Photocatalysis-Based Nanoprobes Using Noble Metal-Semiconductor Heterostructure for Visible Light-Driven in Vivo Detection of Mercury

Article abstract of DOI:10.1021/acs.analchem.7b01602

The development of sensitive and reliable methods to monitor the presence of mercuric ions in cells and organisms is of great importance to biological research and biomedical applications. In this work, we propose a strategy to construct a solar-driven nanoprobe using a 3D Au@MoS₂ heterostructure as a photocatalyst and rhodamine B (RB) as a fluorescent and color change reporter molecule for monitoring Hg²⁺ in living cells and animals. The sensing mechanism is based on the photoinduced electron formation of gold amalgam in the 3D Au@MoS₂ heterostructure under visible light illumination. This formation is able to remarkably inhibit the photocatalytic activity of the heterostructure toward RB decomposition. As a result, OFF-ON fluorescence and color change are produced. Such characteristics enable this new sensing platform to sensitively and selectively detect Hg²⁺ in water by fluorescence and colorimetric methods. The detection limits of the fluorescence assay and colorimetric assay are 0.22 and 0.038 nM for Hg²⁺, respectively; these values are well below the acceptable limits in drinking water standards (10 nM). For the first time, such photocatalysis-based sensing platform is successfully used to monitor Hg²⁺ in live cells and mice. Our work therefore opens a promising photocatalysis-based analysis methodology for highly sensitive and selective in vivo Hg²⁺ bioimaging studies.

Full text of DOI:10.1021/acs.analchem.7b01602

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Article
Photocatalysis-Based Nanoprobes Using Noble Metal-Semiconductor
Heterostructure for Visible Light-Driven in vivo Detection of Mercury
Lihua Zhi, Xiaofan Zeng, Hao Wang, Jun Hai, Xiangliang Yang, Baodui Wang, and Yanhong Zhu
Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b01602 • Publication Date (Web): 14 Jun 2017
Downloaded from http://pubs.acs.org on June 16, 2017
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Photocatalysis-Based Nanoprobes Using Noble
Metal-Semiconductor Heterostructure for Visible
Light-Driven in vivo Detection of Mercury
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Lihua Zhi,†,§ Xiaofan Zeng,‡ Hao Wang,† Jun Hai,† Xiangliang Yang,‡ Baodui Wang,*,†
Yanhong Zhu*‡
†State Key Laboratory of Applied Organic Chemistry and Key Laboratory of Nonferrous Metal
Chemistry and Resources Utilization of Gansu Province, Lanzhou University, Gansu, Lanzhou,
730000, China.
‡College of Life Science and Technology, Huazhong University of Science and Technology,
Wuhan, 430074, P. R. China.
§College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou,
730070, P. R. China.
ABSTRACT
The development of sensitive and reliable methods to monitor the presence of mercuric ions in
cells and organisms is of great importance to biological research and biomedical applications. In
this work, we propose a strategy to construct a solarꢀdriven nanoprobe using a 3D Au@MoS2
heterostructure as a photocatalyst and rhodamine B (RB) as a fluorescent and color change
reporter molecule for monitoring Hg2+ in living cells and animals. The sensing mechanism is
based on the photoinduced electron formation of gold amalgam in the 3D Au@MoS2
heterostructure under visible light illumination. This formation is able to remarkably inhibit the
photocatalytic activity of the heterostructure toward RB decomposition. As a result, “OFF–ON”
fluorescence and color change are produced. Such characteristics enable this new sensing
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platform to sensitively and selectively detect Hg2+ in water by fluorescence and colorimetric
methods. The detection limits of the fluorescence assay and colorimetric assay are 0.22 and
0.038 nM for Hg2+, respectively; these values are well below the acceptable limits in drinking
water standards (10 nM). For the first time, such photocatalysisꢀbased sensing platform is
successfully used to monitor Hg2+ in live cells and mice. Our work therefore opens a promising
photocatalysisꢀbased analysis methodology for highly sensitive and selective in vivo Hg2+
bioimaging studies.
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TOC graphic
As wellꢀknown environmental pollutants, mercury ions (Hg2+), exert serious medical effects
because mercury accumulation in the human body through food chains and drinking water
causes dysfunction of cells and results in a wide variety of diseases in the brain, kidney, central
nervous system, etc.1–4 As a result of these deleterious effects of Hg2+ on humans, highly
sensitive and onꢀsite detection of Hg2+ ions in environmental and biological settings is
important.5,6 Recently, different approaches based on electrochemical and optical sensors,
organic chromophores or fluorophores, conjugated polymers, oligonucleotides, DNAase and
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proteins, as well as inorganic nanostructures, have been developed for the sensitive and selective
detection of Hg2+ ions.7–10 However, these methods might suffer from either low detection
sensitivity and throughput or poor analysis stability and abilities against background
interferences.
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With the development of nanoscience and nanotechnology, noble metal nanomaterialꢀbased
nanozymes have been utilized to probe heavy metal ions such as Hg2+ ions that could inhibit and
stimulate their catalytic activity through a specific Au+–Hg2+ interaction and the change in the
surface properties of Au nanoparticles (NPs) by forming AgꢀHg alloys.11 Such a catalysisꢀbased
analysis methodology may possess some advantages over traditional methods such as
fluorescenceꢀbased ones in terms of detection stability and targeting abilities against interference
from complicated media (i.e., blood). Unfortunately, to the best of our knowledge, no study has
reported the use of catalysisꢀbased analysis methodology to detect Hg2+ in living cells and
animals.
Recently, metalꢀsemiconductor heterostructures have emerged as ideal photocatalytic
materials, with the semiconductor generating charge carriers and the metal acting as a sink for
trapping electrons. For the case of metal Au, electron transfer is facilitated as the surface
plasmon of Au couples with the semiconductor exciton and enhances the excited state lifetime of
the photoelectron.12–17 Among semiconductor counterparts, monolayer MoS2, with a band gap of
1.8 eV,18 is generally considered a feasible candidate for use in photocatalysts19 owing to the
semiconducting property with band gaps ranging from the visible to the nearꢀinfrared and the
catalytic activity of its edge sites. However, heterostructures involving Au and MoS2 have been
studied mainly as photocatalysts20–22 and not as a sensor platform for the sensitive recognition of
target species in biological bodies. Moreover, the synthesis of these materials, which could
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facilitate metal/semiconductor Schottky contact and favorable electron transfer through this
interface for photocatalytic reactions, remains a challenge. Furthermore, previous studies suggest
that 3D architectures based on noble metal NPs and semiconductor materials are ideal
photocatalysts because they could offer long optical paths for efficient light absorption and rapid
electron–hole separation.23 Nonetheless, 3D structures assembled from MoS2 nanosheets (NSs)
and noble metal NPs with a Schottky junction are neither reported nor explored for the detection
of Hg2+ ions or other analytes in living cells and animals.
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The present study is the first to present a novel photocatalysisꢀbased 3D Au@MoS2
heterostructure nanoprobe for sensitive Hg2+ detection. In this work, a 3D Au@MoS2
heterostructure was prepared by photoirradiation of a DMF solution containing HAuCl4 and
MoS2 NSs under visible light illumination. The formed Au NPs directly deposited on the MoS2
NSs to form a 3D frame structure (Figure 1A), in which the effective Au/MoS2 Schottky contact
was produced. In this assembly process, no further ligand exchange steps were required. The
obtained 3D Au@MoS2 heterostructure showed remarkable absorption from the ultraviolet to the
nearꢀinfrared region and exhibited superior photocatalytic activity toward rhodamine B (RB)
decomposition. These effects resulted in the turning OFF of the fluorescence and color of RB
(Figure 1). However, in the presence of Hg2+, Hg2+ wrapped around the Au NPs of the 3D
Au@MoS2 heterostructure because of the strong affinity between Hg (II) and Au NPs.24 The
Hg2+ on the surface of the Au NPs were reduced to Hg0 in the form of gold amalgamation by the
photoinduced electrons. Thus, the photocatalytic activity of the 3D Au@MoS2 heterostructure
toward RB decomposition was suppressed, resulting in the turning ON of the fluorescence and
color of RB (Figure 1). Such characteristics enabled the 3D Au@MoS2 heterostructure to
sensitively and selectively detect Hg2+ in water by both fluorescence and colorimetric methods,
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achieving limits of detection of 0.22 and 0.038 nM, respectively. The detection system could also
monitor Hg2+ in cells and living bodies. Our strategy is the first to provide a new type of
photocatalysisꢀbased nanoprobe with high selectivity and sensitivity and is therefore suitable for
cell and living animal imaging.
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Figure 1. Illustration of the preparation of 3D Au@MoS2 heterostructure (A). Different magnification SEM
images of MoS2 NSs (B) and 3D Au@MoS2 heterostructure (C).
EXPERIMENTAL SECTION
.
Chemicals. HAuCl4 4H2O, Molybdenum(IV) sulfide (MoS2, 99%), 1.6 M nꢀbutyllithium
solution, Rhodamine B (RB) and metallic salts (NaNO3, KNO3, AgNO3, CaCl2, MgSO4,
.
.
.
Cd(NO3)2, Cu(NO3)2 3H2O, Co(NO3)2·6H2O, Ni(NO3)2 6H2O, Zn(NO3)2 6H2O, FeSO4,
.
Al(NO3).9H2O, Fe(NO3)3 9H2O, Hg(NO3)2) were purchased from major suppliers such as Sigmaꢀ
Aldrich and Alfa Aesar and used as received. MoS2 nanosheet solution was prepared by
chemical exfoliation method according to the published method.25
Instrumentation. The morphology of the samples was investigated by fieldꢀemission scanning
electron microscope (FEꢀSEM, FEI, Sirion 200). TEM images were taken on Tecna iꢀG2ꢀF30
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(FEI) transmission electron microscope at an acceleration voltage of 300 kV. Xꢀray powder
diffraction (XRD) patterns of the nanomaterials were recorded on a Bruker AXS D8ꢀAdvanced
diffractometer with Cu Kα radiation (λ=1.5418Å). N2 adsorptionꢀdesorption isotherms were
measured at 77 K after heating the samples at 150 0C for 8 h to remove any moisture and solvent
molecules presented in the pores with Micromeritics TriStar II 3020 analyzer. The Brunauerꢀ
EmmettꢀTeller (BET) method was utilized to calculate the specific surface areas (SBET). By using
the BarrettꢀJoynerꢀHalenda (BJH) model, the pore volumes and pore size distributions were
derived from the adsorption branches of isotherms. Xꢀray photoelectron spectroscopy (XPS)
measurements were performed on a PHIꢀ5702 multifunctional spectrometer using AlKα
radiation. Raman spectra were collected using a confocal microprobe Raman system (Renishaw,
RM2000). (FTꢀIR) spectra were recorded on a Nicolet FTꢀ170SX spectrometer. Au contents are
determined by inductively coupled plasmaꢀatomic emission spectrometry (ICPꢀAES, Varian
VISTAꢀMPX). UVꢀvisible adsorption spectra (UVꢀvis) were carried out on a UV 1750
spectrometer. Photocalysis was performed using Xenon lamp (HSXꢀF300) equipped with a
cutoff glass filter transmitting λ ≥ 420 nm surrounded by a waterꢀcooling quartz jacket to cool
the lamp.
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Synthesis of 3D Au@MoS2 heterostructure. 20 mg of MoS2 nanosheets were dissolved in 20
mL DMF and 20 mL deionized water to form a homogeneous solution. After sonicating for 30
min, 2 mL HAuCl4 (2 mM) solution was added to the above solution. The resulting mixture was
stirred under visible light irradiation (λ ≥ 420 nm, distance 20 cm) for 1h. After reaction finished,
the products were collected by centrifuging and washed thoroughly with EtOH and water. At last,
the 3D Au@MoS2Fs was dried by freezeꢀdrying for 12 h at ꢀ50 0C.
Photocatalytic test. A 60 mL solution (H2O : EtOH = 9:1) containing rhodamine B (100 ꢁM)
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and the photocatalyst (15 mg) was stirred in the dark for 20 min to reach adsorption/desorption
equilibrium. Then, the mixture was stirred under light irradiation. During the stirring period, the
supernatant was taken out at regular intervals and then centrifuged to remove the catalyst.
Finally, the supernatant was analyzed by fluorescence spectra and UVꢀvisible adsorption spectra.
Detection of Hg2+ using 3D Au@MoS2 heterostructure. 1 mg 3D Au@MoS2 heterostructure
was added to the aqueous solution of rhodamine B (4 mL, 100 ꢁM). Then Hg2+ with different
concentration was added to the above solution. Subsequently, the mixture was stirred under
visible light irradiation for 25 min. Finally, the supernatant was analyzed using fluorescence
spectra and UVꢀvisible adsorption spectra.
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Selectivity analyses of 3D Au@MoS2 heterostructure for various metal ions. To measure the
selectivity of metal ions, Na+, K+, Ag+, Ca2+, Mg2+, Cd2+, Cu2+, Co2+, Ni2+, Zn2+, Fe2+, Al3+, Fe3+,
Hg2+ were solved in MilliꢀQ water at higher stock concentrations and repeated the method of
Hg2+ detecting experiments mentioned above. To check if other metal ions have an effect on
Hg2+ detection, all the metal salts (100 ꢁM) were added before Hg2+ addition (50 ꢁM). Then the
fluorescence and absorbance intensity was checked as above.
Cell cytotoxicity. 3T3 cells were seeded at a density of 6 × 104 cells/well in 96ꢀwell plates,
cultured at 37 °C and 5% CO2 for 24 h. Different concentrations of 3D Au@MoS2
heterostructure (0, 100, 200, 300, 400, 500, and 600 ꢁg/mL, diluted in DMEM) were then added
to the wells. The cells were subsequently incubated for 24 or 48 h at 37 °C under 5% CO2. The
numbers of viable and total cells were quantified using by the methyl thiazolyl tetrazolium
(MTT) assay. The following formula was used to calculate the inhibition of cell growth:
Cell viability (%) = (mean Abs value of treatment group/mean Abs value of control) × 100%.
In vitvo image studies. 3T3 cells were washed with PBS buffer for three times, and then the
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cells were incubated with 3D Au@MoS2 heterostructure (30 ꢁL, 2 mg/mL), rhodamine B (20
ꢁL, 0.1 mM) in a mixture of PBS buffer (pH 7.4, 10 mM) and DMSO (4/1, v/v), and the Hg2+
(100 ꢁL, 1 mM in a mixture of water) for 1 h at 37 0C. After irradiating for 25 min under visible
light irradiation, the fluorescence imaging of intracelluar Hg2+ was then carried out after washing
the cells with PBS. The 3T3 cells without the pretreatment of Hg2+ under the dark and with the
pretreatment of Hg2+ under visible light irradiation were set as a control. All confocal images
were performed with a Leica TCS SP8 inverted epifluorescence/reflectance laser scanning
confocal microscope. Excitation was at 550 ± 10 nm, and emission was at 580 ± 10nm.
In vivo image studies. Kunming mice (20ꢀ25 g) were anesthetized by intraperitoneal of xylazine
(10 mg/kg) and ketamine (80 mg/kg). Then the mice were given a subcutaneous of the mixtured
3D Au@MoS2 heterostructure (50 ꢁL, 3 mg/mL), rhodamine B (20 ꢁL, 0.1 mM) in a mixture of
PBS buffer (pH 7.4, 10 mM) and DMSO (4/1, v/v)) and the Hg2+ (50 ꢁL, 1 mM in a mixture of
water) after irradiating for 1 h under the visible light. The mice were then imaged by using an
IVIS Lumina XR in vivo imaging system. The mice that did not inject Hg2+ under the dark and
injected Hg2+ under visible light irradiation were set as a control.
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RESULTS AND DISCUSSION
Synthesis and characterization. The monodisperse monolayer MoS2 NSs were prepared
through a chemical exfoliation method.25 A controlled amount of MoS2 NSs were ultrasonicated
in DMF/water to form a homogeneous dispersed solution. HAuCl4·4H2O was added to the above
ꢀ
dispersed solution. In this aqueous dispersion, the MoS2 NSs interacted with AuCl4 to form
ꢀ
MoS2–AuCl4 . Under visible light irradiation, electron and hole pairs were generated within
ꢀ
MoS2. The photoexcited electrons further facilitated the reduction of AuCl4 ions to Au0 for the
formation of Au NPs, hence the formation of a 3D Au@MoS2 heterostructure (Figure 1A).26 At
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the same time, holes were scavenged by the DMF solvent. The phenomenon of the
photochemical synthesis of metal NPs using a photoreducing agent is well supported in the
literature.26 However, the use of HAuCl4·4H2O alone without MoS2 NSs in DMF/water did not
generate Au NPs under visible light irradiation (Figure S1).
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Figure 2. (A) TEM images of MoS2. (BꢀC) Different magnification TEM images of 3D Au@MoS2
heterostructure. Inset: the nanoparticle size distribution of Au in 3D Au@MoS2 heterostructure. (D) HRTEM
image of 3D Au@MoS2 heterostructure. Inset: Selected area electron diffraction of 3D Au@MoS2
heterostructure (E) Dark field of STEM images. (F–I) Element mapping images of the 3D Au@MoS2
heterostructure.
The surface morphology and structure of the products were examined via scanning electron
microscopy (SEM), which revealed that the obtained samples possessed a 3D honeycombꢀlike
structure with numerous pores (Figure 1C). These pores cross linked with one another to form a
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3D macroporous network, the walls of which were composed of singleꢀ or fewꢀlayer MoS2 NSs
with a clear curved profile, unlike pure 2D MoS2 NSs (Figure 1B). The structure of the 3D
Au@MoS2 heterostructure was further studied by transmission electron microscopy (TEM) and
highꢀresolution TEM (HRTEM). As described in Figure 2A, the bare MoS2 clearly exhibited thin
and transparent sheets. However, after formation of 3D Au@MoS2 heterostructure, the clearly
observed Au NPs were attached on the nanosheets of MoS2 with an average size of 22 nm
(Figure 2BꢀC). The HRTEM image in Figure 2D shows that the 3D Au@MoS2 heterostructure
displayed a sandwichꢀlike structure and that the lattices of Au and MoS2 were in close contact.
Each Au NP embedded in the 3D Au@MoS2 heterostructure showed clear lattice fringes with
interplanar spacing of 0.234 nm, corresponding to the (111) interplane distance of Au (JCPDS
no. 89ꢀ3697).27 Interlayer spacing of 0.27 and 0.635 nm, which correspond to the (100) and (002)
crystal planes of MoS2, were also observed.27 In the HRTEM, the interface between MoS2 and
the Au NPs revealed the close interfacial matching of the Au NPs and disulfide nanostructures,
and the (111) planes of Au (0.234 nm) and the (100) planes of MoS2 (0.27 nm) exist a
considerably small mismatch of 13.1% (Figure 2D). In addition, such close examination of the
interface revealed lattice fringe continuation, which may be the result of epitaxial growth of
nanoparticle. The local composition of the formed 3D Au@MoS2 heterostructure was also
studied using highꢀangle annular darkfield scanning TEM images, corresponding elemental
mapping (Figures 2E–I), and energyꢀdispersive Xꢀray spectroscopy (Figure S2), all of which
clearly showed the presence of gold in the grown NPs and its good dispersion on MoS2 NSs.
The powder Xꢀray diffraction (XRD) pattern of the 3D Au@MoS2 heterostructure is shown in
Figure 3A. The evident diffraction peaks located at about 14.1°, 33.0°, 40.3°, 48.4°, and 58.6°
for MoS2 matched the (002), (100), (103), (105), and (110) indexes of MoS2, as reported
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previously.28 After Au NP modification, new diffraction peaks emerged at 38.0°, 44.5°, 64.7°,
and 77.8° for the 3D Au@MoS2 heterostructure samples; these peaks were ascribed to the (111),
(200), (220), and (311) planes of Au (JCPDS, No. 89ꢀ3697), respectively. According to the
Raman spectra of the 3D Au@MoS2 heterostructure, the two prominent peaks located at 374.4
and 399.3 cm−1 corresponded to the E2g and A1g vibrational bands of MoS2,29,30 thus suggesting
the existence of crystalline MoS2 in the nanohybrid framework (Figure S3). The XRD and
Raman spectra offered preliminary proof of the successful fabrication of the 3D Au@MoS2
heterostructure.
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Figure 3. (A) XRD pattern of the 3D Au@MoS2 heterostructure (a) and MoS2 NSs (b). (B) Nitrogen
adsorption/desorption isotherms of the 3D Au@MꢀoS2 heterostructure. Inset: The pore size distribution of the
3D Au@MoS2 heterostructure. (C) UVꢀvis absorption of 3D Au@MoS2 heterostructure, MoS2 NSs and Au
NPs. (D) Plots of (ahv)0.5 versus photon energy for calculation of bandgap energies of 3D Au@MoS2
heterostructure and MoS2 NSs
.
As shown in Figure 3B, the nitrogen adsorption–desorption curve of the 3D Au@MoS2
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heterostructure is a typeꢀIV adsorption isotherm. The apparent hysteresis loop of H2 in the P/P0
range of 0.45–1.0 signifies irreversible desorption, which is generally observed in specimens
with relatively large mesopores and macropores.31 As indicated by the BJH analysis of the
desorption branch of the isotherm, the pore size distribution fell in the ranges of 3.7–4.3 and 4.3–
30 nm, further confirming the existence of small and large mesopores, as well as macropores.
Here the large mesopores originate from the pore formation between the MoS2 flakes after
inserting the Au NPs.32ꢀ34 The BET specific surface area of the 3D Au@MoS2 heterostructure
was measured as 49.25 m2 g−1 (0.20 m3 g−1), which is 246 times that of the MoS2 nanosheets
(0.19 m2 g−1) and is considerably greater than the value reported the MoS2 aerogel (18 m2 g−1).35
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Figure 4. Absorption spectroscopy (A) and fluorescence spectroscopy of 3D Au@MoS2 heterostructure on the
degradation of RB under visible light irrdiation. Photocatalytic degradation efficiencies of different
photocatalysts toward RB measured by absorption spectroscopy (B) and fluorescence spectroscopy (D).
The optical properties of the 2D MoS2 NSs and asꢀprepared 3D Au@MoS2 heterostructure
were characterized through the UVꢀvis spectroscopy of their suspensions. The UVꢀvis spectrum
of MoS2 exhibited clear characteristic peaks in the region from 350 nm to 500 nm, whereas the
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spectrum of the 3D Au@MoS2 heterostructure showed absorption bands similar to those of
MoS2 and an additional absorption band at 625 nm (Figure 3C). The surface plasmon resonance
(SPR) peak of spherical Au NPs with a diameter of 10–50 nm in diluted aqueous solutions is
known to be centered at 517–533 nm.36 However, the growth of nanoparticles directly on
disulfide nanostructure surfaces leads to a distortion of the spherical shape of Au NPs (Figure
2D). Such distortion can cause a red shift of the maximum of the SPR peak from the position
typical for free spherical Au NPs. Thus, in this work, the SPR transversal band obviously redꢀ
shifted at 625 nm (Figure 3C). Combined with nonspherical morphology of the Au NPs and its
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SPR peak redꢀshift, we can conclude the electronic interactions between Au and MoS2. We
determined the band gaps of the samples by fitting the optical transition at the absorption edges
using the Tauc/David–Mott model.38 As shown in Figure 3D, the band gaps of MoS2 became
increasingly narrow after the formation of the 3D Au@MoS2 heterostructure, which supports the
observation of a red shift in the absorption band edge of 3D Au@MoS2 heterostructure as
compared to the pure MoS2 (Figure 3C). Generally, the formation of chemical bonding results in
a red shift in the absorption band edge of the resulting material.39ꢀ41 In the 3D Au@MoS2
heterostructure, the band gap narrowing and enhanced visible light absorption of the
nanocomposites was due to the formation of of the chemical bonding between Au and the
specific sites of MoS2 (AuꢀS bonding), which can be advantageous to enhancing the visible light
photocatalytic activity of the nanocomposite.
As presented in Figure S4A, the full survey Xꢀray photoelectron spectrometer (XPS)
spectrum of the 3D Au@MoS2 heterostructure revealed that the sample was composed of S, Mo,
and Au elements. However, only S and Mo elements were found in the survey XPS spectrum of
the MoS2 NSs. Figure S4B displays the highꢀresolution spectra of the Mo 3d at ~231.48 and
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~228.27 eV, which correspond to the 3d5/2 and 3d3/2 doublets, as well as the peaks at ~161.25
and ~161.80 eV (Figure S4C), which are attributed to the 2p1/2 and 2p3/2 orbital of S. These
binding energy values closely resemble the spectra of the binding energies of Mo4+ and S2ꢀ ions
in MoS2 alone,42 with the important difference being the small decrease in the binding energy of
0.35 eV of the Mo 3d at ~231.48 eV in comparison with the value for MoS2 alone (231.83 eV).
The S 2p3/2 peak at ~162.1 eV showed a similar downshift of 0.42 eV relative to the value of
MoS2 alone (162.28). The shift in the Mo 3d5/2 peak and S 2p position to low binding energies
is interesting because it reflects electron donation to the MoS2 sheets from gold.43 The peaks
located at 87.5 and 83.9 eV corresponded to the 4f5/2 and 4f7/2 binding energies of the zero
valence state of metallic Au (Figure S4D), respectively. This result further proved that Au NPs
were successfully generated and introduced into the 3D Au@MoS2 heterostructure.
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Scheme 1. Illustration of 3D Au@MoS2 heterostructure for sensing Hg2+.
Inhibition effect of Hg2+ on the photocatalytic activity of 3D Au@MoS2 heterostructure. As
a result of its longꢀwavelength absorption and emission, high absorption coefficient and quantum
efficiency, and good photo stability, RB was selected as the visible signaling reporter to evaluate
the photocatalytic activity of the 3D Au@MoS2 heterostructure. As the control experiment, the
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photocatalytic activities of pure MoS2 NSs and Au NPs were also examined. In the presence of
the 3D Au@MoS2 heterostructure (Figure 4), the degradation of RB was achieved completely
within 25 min under visible light irradiation (λ ≥ 420 nm). However, the degradation of RB
could not be completed with pure MoS2 NSs and Au NPs under the same conditions. From the
above degradation results, we conclude that the formed 3D Au@MoS2 heterostructure exhibits
much higher photocatalytic activities than the singleꢀphase Au and MoS2 (Figure S5). The high
photocatalytic activity observed for the 3D Au@MoS2 heterostructure may be attributed to Au
effectively capturing photoinduced electrons. Such capture by Au inhibited the recombination of
the photoinduced electrons with holes and improved photocatalytic activities. Moreover, recent
studies have indicated that the SPR effect of a noble metal can accelerate charge carrier
generation rate in the semiconductor and enhance solar energy conversion efficiency due to the
transfer of the plasmon energy of the metal to the semiconductor through the HET or EMT
process, or both.44ꢀ46 Thus, the high photocatalytic activity of 3D Au@MoS2 heterostructure may
be inseparable from its SPR effect.
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Figure 5. Selectivity studies. Fluorescence (A) and absorption (C) changes of RB + 3D Au@MoS2
heterostructure under visible light irradiation upon addition of 1 equiv of Hg2+ and 2 equiv of various metal
ions. Black bar: RB + 3D Au@MoS2 heterostructure + metal ions, red bar: RB + 3D Au@MoS2
heterostructure + metal ions + Hg2+. The Photocatalytic activities of 3D Au@MoS2 heterostructure were
inhibited by various metal ions. (B) The photographs were taken under a 365 nm UV lamp. (D) The
photographs were taken under room light.
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As is shown in Figure S6, when a trace amount of Hg2+ was added, the photocatalytic activity
of the 3D Au@MoS2 heterostructure was dramatically decreased. To effectively understand the
photocatalytic mechanism of the 3D Au@MoS2 heterostructure before and after being treated
with Hg2+ under visible light irradiation, we performed scavenger experiments by adding
diisopropylethylamine as a hole scavenger, K2Cr2O7 as an electron scavenger, and benzoquinone
as a radical scavenger during the photocatalytic degradation of RB. As shown in Figure S7, the
photodegradation of RB was greatly inhibited by the addition of the electron scavenger. This
result showed good agreement with the Hg2+ results. In sum, the results indicate the dominant
role of electrons in the photocatalytic activities of nanocomposites.
Based on our experimental results and some previously reported literature,47 the plausible
Hg2+ detection mechanism of the 3D Au@MoS2 heterostructure under visible light irradiation is
shown in Scheme 1. Under the excitation of light, the excited electrons of MoS2 can be
transferred from the VB to the CB and then be directly injected into the Fermi level (Ef) of Au.
When Hg2+ was added to the degradation system, Hg2+ wrapped around the Au NPs of the 3D
Au@MoS2 heterostructure because of the strong affinity between Hg (II) and Au NPs.48 The
Hg2+ on the surface of the Au NPs were reduced to Hg0 in the form of gold amalgamation by the
photoinduced electrons. This process was demonstrated by XPS. As shown in Figure S8, the two
bindingꢀenergy peaks at 100.7 and 104.7 eV were ascribed to Hg 4f7/2 and Hg 4f5/2,
respectively, which indicate that both Hg2+ and Hg0 existed on the surface of Au.27 Given that the
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photoinduced electrons were scavenged by Hg2+, the photocatalysis efficiency of the 3D
Au@MoS2 heterostructure decreased.
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Hg2+ sensing studies. A colorimetric and fluorescent mercury sensor was established through
the use of the 3D Au@MoS2 heterostructure to catalyze degradation of the RB in the presence of
visible light. As a result of the high specificity of the Hg–Au interaction, the 3D Au@MoS2
heterostructure showed excellent selectivity toward Hg2+ over other metal ions. As shown in
Figure 5, the introduction of 2 equiv. of other metal ions (Na+, K+, Ag+, Ca2+, Mg2+, Cd2+, Cu2+,
Co2+, Ni2+, Zn2+, Fe2+, Al3+, and Fe3+) could hardly inhibit the photocatalytic activity of the 3D
Au@MoS2 heterostructure. Correspondingly, the fluorescence of the test solution changed from
yellow to colorless (Figure 5B), and the color of the test solution changed from rose red to
colorless (Figure 5D). However, only the introduction of 1 equiv. of Hg2+ to the above system
could inhibit the photocatalytic activity of the 3D Au@MoS2 heterostructure dramatically.
Comparative experiments were carried out to evaluate the practicability of the 3D Au@MoS2
heterostructure. As depicted in Figures 5A and C, in the presence of various interference species,
Hg2+ could still inhibit the photocatalytic activity of the 3D Au@MoS2 heterostructure. Taken
together, these results indicate that the 3D Au@MoS2 heterostructure exhibits remarkably high
selectivity toward Hg2+ over other metal ions.
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Figure 6. Sensitivity studies. (A) Fluorescence intensity changes caused by various concentration of Hg2+ (5ꢀ
50 ꢁM). (B) Fluorescence response of the detection system vs Hg2+ concentration. (C) Absorption intensity
changes caused by various concentration of Hg2+ (5ꢀ50 ꢁM). (D) Absorption response of the detection system
vs Hg2+ concentration.
To evaluate the sensitivity of such Hg2+ sensor, we used the 3D Au@MoS2 heterostructure in
catalyzing the photodegradation reaction of RB after reacting with different concentrations of
Hg2+. As shown in Figures 6A and C, with the increase of Hg2+ concentration, the absorbance
and fluorescence intensity of RB continuously increased. Moreover, the fluorescence and
absorbance intensity against Hg2+ exhibited a good linear correlation (Figures 6B and D). The
detection limits (3σ/slope) of the fluorescence assay and colorimetric assay were 0.22 and 0.038
nM, respectively (Figure S9), which are below the threshold levels (10 nM) defined by the
United States Environmental Protection Agency (EPA) for drinking water. In addition,
appreciable color (from colorless to rose red) and fluorescence (from colorless to yellow)
changes of the test solution could be distinguished by the naked eye (Figure 6D). Therefore, the
3D Au@MoS2 heterostructure could detect Hg2+ from water through fluorescence and
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colorimetric methods.
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Figure 7. Study on intracellular mercury ion imaging. Confocal images of 3T3 cells: (AꢀC) brightꢀfield and
(DꢀF) fluorescence image of 3T3 cells incubated with different materials under different conditions.
Monitoring Hg2+ in living cells. Before the application of the 3D Au@MoS2 heterostructure in
bioimaging, its possible cytotoxic activity was evaluated. As shown in Figure S10, the cell
viability of the 3D Au@MoS2 heterostructure for 3T3 cells remained above 75% upon
incubation at a concentration of 600 ꢁg/mL for 48 h, thereby indicating the low cytotoxicity of
the 3D Au@MoS2 heterostructure. To demonstrate the applicability of the RB system
photocatalyzed with the 3D Au@MoS2 heterostructure in monitoring intracellular Hg2+, we
incubated 3T3 cells with the 3D Au@MoS2 heterostructure, RB, and Hg2+ successively in a
serumꢀsupplemented cell culture medium for 1 h at 37 °C. As shown in Figures 7A and D, the
3T3 cells incubated with the 3D Au@MoS2 heterostructure and RB for 1 h under dark conditions
at 37 °C showed strong emission at 573 nm. By contrast, the 3T3 cells incubated with the 3D
Au@MoS2 heterostructure and RB for 1 h under visible light irradiation at 37 °C showed only a
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weak emission at 573 nm (Figures 7B and E). When the cells were supplemented with the 3D
Au@MoS2 heterostructure, RB, and Hg2+ in the growth medium for 1 h at 37 °C under visible
light irradiation, a strong enhancement in the red emission was observed in the intracellular
region (Figures 7C and F). The confocal luminescence images demonstrated that the 3D
Au@MoS2 heterostructure photocatalyzed RB system could be successfully applied to monitor
intracellular Hg2+ in living cells via luminescence imaging.
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Figure 8. in vivo mercury ion imaging. In vivo fluorescence image of different materials pretreated living
mice under different conditions.
Hg2+ imaging in mice. We examined the ability of the 3D Au@MoS2 heterostructure
photocatalyzed RB system to visualize Hg2+ in living animals. Kunming mice were selected as
our model and were given a skinꢀpop injection of the 3D Au@MoS2 heterostructure, RB, and
Hg2+ successively. The live mice injected with the 3D Au@MoS2 heterostructure and RB for 0.5
h under dark conditions showed strong emission at 550–650 nm (Figure 8A). When the living
mice were injected with 3D Au@MoS2 heterostructure and RB under visible light irradiation, the
emission significantly weakened (Figure 8B). When the living mice were injected with the 3D
Au@MoS2 heterostructure, RB, and Hg2+ under visible light radiation, strong emission at 550–
650 nm was observed (Figure 8C), thereby indicating that the 3D Au@MoS2 heterostructure
photocatalyzed RB system can serve as a probe for mercury ion imaging in vivo.
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In summary, we proposed a new photocatalysisꢀbased nanoprobe for mercury using a 3D
Au@MoS2 heterostructure as a photocatalyst and rhodamine B (RB) as a fluorescent and color
change reporter molecule for monitoring Hg2+ in living cells and animals. In such detection
system, Hg2+ was reduced by photoinduced electrons to form gold amalgam in the 3D
Au@MoS2 heterostructure under visible light illumination. This formation of gold amalgam
suppressed the photocatalytic activity of the 3D Au@MoS2 heterostructure toward RB
decomposition and led to the “OFF–ON” of the fluorescence and color change of RB. Such
noteworthy signal change features made the 3D Au@MoS2 heterostructure photocatalyzed RB
system as an effective sensor platform for the selective and sensitive detection of Hg2+ through
both fluorescence and colorimetric methods with detection limits of 0.22 and 0.038 nM,
respectively. Such detection limit of Hg2+ is lower than the maximum level (10 nM) for drinking
water set by the US EPA. The nanoprobe was also found to be capable of monitoring Hg2+ in
cells and living bodies via luminescence bioimaging. Our successful photocatalysisꢀbased
nanoprobe for the sensing and bioimaging of Hg2+ provides a new design strategy for future
novel probes for highly sensitive detection and bioimaging studies.
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ASSOCIATED CONTENT
Supporting Information
EDX, Raman spectra, XPS, and Cell cytotoxicity. This material is available free of charge via
the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
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*Eꢀmail: wangbd@lzu.edu.cn; yhzhu@mail.hust.edu.cn.
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ACKNOWLEDGMENTS
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The work was supported by the National Natural Science Foundation of China (21671088,
21401091, 81573013 and 21501080).
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REFERENCES
(1) McNutt, M. Science 2013, 341, 1430.
(2) Li, B. Y.; Zhang, Y. M.; Ma, D. X.; Shi, Z.; Ma, S. Q. Nature Communications 2014, 5,
5537.
(3) Ding, S. Y.; Dong, M.; Wang, Y. W.; Chen, Y. T.; Wang, H. Z.; Su, C. Y.; Wang, W. J. Am.
Chem. Soc. 2016, 138, 3031ꢀ3037.
(4) Sun, Q.; Aguila, B.; Perman, J.; Earl, L. D.; Abney, C. W.; Cheng, Y. C.; Wei, H.; Nguyen,
N.; Wojtas, L.; Ma, S. Q. J. Am. Chem. Soc. 2017, 139, 2786ꢀ2793.
(5) Liu, X. J.; Wu, Z. J.; Zhang, Q. Q.; Zhao, W. F.; Zong, C. H.; Gai, H. W. Anal. Chem. 2016,
88, 2119ꢀ2124.
(6) Jiang, T. Y. Ke, B. W.; Chen, H.; Wang, W. S.; Du, L. P.; Yang, K. Q.; Li, M. Y. Anal.
Chem. 2016, 88, 7462ꢀ7465.
(7) Nie, K. X.; Dong, B.; Shi, H. H.; Liu, Z. C.; Liang, B. Anal. Chem. 2017, 89, 2928ꢀ2936.
(8) Zang, J. C.; Li, C. G.; Zhou, K.; Dong, H. S.; Chen, B.; Wang, F. D.; Zhao, G. H. Anal.
Chem. 2016, 88, 10275ꢀ10283.
(9) Pandeeswar, M.; Senanayak, S. P.; Govindaraju, T. ACS Appl. Mater. Interfaces, 2016, 8,
30362ꢀ30371.
(10) An, J. H.; Park, S. J.; Kwon, O. S.; Bae, J.; Jang, J. ACS Nano 2013, 7, 10563ꢀ10571.
(11) Long, Y. J.; Li, Y. F.; Liu, Y.; Zheng, J. J.; Tang, J.; Huang, C. Z. Chem. Commun. 2011, 47,
11939ꢀ11941.
(12) Yen, Y. T.; Chen, C. W.; Fang, M.; Chen, Y. Z.; Lai, C. C.; Hsu, C. H.; Wang, Y. C.; Lin,
H.; Shen, C. H.; Shieh, J. M.; Ho, J. C.; Chueh, Y. L. Nano Energy 2015, 15, 470ꢀ478.
(13) Manna, G.; Bose, R.; Pradhan, N. Angew. Chem. Int. Ed. 2014, 53, 6743ꢀ6746.
(14) Yu, X.; Shavel, A.; An, X.; Luo, Z.; Ibanez, M.; Cabot, A. J. Am. Chem. Soc. 2014, 136,
9236ꢀ9239.
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2
3
4
5
6
(15) Patra, B. K.; Guria, A. K.; Dutta, A.; Shit, A.; Pradhan, N. Chem. Mater. 2014, 26, 7194ꢀ
7200.
7
8
9
(16) Patra, B. K.; Khilari, S.; Pradhan, D.; Pradhan, N. Chem. Mater. 2016, 28, 4358ꢀ4366.
(17) Li, M.; Yu, X. F.; Liang, S.; Peng, X. N.; Yang, Z. J.; Wang, Y. L.; Wang, Q. Q. Adv. Funct.
Mater. 2011, 21, 1788ꢀ1794.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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30
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50
51
52
53
54
55
56
57
58
59
60
(18) Mak, K. F.; Lee, C.; Hone, J.; Shan, J.; Heinz, T. F. Phys. Rev. Lett. 2010, 105, 136805.
(19) Dinh, C. T.; Nguyen, T. D.; Kleitz, F.; Do. T. O. ACS Appl. Mater. Interfaces 2011, 3,
2228ꢀ2234.
(20) Li, Y.; Cain, J. D.; Hanson, E. D.; Murthy, A. A.; Hao, S. Q.; Shi, F. Y.; Li, Q. Q.;
Wolverton, C.; Chen, X. Q.; Dravid, V. P. Nano Lett. 2016, 16, 7696ꢀ7702.
(21) Shi, Y.; Wang, J.; Wang, C.; Zhai, T. T.; Bao, W. J.; Xu, J. J.; Xia, X. H.; Chen, H. Y. J.
Am. Chem. Soc. 2015, 137, 7365ꢀ7370.
(22) Shi, J. P.; Ma, D. L.; Han, G. F.; Zhang, Y.; Ji, Q. Q.; Gao, T.; Jingyu Sun, J. Y.; Song, X.
J.; Li, C.; Zhang, Y. S.; Lang, X. Y.; Zhang, Y. F.; Liu, Z. F. ACS Nano 2014, 8, 10196ꢀ
10204.
(23) Hou, J. G.; Cheng, H. J.; Takeda, O.; Zhu, H. M. Angew. Chem. Int. Ed. 2015, 54, 8480ꢀ
8484.
(24)
Liu, D. B. Wang, S. J.; Swierczewska, M.; Huang, X. L.; Bhirde, A. A.; Sun, J. S.; Wang,
Z.; Yang, M.; Jiang X. Y.; Chen, X. Y. ACS Nano 2012, 6, 10999ꢀ11008.
,
(25) Liu, T.; Wang, C.; Cui, W.; Gong, H.; Liang, C.; Shi, X. Z.; Li, Z. W.; Sun, B. Q.; Liu, Z.
Nanoscale 2014, 6, 11219ꢀ11225.
(26) Huang, X.; Qi, X. Y.; Huang, Y. Z.; Li, S. Z.; Xue, C.; Gan, C. L.; Boey, F.; Zhang, H. ACS
Nano 2010, 4, 6196ꢀ6202.
(27) Zhi, L. H.; Zuo, W.; Chen, F. J.; Wang, B. D. ACS Sustainable Chem. Eng. 2016, 4, 3398ꢀ
3408.
(28) Chou, S. S.; De, M.; Kim, J.; Byun, S.; Dykstra, C.; Yu, J.; Huang, J. X.; Dravid, V. P. J.
Am. Chem. Soc. 2013, 135, 4584ꢀ4587.
(29) Sreeprasad, T. S.; Nguyen, P.; Kim, N.; Berry, V. Nano Lett. 2013, 13, 4434ꢀ4441.
(30) Zeng, Z. Yin, Z.; Huang, X.; Li, H.; He, Q.; Lu, G.; Boey, F.; Zhang, H. Angew. Chem., Int.
Ed. 2011, 50, 11093ꢀ11097.
23
ACS Paragon Plus Environment

Analytical Chemistry
Page 24 of 24
1
2
3
4
5
6
(31) Sui, Z. Y.; Meng, Y. N.; Xiao, P. W.; Zhao, Z. Q.; Wei, Z. X.; Han, B. H. ACS Appl. Mater.
Interface 2015, 7, 1431ꢀ1438.
7
8
9
(32) Stankovich, S.; Dikin, D. A.; Piner, R. D.; Kohlhaas, K. A.; Kleinhammes, A.; Jia, Y.; Wu,
Y.; Nguyen, S. T.; Ruoff, R. S. Carbon 2007, 45, 1558ꢀ1565.
(33) Lee, J. H.; Park, N.; Kim, B. G.; Jung, D. S.; Im, K.; Hur, J.; Choi, J. W. ACS Nano 2013, 7,
9366ꢀ9374.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(34) Zhi, L. H.; Zhang, H. L.; Yang, Z. Y.; Liu, W. S.; Wang, B. D. Chem. Commun. 2016, 52,
6431ꢀ6434.
(35) Worsley, M. A.; Shin, S. J.; Merrill, M. D.; Lenhardt, J.; Nelson, A. J.; Woo, L. Y.; Gash, A.
E.; Baumann, T. F.; Orme, C. A. ACS Nano 2016, 8, 12836ꢀ12842.
(36) Link, S.; ElꢀSayed, M. A. J. Phys. Chem. B 1999, 103, 4212ꢀ4217.
(37)
Shi, Y. Wang, J.; Wang, C.; Zhai, T. T.; Bao, W. J.; Xu, J. J.; Xia, X. H.; Chen, H. Y. J.
Am. Chem. Soc. 2015, 137, 7365ꢀ7370.
(38) Woomer, A. H.; Farnsworth, T. W.; Hu, J.; Wells, R. A.; Donley, C. L.; Warren, S. C. ACS
Nano, 2015, 9, 8869ꢀ8884.
(39) Lee, J. S.; You, K. H.; Park, C. B. Adv. Mater. 2012 , 24, 1084ꢀ1088.
(40) Valentin, D.; Pacchioni, G.; Selloni, A. Chem. Mater. 2005, 17, 6656ꢀ6665.
(41) Li, Y. B.; Zhang, H. M.; Liu, P.; Wang, D.; Li, Y.; Zhao, H. J. Small 2013, 9, 3336ꢀ3344.
(42) Eda, G. Yamaguchi, H.; Voiry, D.; Fujita, T.; Chen, M.; Chhowalla, M. Nano Lett. 2011, 11,
5111ꢀ5116.
(43) Sørensen, S. G.; Füchtbauer, H. G.; Tuxen, A. K.; Walton, A. S.; Lauritsen, J. V. ACS
Nano 2014, 8, 6788ꢀ6796.
(44) Hong, J. W.; Wi, D. H.; Lee, S. U.; Han, S. W. J. Am. Chem. Soc. 2016, 138, 15766ꢀ15773.
(45) Wu, B. W.; Liu, D. Y.; Mubeen, S.; Chuong, T. T.; Moskovits, M.; Stucky, G. D. J. Am.
Chem. Soc. 2016, 138, 1114ꢀ1117.
(46) Jiang, D.; Wang, W. Z.; Sun, S. M.; Zhang, L.; Zheng, Y. L. ACS Catal. 2015, 5, 613ꢀ621.
(47) Shih, Y. C.; Ke, C. Y.; Yu, C. J.; Lu, C. Y.; Tseng, W. L. ACS Appl. Mater. Interfaces 2014,
6, 17437ꢀ17445.
(48) Maiti, S.; Pezzato, C.; Martin S. G.; Prins, L. J. J. Am. Chem. Soc. 2014, 136, 11288ꢀ11291.
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