Bifunctional nanostructure of magnetic core luminescent shell and its application as solid-state electrochemiluminescence sensor material.
ABSTRACT Bifunctional nanoarchitecture has been developed by combining the magnetic iron oxide and the luminescent Ru(bpy)32+ encapsulated in silica. First, the iron oxide nanoparticles were synthesized and coated with silica, which was used to isolate the magnetic nanoparticles from the outer-shell encapsulated Ru(bpy)32+ to prevent luminescence quenching. Then onto this core an outer shell of silica containing encapsulated Ru(bpy)32+ was grown through the Stöber method. Highly luminescent Ru(bpy)32+ serves as a luminescent marker, while magnetic Fe3O4 nanoparticles allow external manipulation by a magnetic field. Since Ru(bpy)32+ is a typical electrochemiluminescence (ECL) reagent and it could still maintain such property when encapsulated in the bifunctional nanoparticle, we explored the feasibility of applying the as-prepared nanostructure to fabricating an ECL sensor; such method is simple and effective. We applied the prepared ECL sensor not only to the typical Ru(bpy)32+ co-reactant tripropylamine (TPA), but also to the practically important polyamines. Consequently, the ECL sensor shows a wide linear range, high sensitivity, and good stability.
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ABSTRACT: A great deal of research has been carried out on lanthanide organic complex-based organic-inorganic hybrid materials in the last decade. This critical review begins with a formulation of the fundamentals of lanthanide organic complex luminescence, and presents various current designed ideas, synthetic routes, luminescence behaviors and potentials of the latest advanced (a) sol-gel materials, (b) mesoporous materials, (c) titania materials, (d) ionic liquids and ionogels, (e) polymers, and (f) bifunctional magnetic-optical composites based on lanthanide organic complexes. Finally, challenges and opportunities for further improvement of organic-inorganic hybrid luminescent materials based on lanthanide organic complexes will be discussed.Chemical Society Reviews 09/2012; · 24.89 Impact Factor
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ABSTRACT: A simple general strategy was successfully developed for the preparation of magnetic-luminescent multifunctional nanocomposites by incorporating fluorescent (pyrene) and magnetic (Fe(3)O(4)) components simultaneously into a poly(styrene-co-methacrylic acid) [poly(St-co-MAA)] copolymer matrix. The nanospheres so prepared were characterized using scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. The prepared magnetic-fluorescent inorganic-organic nanocomposites have excellent magnetic and photoluminescent properties. They can be used in magnetic separation of trace amounts of sample, fluorescence detection and imaging applications, including magnetic resonance imaging (MRI) and fluorescence imaging. The fluorescence quenching of the nanospheres in the presence of different amounts of Cu(2+) ions was also investigated. Under optimal experimental conditions, the relative fluorescence intensity of the composite nanosphere colloidal solution is proportional to the concentration of Cu(2+) ions, which indicates that these multifunctional nanocomposites can be used for the magnetic separation and fluorescence detection of Cu(2+) ions.Luminescence 06/2011; 27(1):74-9. · 1.27 Impact Factor
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ABSTRACT: Electrochemiluminescence (ECL) of tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)(3)(2+)] has received considerable interest over broad applications due to its remarkably high sensitivity and extremely wide dynamic range. After a brief introduction of the ECL of Ru(bpy)(3)(2+), an overview of our recent research on enhanced ECL, fabrication of solid-state ECL sensors, analytical application of an effective bioassay, and alignment of ECL with capillary electrophoresis (CE) and microchip CE is discussed in detail. Finally, we conclude with a look at the future challenges and prospects of the development of ECL.The Chemical Record 12/2011; 12(1):177-87. · 4.38 Impact Factor
Bifunctional Nanostructure of Magnetic Core Luminescent Shell and Its Application as
Solid-State Electrochemiluminescence Sensor Material
Lihua Zhang, Baifeng Liu, and Shaojun Dong*
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Graduate
School of the Chinese Academy of Sciences, Chinese Academy of Sciences, Changchun, 130022, China
ReceiVed: May 5, 2007; In Final Form: June 29, 2007
Bifunctional nanoarchitecture has been developed by combining the magnetic iron oxide and the luminescent
Ru(bpy)32+encapsulated in silica. First, the iron oxide nanoparticles were synthesized and coated with silica,
which was used to isolate the magnetic nanoparticles from the outer-shell encapsulated Ru(bpy)32+to prevent
luminescence quenching. Then onto this core an outer shell of silica containing encapsulated Ru(bpy)32+was
grown through the Sto ¨ber method. Highly luminescent Ru(bpy)32+serves as a luminescent marker, while
magnetic Fe3O4nanoparticles allow external manipulation by a magnetic field. Since Ru(bpy)32+is a typical
electrochemiluminescence (ECL) reagent and it could still maintain such property when encapsulated in the
bifunctional nanoparticle, we explored the feasibility of applying the as-prepared nanostructure to fabricating
an ECL sensor; such method is simple and effective. We applied the prepared ECL sensor not only to the
typical Ru(bpy)32+co-reactant tripropylamine (TPA), but also to the practically important polyamines.
Consequently, the ECL sensor shows a wide linear range, high sensitivity, and good stability.
Nanoparticles have unique, size-dependent properties; there-
fore, they are of increasing interest for both fundamental research
and numerous applications.1In addition, magnetic nanoparticles
are important materials due to their interesting magnetic
properties, and they have been sophisticatedly employed in many
advanced technology areas.2-6Magnetic adsorbents, carriers,
and modifiers can be used for the immobilization, isolation,
modification, detection, determination, and removal of a variety
of biologically active compounds, xenobiotics, cellular com-
ponents, and cells. Moreover, magnetic separation and labeling
have recently been attracting more attention, particularly in
molecular and cell biology, microbiology, biochemistry, and
bioanalytical chemistry.7-10On the other hand, magneto-
controlled molecular electronics and bioelectronics are new
topics that examine the effect of an external field on electro-
chemical and bioelectrochemical processes of functional mag-
netic particles associated with an electrode, which branches the
application of functional magnetic nanoparticles out into the
field of electrochemistry.11Magnetic functional nanoparticles
have been easily prepared for biosensing, immunosensing, DNA
sensing, ECL sensing, and fuel cells.12-16Therefore, iron oxide
nanoparticles are of great interest for the study of magnetic
properties and for practical applications. Nevertheless, the
reactivity of iron oxide nanoparticles has been shown to greatly
increase as the particle dimensions are reduced, and particles
with relatively small sizes may undergo rapid degradation when
they are directly exposed to certain environments.17Conse-
quently, a suitable coating is essential to overcome such
limitations. With the properties of stability, biocompatibility,
and easy functionality, silica acts as an optimum alternative to
encapsulate these magnetic nanoparticles.18-20
Recently, people are paying more attention to the preparation
and application of dye-encapsulated silica nanoparticles.21-25
On one hand, the encapsulation of fluorescent dye in nanopar-
ticles often increases their photostability and emission quantum
yield due to their isolation from possible quenchers such as
molecular oxygen and water. On the other hand, the silica is
relatively easy to functionalize and conjugate to bioactive
molecules, which shows great potential in bioanalysis. As a
whole, there are two methods to prepare the fluorescent dye-
encapsulated silica nanoparticles: the microemulsion method
and the Sto ¨ber method. Nanoparticles prepared by the reverse
microemulsion method show good promise in size control and
further miniaturization, but this technique requires the use of
large amounts of surfactants and organic solvents, which means
much effort to separate the nanoparticles from the large amount
of surfactants.26Nevertheless, the Sto ¨ber method is simple and
is carried out in an ethanol/water mixture, completely avoiding
the use of potentially toxic organic solvents and surfactants.
Furthermore, slight modification of the ammonia and water
content in the reaction mixture results in monodispersed silica
spheres of different diameters.27Among many dyes encapsu-
lated, Ru(bpy)32+proves to be a suitable one due to its good
stability and high quantum yield. Besides, its strong electrostatic
interaction with silica makes its leaching negligible. Conse-
quently, Ru(bpy)32+-encapsulated silica nanoparticles are ex-
tensively applied in bioanalysis and biodetection.28-29And more
recently, people began to be more aware of their application in
electrochemiluminescence (ECL), as Ru(bpy)32+is a typical
ECL reagent and a large quantity of Ru(bpy)32+molecules are
three-dimensionally encapsulated inside each silica nanoparticle,
which finally leads to the high ECL signal.30-32
Generally, a lot of work has been focused on fabricating
bifunctional nanoarchitecture by combining the magnetic nano-
particles with the luminescent reagents.33-36Here, we synthesize
a new kind of nanoarchitecture containing a magnetic Fe3O4
core and a luminescent Ru(bpy)32+-encapsulated silica shell.
J. Phys. Chem. B 2007, 111, 10448-10452
10.1021/jp0734427 CCC: $37.00© 2007 American Chemical Society
Published on Web 08/15/2007
These complex nanoparticles were characterized by transmission
electron microscopy (TEM), vibrating sample magnetometer
(VSM), and emission spectroscopy. Furthermore, unlike previ-
ous reports, we explored a new application of these bifunctional
nanoparticles to fabricate an efficient ECL sensor. The sensitive
and stable Ru(bpy)32+ECL sensor was based on the multilayer
films of the as-prepared magnetic and luminescent nanoparticles
stimulated by an external magnet. With such sensor, satisfying
results were obtained with both Ru(bpy)32+typical coreactant
TPA and practically significant polyamines.
2. Experimental Section
2.1. Reagents and Instruments. Tris(2,2′-bipyridyl) dichlo-
roruthenium(II) hexahydrate (Ru(bpy)3Cl2‚6H2O) and tripropyl-
amine (TPA) were purchased from Aldrich and used without
further treatment. The polyamines Spd and Spm were purchased
from Sigma. Tetraethylorthosilicate (TEOS) was obtained from
Beijing Yili Chemical Reagent Factory (Beijing, China). Ferric
chloride, ferrous chloride, and ammonium hydroxide (25-28
wt %) were purchased from Beijing Chemical Reagent Factory
(Beijing, China). All other chemicals were of analytical grade,
and the aqueous solutions were prepared with doubly distilled
water. Transmission electron microscopy (TEM) measurements
were performed with a HITACHI H-8100 EM with an accelera-
tion voltage of 200 kV. A drop of the core-shell nanoparticle
aqueous solution was cast on a copper grid and allowed to dry.
Magnetization of the iron oxide nanoparticles and bifunctional
nanoparticles were measured by a vibrating sample magnetom-
eter (VSM, LakeShore). Emission spectroscopy data were
obtained from a LS 55 luminescence spectrometer (Perkin-
Elmer, U.K.) at room temperature, and the excitation wavelength
was selected at 460 nm. Lifetime was measured with PTI (Photo
Technology International, (Canada). Cyclic voltammetric ex-
periments were performed with a CH Instruments 832 volta-
mmetric analyzer. The working electrode was a glassy carbon
wafer coated with a multilayer film of magnetic and luminescent
nanoparticles driven by an external magnet. A platinum wire
was used as the counter electrode, and an Ag/AgCl (saturated
KCl) as a reference electrode. The ECL signal produced in the
electrolytic cell was detected and recorded by a flow injection
chemiluminescence analyzer (IFFD, Xi’an Remax Electronic
Science Tech. Co. Ltd. China), which was operated by a
2.2. Preparation of Magnetic Iron Oxide Nanoparticles.
The iron oxide nanoparticles were prepared according to
Massart’s method.37In a typical experiment, a mixed aqueous
solution of ferric chloride (50 mL, 1 M) and ferrous chloride
(10 mL, 2 M, in 2 M HCl) were added into ammonia solution
(500 mL, 0.7 M) under vigorous stirring for 30 min at room
temperature in a nitrogen atmosphere. The instantaneously
formed black precipitate was separated by centrifugation and
further washed with water at least three times. Then to a mixture
of 3 mL of NH4OH, 28.8 mL of H2O, 27.5 mL of ethanol, and
6.22 mL of as-prepared iron oxide nanoparticle aqueous solution
was added an ethanol solution of TEOS (1.5 mL of TEOS in
30 mL of EtOH) while the solution was vigorously stirred. The
hydrolysis and condensation of TEOS onto the magnetic
nanoparticles was completed in 2 h. Then the prepared nano-
particles were washed with ethanol and water several times,
and finally they were dispersed in ethanol. Here the prepared
silica between magnetic core and the fluorescent dye shell was
to prevent emission quenching through core-dye interactions.
2.3. Preparation of Core-Shell Nanostructure. The lumi-
nescent shell was coated on the magnetic core with the Sto ¨ber
method. First, 1.6 mL of TEOS, 10 mL of ethanol, and 500 µL
of Ru(bpy)32+(1 mg/mL) solutions were premixed. Then 2 mL
of as-prepared Fe3O4@SiO2was added into the mixture. Finally,
750 µL of ammonia solution was added, and the mixture was
vigorously stirred for 3 h. Then the prepared nanoparticles were
washed with ethanol and water. After evaporation of the solvent,
the final core-shell nanostructure was obtained. The as-prepared
Fe3O4@SiO2nanoparticles were used as nucleation sites, and
the outer shell of luminescent Ru(bpy)32+-encapsulated silica
would grow onto them.
2.4. Preparation of Core-Shell Nanostructure Modified
Electrode for ECL Detection. The glassy carbon wafer was
polished before each experiment with 1 and 0.3 µm alumina
powder, respectively, and sonicated thoroughly in acetone and
doubly distilled water. Then an external magnet was positioned
behind the wafer as demonstrated in Figure 1, and the electrode
was placed in the bifunctional nanoparticle aqueous solution.
The fabricated electrode attracted the magnetic luminescent
nanoparticles, and the multilayer film of the bifunctional
nanoparticles was formed within several minutes. The thickness
of the multilayer film can be easily controlled by the variation
of the amount of the magnetic luminescent nanoparticles
introduced into the aqueous solution.
3. Results and Discussion
The Sto ¨ber method has been widely used for preparation of
silica nanoparticles since it was first reported. It is simple,-
convenient, and without surfactants and toxic organic solvents
during the preparation process. Therefore, we use such method
to prepare bifunctional nanoparticles. Figure 1 shows a sche-
matic illustration of the preparation of core-shell nanoparticles
with both magnetic and luminescent functionalities. First, silica-
coated magnetic nanoparticles are synthesized. Since the iron
oxide surface has a strong affinity for silica, no primer is
required to promote the deposition and adhesion of silica.38The
first silica layer covers the magnetic cores to isolate them from
the outer-shell encapsulated dye molecules to prevent fluores-
cence quenching. Then the Fe3O4@SiO2nanoparticles act as
seeds for the deposition of the Ru(bpy)32+-silica shell. In this
process, Ru(bpy)32+is immobilized in siloxane polymers during
the growth of silica nanoparticles via the electrostatic interaction
between positively charged Ru(bpy)32+and negatively charged
silica. At last, the homogeneous Ru(bpy)32+-silica is coated
onto the Fe3O4@SiO2 cores. Figure 2 shows TEM image of
monodisperse and spherical bifunctional nanoparticles. In fact,
nanoparticles, and fabrication of a bifunctional nanoparticle-modified
Scheme for the preparation of magnetic, luminescent
Nanostructure of Magnetic Core Luminescent Shell
J. Phys. Chem. B, Vol. 111, No. 35, 2007 10449
we have carried out a control experiment to synthesize the
bifunctional nanoparticles without the first layer of silica. With
such method, both fluorescent and ECL properties of the
prepared nanoparticles were impacted severely. Therefore, the
first layer of silica plays an important role in preventing
luminescence quenching between iron oxide nanoparticles and
We compare the emission spectrum of the as-prepared
nanoparticles with that of Ru(bpy)32+aqueous solution. The
luminescent excited state of Ru(bpy)32+is assigned to the metal-
to-ligand charge-transfer (MLCT) state. Judging from Figure
3, the bifunctional nanoparticles exhibit an emission peak at a
position slightly red-shifted from that of the pristine Ru(bpy)32+,
which could be attributed to the interaction between Ru(bpy)32+
and silica. Moreover, it is known that O2 can promote
fluorescence quenching because it deactivates the excited state
of Ru(bpy)32+.28However, the Ru(bpy)32+encapsulated in
bifunctional nanoparticles exhibits a longer fluorescence lifetime
compared with Ru(bpy)32+in aqueous solution. In aqueous
solution, the Ru(bpy)32+fluorescence lifetime is about 400 ns,
while the fluorescence lifetime of Ru(bpy)32+encapsulated in
bifunctional nanoparticles is 805 ns. Consequently, it can be
concluded that the silica matrix can protect immobilized Ru-
(bpy)32+from oxygen quenching and improve its photostability.
Magnetization curves, as shown in Figure 4, are measured
on powder samples of iron oxide nanoparticles and bifunctional
nanoparticles at room temperature. Both of them exhibit
negligible coercivity and remanence, typical of superparamag-
netic material. Their saturation magnetization is 68.8 and 9.7
emu/g, respectively. Compared with the iron oxide, the relatively
low saturation magnetization of bifunctional nanoparticles could
be attributed to the thick shells of silica coated outside. Because
of the magnetic iron oxide core, the composite particles can be
directed to specific locations when manipulated by an external
magnetic field, which, in this case, can be easily monitored
through the intense luminescence of the bifunctional nanopar-
ticles. Figure 5 illustrates the dispersion and separation process
of these nanoparticles under UV irradiation. In the absence of
an external magnet, the dispersion is homogeneous and bright
orange. Once the magnet is placed beside the vial, the nano-
particles quickly move and accumulate near it within several
minutes, with the bulk solution clear and transparent. With
removal of the external magnet and vigorous stirring, the
aggregations would be rapidly redispersed again.
With the unique architecture, the silica surface of the
as-prepared nanoparticles remains available for versatile bio-
conjugation with various biomolecules. Therefore, the bifunc-
tional nanoparticles could be extensively applied in imaging
technology and bioanalysis, and a lot of research work has been
explored. However, here we demonstrated a novel application
of these bifunctional nanoparticles in an ECL field. Recently,
extensive research has been devoted to the magnetic control of
bioelectrochemical and electrochemical processes. An external
magnet is used as a means to immobilize the electroactive
Figure 2. TEM of the prepared bifunctional nanoparticles.
Figure 3. Emission spectra of Ru(bpy)32+aqueous solution (solid line)
and Ru(bpy)32+encapsulated in bifunctional nanoparticles (dashed line)
(excitation at 460 nm).
Figure 4. Magnetization curves of iron oxide nanoparticles (a) and
bifunctional nanoparticles (b).
Figure 5. Photographic images of the magnetic luminescent nanopar-
ticles under UV irradiation (a) without and (b) with an external magnetic
10450 J. Phys. Chem. B, Vol. 111, No. 35, 2007
Zhang et al.
molecules onto the electrode surface and trigger the electro-
chemistry process. Such immobilization method is simple and
effective; the key difficulty is how to link the electroactive
molecules to the magnetic nanoparticles. The bifunctional
nanoparticles we prepared just overcome this difficulty. The
encapsulated iron oxide nanoparticles are superparamagnetic,
while the Ru(bpy)32+immobilized in the outer shell still
maintains its ECL property. Therefore, we use an external
magnet to attract the as-prepared nanoparticles onto the electrode
surface to form multilayer films, accordingly, a sensitive and
stable ECL sensor is fabricated.
Cyclic voltammograms (CVs) of the bifunctional nanopar-
ticle-modified electrode in 0.1 M PBS (pH 7.5) at different scan
rates are shown in Figure 6, and a plot of oxidation peak current
versus the square root of scan rate is also shown in the inset of
Figure 6. The anodic peak current is proportional to the square
root of the scan rate over the range of 50-500 mV/s, indicating
that the immobilized Ru(bpy)32+undergoes a diffusion process.
The ECL behavior of Ru(bpy)32+encapsulated in the bifunc-
tional nanoparticle-modified electrode is studied with tripropyl-
amine (TPA), since the Ru(bpy)32+-TPA system has been fully
investigated and gives a stronger ECL signal than other
reductants.39Figure 7 shows ECL curves of the prepared
electrode with and without 7.4 × 10-5M TPA at a scan rate of
10 mV/s in 0.1 M PBS (pH 7.5). The ECL signal increases
considerately once the TPA is added. The excellent ECL
behavior is attributed to large amounts of Ru(bpy)32+im-
mobilized on the electrode surface. With TPA as the probe, we
evaluate the sensitivity and stability of the prepared ECL sensor.
The ECL signal varies linearly with the concentration of TPA
from 6.9 × 10-8to 7.3 × 10-4M (Figure 8) with a remarkable
detection limit of 6.5 nM (S/N ) 3). Compared with the
effective Ru(bpy)32+preconcentration medium Nafion, the
detection limit of the present ECL sensor is 2 orders of
magnitude lower. The improved sensitivity could be attributed
to the large amount of Ru(bpy)32+encapsulated in each
bifunctional nanoparticle. The relative standard deviation of the
ECL emission from the modified electrode under continuous
potential scanning for 16 cycles in 0.1 M PBS (pH 7.5)
containing 3.8 × 10-4M TPA was 0.5%. After two-week
storage of the as-prepared ECL sensor under the external magnet
in the air, the ECL response could retain 85% of its initial value.
The good stability of the ECL sensor may be attributed to the
two different kinds of interactions: the electrostatic interaction
between positively charged Ru(bpy)32+and negatively charged
silica, and the magnetic interaction between bifunctional nano-
particles and the external magnet.
With high sensitivity, here we put the as-prepared ECL sensor
to the practical application of detecting polyamines. The
polyamines are constituents of eukaryotic and prokaryotic cells,
fulfilling indispensable roles in human metabolism.40Moreover,
some types of malignant cell proliferation are associated with
increased cellular polyamine metabolism, and several investiga-
tors have suggested a possible role of polyamine determination
in blood and urine samples as markers of the presence of
malignancies.41The studies of polyamines are of great interest
not only for their suitability as cancer markers, but also as an
indicator of food quality and plant study.42,43However, since
polyamines show neither UV absorption nor fluorescence, they
cannot be determined with adequate sensitivity by spectropho-
tometric or fluorescence detection. Polyamines have to be
derivatized or labeled before spectral detection.44,45However,
the derivatization procedure makes the whole analytical process
tedious and time-consuming. Polyamines are aliphatic amines
containing different amine groups, that can be oxidized directly
by Ru(bpy)32+, so polyamines can be treated as analytes when
Figure 6. CVs of the ECL sensor at various scan rates in 0.1 M PBS
(pH 7.5): (a) 50, (b) 100, (c) 200, (d) 300, (e) 400, and (f) 500 mV/s.
(Inset) The relationship between the anodic peak current and the square
root of the scan rate.
Figure 7. ECL curves of the prepared electrode with (solid line) and
without (dashed line) 7.4 × 10-5M TPA at a scan rate of 10 mV/s in
0.1 M PBS (pH 7.5).
Figure 8. Calibration of TPA with the as-prepared ECL sensor in PBS
(pH 7.5) at the scan rate of 100 mV/s.
Nanostructure of Magnetic Core Luminescent Shell
J. Phys. Chem. B, Vol. 111, No. 35, 2007 10451
Ru(bpy)32+-ECL detection is adopted without derivatization.
Here, we chose polyamine spermidine (Spd) and spermine
(Spm) as analytes. With our method, the linear ranges are 4 ×
10-6M to 5 × 10-3M (R ) 0.988) and 5.5 × 10-7M to 10-4
M (R ) 0.999) for Spd and Spm, respectively. And their
detection limits are 8.4 × 10-7M and 3.3 × 10-7M (S/N )
3), respectively, which are 2 orders of magnitude lower than
that reported for the ultraviolet method.41The reproducibil-
ity of the as-prepared ECL sensor was also examined. For
three electrodes fabricated in the same manner, the relative
standard deviation was 9.4% with an Spm concentration of
4.7 × 10-5M.
The present work successfully prepared a new type of
bifunctional nanoparticles containing a magnetic core and a Ru-
(bpy)32+encapsulated luminescent shell with the Sto ¨ber method.
Highly luminescent Ru(bpy)32+acts as effective ECL reagent,
while magnetic Fe3O4nanoparticles allow external manipulation
through a magnetic field. On the basis of their unique
characteristics, we fabricated a novel ECL sensor. A good linear
range from 6.9 × 10-8M to 7.3 × 10-4M with a remarkable
detection limit of 6.5 nM (S/N ) 3) to TPA was obtained, and
the ECL relative standard deviation was only 0.5% during
continuous potential scanning for 16 cycles. Moreover, we
applied a prepared ECL sensor to polyamine detection, since
these polyamines play a significant role but are difficult to detect
directly. The detection limit with our method is 2 orders of
magnitude lower than that reported for the ultraviolet method.
Furthermore, because of the good biocompatibility and easy
functionalization of silica, such bifunctional nanoparticles also
have great potential in combination with ECL detection in
Acknowledgment. This work was supported by the National
Natural Science Foundation of China (No. 20427003, 20675076).
References and Notes
(1) Graf, C.; Dembski, S.; Hofmann, A.; Ru ¨hl, E. Langmuir 2006, 22,
(2) Doyle, P.; Bibette, J.; Bancaud, A.; Viovy, J. Science 2002, 295,
(3) Kouassi, G. K.; Irudayaraj, J. Anal. Chem. 2006, 78, 3234.
(4) Josephson, L.; Perea, J. M.; Weissleder, R. Angew. Chem., Int. Ed.
2001, 40, 3204.
(5) Ito, A.; Shinkai, M.; Honda, H.; Kobayashi, T. Cancer Gene Ther.
2001, 8, 649.
(6) (a) Shinkai, M. J. Biosci. Bioeng. 2002, 94, 606. (b) Jeong, U.;
Teng, X.; Wang, Y.; Yang, H.; Xia, Y. AdV. Funct. Mater. 2007, 19, 33.
(c) Gupta, A. K.; Gupta, M. Biomaterials 2005, 26, 3995.
(7) Safarikova, M.; Safarik, I. Magn. Electr. Sep. 2001, 10, 223.
(8) Pankhurst, Q. A.; Connolly, J.; Jones, S. K.; Dobson, J. J. Phys.
D: Appl. Phys. 2003, 36, 167.
(9) Tartaj, P.; Morales, M. D. P.; Verdaguer, S. V.; Carreno, T. G.;
Serna, C. J. J. Phys. D: Appl. Phys. 2003, 36, 182.
(10) Berry, C. C.; Curtis, A. S. G. J. Phys. D: Appl. Phys. 2003, 36,
(11) Willner, I.; Katz, E. Angew. Chem.. Int. Ed. 2003, 42, 4576.
(12) Mavre ´, F.; Bontemps, M.; Ammar-Merah, S.; Marchal, D.; Limoges,
B. Anal. Chem. 2007, 79, 187.
(13) Hirsch, R.; Katz, E.; Willner, I. J. Am. Chem. Soc. 2000, 122, 12053.
(14) Katz, E.; Ichia, L. S.; Willner, I. Chem. Eur. J. 2002, 8, 4138.
(15) Kim, D. J.; Lyu, Y. K.; Choi, H. N.; Min, I.; Lee, W. Y. Chem.
Commun. 2005, 2966.
(16) Wang, J.; Musameh, M.; Laocharoensuk, R.; Oni, J.; Gervasio, D.
Electrochem. Commun. 2006, 8, 1106.
(17) Maceira, V. S.; Correa-Duarte, M. A.; Spasova, M.; Liz-Marza ´n,
L. M.; Farle, M. AdV. Funct. Mater. 2006, 16, 509.
(18) Yi, D. K.; Lee, S. S.; Papaefthymiou, G. C.; Ying, J. Y. Chem.
Mater. 2006, 18, 614.
(19) Yoon, T. J.; Kim, J. S.; Kim, B. G.; Yu, K. N.; Cho, M. H.; Lee,
J. K. Angew. Chem., Int. Ed. 2005, 44, 1068.
(20) (a) Liz-Marza ´n, L. M.; Giersig, M.; Mulvaney, P. Chem. Commun.
1996, 731. (b) Tartaj, P.; Serna, C. J. J. Am. Chem. Soc. 2003, 125, 15754.
(c) Tartaj, P.; Gonza ´lez-Carren ˜o, T.; Serna, C. J. AdV. Mater. 2001, 13,
1620. (d) Ennas, G.; Musinu, A.; Piccaluga, G.; Zadda, D.; Gatteschi, D.;
Sangregorio, C.; Stanger, J. L.; Concas, G.; Spano, G. Chem. Mater. 1998,
(21) Santra, S.; Yang, H.; Dutta, D.; Stanley, J. T.; Holloway, P. H.;
Tan, W. H.; Moudgil, B. M.; Mericle, R. A. Chem. Commun. 2004, 2810.
(22) Xian, Y. Z.; Liu, F.; Xian, Y.; Zhou, Y. Y.; Jin. L. T. Electrochim.
Acta 2006, 51, 6527.
(23) Montalti, M.; Prodi, L.; Zaccheroni, N.; Battistini, G.; Marcuz, S.;
Mancin, F.; Rampazzo, E.; Tonellato, U. Langmuir 2006, 22, 5877.
(24) Yao, H.; Li, N.; Xu, S.; Xu, J. Z.; Zhu, J. J.; Chen, H. Y. Biosens.
Bioelectron. 2005, 21, 372.
(25) Bagwe, R. P.; Yang, C.; Hilliard, L. R.; Tan, W. H. Langmuir 2004,
(26) Santra, S.; Zhang, P.; Wang, K.; Tapec, R.; Tan, W. H. Anal. Chem.
2001, 73, 4988.
(27) Sto ¨ber, W.; Fink, A.; Bohn, E. J. Colloid Interface Sci. 1968, 26,
(28) Herr, J. K.; Smith, J. E.; Medley, C. D.; Shangguan, D.; Tan, W.
Anal. Chem. 2006, 78, 2918.
(29) Smith, J. E.; Medley, C. D.; Tang, Z.; Shangguan, D.; Lofton, C.;
Tan, W. Anal. Chem. 2007, 79, 3075.
(30) Zhang, L. H.; Dong, S. J. Anal. Chem. 2006, 78, 5119.
(31) Zhang, L. H.; Dong, S. J. Electrochem. Commun. 2006, 8, 1687.
(32) Chang, Z.; Zhou, J.; Zhao, K.; Zhu, N.; He, P. G.; Fang, Y. Z.
Electrochim. Acta 2006, 52, 575.
(33) Hong, X.; Li, J.; Wang, M.; Xu, J.; Guo, W.; Li, J.; Bai, Y.; Li, T.
Chem. Mater. 2004, 16, 4022.
(34) Kim, J.; Lee, J. E.; Lee, J.; Jang, Y.; Kim, S.; An, K.; Yu, J. H.;
Hyeon, T. Angew. Chem., Int. Ed. 2006, 45, 4789.
(35) Lu, H.; Yi, G.; Zhao, S.; Chen, D.; Guo, L. H.; Cheng, J. J. Mater.
Chem. 2004, 14, 1336.
(36) Ma, D.; Guan, J.; Normandin, F.; De ´nomme ´e, S.; Enright, G.; Veres,
T.; Simard, B. Chem. Mater. 2006, 18, 1920.
(37) Massart, R. IEEE Trans. Magn. 1981, 17, 1247.
(38) Vero ´nica, S.; Correa-Duarte, A. M.; Farle, M.; Quintela, A.;
Sieradzki, K.; Diaz, R. Chem. Mater. 2006, 18, 2701; Lu, Y.; Yin, Y.;
Mayers, B. T.; Xia, Y. Nano Lett. 2002, 2, 183.
(39) Noffsinger, J. B.; Danielson, N. D. Anal. Chem. 1987, 59,
(40) Khuhawar, M. Y.; Qureshi, G. A. J. Chromatogr., B 2001, 764,
(41) (a) Uehara, N.; Shirakawa, S.; Uchino, H.; Saeki, Y. Cancer 1980,
45, 108. (b) Russell, D. H. Clin. Chem. 1977, 23, 22.
(42) Kova ´cs, A.; Simon-Sarkadi, L.; Ganzler, K. J. Chromatogr., A 1999,
(43) Bouchereau, A.; Aziz, A.; Larher, F.; Martin-Tanguy, J. Plant. Sci.
1999, 140, 103.
(44) Fu, S.; Zou, X.; Wang, X.; Liu, X. J. Chromatogr., B 1998, 709,
(45) Taibi, G.; Schiavo, M. R.; Rindina, P. C.; Muratore, R.; Nicotra,
C. M. A. J. Chromatogr., A 2001, 921, 323.
10452 J. Phys. Chem. B, Vol. 111, No. 35, 2007
Zhang et al.