PEGylated gold nanoparticles functionalized with β-cyclodextrin inclusion complexes: Towards metal nanoparticle-polymer-carbohydrate cluster biohybrid materials

Article abstract of DOI:10.1071/CH10091

A cholesterol-functional trithiocarbonate reversible additionfragmentation chain transfer (RAFT) agent was synthesized and employed to generate well-defined poly(polyethylene glycol) acrylate with cholesterol chain termini using RAFT polymerization. Subsequently, the polymers were grafted onto the surface of gold nanoparticles using the trithiocarbonate functionality to bind to the gold surface. The cholesterol moieties were then modified via complexation with β-cyclodextrin. The step-by-step modification of gold nanoparticles was characterized by dynamic light scattering, attenuated total reflection infrared spectroscopy and surface plasmon resonance analysis. CSIRO 2010.

Full text of DOI:10.1071/CH10091

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2010, 63, 1245–1250
PEGylated Gold Nanoparticles Functionalized with
β-Cyclodextrin Inclusion Complexes: Towards Metal
Nanoparticle–Polymer–Carbohydrate Cluster
Biohybrid Materials
Jingquan Liu,A,B Eki Setijadi,A Yingkai Liu,A Michael R. Whittaker,A
Cyrille Boyer,A and Thomas P. DavisA,B
ACentre for Advanced Macromolecular Design (CAMD), School of Chemical Engineering,
The University of New South Wales, Sydney, NSW 2052, Australia.
BCorresponding authors. Email: jingquan.liu@unsw.edu.au, t.davis@unsw.edu.au
A cholesterol-functional trithiocarbonate reversible addition–fragmentation chain transfer (RAFT) agent was synthesized
and employed to generate well-defined poly(polyethylene glycol) acrylate with cholesterol chain termini using RAFT
polymerization. Subsequently, the polymers were grafted onto the surface of gold nanoparticles using the trithiocarbonate
functionality to bind to the gold surface.The cholesterol moieties were then modified via complexation with β-cyclodextrin.
The step-by-step modification of gold nanoparticles was characterized by dynamic light scattering, attenuated total
reflection infrared spectroscopy and surface plasmon resonance analysis.
Manuscript received: 18 February 2010.
Manuscript accepted: 23 June 2010.
Introduction
resistant to biomolecule adsorption.[16,17] Reversible addition–
fragmentation chain transfer (RAFT) polymerization has been
employed to synthesize polyPEG acrylate and other polymers
for modification of metal nanoparticles.[18–27] Gold–thiol chem-
istry has been used extensively to modify gold surface and
nanoparticles for the fabrication of sensors and devices.[28–33] A
few groups have found that the dithioester and trithiocarbonate
groups can bind directly with gold surfaces, though the interac-
tion was found to be less stable than the gold–thiol affinity.[34,35]
Therefore, polymers prepared using RAFT polymerization have
end-groups with di- and trithio-terminal functionalities that can
bind to gold surfaces without further modification.[34–37]
Several targeting ligands such as monoclonal antibodies,
sugars, hormones, peptides, vitamins, or other small organic
molecules can be used for specific biological recognition. Spe-
cific recognition events are particularly useful for therapeutic
and diagnostic applications. Targeting groups can be attached
onto polymer-modified nanoparticle surfaces by covalent bond-
ing, e.g. amine–carboxylic acid and thio–maleimide coupling
chemistry.[38,39] An alternative (and novel) functionalization
strategy is to use host–guest cyclodextrin (CD) inclusion com-
plexes to assemble targeting functionality, as described in a
recent review by van de Manakker et al.[40] The formation of
CD-inclusion complexes with cholesterol has been described
recently and can be exploited to functionalize nanoparticles or
to build up hydrogel materials. The inclusion complexes thus
formed retain their full complement of CD hydroxyl functional-
ity, and so this can be seen as the first step in using polysaccharide
clusters to functionalize nanoparticles (or surfaces in the broader
sense). Stoddart and coworkers (and others) have published sev-
eral papers describing the synthesis of polysaccharide clusters
Over the past decade, metallic nanoparticles, especially gold
nanoparticles (AuNPs) have been investigated extensively
as they possess unique electronic, optical, and catalytic
properties.[1] AuNPs can be used as multifunctional platforms
for biomedical applications such as gene and drug delivery and
contrast or imaging agents for diagnostic purposes.[2–6] Like
most other noble-metallic nanoparticles, gold produces intense
colours originating from surface plasmon resonance (SPR) phe-
nomena appearing in the visible spectrum.[7] SPR describes the
collective oscillation of the conduction band electrons on a par-
ticle surface induced by an interacting electromagnetic field.
The size and shape of the particles, local environment such as
the stabilizing ligand shell, surrounding solvent, and the charge
state of the metal cores are all factors that affect the SPR.[8,9]
Irregular gold nanoparticles such as nanorods, nanocaps, nano-
triangles and nanocages usually exhibit red-shifted SPR to
the near IR (NIR) region, leading to potential applications in
the thermotreatment of tumours via laser illumination.[10–13]
Applications of AuNPs in the biomedical field often necessi-
tate their surface stabilization and modification using organic
polymers.[14,15] The primary methods of nanoparticle and/or
polymer brush preparation are ‘grafting-to’and ‘grafting-from’.
The ‘grafting-from’ method usually involves initiation from the
nanoparticle surface, followed by polymerization to afford a
dense polymer. The ‘grafting-to’ method involves the attach-
ment of preformed polymer chains to the nanoparticle surface,
leading to less densely packed brush structures. Polyethy-
lene glycol (PEG) and polyPEG acrylate are often known as
‘stealth materials’ as they are relatively inert in physiologi-
cal media; therefore, they are often used to render surfaces
© CSIRO 2010
10.1071/CH10091
0004-9425/10/081245

RESEARCH FRONT
1246
J. Liu et al.
starting from cyclodextrin molecules.[41,42] Cyclodextrin can
thus be used as a multifunctional unit for attachment to other
groups through its multiple hydroxyl groups.[40,43,44] Cyclodex-
trin has previously been tailored with polymers to create hybrid
materials for versatile applications.[45–48] Herein, we report the
synthesis of cholesterol-terminated poly(polyethylene glycol)
acrylate (polyPEG-A) using a cholesterol-modified RAFT agent
for the modification ofAuNPs to generate a β-CD functional sur-
face as a precursor to creating nanoparticle–carbohydrate cluster
materials.
(a)
b
HO
CDCl3
a
a
b
7
6
5
4
3
2
1
0
ppm
Experimental
Materials
(b)
S
CN
Ethanethiol (Acros, >99%), potassium hydroxide (Analar),
carbon disulfide (Analar, >99%), p-toluenesulfonyl chloride
(Aldrich, 98%), N,Nꢀ-dicyclohexylcarbodiimide (DCC) (Fluka,
99%), 4-dimethylaminopyridine (DMAP) (Aldrich, 99%), p-
toluenesulfonic acid monohydrate (Sigma–Aldrich, 98.5%),
acetone (Univar, >99.5%), poly(ethylene glycol) acrylate
(PEG-A, average molecular weight 454, ethylene unit
number n = 8–9) (Aldrich), n-hexane (Ajax, 95%), 2,2ꢀ-
azobis(isobutyronitrile) (AIBN, 98%, Sigma–Aldrich), diethyl
ether(Univar, >99%), N,N-dimethylacetamide(DMAc)(Aldrich,
99%), thiocholesterol (Sigma, 95%), β-cyclodextrin (β-CD)
(Sigma, 98%), nitric acid (Ajax, 70%), hydrochloric acid (Ajax,
32%), hydrogentetrachloroaurate(iii) hydrate (HAuCl4, 99.9%,
Aldrich); deionized water used for these experiments was puri-
c
O
b
C
O
S
S
a
CDCl3
c
a
b
7
6
5
4
3
2
1
0
ppm
(c)
S
CN
fied by Milli-Q system with a resistivity of 17.9 mꢀ cm−1
,
O
C
S
S
n
sodium citrate dihydrate (Sigma–Aldrich 99%), 4,4ꢀ-azobis(4-
cyanovaleric acid) (Fluka, 98%), tetrahydrofuran (THF,
Honeywell, HPLC grade), dioxan (Tedia, 99%), [D]chloroform
(CDCl3, Cambridge Isotope Laboratories Inc., 99.8%).
O
a
O
O
CDCl3
O
8–9
Synthesis of Gold Nanoparticles (AuNPs)
AuNPs were prepared using a slight modification of a pub-
lished method.[49] Initially, all the glass apparatus was washed
with aqua regia solution (25% nitric acid, 75% hydrochloric
acid) and then rinsed with Milli-Q water several times. Milli-Q
water (100 mL) and hydrogentetrachloroaurate(iii) (HAuCl4)
were mixed and heated to boiling point with vigorous stir-
ring. Trisodium citrate dehydrate (5 mL, 1.053 g of trisodium
citrate) was then added rapidly into the boiling solution. The
resulting solution was boiled and stirred vigorously for another
30 min.The solution was then cooled down to room temperature,
accompanied by a colour change from yellow to wine red. The
particle sizes and distribution were characterized by dynamic
light scattering (DLS) and examined using transmission electron
microscopy (TEM).
a
8
7
6
5
4
3
2
1
0
ppm
Fig. 1. (a) 1H NMR spectra of cholesterol; (b) cholesterol-functional
RAFT (reversible addition–fragmentation chain transfer) agent; and
(c) the subsequent polyPEG-A (poly(polyethylene glycol) acrylate; Mn,
22400 g mol−1 from GPC (gel permeation chromatography); PDI (polydis-
persity index), 1.24).
3.30–3.38 (q, 2H, S–CH2–CH3). δC (75 MHz, CDCl3) 14.54
(CH3–CH2), 21.8 (CH3–C), 29.5 (CH2–COOH), 33.74 (C–
CH2–CH2), 35.40 (–CH2–CH3), 38.5 (CN), 45.23 (CH2S),
183.1 (COOH), 221.34 (C=S).
Synthesis of RAFT Agent, 4-Cyano-4-ethyl-trithiopentanoic
Acid (CETP)
CETP was synthesized using a precursor, bis(ethylsulfanylthio-
carbonyl) disulfide (BETD), which was synthesized according to
the method reported by Weber et al.[50] BETD (2.26 g, 82 mmol)
was added to a solution of 4,4ꢀ-azobis(4-cyanovaleric acid)
(2.77 g, 99 mmol) in ethyl acetate (40 mL). The resulting mix-
ture was refluxed for 12 h under stirring. After removal of the
solvent under vacuum, the residue was purified by silica gel
chromatography using hexane/ethyl acetate (50:50) as the elu-
ent to afford the expected product (3.78 g, 87%). δH (CDCl3,
298 K, 300 MHz) 1.33–1.38 (t, 3H, S–CH2–CH3), 1.88 (s, 3H,
R–C(–CH3)–CN), 2.33–2.71 (m, 4H, CH2–CH2, CH2–CH2),
Synthesis of Cholesterol-functionalized RAFT Agent
CETP (0.478 g, 181 mmol) was dissolved in THF (15 mL), fol-
lowed by the addition of cholesterol (0.702 g, 181 mmol). The
resulting mixture was stirred for 4 h in the presence of DMAP-
p-toluenesulfonic acid salt (DPTS) (22 mg, 0.075 mmol) and
DCC (0.450 g, 218 mmol). Solvent was removed under vacuum
and the residue was purified by silica gel chromatography with
dichloromethane/hexane (50:50) as eluent to afford the expected
product (0.88 g, 75%). The 1H NMR spectrum (CDCl3, 298 K,
300 MHz) is shown in Fig. 1a.

RESEARCH FRONT
PEGylated Gold Nanoparticles Functionalized with β-Cyclodextrin
1247
S
CN
DCC/DPTS
OH
HO
ϩ
S
S
THF
O
S
PEG-A/AIBN
Dioxane
CN
O
S
S
C
O
S
CN
AuNP
O
S
S
n
O
C
O
O
O
8–9
CN
S
C
O
S
n
C
O
ϭ
AuNP
O
S
O
O
8–9
AuNP
AuNP
β-Cyclodextrin
Cholesterol
Polymer chain
Scheme 1. Synthesis of cholesterol-terminated RAFT (reversible addition–fragmentation chain transfer) agent, subsequent
polymerization of poly(ethylene glycol) acrylate (PEG-A) and attachment onto gold nanoparticles (AuNPs) to tailor the AuNP
surface with cholesterol molecules, and the subsequent complexation with β-cyclodextrin (β-CD).
Homopolymerization of PEG-A Controlled
by the Cholesterol-functionalized RAFT
β-Cyclodextrin Inclusion Complex with
Cholesterol-functionalized AuNPs
A solution of PEG-A (1.484 g, 3.27 × 10−3 mol), cholesterol-
RAFT agent (21 mg, 3.27 × 10−5 mol), and AIBN (1.4 mg,
8 × 10−6 mol) in dioxan(5 mL) was prepared.The resulting mix-
ture was deoxygenated with nitrogen for 30 min, followed by
incubation in a water bath at 65◦C. Six samples were taken from
the incubating mixture using a degassed needle at 0.5, 1, 2, 3, 4,
and 5 h polymerization times. The monomer conversion for each
polymerization sample was determined by 1H NMR in CDCl3.
The polymers were purified by precipitation in diethyl ether
three times before drying under vacuum. The pure polymer was
characterized by 1H NMR and gel permeation chromatography
(GPC).
The polymer-coated AuNPs were redispersed in water (10 mL)
and β-CD (4 mg, 3.52 × 10−6 mol) was added under stirring.The
mixture was stirred for another 5 h and the particles were purified
by centrifugation at 20800 g for 20 min at 5◦C.The same process
was repeated three times. The particles were characterized by
DLS, AT-IR, UV-visible spectroscopy, and TEM.
Analyses
Gel permeation chromatography was performed in DMAc
(0.03% w/v LiBr, 0.05% butylated hydroxy toluene stabilizer)
at 50◦C (flow rate: 0.85 mL min−1) using a Shimadzu modular
system composed of a DGU-12A solvent degasser, an LC-10AT
pump, a CTO-10A column oven, and an RID-10A refractive
index detector. The system was equipped with a Polymer Lab-
oratories (PL) 5.0-mm bead-size guard column (50 × 7.8 mm2)
followed by four 300 × 7.8 mm2 linear PL columns (105, 104,
103, and 500 g mol−1). Calibration was performed with nar-
rowly polydisperse polystyrene standards ranging from 500 to
Grafting of Cholesterol-functionalized PEG-A Polymer
to AuNPs
Cholesterol-terminated PEG-A polymer (10 mg, 5 × 10−7 mol)
was dissolved in water (10 mL) before dropwise addition to the
previously prepared AuNPs solution (10 mL, 0.05 mg mL−1),
followed by stirring for 3 h. The particles were purified by repet-
itive centrifugation and redispersion with water for three cycles.
The particles were characterized by DLS, attenuated total reflec-
tion infrared spectroscopy (ATR-IR), UV-visible spectroscopy,
and TEM.
106 g mol−1
.
1H NMR spectra were obtained using a Bruker AC300F
(300 MHz) spectrometer or a Bruker DPX300 (300 MHz)
spectrometer.

RESEARCH FRONT
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J. Liu et al.
Table 1. Results for the homopolymerization of poly(ethylene glycol)
acrylate (PEG-A) using cholesterol-functional RAFT (reversible
addition–fragmentation chain transfer) agent
Electrospray ionization mass spectroscopy (ESI-MS) was
carried out on a Finnigan LCQ Deca mass spectrometer (Thermo
Finnigan, San Jose, CA, USA) equipped with an atmospheric
pressure ionization source operating in the nebulizer-assisted
electrospray mode.
A
B
Time [h]
Conversion [%]
Mn
ln[Mo/Mt]
Mn
PDI
TheAuNPs sizes before and after modification were analyzed
at 25◦C using DLS on a Malvern analyzer (Laser type: HeNe gas
laser; beam wavelength 633 nm).
0.5
1
2
3
4
11.2
30.9
56.1
69.8
76.2
81.2
3600
8900
15700
19300
21000
22400
0.12
0.37
0.82
1.16
1.44
1.68
3100
8000
12800
17500
18600
20200
1.23
1.19
1.24
1.21
1.25
1.24
UV-visible spectra were recorded using a Cary 300 spectro-
photometer (Bruker) equipped with a temperature controller.
ATR-IR spectra were obtained using a Bruker Spectrum BX
ATR-IR system using diffuse reflectance sampling accessories.
Transmission electron microscopy images were obtained
on JEOL1400 TEM at an accelerating voltage of 100 kV. Phos-
photungsten acid was used as contrast agent for imaging of
polymer-modified AuNPs.
5
AMeasured by gel permeation chromatography (GPC); Bmeasured from
1H NMR. PDI, polydispersity index.
(a)
100
80
60
40
20
0
1.8
1.6
1.4
1.2
1
Results and Discussion
Thesynthesisofcholesterol-terminatedRAFTagent,polyPEG-A
and the subsequent modification of AuNPs are illustrated in
Scheme 1. The synthesis of cholesterol-functional RAFT agent
was achieved by an esterification reaction in the presence of
DCC and DPTS. The utilization of neutral DPTS instead of the
weakly basic DMAP was to minimize any decomposition of the
trithiocarbonate core of the RAFT agent. The successful synthe-
sis of the cholesterol-terminated RAFT agent was evidenced by
1H NMR spectra, as shown in Fig. 1a and 1b. The peak signals
at 5.2–5.3 ppm (a), 4.5–4.6 ppm (b), and 3.2–3.3 ppm (c) corre-
spondtotheprotonofthecycloalkeneincholesterol, themethane
proton of cholesterol (linked to the RAFT functionality) and the
two protons adjacent to the RAFT S atom respectively. The shift
of the signal assigned to the methine proton (b) in cholesterol
from 3.5 ppm (Fig. 1a) to 4.55 ppm (Fig. 1b) after esterification
confirmedasuccessfulcouplingreaction.Thesuccessfulsynthe-
sis of the cholesterol-functional RAFT agent was also supported
by the presence of a parent sodium ion at m/z 654.72 (calc. m/z
654.65) measured by ESI-MS.
0.8
0.6
0.4
0.2
0
0
1
2
3
4
5
6
Polymerization time [h]
(b)
1.5
1.4
1.3
1.2
1.1
1
40000
30000
20000
10000
0
Homopolymerization of PEG-A Controlled by the
Cholesterol-functionalized RAFT Agent
The results of the synthesis of polyPEG-A using the cholesterol-
functional RAFT agent are summarized in Table 1 and Fig. 2.
It is evident that the monomer conversion increased concomi-
tantly with polymerization time, and the radical concentration
remained constant with conversion as indicated by the pseudo-
first-orderplot(Fig. 2a). Fig. 2bshowsthatboththeexperimental
(measured by GPC) and the theoretical molecular weights (MW)
were found to be proportional to the monomer conversion. The
theoretical MW values were slightly higher than the experimen-
tal ones and the polydispersity indices (PDI) of the purified
polyPEG-A were less than 1.25, indicating a well-controlled
polymerization, consistent with the known traits of living rad-
ical polymerization.[51–53] The MWs obtained from GPC and
1H NMR are quite consistent, indicative of reliable molecular
weight characterization (Table 1). A purified polyPEG-A (Mn
22400 g mol−1 from GPC; PDI 1.24) was analyzed by 1H NMR
using CDCl3 as the deuterated solvent (Fig. 1b). The signal at
5.3 ppm can be assigned to the proton of cycloalkene in choles-
terol, showing that the integrity of the cholesterol structure is
maintained after polymerization.
0
20
40
60
80
100
Conversion [%]
Fig. 2. Polymerization of poly(ethylene glycol) acrylate (PEG-A) using
the cholesterol-functional RAFT (reversible addition–fragmentation chain
transfer) agent in dioxan at 65◦C ([M]/[RAFT]/[AIBN] = 100:1:0.25
(AIBN, 2,2ꢀ-azobis(isobutyronitrile)). (a) Monomer conversion at vary-
ing polymerization times. (b) Molecular weight (MW) and polydispersity
indices (PDI) of the polyPEG-A (poly(polyethylene glycol) acrylate) against
monomer conversion (filled and empty diamonds represent the experimental
(obtained by GPC (gel permeation chromatography)) and theoretical MW
values, respectively, whereas the filled triangles represent PDIs).
Synthesis of Gold Nanoparticles and the Subsequent
Modification with Cholesterol-terminal Polymer and β-CD
The synthesis of citrate-stabilizedAuNPs was carried out follow-
ing a literature method (see Experimental section),[49] resulting
in relatively uniform AuNPs with an average size of 18 nm

RESEARCH FRONT
PEGylated Gold Nanoparticles Functionalized with β-Cyclodextrin
1249
(a) 0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
(a)
(b)
528 nm
524 nm
100 nm
20 nm
400
450
500
550
600
650
700
Wavelength [nm]
30
25
20
15
10
5
(c)
(b)
AuNPs after β-CD attachment
AuNPs after polymer grafting
0.10
0.08
0.06
0.04
0.02
0.00
0
10 12 14 16 18 20 22 24 26 28 30 32
Average size [nm]
Ϫ0.02
4000 3500 3000 2500 2000 1500 1000
Wavelength [cmϪ1
Fig. 3. Transmission electron microscopy (TEM) image of gold nanoparti-
cles (AuNPs) before (a), and after (b) modification with cholesterol-terminal
polyPEG-A (poly(polyethylene glycol) acrylate) (phosphotungsten acid was
used as contrast agent for imaging of polymer-modified AuNPs); and
(c) dynamic light scattering (DLS) analysis of AuNPs before (dashed curve)
and after (dotted curve) polymer grafting and subsequent β-cyclodextrin
(β-CD) complexation (solid curve).
]
Fig. 4. (a) UV-visible spectra of unmodified gold nanoparticles (AuNPs)
(dashed curve) and after attachment of polymers (solid curve). (b) Attenu-
ated total reflection infrared (ATR-IR) spectra of polymer modified AuNPs
(dashed curve) and after further complexation with β-cyclodextrin (β-CD)
(solid curve).
as characterized by TEM, as shown in Fig. 3a. A few groups
have found that the dithioester and trithiocarbonate groups can
bind directly with gold surfaces, although the interaction was
found to be less stable than the gold–thiol affinity.[24] No colour
change was observed when the AuNPs were modified with
cholesterol-functionalized PEG-A polymer in aqueous solu-
tion, indicating minimal agglomeration. The TEM image of the
polymer-modified AuNPs revealed a light polymer corona as
shown in the inset of Fig. 3b; this light corona might be an arte-
fact caused by Fresnel fringes, and therefore cannot confirm the
presenceofpolymer. However, DLSmeasurementsconfirmedan
increase in the hydrodynamic diameter of the AuNPs after poly-
mer grafting from 18 to 20 nm. Further β-CD complexation onto
the cholesterol groups was hard to detect by light scattering as the
size change was too small to detect reliably (Fig. 3b). However,
ATR-IR analysis (described below) furnished some evidence of
successful β-CD attachment. Zeta potential measurements were
also performed along with the DLS analysis to monitor the step-
by-step modification of the AuNPs. The zeta potential of the
unmodified AuNPs was measured to be ∼−40 mV, correspond-
ing to the presence of negatively charged citrate ions stabilizing
the GNPs. After polymer grafting, the zeta potential dropped
to ∼0 mV, indicating the successful attachment of polymers on
the AuNPs surface. Further attachment of β-CD did not cause
further zeta potential change, as expected.
corresponding to the frequency at which a plasmon resonance
occurs within the gold.[7] It has been reported that plasmon
adsorption for alkanethiol-coated spherical silver nanoparticles
is hardly influenced by modification with alkanethiol and only
slightly red-shifted for gold nanoparticles.[54] In our work, graft-
ing the AuNPs with cholesterol-functionalized polyPEG caused
a 4-nm red shift compared with that of unmodified AuNP pre-
cursors at 524 nm (Fig. 4a). This slight absorption shift can be
attributed to a refractive index variation caused by the surface-
grafted polymer layer on AuNPs, in accord with previously
reported results.[8,9,55]
The presence of a grafted polyPEG-A layer on theAuNPs was
confirmed byATR-IR analyses.As shown in Fig. 4b, theATR-IR
analysis revealed characteristic polyPEG-A absorption signals:
2900–2850 cm−1 (CH2 stretching), 1730 cm−1 (C=O bond),
1480 cm−1 (C–O ether bond), 1041 cm−1 (C–O–C stretching).
The subsequent complexation with β-CDon cholesterol bound to
the gold surface was clearly evidenced by the ATR-IR analysis
(Fig. 4b). The AuNPs modified with β-CD exhibited a signif-
icant increase in the signals at 3200–3600 cm−1, originating
from the O–H stretching of the β-CD, and signals observed
at 1550–1600 cm−1, attributed to typical O–H bending from
β-CD.[56]
In conclusion, we have demonstrated a facile method
for the synthesis of cholesterol-terminal polyPEG-A using a
cholesterol-functionalized RAFT agent. These polymers were
It is well known that when AuNPs are small enough, their
colour is ruby red as they strongly absorb green light at ∼520 nm,

RESEARCH FRONT
1250
J. Liu et al.
grafted onto gold surfaces using the trithiocarbonate end-groups.
Further facile functionalization was achieved using host–guest
chemistry with β-CD. This work points towards further com-
plex material syntheses exploiting the retained OH functionality
on the CD to build up carbohydrate clusters applicable to
multiligand recognition events and binding.
[25] M. Nuopponen, H. Tenhu, Langmuir 2007, 23, 5352. doi:10.1021/
LA063240M
[26] C. Boyer, M. R. Whittaker, K. Chuan, J. Liu, T. P. Davis, Langmuir
2010, 26, 2721. doi:10.1021/LA902746V
[27] C. Boyer, M. R. Whittaker, V. Bulmus, J. Liu, T. P. Davis, NPG Asia
Materials 2010, 2, 23. doi:10.1038/ASIAMAT.2010.6
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[30] J. J. Gooding, R. Wibowo, J. Q. Liu, W. R. Yang, D. Losic, S. Orbons,
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Acknowledgements
T.P.D. thanks the Australian Research Council for a Federation Fellow-
ship Award. J.L. acknowledges the UNSW Vice Chancellor’s Post-doctoral
Research Fellowship.
[31] J. Q. Liu, J. J. Gooding, M. N. Paddon-Row, Chem. Commun. 2005,
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