balanced charge at high pH (pH 4 6), the dipole of the PC may
fit themselves as an energy favorable antiparallel orientation
with strong non-specific resistance to other colloid particles
Fig. 3(C) (right). However, the phosphate groups of the phos-
phorylcholine became partially protonated at pH 4–614 and the
unbalanced charge might destroy the antiparallel orientation.
The NPs then aggregated, probably due to the ion-pair inter-
actions between the net positively charged quaternary ammo-
nium with the phosphate group on the other nanoparticles,
Fig. 3(C) (Middle).
The zwitterionic PC showed much better stabilizing ability
than the neutral EG4. The fact that these nanoparticles
systems with zwitterionic surfaces have excellent biostability,
biocompatibility and ligand exchange ability indicate that they
can be potentially served as a versatile nanoplatform for the
biomedical applications including sensitive diagnostic assays,
drug and gene delivery.
Financial support from Natural Science Foundation of China
(NSFC-20774082, 50703036) and Program for New Century
Excellent Talents in University (NCET-05-0527) and National
High Technology Research and Development Program of China
(2006AA03Z329, 2006AA032444) is greatly appreciated.
Many biological reactions arise from protein adsorption
and nonspecific protein binding could be a serious issue in
nanomedicine. Even though a lot of articles have been pub-
lished dealing with the interactions between nanoparticles and
proteins, the issue of nonspecific protein binding with nano-
particles has generally not been addressed.15 In addition to
improving the stability of Au-NPs in high ionic strength
media, one potential advantage of zwitterionic phosphoryl-
choline monolayers is the prevention of nonspecific protein
adsorption. Protein binding to Au-NPs can be conveniently
monitored by gel electrophoresis, since protein–nanoparticle
complexes are expected to migrate differently than the free Au-
NPs. Lysozyme and bovine serum albumin (BSA), represen-
tative of positively and negatively charged proteins at neutral
pH as well as having different hydrophobicities, were chosen
for the protein binding test. For comparison, tiopronin pro-
tected Au-NPs (Au-Tp), a water soluble nanoparticle, was
synthesized and tested for protein binding. Gel electrophoresis
results are shown in Fig. 4. When Au-Tp nanoparticles were
cultured with lysozyme and BSA, different band-shifts were
observed, indicating different degrees of nonspecific adsorp-
tion. Incredibly, the Au-Tp nanoparticle solution became
turbid on addition of lysozyme, indicating that Au-NPs form
aggregates. This is presumably because the negative charged
Au-TP nanoparticles were cross-linked by positive charged
lysozyme molecules (lane 6 in Fig. 4). When the same experi-
ment was done with HS-PC protected Au-NPs, no change in
the nanoparticle migration was observed (lane 1, 2, 3 in
Fig. 4). The zwitterionic phosphorylcholine monolayers pro-
tected Au-NPs showed strong resistance to protein adsorption.
In conclusion, we have proposed zwitterionic PC as a novel
zwitterionic ligand for preparation of biocompatible mono-
layer protected Au-NPs. These nanoparticles showed out-
standing stability in physiological PBS solution and plasma.
Notes and references
1. (a) N. L. Rosi and C. A. Mirkin, Chem. Rev., 2005, 105, 1547;
(b) Y. W. Cao, R. C. Jin and C. A. Mirkin, Science, 2002, 297,
1536; (c) C. Lu and Y. B. Zu, Chem. Commun., 2007, 3871.
2. (a) C. S. Tsai, T. B. Yu and C. T. Chen, Chem. Commun., 2005,
4273; (b) G. Han, C. C. You, B. J. Kim, R. S. Turingan,
N. S. Forbes, C. T. Martin and V. M. Rotello, Angew. Chem.,
2006, 118, 3237 (Angew. Chem., Int. Ed., 2006, 45, 3165);
(c) A. G. Kanaras, Z. Wang, I. Hussain, M. Brust, R. Cosstick
and A. D. Bates, Small, 2007, 3, 67.
3. (a) J. Shan and H. Tenhu, Chem. Commun., 2007, 4580; (b) S. Takae,
Y. Akiyama, H. Otsuka, T. Nakamura, Y. Nagasaki and
K. Kataoka, Biomacromolecules, 2005, 6, 818; (c) W. B. Tan and
Y. Zhang, J. Biomed. Mater. Res., A, 2005, 75, 56.
4. (a) A. G. Kanaras, F. S. Kamounah, K. Schaumburg, C. J. Kiely
and M. Brust, Chem. Commun., 2002, 2294; (b) T. R. Tshikhudo,
Z. Wang and M. Brust, Mater. Sci. Technol., 2004, 20, 980;
(c) C.-C. You, M. De, G. Han and V. M. Rotello, J. Am. Chem.
Soc., 2005, 127, 12873; (d) M. Zheng, F. Davidson and X. Huang,
J. Am. Chem. Soc., 2003, 125, 7790; (e) C. Chen, M.-C. Daniel,
Z. T. Quinkert, M. De, B. Stein, V. D. Bowman, P. R. Chipman,
V. M. Rotello, C. C. Kao and B. Dragnea, Nano Lett., 2006, 6,
611; (f) D. Li, Q. He, H. Zhu, C. Tao and J. Li, J. Nanosci.
Nanotechnol., 2007, 7, 3089.
5. (a) D. J. Vanderah, H. La, J. Naff, V. Silin and K. A. Rubinson,
J. Am. Chem. Soc., 2004, 126, 13639; (b) A. J. Pertsin and
M. Grunze, Langmuir, 2000, 16, 8829; (c) Y. Liu,
M. K. Shipton, J. Ryan, E. D. Kaufman, S. Franzen and
D. L. Feldheim, Anal. Chem., 2007, 79, 2221; (d) X. Shi,
S. Wang, H. Sun and J. R. Baker, Soft Matter, 2007, 3, 71.
6. S. Link and M. A. El-Sayed, J. Phys. Chem. B, 1999, 103, 8410.
7. R. E. Holmlin, X. Chen, R. G. Chapman, S. Takayama and
G. M. Whitesides, Langmuir, 2001, 17, 2841.
8. S. Chen, J. Zheng, L. Li and S. Y. Jiang, J. Am. Chem. Soc., 2005,
127, 14473.
9. (a) J.-P. Xu, J. Ji, W.-D. Chen and J.-C. Shen, J. Controlled
Release, 2005, 107, 502; (b) J.-P. Xu, J. Ji, W.-D. Chen and
J.-C. Shen, Macromol. Biosci., 2005, 5, 164; (c) M. Licciardi,
Y. Tang, N. C. Billingham, S. P. Armes and A. L. Lewis, Bioma-
cromolecules, 2005, 6, 1085.
10. L. L. Rouhana, J. A. Jaber and J. B. Schlenoff, Langmuir, 2007,
23, 12799.
11. (a) J.-P. Xu, J. Ji, W.-D. Chen, D.-Z. Fan, F.-Y. Sun and J.-C. Shen,
Eur. Polym. J., 2004, 40, 291; (b) Y. Iwasaki and K. Ishihara, Anal.
Bioanal. Chem., 2005, 381, 534; (c) S. F. Rose, A. L. Lewis,
G. W. Hanlon and A. W. Lioyd, Biomaterials, 2004, 25, 5125.
12. (a) H. Takahashi, Y. Niidome, T. Niidome, K. Kaneko,
H. Kawasaki and S. Yamada, Langmuir, 2006, 22, 2;
(b) J.-J. Yuan, A. Schmid, S. P. Armes and A. L. Lewis, Langmuir,
2006, 11, 22022.
13. C. S. Weisbecker, M. V. Merritt and G. M. Whitesides, Langmuir,
1996, 12, 3763.
14. P. Chavez, W. Ducker, J. Israelachvili and K. Maxwell, Langmuir,
1996, 12, 4111.
15. (a) C. Xu, K. Xu, H. Gu, X. Zhong, Z. Gu, R. Zheng, X. Zhang
and B. Xu, J. Am. Chem. Soc., 2004, 126, 3392; (b) B. Dubertret,
P. Skourides, D. J. Norris, V. Noireaux, A. H. Brivanlou and
A. Libchaber, Science, 2002, 298, 1759.
Fig. 4 Gel image of protein adsorption assay. Lane 1: 10 mL of HS-
PC protected Au-NPs at B0.1 mM. Lanes 2 and 3 are the same
amount of Au-NPs mixed with 1 mL of BSA and lysozyme, respec-
tively. Protein concentrations are all 10 mg mLÀ1. Lanes 4–6 are
similar to lanes 1–3, except that Au-Tp nanoparticles were used.
ꢀc
This journal is The Royal Society of Chemistry 2008
3060 | Chem. Commun., 2008, 3058–3060