Mesoporous material-based manipulation of the enzyme-like activity of CoFe2O4 nanoparticles

Article abstract of DOI:10.1039/c3ta14697a

Mesoporous material supported CoFe₂O₄ magnetic nanoparticles possess unique peroxidase/oxidase-like activity, and react with luminol to yield a novel chemiluminescence without the need of H ₂O₂. Their oxidase-like activity shows pH and support dependence, and could be reversibly controlled by their pH. This offers a new method for manipulating the enzyme-like activity of nanoparticles.

Full text of DOI:10.1039/c3ta14697a

Journal of
Materials Chemistry A
View Article Online
View Journal | View Issue
COMMUNICATION
Mesoporous material-based manipulation of the
enzyme-like activity of CoFe2O4 nanoparticles†
Cite this: J. Mater. Chem. A, 2014, 2,
2482
a
a
Yingwei Fan,ab Wenbing Shi,ac Xiaodan Zhang and Yuming Huang
*
Received 14th November 2013
Accepted 13th December 2013
DOI: 10.1039/c3ta14697a
www.rsc.org/MaterialsA
Mesoporous material supported CoFe2O4 magnetic nanoparticles and the supported CoFe2O4 NPs were found to exhibit signi-
possess unique peroxidase/oxidase-like activity, and react with lumi- cant oxidase activity varied with their pH in luminol chem-
nol to yield a novel chemiluminescence without the need of H2O2. iluminescence (CL) reaction in the absence of H2O2; and (iii) the
Their oxidase-like activity shows pH and support dependence, and pH tunable catalytic activity of the CoFe2O4 NPs enzyme mimic
could be reversibly controlled by their pH. This offers a new method was dependent on the used mesoporous materials and could be
for manipulating the enzyme-like activity of nanoparticles.
reversibly controlled by their pH. The results we present herein
offer a strategy for the preparation of simple and efficient multi-
functional catalysts with magnetism, oxidase-like activity, and
pH-sensitivity.
Recently, engineering nanoparticles (NPs) that mimic enzymes
have received great attention due to their potential improve-
ment of properties relative to native enzymes (e.g., greater
resistance to extremes of pH and temperature) and potential
applications in biochemical analysis, catalysis, sensor tech-
nology, and degradation of organic pollutants.1 Compared with
natural enzymes, the NPs mimetics are stable against denatur-
ation, resistant to high concentration of substrate, low in cost,
and easy to store and treat. The applications of these novel
materials are currently under intensive investigation. And
various NPs have been evaluated as catalysts of enzymatic
mimetics.2
On the other hand, the mesoporous materials have attracted
an extraordinary scientic interest due to their large specic
surface area, uniform pore size distribution, tunable porosity,
well-dened surface properties and their strong inuence on
the catalytic efficiency.3 However, their use in enzyme mimetics
has not been reported. In this communication, for the rst time,
we report mesoporous material supported CoFe2O4 NPs with
unique tunable enzyme-like activity. Our results are (i) the
mesoporous material supported CoFe2O4 NPs were successfully
synthesized via a simple adsorption process; (ii) the CoFe2O4
For our rst set of experiments, we investigated the kinetic
characteristics of the luminol CL system in the presence of
CoFe2O4 NPs (Fig. S1, ESI†). As can be seen, no signicant CL
was observed for luminol itself. However, CoFe2O4 NPs show the
enhancement effects of luminol CL. In order to study the role of
CoFe2O4 NPs, the CL spectra of the following systems were
studied by F-4500 uorimetry: (a): luminol solution; (b):
CoFe2O4 + luminol; (c): SBA-15 supported CoFe2O4 + luminol;
(d): SiO2 supported CoFe2O4 + luminol; and (e): Al2O3 supported
CoFe2O4 + luminol. The results demonstrate that all the above
systems give one peak situated at about 425 nm, indicating that
the role of CoFe2O4 NPs or supported CoFe2O4 NPs is only an
enhancement reagent because there is no new emitter produced
in the reaction. In other words, the presence of support mate-
rials has not caused the production of the new CL emitter.
Therefore, it can be concluded that addition of CoFe2O4 NPs or
supported CoFe2O4 NPs does not produce a new luminophor of
luminol CL reaction. The luminophor for the CL system was still
the excited-state 3-aminophthalate anions (AP2À). The
enhanced CL signals were thus ascribed to the possible catalysis
from CoFe2O4 NPs or supported CoFe2O4 NPs. The catalytic
activity of CoFe2O4 NPs may be derived from their characteristic
of peroxidase enzyme mimic. Recently, Fe3O4 nanoparticle, an
inorganic nanomaterial, has been discovered to possess an
intrinsic enzyme mimetic activity similar to that found in
natural peroxidases.4 Compared with the natural HRP, the
Fe3O4 NPs exhibited higher catalytic activity and were more
robust when exposed to a wide range of temperature and pH
values. Based on the above advantages of the Fe3O4 NPs, Wang
aThe Key Laboratory of Luminescence and Real-time Analysis, Ministry of Education,
College of Chemistry and Chemical Engineering, Southwest University, Beibei,
Chongqing 400715, China. E-mail: ymhuang@swu.edu.cn
bLuohe Medical College, Luohe, Henan 462002, China
cCollege of Chemistry and Chemical Engineering, Yangtze Normal University, Fuling,
Chongqing 408003, China
† Electronic supplementary information (ESI) available: Experimental details and
supporting gures. See DOI: 10.1039/c3ta14697a
2482 | J. Mater. Chem. A, 2014, 2, 2482–2486
This journal is © The Royal Society of Chemistry 2014

View Article Online
Communication
Journal of Materials Chemistry A
and co-workers used Fe3O4 as an articial peroxidase to deter-
mine H2O2 and glucose.2b The peroxidase enzyme mimetic
activity of CoFe2O4 NPs or supported CoFe2O4 NPs was
demonstrated by using TMB, which is typically HRP substrate in
various bioassays, and most recently was used to demonstrate
the peroxidase-like activity of iron oxide NPs.2b,4 Upon the
addition of H2O2 and TMB, CoFe2O4 NPs or supported CoFe2O4
NPs can produce a blue color reaction (Fig. S2, ESI†), indicating
that CoFe2O4 NPs or supported CoFe2O4 NPs have peroxidase-
like catalytic activity. Interestingly, the supported CoFe2O4 NPs
catalyze the fast oxidation (within minutes) of TMB even in the
absence of H2O2 (Fig. 1a), which is a commonly used electron
acceptor or oxidizing agent in the peroxidase-catalyzed reac-
tions. This demonstrated that CoFe2O4 NPs or supported
CoFe2O4 NPs also exhibit oxidase-like activity. Furthermore,
results in Fig. 1b suggest that the catalytic activity of the sup-
ported CoFe2O4 NPs is pH-dependent and support-dependent
clearly. The ability of the supported CoFe2O4 NPs to oxidize
TMB decreases with increase of solution pH from 4.0 to 6.0.
To investigate the effect of supporting materials on the CL
response, three mesoporous materials, namely Al2O3, SiO2, and
SBA-15, were used. Microscope images suggest sphere-like
shape of SiO2 and Al2O3 particles with diameter of micrometer
Fig. 2 (A) SEM images of the commercial SiO2, the commercial Al2O3,
and SBA-15 (from left to right). (B) N2 adsorption–desorption isotherm
curves of three mesoporous materials. Inset: pore size distribution
curves of SBA-15, the commercial SiO2, and the commercial Al2O3.
range (Fig. S3A, ESI†). SEM micrographs (Fig. 2A) show that the like with ordered porous structure. SBA-15 has the typical
disordered wormhole like arrangement of pores is observed on wheat-like morphology and consists of aggregates of uniform
the surface of SiO2 particles, indicating the formation of the rope-like particles, in agreement with the results reported
mesoporous structure. The Al2O3 particle morphology is layer- elsewhere.5 The N2 adsorption–desorption isotherms of the
three supports (Fig. 2B) exhibiting a type IV isotherm with a
hysteresis loop, clearly demonstrate the mesoporous charac-
teristics of the three supports. The pore size distribution curves
of the three supports are shown in the inset of Fig. 2B. The pore
sizes of Al2O3, SBA-15 and SiO2 calculated using the BJH method
(Table S1, ESI†) were 4.47 nm, 5.85 nm, and 13.40 nm, respec-
tively. The surface areas of Al2O3, SBA-15 and SiO2 are 183.8 m2
gÀ1, 320.2 m2 gÀ1 and 354.5 m2 gÀ1, respectively. Compared
with SBA-15 and Al2O3, SiO2 shows signicant elevation of the
adsorption plateau in the isotherm, indicating large pore
volume. However, the pore volume of Al2O3 is lower than that of
SBA-15. This may be due to its more condensed network
construction. Due to the mesoporous characteristics of the
three supports, good adsorbing capability for CoFe2O4 NPs is
expected. The results of FTIR indicate that the spectrum of
CoFe2O4-coated support is very similar to that of the support
(Fig. S3B†). The difference spectrum shows characteristic
CoFe2O4 absorption bands (inset of Fig. S3B†), suggesting
unambiguously that CoFe2O4 was coated on the surface of the
support, which was further conrmed by the very similar
particle size distribution between coated particles and uncoated
ones (Fig. S3A†).
The as-prepared particles were characterized via CL to study
the response to their pH. In order to do this, rst, we performed
pH optimization of the luminol solution on the CL response.
Due to the nature of the luminol reaction, which is more favored
under basic conditions, the effects of pH of the luminol solution
on the CL intensity were investigated in the range of pH 10.9–
Fig. 1 (a) Images of production of colored product upon addition of
CoFe2O4 and supported CoFe2O4 NPs to TMB at pH 3.5 (0.2 mol LÀ1
acetate buffer), and subsequently being quenched by H2SO4. (b) Effect
of pH on oxidation of TMB catalyzed by the supported CoFe2O4 NPs in
12.3 (Fig. S4, ESI†). As shown, the highest CL intensity was
obtained at pH 11.7 (0.1 mol LÀ1 carbonate buffer). It was found
the absence of H2O2, (A): SBA-15/CoFe2O4 NPs; (B): SiO2/CoFe2O4
NPs; and (C): Al2O3/CoFe2O4 NPs.
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 2482–2486 | 2483

View Article Online
Journal of Materials Chemistry A
Communication
that the pH of the whole CL reaction was close to the pH of the
luminol solution, revealing that the pH of the luminol-dissolved
oxygen CL reaction system was dominated by the pH of the
luminol solution. So, we selected 11.7 as optimal luminol
solution pH.
Next, we investigated the response to pH of the as-prepared
particles from 2.0 to 7.0 and from 7.0 back to 2.0 (Fig. 3).
Interestingly, the CL emission clearly decreased when the pH
was increased from 2.0 to 7.0. As seen, the pH of the CL reaction
system increased slightly with an increase in the pH of the
mesoporous material supported CoFe2O4 NPs (Fig. S5, ESI†).
Thus, it was expected that the CL response would increase
somewhat with the increase in the pH of the CL reaction due to
the nature of the luminol CL reaction. This result suggests that
the pH of the mesoporous material supported CoFe2O4 NPs
could affect not only the pH of the CL reaction, but also their
activities. Result of the control experiment indicated that this
pH-dependent catalytic activity is not caused by the nature of
the luminol CL reaction, but the mesoporous material sup-
ported CoFe2O4 NPs themselves (Fig. 3). This was conrmed by
the difference of the color variation of TMB oxidation at
different pH values in the presence of the supported CoFe2O4
NPs (Fig. 1).
In a reversibility experiment, the pH of the SiO2 supported
CoFe2O4 NPs was changed from 7.0 to 2.0 and back to 7.0 three
times, and the CL emission reached the expected value in all
cases (Fig. 4), indicating a good reversibility of this sensing
material. The effect of the nanoparticle size on the present CL
reaction in the size (hydrated diameter) from 152 to 606 nm was
investigated. As seen, the CL intensity decreased with
increasing the diameter of CoFe2O4 NPs (Fig. S6, ESI†). The
supported NPs samples showed good dispersion of CoFe2O4
NPs on the surface of the mesoporous supports (Fig. S7, ESI†).
Fig. 4 Reversibility of the pH tunable catalytic activity of CoFe2O4 NPs
supported on SiO2. The pH of SiO2 supported CoFe2O4 NPs was
changed from 7.0 to 2.0 repeatedly. The CL emission intensity was
plotted for each measurement. Conditions: 2.0 Â 10À6 mol LÀ1
luminol in 0.1 mol LÀ1 Na2CO3–NaHCO3 buffer (pH 11.7); SiO2 sup-
ported CoFe2O4 were made by 2.14 mg LÀ1 CoFe2O4 and 20 mg LÀ1
SiO2.
The size of CoFe2O4 NPs on three supports is almost the same.
Clearly, the size of the supported CoFe2O4 NPs on three
supports is smaller than that of the unsupported CoFe2O4 NPs.
The dispersion of CoFe2O4 NPs on the supports made them
more stable and exposed more active sites to participate in the
CL reaction, leading to much better catalytic activities than the
unsupported NPs. This size effect on the CL response is
consistent with that reported by Cui et al.6
Fig. 5 illustrates the dependency of CL response on super-
cial charge of the as-prepared NPs. As seen, the catalytic activity
increased dramatically in varying the zeta potential from
negative to positive. The catalytic ability of the CoFe2O4 NPs
increased with increasing zeta potential and varied with support
in the order Al2O3 > SiO2 > SBA-15. This can be tentatively
explained by the affinity improvement by enhancing electro-
static interaction between the substrate and the nanoparticle
surface.7 Luminol carries two amine groups with negative
charge under strong basic conditions,2d likely yielding stronger
affinity towards positively charged support. Hence, the sup-
ported CoFe2O4 NPs should be of positive charge and the
employed SiO2 or Al2O3 might provide the source of positive
charge at appropriate pH values. Hence, the rationale for varied
Fig. 3 Reversible variation of the CL response with pH of CoFe2O4
NPs (A), SBA-15 supported CoFe2O4 NPs (B), SiO2 supported CoFe2O4
NPs (C) and Al2O3 supported CoFe2O4 NPs (D). Conditions: 2.0 Â 10À6
mol LÀ1 luminol in 0.1 mol LÀ1 Na2CO3–NaHCO3 buffer (pH 11.7);
CoFe2O4 concentration: 2.14 mg LÀ1; SBA-15, SiO2, Al2O3 supported Fig. 5 Plots of CL responses versus zeta potential for different
CoFe2O4 were made by 2.14 mg LÀ1 CoFe2O4 and 20 mg LÀ1 SiO2, CoFe2O4 NPs with luminol as the substrate. Zeta potentials were from
20 mg LÀ1 Al2O3, and 8 mg LÀ1 SBA-15, respectively.
Fig. S8.†
2484 | J. Mater. Chem. A, 2014, 2, 2482–2486
This journal is © The Royal Society of Chemistry 2014

View Article Online
Communication
Journal of Materials Chemistry A
CL response was that affinity was alerted by changes in elec-
trostatic interaction between supported CoFe2O4 NPs and
luminol. Furthermore, the intensity of supercial charge on
NPs appeared to inuence the degree to which CL response was
alerted, as the CL response varied with the varied zeta potential.
Among three studied mesoporous materials, Al2O3 supported
CoFe2O4 NPs had the highest positive charge at given pH.
Hence, Al2O3 supported CoFe2O4 NPs showed the highest
catalytic activity in the luminol CL reaction.
Results shown in Fig. S1† clearly demonstrated that luminol
was oxidised to AP2À during the CL reaction because the lumi-
nophor for the CL system was still AP2À. In order to understand
the possible mechanism of the enhanced CL reaction, the
inuence of O2 on the present CL reaction was studied. When
the solutions were purged with O2, the relative CL response
increased by 30%. However, when purged with N2, it decreased
by 35% (Fig. S9, ESI†). These results implied that O2 partici-
pated in the CL process, indicating the important role of the
dissolved O2 in the luminol CL reaction. However, enhance-
ment of the CL signal by CoFe2O4 or supported CoFe2O4 NPs
suggested that the oxidative activity of the dissolved O2 was
activated by CoFe2O4 or supported CoFe2O4 NPs, which was
further conrmed by TMB oxidation by O2 catalyzed by CoFe2O4
NPs under acidic conditions (Fig. 1). Also, the scavengers of
various reaction oxygen species were used to conrm the
emitting species. As shown in Table 1, the CL intensity was
almost totally quenched by the addition of 1 mmol LÀ1 ascorbic
acid (scavengers of cOH radical and O2cÀ radical) or 1 mM
thiourea (scavengers of cOH radical), showing that abundant
cOH radicals were generated in the reaction.8 More than 99% of
the CL emission was inhibited by the addition of 0.5 mg mLÀ1
SOD, suggesting that O2cÀ was produced and played a role in the
CL emission process. O2cÀ may come from the oxygen dissolved
in the solution.9 Aer production, the recombination reaction
Scheme
1
Possible CL mechanism from the reaction between
CoFe2O4 or SBA-15 supported CoFe2O4 NPs and luminol.
support CoFe2O4 NPs and negatively charged luminol anions
occurred, this could produce much more active radical species,
such as cOH and O2cÀ, and lead to yield more 1O2 on the surface
of mesoporous material support CoFe2O4 NPs accompanied by
strong CL emission. Based on the above discussion, the
possible CL mechanism, using SBA-15 as a model mesoporous
material, could be expressed in a simple form as shown in
Scheme 1.
In summary, we have successfully synthesized three meso-
porous material (SBA-15, SiO2 and Al2O3) supported CoFe2O4
NPs through a simple adsorption method, and demonstrated
that the mesoporous material supported CoFe2O4 NPs exhibited
different levels of unique oxidase-like activity in the order of
Al2O3 > SBA-15 > SiO2 in terms of TMB color reaction, showing
support dependence; this order was probably related to their
supercial charge. Their oxidase-like activity also showed pH
dependence, and could be reversibly controlled by their pH. The
result clearly demonstrated the effective manipulation of the
enzyme-like activity of NPs by the mesoporous materials. The
unique properties of the as-prepared CoFe2O4 NPs offer a
strategy for the preparation of simple and efficient multi-func-
tional catalysts with magnetism, oxidase-like activity, and pH-
sensitivity.
1
of OHc and O2cÀ would generate O2,10 which was conrmed
with the signicantly quenching effects upon the addition of
NaN3 (scavenger of singlet oxygen). The reaction of the
produced 1O2 with luminol might be responsible for the CL
emission at 425 nm. A 1O2-induced luminol CL mechanism was
also suggested recently by Huang et al.9,10
When mesoporous materials, such as Al2O3, SiO2 and SBA-
15, were used to support CoFe2O4 NPs, strong electrostatic
interaction between positively charged mesoporous material
Acknowledgements
The nancial support of the research by the Natural Science
Foundation of China (no. 21075099, no. 21275021) and the
Fundamental Research Funds for the Central Universities
(XDJK2013C114, XDJK2013A022) are acknowledged.
Table 1 Effects of different radical scavengers on the CL of the
luminol–O2 system in the presence of Al2O3 supported CoFe2O4 NPsa
Scavengers
H2O
Intermediates Concentration Percent inhibitionb (%)
Notes and references
/
/
0
97.2
99.3
1 H. Wei and E. Wang, Chem. Soc. Rev., 2013, 42, 6060.
2 (a) X. Liu, Q. Wang, H. Zhao, L. Zhang, Y. Su and Y. Lv,
Analyst, 2012, 137, 4552; (b) H. Wei and E. Wang, Anal.
Chem., 2008, 80, 2250; (c) Z. Wang, F. Liu and C. Lu,
Biosens. Bioelectron., 2012, 38, 284; (d) Z. Wang, F. Liu and
C. Lu, Chem. Commun., 2011, 47, 5479; (e) S. Nath,
C. Kaittanis, V. Ramachandran, N. S. Dalal and J. M. Perez,
Ascorbic acid OHc, O2cÀ
1 mmol LÀ1
1 mmol LÀ1
Thiourea
NaN3
SOD
OHc
1O2
10 mmol LÀ1 44.2
0.5 mg mLÀ1 99.1
O2cÀ
a
Solution conditions were 2 Â 10À6 mol LÀ1 luminol in 0.1 mol LÀ1
Na2CO3–NaHCO3 buffer (pH 11.7) and 2.14 mg LÀ1 CoFe2O4 in 20 mg
LÀ1 Al2O3. Mean value of three measurements.
b
This journal is © The Royal Society of Chemistry 2014
J. Mater. Chem. A, 2014, 2, 2482–2486 | 2485

View Article Online
Journal of Materials Chemistry A
Communication
Chem. Mater., 2009, 21, 1761; (f) X.-Q. Zhang, S.-W. Gong,
Y. Zhang, T. Yang, C.-Y. Wang and N. Gu, J. Mater. Chem.,
2010, 20, 5110; (g) Y. Song, K. Qu, C. Zhao, J. Ren and
X. Qu, Adv. Mater., 2010, 22, 2206; (h) Y. Song, X. Wang,
C. Zhao, K. Qu, J. Ren and X. Qu, Chem.–Eur. J., 2010, 16,
3617; (i) W. Shi, Q. Wang, Y. Long, Z. Cheng, S. Chen,
H. Zheng and Y. Huang, Chem. Commun., 2011, 47, 6695;
(j) X. Wang, K. Qu, B. Xu, J. Ren and X. Qu, Nano Res.,
2011, 4, 908; (k) Y. Guo, L. Deng, J. Li, S. Guo, E. Wang and
S. Dong, ACS Nano, 2011, 5, 1282; (l) Y. Tao, Y. Lin,
Z. Huang, J. Ren and X. Qu, Adv. Mater., 2013, 25, 2594; (m)
A. Asati, S. Santra, C. Kaittanis, S. Nath and J. M. Perez,
Angew. Chem., Int. Ed., 2009, 48, 2308; (n) J. M. Slocik,
A. O. Govorov and R. R. Naik, Angew. Chem., Int. Ed., 2008,
47, 5335; (o) T. Kwon, M. Min, H. Lee and B. J. Kim,
J. Mater. Chem., 2011, 21, 11956; (p) H. Chen, Y. Li,
F. Zhang, G. Zhang and X. Fan, J. Mater. Chem., 2011, 21,
3 C. Perego and R. Millinib, Chem. Soc. Rev., 2013, 42, 3956.
4 L. Gao, J. Zhuang, L. Nie, J. Zhang, Y. Zhang, N. Gu, T. Wang,
J. Feng, D. Yang, S. Perrett and X. Yan, Nat. Nanotechnol.,
2007, 2, 577.
5 T. Kang, Y. Park, K. Choi, J. S. Lee and J. Yi, J. Mater. Chem.,
2004, 14, 1043.
6 H. Cui, J. Z. Guo, N. Li and L. J. Liu, J. Phys. Chem. C, 2008,
112, 11319.
7 (a) F. Zhang, Z. Ali, F. Amin, A. Feltz, M. Oheim and
W. J. Parak, ChemPhysChem, 2010, 11, 730; (b) F. Yu,
Y. Huang, A. J. Cole and V. C. Yang, Biomaterials, 2009, 30,
4716.
8 (a) R. B. Li, T. Kameda, A. Toriba, K. Hayakawa and J. M. Lin,
Anal. Chem., 2012, 84, 3215; (b) L. Zhang, Z. Zhang, C. o. Lu
and J.-M. Lin, J. Phys. Chem. C, 2012, 116, 14711.
9 D. M. Wang, M. X. Gao, P. F. Gao, H. Yang and C. Z. Huang,
J. Phys. Chem. C, 2013, 117, 19219.
17658; (q) J. Yin, H. Cao and Y. Lu, J. Mater. Chem., 2012, 10 D. M. Wang, Y. Zhang, L. L. Zheng, X. X. Yang and
22, 527.
C. Z. Huang, J. Phys. Chem. C, 2012, 116, 21622.
2486 | J. Mater. Chem. A, 2014, 2, 2482–2486
This journal is © The Royal Society of Chemistry 2014