Pillar[5]arene-mediated synthesis of gold nanoparticles: Size control and sensing capabilities

Article abstract of DOI:10.1002/chem.201402073

We present a simple procedure for the synthesis of quasi-spherical Au nanoparticles in a wide size range mediated by macrocyclic host molecules, ammonium pillar[5]arene (AP[5]A). The strategy is based on a seeded growth process in which the water-soluble

Full text of DOI:10.1002/chem.201402073

DOI: 10.1002/chem.201402073
Full Paper
&
Sensors
Pillar[5]arene-Mediated Synthesis of Gold Nanoparticles: Size
Control and Sensing Capabilities
[a]
[a]
[b]
[a]
Verꢀnica Montes-Garcꢁa, Cristina Fernꢂndez-Lꢀpez, Borja Gꢀmez, Ignacio Pꢃrez-Juste,
[b]
[a, c, d]
[a]
[a]
Luis Garcꢁa-Rꢁo, Luis M. Liz-Marzꢂn,
Jorge Pꢃrez-Juste,* and Isabel Pastoriza-Santos*
Abstract: We present a simple procedure for the synthesis
of quasi-spherical Au nanoparticles in a wide size range
mediated by macrocyclic host molecules, ammonium pil-
lar[5]arene (AP[5]A). The strategy is based on a seeded
growth process in which the water-soluble pillar[5]arene un-
dergoes complexation of the Au salt through the ammoni-
um groups, thereby avoiding Au nucleation, while acting as
a stabilizer. The presence of the pillar[5]arene onto the Au
nanoparticle particle surface is demonstrated by surface-en-
hanced Raman scattering (SERS) spectroscopy, and the most
probable conformation of the molecule when adsorbed on
the Au nanoparticles surface is suggested on the basis of
theoretical calculations. In addition, we analyze the host–
guest interactions of the AP[5]A with 2-naphthoic acid (2NA)
1
by using H NMR spectroscopy and the results are compared
with theoretical calculations. Finally, the promising synerget-
ic effects of combining supramolecular chemistry and metal
nanoparticles are demonstrated through SERS detection in
water of 2NA and a polycyclic aromatic hydrocarbon, pyrene
(PYR).
Introduction
compared with the most traditional macrocyclic hosts: High
selectivity toward guests (provided by their high symmetry
and rigidity), easy functionalization, and solubility in organic
solvents. Therefore, this new type of macrocyclic compounds
The development of supramolecular chemistry relies on the
design and synthesis of macrocyclic host molecules. A number
of successful examples have been reported in the literature in-
[8]
has become very popular since their invention in 2008.
[
1]
[2]
[3]
cluding crown ethers, cyclodextrins, cucurbit[n]urils, calix-
On the other hand, there has been common interest in the
synthesis and development of new applications based on
nanomaterials. For instance, there has been tremendous prog-
ress over the past two decades in the synthesis of gold and
[
4]
[5,6]
arenes, and more recently, pillar[n]arenes.
These macrocy-
cles allowed not only the development of new materials based
on the theory of self-assembly at the molecular level, but also
the binding of chemical moieties through host–guest noncova-
silver nanoparticles of various sizes and shapes and with good
[
7]
[9–11]
lent interactions. Pillar[n]arenes present several advantages as
yield and monodispersity,
which led to significant progress
in different areas due to their unique properties and applica-
tions in electronics, photonics, catalysis, sensing, and medicine.
However, a prerequisite for every possible application is the
proper functionalization of the nanoparticles surface, because
this may determine the stability (against aggregation or degra-
dation), biocompatibility, the assembly into extended nano-
structures and functional systems, targeting, sensing capabili-
ties, and so on.
+
+
[
a] V. Montes-Garcꢀa, C. Fernꢁndez-Lꢂpez, Dr. I. Pꢃrez-Juste,
Prof. L. M. Liz-Marzꢁn, Dr. J. Pꢃrez-Juste, Dr. I. Pastoriza-Santos
Departamento Quꢀmica Fꢀsica
Universidade de Vigo
6310 Vigo (Spain)
E-mail: juste@uvigo.es
pastoriza@uvigo.es
3
[
b] B. Gꢂmez, Prof. L. Garcꢀa-Rꢀo
Departamento de Quꢀmica Fꢀsica y
Centro Singular de Investigaciꢂn en
Quꢀmica Biolꢂgica y
A very attractive application of macrocyclic host molecules is
their combination with nanoparticles, since they can be used
to enhance the colloidal stability while providing molecular se-
lectivity toward binding of guest molecules. In the case of
metal nanoparticles, this can be exploited for improving plas-
monic sensing applications, such as those related to surface
enhanced Raman scattering (SERS). Several approaches toward
nanoparticle–macrocycle hybrids involve the surface modifica-
tion of preformed particles. For instance, Kaifer et al. reported
the surface modification of gold nanoparticles with cyclodex-
trins and studied their assembly and phase-transfer possibili-
Materiales Moleculares (CIQUS)
Universidad de Santiago
5782 Santiago (Spain)
1
[
c] Prof. L. M. Liz-Marzꢁn
Bionanoplasmonics Laboratory
CIC biomaGUNE, Paseo de Miramꢂn 182
2
0009 Donostia, San Sebastiꢁn (Spain)
[
d] Prof. L. M. Liz-Marzꢁn
Ikerbasque, Basque Foundation for Science
8011 Bilbao (Spain)
4
+
[
] These authors contributed equally to this work
[12,13]
ties.
Metal nanoparticles have also been modified with cal-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201402073.
ixarenes, thereby enhancing their dispersion and self-assembly
Chem. Eur. J. 2014, 20, 1 – 7
1
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
[
14]
into well-defined structures,
but also acting as effective
SERS detection in water of 2NA and a polycyclic aromatic hy-
drocarbon, pyrene (PYR).
supramolecular hosts for detection based on SERS. Guerrini
et al. have functionalized Ag nanoparticles with calixarenes for
SERS detection of polycyclic aromatic hydrocarbons
[
15,16]
(
[
PAHs).
Manahan and Scherman et al. employed cucurbit- Results and Discussion
n]urils to functionalize gold nanoparticles
[17]
and evaluated
Synthesis of gold nanoparticles with size control
their self-assembly capabilities for quantitative SERS analysis,
although no control over the self-assembly process was
The growth of spherical gold nanoparticles requires a good
control over the nucleation and growth processes. The seeded
growth method has been demonstrated to be the most relia-
ble method to achieve size control with rather low polydispers-
ity. Among the existing approaches, the seeded growth
method based on using ascorbic acid as a mild reducing agent
and quaternary ammonium surfactants (usually cetyl trimethyl-
[
18]
shown. Few reports can also be found regarding the synthe-
sis of small gold nanoparticles stabilized by either pillar[5]ar-
[
19,20]
[21]
enes
or cucurbit[n]urils
but no size or shape control
have been described so far. Nevertheless, the synthesis of
metal nanoparticles mediated by supramolecular chemistry
with size and shape control can be considered as a quite
promising approach to take advantage of synergetic effects.
Here, we show for first time the use of macrocyclic host mol-
ecules as capping agents for the synthesis of quasi-spherical
Au nanoparticles in a wide size range (see Scheme 1), through
[22,23]
ammonium bromide, CTAB) as stabilizers,
additionally pro-
vides shape control (spheres, rods, plates, concave cubes,
[24]
etc.). A key element in this method is the complexation of
the gold salt precursor with the quaternary ammonium group
[25]
of the surfactant, which increases its redox potential. There-
À
fore, upon addition of ascorbic acid, [AuCl ] is selectively re-
4
À
duced to [AuCl ] and just after seed addition further reduc-
2
0
tion into Au proceeds catalytically on the seed surfaces.
We selected for this work a cationic water-soluble pillar[5]ar-
ene, which has quaternary ammonium groups at both rims
(
hereafter is named ammonium pillar[5]arene or AP[5]A; see
[26]
Scheme 1), to act as stabilizer. As in the case of CTAB, addi-
À
tion of [AuCl4] ions is expected to yield formation of an ion
pair with the quaternary ammonium groups of the macrocycle.
Indirect evidence of such complexation is provided by the ab-
sence of nucleation upon addition of ascorbic acid, meaning
III
I
that it is only able to reduce Au into Au (see Figure S6, the
I
0
Supporting Information). The final reduction of Au into Au
occurs only after the addition of gold seeds, in a similar fashion
to the CTAB-mediated growth. Thus, quasi-spherical Au nano-
particles with a narrow size distribution can be readily pre-
pared (see Figure 1), whereas a second population of plates
and rods was also obtained through the CTAB-mediated
[23]
growth. Although the process is similar to that with CTAB,
I
0
the catalytic reduction of Au into Au is faster (20–30 min for
CTAB, but 3–5 min for AP[5]A). Therefore, to obtain monodis-
perse samples or avoid free nucleation, careful temperature
control (around 258C) and stepwise ascorbic acid addition are
required (see the Experimental Section in the Supporting Infor-
mation). This protocol can also be used to grow larger Au par-
Scheme 1. Schematic representation of the synthesis of quasi-spherical Au
nanoparticles through the AP[5]A-mediated seeded growth process and
their sensing capabilities based on host–guest interactions.
III
0
a seeded growth method. The strategy is based on a water-
soluble pillar[5]arene bearing ammonium groups (hereafter
ammonium pillar[5]arene or AP[5]A), which form a complex
with the Au salt, thereby avoiding Au nucleation, while acting
as a stabilizer. The presence of the pillar[5]arene onto the parti-
cle surface can easily be demonstrated by SERS spectroscopy.
The most probable conformation of the molecule when ad-
sorbed on the Au nanoparticles surface was suggested by the-
oretical calculations. The host–guest interactions of the AP[5]A
ticles by simply varying the Au /Au molar ratio. Figure 1
shows representative TEM images of Au spheres with sizes of
33, 78, and 95 nm (see histograms in Figure S7, the Supporting
Information), all of which were obtained by seeded growth of
20 nm seeds (Figure S8, the Supporting Information) in one
III
0
step, with Au /Au molar ratios of 2.3, 52, and 88.8, respective-
ly. The obtained diameters, which closely match the calculated
[27]
diameters,
together with the relatively low polydispersity
(around 10%) suggest that no nuclei are formed and only
seeded growth occurs. Although the spherical shape is pre-
served for sizes up to 95 nm, larger spherical particles can only
be obtained through two or three growth steps. As mentioned
1
with 2-naphthoic acid (2NA) were studied by H NMR spectro-
scopic titrations and the results were compared with theoreti-
cal calculations. Finally, the sensing capability of the AP[5]A-
stabilized Au nanoparticles was demonstrated through the
I
0
above, the catalytic reduction of Au to Au in the presence of
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
2
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
The adsorption of AP[5]A was characterized by Zeta poten-
tial measurements, which revealed a positive value of +(19.5Æ
1.7) mV. Since the starting Au seeds presented negative charge
(
around À30 mV) due to the presence of citrate ions on the
metal surface, the positive charge of the resulting particles in-
dicates that the adsorption of AP[5]A onto the metal surface is
[30]
likely to be mediated by the bromide ions. Additional evi-
dence for the adsorption of pillar[5]arene was provided by
SERS data. Figure 3 shows the Raman spectrum of a pillar[5]ar-
ene solution and the corresponding SERS spectrum of the col-
loid. Assignment of the bands was performed on the basis of
DFT calculations (see more details in Figure 3A and in the Sup-
porting Information: the Experimental Section and Table S1).
Thus, the measured Raman spectrum of AP[5]A (Figure 3B) is
À1
mainly dominated by the aromatic ring stretching (1613 cm ),
À1
ring breathing (1267 cm ), ring deformation (956 and
Figure 1. A–C) Representative TEM images of AP[5]A-stabilized Au nanoparti-
cles prepared by a seeded growth method, with average sizes of (33.6Æ4.0)
À1
À1
541 cm ), CH bending (1449 and 793 cm ) and CN stretching
(
A), (77.5Æ7.0) (B), and (94.8Æ8.5) nm (C). All scale bars correspond to
À1
(
877 and 722 cm ). As shown in Figure 3C, the SERS spectrum
2
00 nm. (D) Extinction spectra of the Au nanoparticles shown in images A–
C: (c) (A), (b) (B), and (d) (C). All spectra were normalized to 1 at
00 nm to facilitate comparison.
for AP[5]A-stabilized Au nanoparticles (NPs) displays additional
signals mainly associated with CH bending of the chain bear-
4
ing the ammonium groups (1537, 1443, 1394 1335, 1311, 1207,
À1
1
137, and 1073 cm ) and ring vibrations (1588, 758, 700, 661,
À1
AP[5]A is rather fast (several minutes), which leads to the
growth of tips when using large molar ratios of Au salt to Au
seeds (>106), due to fast overgrowth (leading, eventually, to
star-shaped nanoparticles). Figure 2 shows representative TEM
images of nanoparticles of about 120 nm in diameter prepared
in a single growth step (A) and in two sequential growth steps
622, 573, 509, and 424 cm ; a detailed description of the vi-
brational assignments can be found in the Supporting Informa-
tion, Table S1). Thus, SERS enhancement of the vibrations asso-
ciated with the ammonium side chains is indeed related to ad-
sorption through the vicinal bromide atoms. On the other
hand, the SERS enhancement is especially significant for the
À1
(B; 20 to 60 to 120 nm). The formation of spikes is clearly seen
ring out-of-plane deformation at 700 cm , ring breathing at
À1
for the one-step growth, whereas spherical nanoparticles form
when the growth is performed in two sequential steps. As ex-
pected, such morphological changes are reflected in the opti-
cal response of the colloids, see Figure 2C. The presence of
tips and spikes produces a strong redshift and broadening of
the extinction spectrum in contrast with the narrow band for
1266 cm and for the CH bending of the lateral chain at 1394
À1
and 1537 cm . This indicates that the central aromatic rings of
the AP[5]A are perpendicularly oriented on the Au surface as
[31]
a preferential configuration.
Assuming that the molecules are adsorbed to the gold sur-
face through the bromide ions, in principle it is possible to
identify up to three different conformations; two of which
would have the pillar[5]arene cavity oriented parallel to the
gold surface, whereas the other one features the cavity per-
pendicular to the gold surface, as schematically depicted in
[
28,29]
quasi-spherical particles (lmax =700 vs. 600 nm).
However,
the spiky Au nanoparticles are not stable and evolve toward
more rounded shapes after several days (see Figure S9, the
Supporting Information).
Figure 2. Representative TEM images of about 120 nm Au nanoparticles pre-
pared in A) a single growth step, or B) in two growth steps; C) Vis-NIR ex-
tinction spectra of the particles prepared in a single step (b) or after se-
quential growth (c).
Figure 3. A) Calculated Raman, B) measured Raman, and C) SERS spectra of
ammonium pillar[5]arene.
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
3
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
Figure 4. A–C) Proposed configurations for the ammonium pillar[5]arene
when it is adsorbed on a gold monolayer: one perpendicular (A) and parallel
1
(B,C) to a gold surface; D) Variation of the adsorption energy for the differ-
Figure 5. Top: Chemical structure of 2-naphthoic acid. Bottom: H NMR spec-
ent AP[5]A configurations A–C (as indicated in the labels) with the number
of gold layers. The distance of the molecule to the metal surface was 2.5 ꢅ.
tra (D O, 293 K, 400 MHz) of 2-naphthoic acid (2 mm) with different concen-
trations of ammonium pillar[5]arene: a) 0.0, b) 0.3, c) 0.5, d) 0.7, e) 1.0, f) 2.0,
2
and g) 3.0 mm.
1
Figure 4. The most probable conformation was identified by
theoretical determination of the adsorption energy of an
AP[5]A molecule on a gold monolayer as a function of the dis-
tance between the molecule and the metal surface, r (Fig-
ure S10, the Supporting Information). All possible conforma-
tions show a minimum in the adsorption energy at a distance
of 2.5 ꢅ, but the adsorption energy is more negative when the
pillar[5]arene cavity is perpendicularly adsorbed to the gold
surface. Analysis of the influence of the number of gold layers
on the adsorption energy for the three configurations (Fig-
ure S10, the Supporting Information) shows a decrease of the
adsorption energy with increasing the number of gold layers
were investigated by using H NMR spectroscopy. Figure 5
1
shows the H NMR spectroscopic titration spectra of pillar[5]ar-
ene in a 2 mm solution of 2NA in water. Whereas the increase
of AP[5]A concentration barely affects (ca., Dd=0.1 ppm) the
proton NMR spectroscopic signals corresponding to H , H ,
a
b
and H , thus suggesting that they are located outside of the
c
macrocyclic cavity, the NMR spectroscopic signals of H and He
d
are shifted upfield considerably (Dd=0.8 and 1.75 ppm, re-
spectively). These upfield chemical shifts are a consequence of
the interaction between the CÀH bonds of 2NA and the large
fraction of p surfaces offered by the pillar[5]arene cavity. Be-
sides the more pronounced shift for H than for H protons,
e
d
(
Figure 4). Thus, these theoretical calculations suggest the per-
this also suggests that the host–guest complex is located close
to the aromatic ring region, that is, forming a [2]pseudorotax-
ane. This conformation might also favor the electrostatic inter-
action between the cationic ammonium group from pillar[5]ar-
ene and the carboxylic group from 2NA. Finally, it is remark-
able that the chemical shifts of H and H barely changed (Dd
pendicular adsorption of pillar[5]arene configuration as the
most probable configuration, in agreement with the results ob-
tained by SERS.
e
d
Host–guest chemistry and sensing capabilities
ꢀ
0.1 ppm) when the molar ratio of pillar[5]arene to 2NA in-
Within supramolecular chemistry, the macrocyclic host–guest
chemistry can be used to bind two chemical moieties to each
other, through noncovalent interactions. The host–guest com-
plex formation involving the above-mentioned macrocycles
creased to 3:2 (see Figure 5). This indicates that the stoichiom-
etry of the complex between the AP[5]A and 2NA has an 1:1
stoichiometry and, more importantly, that more than 90% of
the guest molecules were already encapsulated at equimolar
concentrations, meaning that they have a relatively high bind-
ing constant.
[
32]
takes place usually in aqueous media. In particular, the pres-
ence of ten positive charges on the AP[5]A macrocycle render
its host–guest chemistry to be mainly driven by hydrophobic
To further confirm the proposed conformation, we per-
formed B3LYP/6-31G* geometrical optimizations for the two
possible orientations of the 2-naphthoate anion within the
AP[5]A cavity, that is, with the carboxylate group oriented to-
wards both inside and outside the cavity (see Figure S11, the
Supporting Information). We also computed theoretical values
[
20,26]
and electrostatic interactions.
Therefore, prior to evaluat-
ing the sensing capabilities of the AP[5]A-stabilized gold nano-
particles, we studied the inclusion properties of this pillar[5]ar-
ene with a guest of interest. We selected 2-naphthoic acid
(
2NA, see Figure 5Top) as a model guest, not only because it
1
presents a low adsorption capability on citrate-stabilized metal
colloids, but also because it contains a negatively charged
functional group (a carboxyl that is deprotonated at pH above
of the H isotropic magnetic shielding for both orientations
and the results obtained were compared with those for the
isolated 2-naphoate anion (see Table S2, the Supporting Infor-
[
33]
1
its pKa).
The host–guest interactions of AP[5]A with 2NA
mation). Interestingly, the theoretical H magnetic shielding
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
4
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
values show an agreement with the experimental observations
only if the carboxylate group is oriented to the outside of the
pillar[5]arene cavity. In this situation the nuclei (H and H ) that
Supporting Information). Significantly, only the bands associat-
ed with in-plane ring vibrations at 1391, 1022, 772, and
À1
519 cm are enhanced in the SERS spectra. This suggests
d
e
are close to the aromatic rings are more shielded, that is, they
appear at smaller chemical shifts than in the isolated 2-naph-
thoate anion (around d=2–3 ppm). However, for the opposite
orientation with the carboxylate group clearly inside the cavity,
a perpendicular orientation of the 2-naphthoate anion relative
to the gold surface, which is in agreement with the proposed
perpendicular adsorption preference of AP[5]A over the gold
À1
surface. Finally, SERS signals at 770 and 1388 cm are perfectly
1
the theoretical values of the H magnetic shieldings for the
recognized down to 1 mm. It should be pointed out as an im-
portant advantage that the detection can be performed direct-
ly in the colloidal suspension in water, which contributes to
the reliability and reproducibility of the detection.
nuclei closer to the carboxylate group would be larger than in
the isolated 2-naphthoate anion (around d=4 ppm).
So far we have proven that the AP[5]A is adsorbed onto the
quasi-spherical Au nanoparticles with the pillar[5]arene cavity
perpendicularly oriented to the metal surface. In addition, we
have also confirmed the ability of this water-soluble pillar[5]ar-
ene to bind 2NA, forming a [2]pseudorotaxane. With this infor-
mation at hand, we are ready to analyze the sensing ability of
the pillar[5]arene-stabilized gold nanoparticles towards 2NA by
SERS. On one hand, it is important to note that 2NA cannot be
detected by SERS spectroscopy using citrate-stabilized Au (or
Finally, we analyzed the possibility of detecting a polycyclic
aromatic hydrocarbon, such as pyrene, again using the AP[5]A-
stabilized Au nanoparticles in solution. PYR belongs to a family
of hazardous pollutants with a condensed benzene ring struc-
[16]
ture, which confers a very low affinity by metals. Therefore,
its detection by SERS requires the presence of an appropriate
host, that is, with strong affinity towards plasmonic surfaces
and a high selectivity for interaction with a molecule contain-
ing four benzene rings. In agreement with previous assign-
[
33]
Ag) nanoparticles, as reported in the literature, because of
its low affinity to metallic surfaces, as well as electrostatic re-
pulsions. On the other hand, 2NA presents several characteris-
tic Raman signals that do not overlap with those from AP[5]A
[16]
ments, the Raman spectrum of PYR (Figure 7A) is dominated
À1
by ring C=C stretching (1407 and 1242 cm ), ring deformation
À1
À1
(409 cm ), ring breathing (594 cm ), ring C=C stretching
À1
À1
(see the calculated Raman spectra for 2NA and AP[5]A in Fig-
(1594 and 1628 cm ), and CH bending (1067 and 1143 cm ).
Most of the signals do not overlap with those from AP[5]A (see
the calculated Raman spectra for PYR and AP[5]A in Figure S14,
the Supporting Information), therefore PYR can in principle be
detected by SERS using AP[5]A as the host molecule. Fig-
ure 7B–D shows the SERS spectra of PYR after subtracting the
AP[5]A peaks (the SERS spectra including AP[5]A contributions
are shown in Figure S15, the Supporting Information). Remark-
ably, the most intense signals in the SERS spectra correspond
to ring vibrational modes of ag symmetry (see Table S4, the
Supporting Information). Again, this can be explained if pyrene
is oriented perpendicularly to the metal surface because for
ure S12, the Supporting Information). In agreement with previ-
[
33,34]
ous assignments,
the Raman spectrum for the 2-naphthoic
acid (Figure 6A) is characterized by ring stretching (1633, 1391,
À1
À1
and 1022 cm ), CH bending (1470 cm ), ring breathing
À1
À1
(
772 cm ), and ring deformation (519 cm ). Additional vibra-
tional assignments for CH bending based on theoretical DFT
calculations can be found in the Supporting Information (see
Table S3). As shown in Figure 6, a well-defined SERS spectrum
was obtained when 2NA was added to AP[5]A-stabilized 80 nm
Au nanoparticles in water at pH above the pK (4.17) of 2NA. It
a
also confirms the complexation between 2NA and pillar[5]ar-
ene. To facilitate the analysis, Figure 6 shows the SERS spectra
after subtracting the SERS signals from AP[5]A (the SERS spec-
tra including AP[5]A contributions are shown in Figure S13, the
the a modes the Raman polarizability change would be large
g
along the molecular axis normal to the surface (see Figure S16,
[35]
the Supporting Information). Finally, SERS signals at 594 and
À4
Figure 6. A) Raman spectrum of 2NA; B–D) SERS spectra of 2NA at 10 (B),
Figure 7. A) Raman spectrum of solid pyrene; B–D) SERS spectra of pyrene
at 10 (B), 10 (C), and 10 m (D). The excitation laser line was 785 nm. In
À5
À6
À6
À7
À8
10
(C), and 10 m (D). The excitation laser line was 785 nm. In spectra B–
D, the SERS contributions from AP[5]A were subtracted.
spectra B–D, the SERS contributions from AP[5]A were subtracted.
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
5
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
À1
À8
1
242 cm are perfectly recognized down to 10 m, which is
[10] M. Grzelczak, J. Pꢃrez-Juste, P. Mulvaney, L. M. Liz-Marzꢂn, Chem. Soc.
Rev. 2008, 37, 1783–1791.
a limit of detection similar to those reported for calix[4]arene-
[
11] M. Rycenga, C. M. Cobley, J. Zeng, W. Li, C. H. Moran, Q. Zhang, D. Qin,
[
16]
stabilized silver nanoparticles (more sensitive) or using chro-
Y. Xia, Chem. Rev. 2011, 111, 3669–3712.
[12] J. Liu, S. Mendoza, E. Roman, M. J. Lynn, R. Xu, A. E Kaifer, J. Am. Chem.
Soc. 1999, 121, 4304–4305.
[
36]
matographic techniques.
[
13] J. Liu, J. Alvarez, W. Ong, E. Roman, A. E. Kaifer, J. Am. Chem. Soc. 2001,
123, 11148–11154.
Conclusion
[
14] A. Wei, Chem. Commun. 2006, 1581–1591.
Ammonium pillar[5]arene-stabilized Au nanoparticles with
quasi-spherical morphology and size control (up to 120 nm)
were successfully synthesized by using seeded growth. Apart
from acting as stabilizer, which was demonstrated by SERS,
AP[5]A plays an important role during synthesis through com-
plexation of the Au salt and avoiding further nucleation. Theo-
retical calculations of the adsorption energy demonstrate that
AP[5]A is perpendicularly adsorbed onto the Au nanoparticle
surface as the most probable conformation. After identifying
the strong host–guest interaction of the AP[5]A with 2NA by
[15] L. Guerrini, J. V. Garcꢁa-Ramos, C. Domingo, S. Sꢂnchez-Cortꢃs, Langmuir
2006, 22, 10924–10926.
[
16] L. Guerrini, J. V. Garcꢁa-Ramos, C. Domingo, S. Sꢂnchez-Cortꢃs, Anal.
Chem. 2009, 81, 953–960.
[
17] R. W. Taylor, T.-C. Lee, O.A. Scherman, R. Esteban, J. Aizpurua, F. M.
Huang, J. J. Baumberg, S. Mahajan, ACS Nano 2011, 5, 3878–3887.
[18] S. Kasera, F. Biedermann, J. J. Baumberg, O.A. Scherman, S. Mahajan,
Nano Lett. 2012, 12, 5924–5928.
[
19] Y. Yao, M. Xue, X. Chi, Y. Ma, J. He, Z. Abliz, F. Huang, Chem. Commun.
012, 48, 6505–6507.
2
[20] H. Li, D.-X. Chen, Y.-L. Sun, Y. B. Zheng, L.-L. Tan, P. S. Weiss, Y.-W. Yang, J.
Am. Chem. Soc. 2013, 135, 1570–1576.
[21] T.-C. Lee, O.A. Scherman, Chem. Eur. J. 2012, 18, 1628–1633.
1
using H NMR spectroscopy, the AP[5]A-stabilized Au nanopar-
[
[
22] N. R. Jana, L. Gearheart, C. J. Murphy, Langmuir 2001, 17, 6782–6786.
23] J. Rodrꢁguez-Fernꢂndez, J. Pꢃrez-Juste, F. J. Garcꢁa deAbajo, L. M. Liz-
Marzꢂn, Langmuir 2006, 22, 7007–7010.
ticles were successfully tested for SERS detection of guest mol-
ecules such as 2NA or polycyclic aromatic hydrocarbons (such
À6
as PYR), directly in water and achieving detection limits of 10
[24] M. R. Langille, M. L. Personick, J. Zhang, C.A. Mirkin, J. Am. Chem. Soc.
2012, 134, 14542–14554.
À8
and 10 m, respectively.
[
[
[
25] J. Rodrꢁguez-Fernꢂndez, J. Pꢃrez-Juste, P. Mulvaney, L. M. Liz-Marzꢂn, J.
Phys. Chem. B 2005, 109, 14257–14261.
26] Y. Ma, X. Ji, F. Xiang, X. Chi, C. Han, J. He, Z. Abliz, W. Chen, F. Huang,
Chem. Commun. 2011, 47, 12340–12342.
Acknowledgements
27] The expected size can be calculated from a simple theoretical Equation:
1
/3
This work was supported by the Spanish MINECO (MAT2010-
r=rseed{([Madded]+[Mseed])/[Mseed]} , in which rseed and r indicate particle
radius for the seed and the final particle, respectively, and [Mseed] and
[Madded] are the metal concentrations in the seed and the added ion, re-
spectively.
1
5374, CTQ2011-22436 and CTQ 2010-16390) and by the Xunta
de Galicia FEDER (2007/085, GPC 2013/006 10PXIB314218PR
and INBIOMED, “unha maneira de facer Europa”). V.M.-G ac-
knowledges receipt of a fellowship from Xunta de Galicia.
[
[
28] P. S. Kumar, I. Pastoriza-Santos, B. Rodrꢁguez-Gonzꢂlez, F. J. Garcꢁa deA-
bajo, L. M. Liz-Marzꢂn, Nanotechnology 2008, 19, 015606(1–5).
29] L. Rodrꢁguez-Lorenzo, J. M. Romo-Herrera, J. Pꢃrez-Juste, R. Alvarez-
Puebla, L. M. Liz-Marzꢂn, J. Mater. Chem. 2011, 21, 11544–11549.
Keywords: gold · host–guest chemistry · nanoparticles ·
macrocycles · surface chemistry
[30] D. I. Gittins, F. Caruso, Angew. Chem. 2001, 113, 3089–3092; Angew.
Chem. Int. Ed. 2001, 40, 3001–3004.
[
[
[
31] M. Moskovits, J. S. Suh, J. Phys. Chem. 1984, 88, 5526–5530.
32] X. J. Loh, Mater. Horiz. 2014, 1, 185–195.
33] R. Contreras-Cꢂceres, I. Pastoriza-Santos, R. A. Alvarez-Puebla, J. Pꢃrez-
Juste, A. Fernꢂndez-Barbero, L. M. Liz-Marzꢂn, Chem. Eur. J. 2010, 16,
[
[
1] W. Gokel, W. M. Leevy, M. E. Weber, Chem. Rev. 2004, 104, 2723–2750.
2] A. Harada, A. Hashidzume, H. Yamaguchi, Y. Takashima, Chem. Rev.
2
009, 109, 5974–6023.
3] A. C. Bhasikuttan, H. Pal, J. Mohanty, Chem. Commun. 2011, 47, 9959–
971.
4] H. J. Kim, M. H. Lee, L. Mutihac, J. Vicens, J. S. Kim, Chem. Soc. Rev. 2012,
1, 1173–1190.
9462–9467.
[
[
[
34] V. Krishnakumar, R. Mathammal, S. Muthunatesan, Spectrochim. Acta
Part A 2008, 70, 201–209.
9
[
[
35] M. Moskovits, J. S. Suh, J. Phys. Chem. 1988, 92, 6327–6329.
36] M. Bourdat-Deschamps, J. J. Daudin, E. Barriuso, J. Chromatogr. A 2007,
4
[
[
5] P. J. Cragg, K. Sharma, Chem. Soc. Rev. 2012, 41, 597–607.
6] M. Xue, Y. Yang, X. Chi, Z. Zhang, F. Huang, Acc. Chem. Res. 2012, 45,
1167, 143–153.
1294–1308.
[
[
7] R. N. Dsouza, U. Pischel, W. M. Nau, Chem. Rev. 2011, 111, 7941–7980.
8] T. Ogoshi, S. Kanai, S. Fujinami, T. Yamagishi, Y. Nakamoto, J. Am. Chem.
Soc. 2008, 130, 5022–5023.
[9] J. Pꢃrez-Juste, I. Pastoriza-Santos, L. M. Liz-Marzꢂn, P. Mulvaney, Coord.
Received: February 7, 2014
Chem. Rev. 2005, 249, 1870–1901.
Published online on && &&, 2014
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
6
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Sensing platform: Ammonium pillar[5]-
arene (AP[5]A)-stabilized Au nanoparti-
cles with quasi-spherical morphology
and size control (up to 120 nm) were
successfully synthesized by a seeded
growth method (see figure). The pres-
ence of AP[5]A onto the Au nanoparti-
cle surface allows the detection based
on surface-enhanced Raman scattering
&
Sensors
V. Montes-Garcꢀa, C. Fernꢁndez-Lꢂpez,
B. Gꢂmez, I. Pꢃrez-Juste, L. Garcꢀa-Rꢀo,
L. M. Liz-Marzꢁn, J. Pꢃrez-Juste,*
I. Pastoriza-Santos*
&
& – &&
Pillar[5]arene-Mediated Synthesis of
Gold Nanoparticles: Size Control and
Sensing Capabilities
(SERS) of guest molecules, such as 2-
naphthoic acid (2NA) or polycyclic aro-
matic hydrocarbons (pyrene), directly in
water achieving limits of detection of
À6
À8
10
and 10 m, respectively.
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
7
ꢄ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ