at 286.30 eV related to the C–O–C of the AuNP nents of electrochemical sensors. The coupling-based strategy
glycol units, while the high-resolution oxygen 1s spectrum introduced here can be exploited for exploring and creating a
(Fig. 1b, right) shows an increase of the corresponding compo- wide variety of bioorthogonal nanostructured materials for
nent at 532.63 eV. The Au 4f7/2 core line of AuNP is at 84.5 eV, device applications. For example, it is possible to take advan-
this binding energy is shifted upwards from that of bulk Au tage of the intrinsic presence of carboxylic acid groups on the
(83.95 eV) due to particle size effects (Fig. S13, ESI†).22,23 The N 1s surface of carbonaceous material (i.e. graphene, nanodia-
core line after the interfacial I-SPAAC reaction shows a new monds, glassy carbon) to introduce strained alkynes through
component centered at 401.08 eV (Fig. S13, ESI†). While the major the coupling reaction here described. These bioorthogonal
component at 399.98 eV is due to the DBCO-CNT amide nitrogens materials would then be able to bind the azide-functionalized
and to the nitrogen of the triazole rings; this new component is AuNP or other azide modified biomolecules through the I-SPAAC
most likely related to the formation of –NH3+ as a consequence of reaction.
the photolysis of the unreacted –N3 by the high energy incident
We acknowledge NSERC Canada and UWO for financial
radiation.24 TEM images of the hybrid nanomaterial (Fig. 1c, support.
right) show that AuNP are dispersed on the CNT surface, that
Notes and references
they kept their original size and shape, and that there are no
unbound particles present, confirming the efficiency of our
purification procedure. Indeed, the use of sonication favours the
detachment of the AuNP that are only physisorbed on the CNT
leaving just those that are covalently bonded.
To further exclude the possibility of unspecific physisorp-
tion or bonding of the AuNP to the SWCNT-DBCO, a control
experiment was carried out under identical conditions and
following the same experimental procedure but using
the model Me-EG3-AuNP instead of the N3-EG4-AuNP. The
Me-EG3-AuNP, with the absence of the azide functionalities,
is not expected to react with the DBCO-modified CNT because
they cannot undergo the I-SPAAC reaction. Fig. S14c (ESI†) is
1 M. D. Best, Biochemistry, 2009, 48, 6571.
2 J. C. Jewett and C. R. Bertozzi, Chem. Soc. Rev., 2010, 39, 1272.
3 M. F. Debets, S. S. Van Berkel, J. Dommerholt, A. J. Dirks, F. P. J. T.
Rutjes and F. L. Van Delft, Acc. Chem. Res., 2011, 44, 805.
4 N. J. Agard, J. A. Prescher and C. R. Bertozzi, J. Am. Chem. Soc., 2004,
126, 15046.
5 E. Lallana, E. Fernandez-Megia and R. Riguera, J. Am. Chem. Soc.,
2009, 131, 5748.
6 J. M. Baskin, J. A. Prescher, S. T. Laughlin, N. J. Agard, P. V. Chang,
I. A. Miller, A. Lo, J. A. Codelli and C. R. Bertozzi, Proc. Natl. Acad.
Sci. U. S. A., 2007, 104, 16793.
7 A. Kuzmin, A. Poloukhtine, M. A. Wolfert and V. V. Popik, Bioconju-
gate Chem., 2010, 21, 2076.
8 D. H. Ess, G. O. Jones and K. N. Houk, Org. Lett., 2008, 10, 1633.
9 J. C. Jewett, E. M. Sletten and C. R. Bertozzi, J. Am. Chem. Soc., 2010,
132, 3688.
from this control experiment and shows, as expected, clean 10 J. Dommerholt, S. Schmidt, R. Temming, L. J. A. Hendriks,
F. P. J. T. Rutjes, J. C. M. Van Hest, D. J. Lefeber, P. Friedl and
SWCNT-DBCO comparable to those of Fig. S14a (ESI†). This
F. L. Van Delft, Angew. Chem., Int. Ed., 2010, 49, 9422.
confirms the successful synthesis of AuNP-decorated SWCNT
11 K. E. Beatty, J. D. Fisk, B. P. Smart, Y. Y. Lu, J. Szychowski,
through the new I-SPAAC reaction between SWCNT-DBCO and
N3-EG4-AuNP.
M. J. Hangauer, J. M. Baskin, C. R. Bertozzi and D. A. Tirrell,
ChemBioChem, 2010, 11, 2092.
12 N. E. Mbua, J. Guo, M. A. Wolfert, R. Steet and G.-J. Boons,
ChemBioChem, 2011, 12, 1911.
Finally, sonication was employed to test the stability and
resilience of the final hybrid material. A fraction of SWCNT– 13 H. Koo, S. Lee, J. H. Na, S. H. Kim, S. K. Hahn, K. Choi, I. C. Kwon,
S. Y. Jeong and K. Kim, Angew. Chem., Int. Ed., 2012, 51, 11836.
14 J. A. Johnson, J. M. Baskin, C. R. Bertozzi, J. T. Kobersteind and
AuNP were dispersed in PBS pH 7.0 and ultra-sonicated for one
hour. The TEM images obtained from these samples were
N. J. Turro, Chem. Commun., 2008, 3064.
´
compared with those of the freshly prepared SWCNT–AuNP 15 A. Bernardin, A. Cazet, L. Guyon, P. Delannoy, F. Vinet, D. Bonnaffe
and they did not show any appreciable difference either in the
and I. Texier, Bioconjugate Chem., 2010, 21, 583.
16 S. V. Orski, A. A. Poloukhtine, S. Arumugam, L. Mao, V. V. Popik and
density of chemisorbed AuNP or in the AuNP size distribution.
J. Locklin, J. Am. Chem. Soc., 2010, 132, 11024.
This supports the efficiency of our synthetic approach and the 17 N. Chauhan, A. Singh, J. Narang, S. Dahiya and S. C. Pundir, Analyst,
2012, 137, 5113.
resilience of the resulting AuNP–CNT hybrid. The reaction of
the N3-EG4-AuNP with DBCO as a model leads to efficient and
18 J. Huang, X. Xing, X. Zhang, X. He, Q. Lin, W. Lian and H. Zhu, Food
Res. Int., 2011, 44, 276.
total loading (complete reaction) on the AuNP. Because of this 19 D. Cai, Y. Yu, Y. Lan, F. J. Dufort, G. Xiong, T. Paudel, Z. Ren,
D. J. Wagner and T. C. Chiles, BioFactors, 2007, 30, 271.
20 Y. Guo, S. Guo, Y. Fang and S. Dong, Electrochim. Acta, 2010,
and the high effective concentration of the N3 moiety on each
AuNP we believe that every accessible DBCO on the DBCO-
55, 3927.
SWCNT reacts with N3-EG4-AuNP.
In summary, we introduce a simple and efficient copper-free
interfacial strain-promoted alkyne–azide cycloaddition (I-SPAAC)
21 P. Gobbo and M. S. Workentin, Langmuir, 2012, 28, 12357.
22 H. Liu, B. S. Mun, G. Thornton, S. R. Isaacs, Y.-S. Shon,
D. F. Ogletree and M. Salmeron, Phys. Rev. B, 2005, 72, 155430.
23 C. R. Henry, Surf. Sci. Rep., 1998, 31, 231.
reaction at the interface between different nanosystems: a new 24 A. Devadoss and C. E. D. Chidsey, J. Am. Chem. Soc., 2007, 129, 5370.
c
3984 Chem. Commun., 2013, 49, 3982--3984
This journal is The Royal Society of Chemistry 2013