Enhanced oxidase/peroxidase-like activities of aptamer conjugated MoS2/PtCu nanocomposites and their biosensing application

Article abstract of DOI:10.1039/c6ra03507h

Hybrid composite materials are particularly useful and offer great opportunities for catalysis due to their multifunctionalities. Taking advantage of the high catalytic properties of bimetallic alloy nanoparticles, the large specific surface area and co-catalytic function of MoS₂ nanosheets, we prepare a novel MoS₂/PtCu nanocomposite with intrinsic high oxidase- and peroxidase-like activity. The preparation of MoS₂/PtCu nanocomposites does not require organic solvents or high temperature. The introduction of single-layer MoS₂ nanosheets not only improves porous PtCu nanoparticles with a fine dispersion, but also readily incorporates recognition elements. As a mimic oxidase, the independence of hydrogen peroxide shows the good biocompatibility of MoS₂/PtCu for promising bioapplications. On the basis of oxidase-like activity, a novel colorimetric aptasensor (apt-MoS₂/PtCu) was developed and its application in the colorimetric detection of cancer cells with different MUC1-protein densities was demonstrated. The as-prepared apt-MoS₂/PtCu shows good sensitivity and selectivity to targeting cells. The proposed strategy will facilitate the utilization of MoS₂-based nanocomposites with high oxidase/peroxidase activities in biotechnology, biocatalysis etc.

Full text of DOI:10.1039/c6ra03507h

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Enhanced Oxidase/peroxidase-like Activities of Aptamer
Conjugated MoS /PtCu Nanocomposites and Their Biosensing
2
Application
Received 00th January 20xx,
Accepted 00th January 20xx
†
†
Cui Qi , Shuangfei Cai , Xinhuan Wang, Jingying Li, Zheng Lian, Shanshan Sun, Rong Yang* and
Chen Wang*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Hybrid composite materials are particularly useful and offer great opportunities for catalysis due to their
multifunctionalities. Taking advantage of the high catalytic properties of bimetallic alloy nanoparticles, the
large specific surface area and co-catalytic function of MoS
nanocomposite with intrinsic high oxidase- and peroxidase-like activity. The preparation of MoS
nanocomposites does not require organic solvents or high temperature. The introduction of single-layer
MoS nanosheets not only improves porous PtCu nanoparticles with a fine dispersion, but also readily
incorporates recognition elements. As a mimic oxidase, the independence of hydrogen peroxide shows
good biocompatibility of MoS /PtCu for promising bioapplication. On the basis of oxidase-like activity, a
novel colorimetric aptasensor (apt-MoS /PtCu) was developed and its application in colorimetric detection
of cancer cells with different MUC1-protein densities was demonstrated. The as-prepared apt-MoS /PtCu
shows good sensitivity and selectivity to targeting cells. The proposed strategy will facilitate the utilization
2
nanosheets, we prepare a novel MoS
2
/PtCu
2
/PtCu
2
2
2
2
of MoS
2
-based nanocomposites with high oxidase/peroxidase activities in biotechnology, biocatalyst and
etc.
to exhibit improved catalytic performance because of the synergistic
17ꢀ22
Introduction
effect and the electronic effect.
Among the enzyme nanomimics,
Owing to their unique properties, nanomaterials are attractive for
highꢀefficiency catalysts and have been extensively studied during
hybrid composite materials are particularly impressive and offer
great opportunities for catalysis, since the combination of the
respective properties of each component can achieve cooperatively
enhanced performances. An increasing number of hybrid complexes
with inorganic nanomaterials incorporated with different matrixes
1
, 2
the past decade. In addition, nanomaterialꢀbased enzyme mimics
for colorimetric sensing have been applied in catalyst and bioassay.
In comparison with natural enzymes, nanomaterialꢀbased enzyme
mimics have advantages of low costs, tunable catalytic activities,
high stability against stringent reaction conditions, and ease of
storage and treatment. The above robust physical or chemical
properties make them promising candidates for colorimetric
biosensing. Although a number of different nanomaterials were
found with peroxidaseꢀ or oxidaseꢀlike activity, such as metal
23ꢀ26
27, 28
have been applied in catalyst.
magnetic nanoparticle/CNT
nanocomposites and noble metalꢀgraphene hybrids
Grapheneꢀhemin composites,
2
9
nanocomplexs,
3 4
GOꢀFe O
30
31, 32
have been
proved to possess new and/or enhanced functionality that cannot be
realized by either component alone. Therefore, to design and
fabricate new multifunctional hybrid nanocomposites with high
enzymeꢀlike activity would be helpful to expand their applications in
biomedical fields, such as optical biosensors and biocatalysts.
Considered as typical transition metal dichalcogenides and novel
3ꢀ8
9ꢀ12
13
oxides, carbon nanomaterials,
quantum dots, noble metal
1
4ꢀ16
complex,
and etc., bimetallic nanoalloys have been demonstrated
inorganic graphene analogues, MoS has been widely studied and
2
3
3ꢀ
applied in catalyst, sensing, energy storage and electronic devices.
3
8
Besides the advantages of good chemical stability, low cost and
3
2
9ꢀ42
environmental friendliness, porous MoS
with large specific
surface area and catalytically active sites make them excellent
candidates for capturing numerous biomolecules and provides
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promising opportunities for the development of the signal monometallic counterparts, and the porous nanostructure could also
amplification strategy, which should be extremely attractive in the increase the contact with substrates; (iii) as the large surface area of
area of biosensors. Recently, it has been reported that MoS
2
2
singleꢀlayer MoS nanosheets, large amounts of porous PtCu
nanosheets possessed an intrinsic peroxidaseꢀlike catalytic activity, nanoparticles could be immobilized on it with a fine dispersion,
which could catalyze the oxidation of 3,3,5,5ꢀtetramethylbenzidine resulted in remarkable amplification of the colorimetric signal and
(
TMB) in the presence of hydrogen peroxide (H O ) to produce a improved sensitivity. The large surface area could also improve
2 2
4
3, 44
blue color.
The higher peroxidaseꢀlike activity with greater immobilization sites for biological molecules (such as streptavidin);
nanosheet composites (iv) considering that most of the reported colorimetric biosensors
than hemin alone was also demonstrated. Although a number of need to go through complicated covalent modifications, our
dispersity in aqueous solution of hemin/ MoS
2
4
5
4
6ꢀ49
metal/ MoS nanosheet hybrids were successfully synthesized,
approach appeared to be simpler, and provided a general surface
their functionalities have not been well explored and very few modification method through biotinꢀstreptavidin interactions. By
biosensor applications have been reported. altering different recognition elements, one can develop different
Here, we designed a colorimetric biosensor based on aptamerꢀ colorimetric biosensors with desired demands.
functionlizationed MoS /PtCu nanocomposites with high oxidaseꢀ
2
2
like activity and demonstrated its biosensor application for the
detection of cancer cells. The working principle is illustrated in
Results and discussion
Characteration of MoS
2
/PtCu nanocomposites
Scheme 1.The synthesis of the MoS
2
/PtCu nanocomposites is based
on the surface of MoS
on coꢀreduction of two metal salts by NaBH
4
2
The synthesis of MoS /PtCu nanocomposites was carried out
2
nanosheets. On the basis of the oxidaseꢀlike activity of MoS /PtCu without organic solvents or high temperature, and the obtained
2
nanocomposites and mucin 1 (MUC1) aptamers, selective binding solution with good dispersity showed high stability against
2
aptꢀMoS /PtCu nanocomposites on the MUC1 overexpressed cells aggregation (Fig. S1). Transmission electron microscopy (TEM)
can convert the recognition process into quantitative colorimetric image (Fig. 1a) revealed that porous PtCu nanoparticles had a
signal. This aptameric nanobiosensor has several advanced homogeneous distribution on the surface of MoS nanosheets with an
2
2
2
properties: (i) the preparation of MoS /PtCu nanocomposites were average size less than 20 nm. The crystal structure of MoS /PtCu
simple and rapid, without organic solvents or high temperature was characterized by Xꢀray diffraction (XRD). The four peaks
involved in the entire synthesis process; (ii) the formation of porous appeared at 40.48, 46.86, 68.85 and 82.67 were coincidently located
PtCu nanoalloys improved catalytic activity comparing with between Pt (reference code: 01ꢀ087ꢀ0646) and Cu (reference code:
0
1ꢀ085ꢀ1326), which could be indexed as the (111), (200), (220) and
(
(
311) planes of PtCu nanoalloys (Fig. 1c). Highꢀresolution TEM
HRꢀTEM) and Xꢀray photoelectron spectroscopy (XPS) were
further used to investigate the structure and element distributions of
the MoS /PtCu nanocomposites. As shown in HRꢀTEM image (Fig.
b), the lattice spacing of 0.19 nm and 0.22 nm are corresponding to
2
1
the (200) plane and the (111) plane of PtCu nanoalloys respectively.
The lattice spacing of 0.27 nm was corresponding to the (100) plane
2
of MoS nanosheets. Pt 4f peak, Cu 2p peak, Mo 3d peak and S 2p
peak observed from XPS spectra (Fig. 1d and Fig. S2) were further
confirmed the chemical state and the successful location of PtCu
2
nanoalloys on MoS nanosheets. The nanocomposite content was
also analyzed by inductively coupled plasma optical emission
spectroscopy (ICPꢀOES). The element concentrations of Pt and Cu
were 0.117 mM and 0.016 mM respectively. The atomic ratio of
Pt/Cu was 88:12.
Scheme 1. Schematic representation of preparation of aptamer-
functionlized MoS /PtCu colorimetric biosensor and its application
for cancer-cell detection.
2
2
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Enzyme-like activity of MoS
2
/PtCu nanocomposites
bubbling MoS
2
/PtCu nanocomposite dispersion with nitrogen to
remove dissolved oxygen, the reaction rate of TMB oxidation
decreased dramatically (Fig. 2b). The above results indicated that
The oxidaseꢀlike activity of MoS /PtCu nanocomposites was
2
investigated in catalysis of the substrates 2,2’ꢀazinoꢀbis(3ꢀ
ethylbenzoꢀthiazolineꢀ6ꢀsulfonic acid) diammonium salt (ABTS),
TMB and oꢀphenylenediamine (OPD), which had been used to
demonstrate the oxidaseꢀ or peroxidaseꢀlike activities of other
2
MoS /PtCu nanocomposites exhibited an intrinsic oxidaseꢀlike
activity, and the dissolved oxygen was the electron acceptors for the
oxidation in the absence of H O .
2
2
In order to elucidate the catalytic reaction mechanism, it is
essential to confirm the reactive oxygen species produced during the
reaction. Terephthalic acid (TA) was reported as a fluorescence
nanoparticles. As shown in Fig. 2a, MoS /PtCu nanocomposites
2
could quickly catalyze the oxidation of the three common
chromogenic substrates without H
2
O
2
in phosphate buffer, producing
/PtCu
•
probe to confirm the generation of OH, which formed highly
the typical colors. The control experiment without MoS
2
•
50, 51
fluorescent 2ꢀhydroxy terephthalic acid after reacting with OH.
nanocomposites showed negligible color variation. Moreover, after
As shown in Fig. S3, the appearance of an emission peak at 425nm
suggested the formation of the fluorescent products, which implied
•
the production of OH after the interaction between MoS
2
/PtCu
nanocomposites and the dissolved oxygen in solution.
The influence of the composition for the catalytic activity was
studied. As shown in Fig. 3, MoS /PtCu nanocomposites had the
highest oxidaseꢀlike activity among different composites. MoS
2
2
nanosheets and MoS /Cu nanocomposites can’t catalyze the
2
oxidation of TMB by dissolved oxygen in water, suggesting that
they didn’t have oxidaseꢀlike activity. MoS
2
/PtCu nanocomposites
/Pt
showed level of activity times higher than MoS
a
5
2
nanocomposites at the same molar concentration. The above results
indicated that the significant enhancement of the oxidaseꢀlike
activity for MoS
bimetallic catalyst and the porous nanostructure of the PtCu
nanoalloys. In addition, MoS /PtCu nanocomposites also had higher
oxidaseꢀlike activity than the free PtCu nanoalloys, which suggested
that MoS nanosheets might also contribute to the high catalytic
2
/PtCu nanocomposites might benefit from the
2
2
Fig. 1 (a) Representative TEM images, (b) HRTEM image, (c) XRD
activity of the nanocomposites. For the high surfaceꢀtoꢀvolume ratios
and strong surface adsorption capability, the substrates (such as
spectrum and (d) XPS spectrum of as-prepared MoS /PtCu
nanocomposites.
2
TMB) could be absorbed onto MoS nanosheets efficiently. Hence
2
the substrates and the active sites of PtCu nanoalloys located on
2
MoS nanosheets were confined in a nanoscale region, which could
enhance the catalytic activity of PtCu nanoalloys.
Furthermore, the peroxidaseꢀlike activity of MoS /PtCu
2
nanocomposites was also studied. As shown in Fig. S4, after
saturation with N
MoS /PtCu nanocomposites could catalyze the oxidation of TMB in
the presence of H to produce a blue color with maximum
absorbance at 652 nm. In contrast, no obvious reaction occurred in
2
for 1.5 h to clear dissolved oxygen in buffer,
2
2
O
2
Fig. 2 (a) Color evolution of ABTS, TMB and OPD oxidation by
the absence of MoS
2
/PtCu, suggesting the peroxidaseꢀlike activity of
dissolved oxygen using MoS /PtCu as catalysts. (b) The oxidase-like
2
2 2
activity of MoS /PtCu before and after saturation with N .
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aptamer S2.2 was conjugated to MoS /PtCu via the adsorption of
2
streptavidin on the nanocomposites. To maintain a high catalytic
activity and acquire a good effect on cell recognition, the adsorbent
concentrations of streptavidin and aptamer were optimized (Fig. S5).
2
Then the conjugation of aptamer S2.2 to MoS /PtCu was confirmed
by UV/Vis (Fig. S6), FTIR (Fig. S7) and zetaꢀpotential (Table S2)
measurements. In the UV/Vis spectra of the nanoconjugates, the new
peak at 265 nm, which due to the overlap interference of spectrum
peak at 260 nm for S2.2 aptamer and spectrum peak at 280 nm for
streptavidin, suggested the formation of aptꢀMoS /PtCu
2
nanoconjugates. The appearance of characteristic absorption bands
for ꢀNH, ꢀCH
considerable decrease in the zetaꢀpotential also indicated the
successful modification of aptamers on MoS /PtCu.
2
and phosphodiester bond in FTIR spectra and the
Fig.
3 The different oxidase-like activities of as-prepared
nanomaterials (MoS , MoS /Cu, MoS /Pt, PtCu and MoS /PtCu).
2
2
2
2
2
the nanocomposites. For comparison between MoS /PtCu and HRP,
2
Like oxidase and other nanomaterialsꢀbased oxidase mimics, the
catalytic activity of the prepared nanoconjugates was also dependent
on pH, temperature, and the concentration of substrates and catalyst
Michaelis constant (K
obtained using LineweaverꢀBurk plot and shown in Table S1. The
apparent K value of MoS /PtCu with H as the substrate was
m
) and maximal reaction velocity (Vmax) were
m
2
2 2
O
(
2
Fig. 4). For the catalytic oxidation of TMB by using aptꢀMoS /PtCu,
higher than that for HRP, consistent with the observation that a
higher H O concentration was required to achieve maximal activity
the optimal pH is 3.5. The nanoconjugates exhibited good stability
and high oxidaseꢀlike activity over a broad temperature range (30ꢀ60
2
2
for MoS
as the substrate was about two times lower than HRP, suggesting
that MoS /PtCu has a higher affinity to TMB than HRP.
2
/PtCu. The apparent K
m
value of the MoS
2
/PtCu with TMB
o
C). It was also found that the reaction speed depended on the
catalyst concentration with excess reactants. To get the optimal
2
colormetric signal for detection, the standard reaction were carried
o
out at 30 C by using 1 ꢁg aptꢀMoS
2
/PtCu in 1 mL of 20 mM
2
Production of aptamer-functionlizationed MoS /PtCu
nanoconjugates and application in cancer-cell immunoassay
A number of folic acidꢀfunctionalized colormetric biosensors based
on nanomaterial enzyme mimics have been reported to detect cancer
15, 22, 28, 31, 32
cells.
However, most of the reported colorimetric
biosensors need to go through complicated covalent modifications.
Simple and facile preparation processes for colorimetric biosensors
2
are highly desired. Here we introduce streptavidin to MoS /PtCu
nanocomposites via physical adsorption, and then biotinylated
aptamers were connected to surfaces. Our approach provides a
general surface modification method through biotinꢀstreptavidin
interactions. The asꢀprepared nanocomposites were functionalized
5
2, 53
with a MUC1 aptamer termed S2.2 for cancerꢀcell detection.
MUC1 is a large transmembrane glycoprotein of the mucin family
overexpressed on the surface of most epithelial cancers (breast, lung,
5
2ꢀ55
prostate and ovarian cancer, etc.).
target for cancer therapy. The extraordinary surfaceꢀareaꢀtoꢀmass
ratio of MoS nanosheets and the negatively charged surface of
MoS /PtCu nanocomposites provide a convenient way for absorption
of streptavidin without needs of other modifications. Biotinylated
MUC1 is an attractive protein
2
Fig. 4 Dependence of the oxidase-like activity of apt-MoS
a) pH, (b) temperature, (c) TMB concentration and (d) apt-
MoS /PtCu nanocomposite concentration.
2
/PtCu on
2
(
2
4
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phosphate buffer solution (pH 3.5) with 10 ꢁL TMB (0.4 mM) as the whether S2.2 aptamer functionalized MoS /PtCu (aptꢀMoS /PtCu)
2
2
substrate.
could efficiently differentiate between target cells and control cells.
5
6ꢀ
By taking advantage of the oxidesꢀlike activity, selective binding In this study, two MUC1 negative cell lines (HEK293 and HepG2)
5
8
57ꢀ61
aptꢀMoS
2
/PtCu on the tumor cells can convert the recognition
and two MUC1 overexpressed cell lines (MCFꢀ7 and A549)
process into quantitative colorimetric signal (as shown in Scheme 1). were employed as control groups and target cells respectively.
For the colorimetric detection of cancer cells, it was first studied
Fig. 5 (a) Response of different cells using apt-MoS
2
/PtCu to TMB. (b) Colorimetric response of MCF-7 after incubation with different
nanoconjugates (i: no nanoconjugates; ii: MoS /PtCu; iii: ram-MoS /PtCu; iv: apt-MoS /PtCu). (c) The absorption values at 652 nm after
2
2
2
2
incubation with apt-MoS /PtCu depend on the number of MCF-7 cells.
As shown in Fig. 5a, an obvious difference of absorbance was demonstrate that the selective bound of aptꢀMoS
observed between target cells and control cells, which suggested that cells was indeed through the interaction between MUC1 proteins of
aptꢀMoS /PtCu could bind selectively to MUC1 overexpressed cells target cells and S2.2 aptamers. The proposed method might be
MCFꢀ7 and A549) and catalyze a color change reaction in the generalized for cancerꢀcell detection.
presence of TMB. The above results also indicated that the The nanoconjugates were then used for quantitative colorimetric
nanoconjugates could give specific response to cancer cells with detection of MUC1 overexpressed cells (MCFꢀ7). An increasing
different level of MUC1ꢀprotein expression. number of MCFꢀ7 cells were incubated with a constant amount of
To further demonstrate the selectivity to target cells through the aptꢀMoS /PtCu in PBS containing 0.5 % BSA for 1 h and
2
/PtCu to targets
2
(
2
interaction between MUC1 proteins and S2.2 aptamers, random subsequently washed. In the presence of TMB, the aptꢀMoS
2
/PtCu
DNA modified MoS /PtCu nanoconjugates (ramꢀMoS /PtCu) was conjugated cells catalyzed a color reaction that could be judged by
2
2
prepared and free S2.2 aptamers were used to locate the binding sites. the naked eye easily and be quantitatively monitored by the
The four samples are as follow: MCFꢀ7 cells only, 0.2 ꢁg absorbance change at 652 nm. The results were shown in Fig. 5c. As
MoS /PtCu with MCFꢀ7 cells, 0.2 ꢁg ramꢀMoS /PtCu with MCFꢀ7 the number of target cells increased, the absorbance at 652 nm
2
2
cells, and 0.2 ꢁg aptꢀMoS
2
/PtCu with MCFꢀ7 cells. As a result (Fig. changed rapidly, suggested that the increasing number of target cells
5
b), the absorbance of aptꢀMoS
2
/PtCu with MCFꢀ7 cells was translates into an increasing number of MUC1 proteins available for
/PtCu with MCFꢀ binding to aptꢀMoS /PtCu nanoconjugates. Using this method, as
significantly higher than the same amount of MoS
2
2
7
cells and the same amount of ramꢀMoS /PtCu with MCFꢀ7 cells, low as 300 MCFꢀ7 cells could be detected, demonstrating good
2
which suggested that aptꢀMoS
2
/PtCu show much stronger binding sensitivity of the method.
2 2
ability to MCFꢀ7 cells than MoS /PtCu and ramꢀMoS /PtCu. In
addition, MCFꢀ7 cells pretreated with free S2.2 aptamers showed a
marked decrease in the absorbance, given that the binding of aptꢀ
Conclusion
In summary, we have successfully prepared novel MoS
nanocomposites with excellent oxidaseꢀlike activity. As a mimic
oxidase, MoS /PtCu nanocomposites show several advantages over
natural enzymes and other existing alternatives. First, MoS /PtCu
2
/PtCu
2
MoS /PtCu to cells was blocked by S2.2 aptamers (Fig. S8). The
corresponding results could also be observed visually from the
images shown in Fig. S9. Consequently, the above results could
2
2
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can be prepared easily in a short time and have high stability against photoelectron spectrometer (Thermo Fisher ESCALAB 250Xi). The
aggregation. Second, the employment of MoS nanosheets as an composition of the products was determined by the inductively
2
ideal carrier improves the catalytic activity and leads to be ease of coupled plasma optical emission spectrometer (ICPꢀOES, Thermo
functional modification and effective absorption of modifiers or Scientific iCAP 6300). Zeta potential data was obtained using a
drugs. Furthermore, the oxidation of substrates is independent of nanoparticle analyzer (Malvern Zetasizer Nano ZS). FTꢀIR spectra
hydrogen peroxide, introducing better biocompatibility for were recorded on PerkinElmer Spectrum One FTꢀIR spectrometer in
promising biosensor applications. By taking advantage of MUC1 the transmission mode using CaF
aptamer conjugated MoS /PtCu, we develop a sensitive and selective
colorimetric aptasensor for cancerꢀcell detection based on the
oxidesꢀlike activity of MoS /PtCu nanocomposites. As the
preparation processes of the proposed aptasensor are easy and timeꢀ
saving, our work will facilitate the utilization of MoS /PtCu with
2
.
2
2
Enzyme-like activity of MoS /PtCu nanocomposites
2
To investigate the oxidaseꢀlike activity of MoS
2
/PtCu
nanocomposites, the reaction was carried out at 30 C by using 1ꢁg
MoS /PtCu in 1 mL of 20 mM phosphate buffer solution (pH 3.5)
o
2
2
intrinstic oxidase activity in bioassays and biotechnology by altering
different recognition elements with the practical demands, such as
aptamers, nuclei acids, antibodies and peptides.
with 10 ꢁL TMB (0.4 mM) as the substrate. The absorption spectra
were collected on a 96ꢀwell plate in Molecular Devices Spectramax
M5 microplate reader.
To investigate the apparent kinetic parameters, assays were
carried out under standard reaction conditions as described above by
Experimental Section
varying concentrations of TMB with a fixed concentration of H
or vice versa. The apparent kinetic parameters were calculated based
on the function ν =Vmax × [S] / (K + [S]), where ν is the initial
velocity, max is the maximal reaction velocity, [S] is the
concentration of the substrate and K is the Michaelis constant.
2 2
O
Preparation of MoS
2
/PtCu nanocomposites
Chitosanꢀmodified singleꢀlayer MoS
produced by a modified oleum treatment exfoliation process.
For a typical synthesis of MoS /PtCu nanocomposites, 3 mL
25 mg/L) MoS nanosheet aqueous dispersion was mixed with
3.3 ꢁL H PtCl aqueous solution (19.3 mM) and 7.5 ꢁL
Cu(OAc)
aqueous solution (20 mM). The mixture was stirred aptamers
in an iceꢀwater bath at 0°C for 15 min. Then
mM, 1 mL) aqueous solution was dropwise added into the
mixture under vigorous stirring. The addition time of NaBH
2
nanosheets were
m
6
2
V
2
m
(
2
2
2
6
2
Modification of MoS /PtCu nanocomposites with S2.2
2
，
4
NaBH (10.5
MoS /PtCu nanocomposite dispersion was mixed with streptavidin
2
aqueous solution (1.5 ꢁM) at first. The mixture was incubated at
room temperature for 5 h with shaking. Then streptavidin was
4
was 30min. After the reaction of 2 h, the resulting solution was
centrifuged and washed by water. The obtained precipitate was
reꢀdispersed in water before further characterization or
modification.
adsorbed onto MoS
was removed by centrifugation and repeatedly washing the sample
with water. The resulting stvꢀMoS /PtCu was reꢀdispersed in water
and then incubated with biotinylated S2.2 aptamer (2 ꢁM) at room
temperature for h. Unbound aptamers were removed by
centrifugation. The obtained aptꢀMoS /PtCu were reꢀdispersed in
2
/PtCu nanocomposites. Unbound streptavidin
2
1
Characterization
2
o
PBS after washing twice and stored at 4 C.
2
Transmission electron microscopy (TEM) images of MoS /PtCu
were obtained by a transmission electron microscope (FEI Tecnai
G2 20 SꢀTWIN) operating at an accelerating voltage of 200 kV.
Cell culture and treatment
High resolution TEM (HRꢀTEM) images were obtained by a highꢀ The human breast cancer cells (MCFꢀ7), human liver
resolution transmission electron microscopy (HRTEM, FEI Tecnai carcinoma cells (Hep G2) and human embryonic kidney 293
G2 F20 UꢀTWIN). The crystalline structure of the nanocomposites cells (HEK 293) were cultured in Dulbecco's modified Eagle's
was determined using a Xꢀray powder diffractometer (XRD, Bruker medium (Corning) supplemented with 10 % fetal bovine serum
o
D8 focus) with Cu Kα radiation (l= 1.5406 Å) at room temperature. in a humidified 37 C incubator with 5 % CO . The human lung
2
Xꢀray photoelectron spectra (XPS) were measured using an Xꢀray adenocarcinoma cells (A549) were cultured in Fꢀ12K medium
6
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(Corning) supplemented with 10 % fetal calf serum. For cell 16 J. Fan, J. J. Yin, B. Ning, X. C. Wu, Y. Hu, M. Ferrari, G. J.
Anderson, J. Y. Wei, Y. L. Zhao and G. J. Nie, Biomaterials,
2
assay, 1 ꢁg/mL aptꢀMoS /PtCu nanocomposites were incubated
2
011, 32, 1611ꢀ1618.
with different cell lines in 200 µL PBS containing 0.5 % BSA
for 1 h at room temperature and then centrifuged. The
precipitates were washed three times with PBS and then 150 µL
1
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0
.4 mM TMB was added. The samples were incubated in
phosphate buffer (pH 3.5) for 20 min to allow development of
the blue color. The absorbance of the oxidation product was
monitored at 652 nm with a microplate reader.
2
2
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This work was supported by National Natural Science Foundation of
China (21405027, 21573050 and 21501034) and Chinese Academy
of Sciences (XDA09030303). Financial support from CAS Key
Laboratory of Biological Effects of Nanomaterials and Nanosafety is
also gratefully acknowledged.
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DOI: 10.1039/C6RA03507H
Enhanced Oxidase/peroxidase-like Activities of Aptamer Conjugated MoS
2
/PtCu
Nanocomposites and Their Biosensing Application
†
†
Cui Qi , Shuangfei Cai , Xinhuan Wang, Jingying Li, Zheng Lian, Shanshan Sun,
Rong Yang* and Chen Wang*
2
Taking advantage of bimetallic alloy nanoparticles and MoS nanosheets, a
colorimetric aptasensor was developed for MUC1 overexpressed cancer cell
detection.