Ligand conjugation of chemically exfoliated MoS2

Article abstract of DOI:10.1021/ja310929s

MoS₂ is a two-dimensional material that is gaining prominence due to its unique electronic and chemical properties. Here, we demonstrate ligand conjugation of chemically exfoliated MoS₂ using thiol chemistry. With this method, we modulate the ζ-potential and colloidal stability of MoS₂ sheets through ligand designs, thus enabling its usage as a selective artificial protein receptor for β-galactosidase. The facile thiol functionalization route opens the door for surface modifications of solution processable MoS₂ sheets.

Full text of DOI:10.1021/ja310929s

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Communication
Ligand conjugation of chemically exfoliated MoS</sub>2<sub>
Stanley S. Chou, Mrinmoy De, Jaemyung Kim, Segi Byun,
Conner Dykstra, Jin Yu, Jiaxing Huang, and Vinayak P Dravid
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja310929s • Publication Date (Web): 11 Mar 2013
Downloaded from http://pubs.acs.org on March 12, 2013
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Ligand conjugation of chemically exfoliated MoS2
Stanley S. Chou,+ Mrinmoy De,+ Jaemyung Kim,+ Segi Byun,+║ Conner Dykstra,+ Jin Yu,║ Jiaxing Huang,
+* Vinayak P. Dravid.+ *
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+Department of Material Science & Engineering, International Institute for Nanotechnology, Northwestern University, Ev-
anston, Illinois 60208, United States
║ Department of Material Science and Engineering, Korea Advanced Institute Science and Technology, Yuseong-gu, Dae-
jeon, Republic of Korea, 305-701
ABSTRACT: MoS2 is a two-dimensional material that is
gaining prominence due to its unique electronic and chemical
properties. Here, we demonstrate ligand conjugation of chemi-
cally exfoliated MoS2 using thiol chemistry. Using this meth-
od, we modulate the zeta-potential and colloidal stability of
MoS2 sheets through ligand designs, thus enabling its usage as
a selective artificial protein receptor for β-galactosidase. The
facile thiol functionalization route opens the door for surface
modifications of solution processable MoS2 sheets.
The recent excitement over two dimensional atomically-
layered materials has been fueled in large part by desires to
exploit their low-dimensional properties, which can be distinct
from their bulk counter-parts. One of these emerging materi-
als, MoS2, has received a fair share of attention due to its ap-
plicability in areas ranging from catalysis1 and electronics2-5 to
biomedicine.6 Nevertheless, to fully harness the capabilities of
Figure 1. Structural models illustrating ligand conjugation
of ce-MoS2 sheets.
such new materials, ligand conjugations were often necessity.
For example, it is typically a crucial step for solution pro-
sheets by thiol-terminated ligands (Figure 1, Supplemental
Information S1-5). This was used to conveniently tune ce-
MoS2 and its biomolecular interactions. This route opens
pathways for making solution processable MoS2 with tunable
colloidal properties and can potentially facilitate improve-
ments in its processing.
cessing, which enables the usage of nanoparticles as functional
assembly blocks in bio-imaging,7 electronics,8 sensing,9 and
photovoltaics.10 Previously, attempts to functionalize MoS2
have been limited to bulk-like materials characterized by hy-
drophobic cleavage planes.11,12 Specifically, Tremel and
coworkers13 have modified hydrophobic MoS2 particles using
nickel-nitrilotriacetic acid chelation.13 However, colloidal sur-
face modification of water dispersible, chemically exfoliated
MoS2 (ce-MoS2) sheets has not been demonstrated.
In this report, the as-made ce-MoS2was first purified using
exhaustive dialysis (7 days under continuous water flow). Sur-
vey of the material using X-Ray Diffraction (XRD) showed
primary peak at 2θ = 14, thus indicating absence of mixed
lithium phase (Figure 2a).3,21 This was confirmed using Induc-
tive Coupled Plasma-Mass Spectrometry (ICP-MS), which
showed molecular ratios of samples obtained through dialysis
to contain more than ten-fold less Li than the typical centrifu-
gation purification process (vide infra). Atomic Force Micros-
copy (AFM) revealed sheets with average diameters of 0.7ꢀm,
and average thicknesses between ~0.8 and 1.5 nm, consistent
with reported values of monolayers.22 Additionally, the inter-
nal edges mentioned previously become are visible (Figure 2b,
S6).18 Transmission Electron Microscopy (TEM) Selective
Area Diffraction (SAD) showed six-fold symmetrical diffrac-
tion spots (2H phase) with additional points in between those
diffraction points (1T phase, Figure S7). This is consistent
with previous reports by Dungey, et al,17 for ce-MoS2, thus
indicating a mixed 1T and 2H material. Separately, Dynamic
To obtain large quantities of single-layer MoS2 sheets, solu-
tion based exfoliation methods are often used. Most typically,
this involves chemical exfoliation using lithium intercalation,
which can produce single layer MoS2 sheets in scalable quanti-
ties.14-16 In this method, lithium is inserted between MoS2 lay-
ers and then reacted with water to produce hydrogen gas at the
interface. This, in combination with ultrasoncation, then ena-
bles the high yield production of water dispersible ce-MoS2
sheets.14 Due to the violent nature of this reaction however,
MoS2’s crystal structure becomes deformed,3,17 and internal
edges (tears, pinholes and defects) can become visible.18 Pre-
vious work has suggested these edge sites to possess higher
molecular affinities,19 with theoretical suggestions of thiol
edge absorption.20 It is thus possible that ce-MoS2, which pos-
sesses defects in both internal edges and perimeter edges, may
be amenable to thiol ligand modifications. As this has not been
explicitly demonstrated, we show conjugation of ce-MoS2
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Figure 2. (a) XRD spectra of ce-MoS2. (b) Low and high
magnification AFM micrograph of ce-MoS2.
Light Scattering (DLS) show native ce-MoS2 sheets to have a
ζ-potential of –50 mV (Figure 3a).To this end, there are dif-
ferent models in literature regarding the origin of this negative
charge. Principally, Divigalpitiya, et al,19 proposed a model
with charges at edges. Separately Heising, et al,23 has a model
based on partially oxidized Mo atoms on the basal plane due
to Li intercalation. However, both agree that the sheets are
defective, thus there is the possibility of chemical modifica-
tion.
To illustrate this process, we first sought to understand the
ligand affinity of chemically exfoliated MoS2. For this, we
synthesized a series of polyethylene glycol (PEG) ligands with
head-groups of different charge (Figure 1, S1-S5). By includ-
ing and excising the thiol moiety, we show that the thiol group
is responsible for the ce-MoS2 modification (ligand 1a vs. 1b).
Figure 3. (a) ζ-potential, (b) FT-IR spectra focused upon the
thiol peak, (c) FT-IR spectra showing all peaks and (d) HER
polarization curve before and after ligand conjugation
We first examined the conjugation results using ligand 1a
and ligand 1b. As can be seen in Figure 1, these ligands are
nearly identical except for the thiol group on ligand 1a. De-
spite their similarities however, only the ce-MoS2 samples
incubated with ligand 1a showed significant ζ-potential shifts
after purification. The resultant ζ-potential of -7 mV repre-
sents a 43 mV shift from native ce-MoS2, and is consistent
with a neutral PEG functionalized colloid.19 Comparatively,
ligand 1b produced no ζ-potential change, indicating no mod-
ification (Figure 3a). Due to the attenuated ζ-potential, ligand
1a conjugate was found to be less stable in water.
stability. We believe this to be attributed to the pH independ-
+
ent nature of the charged NMe3 group on ligand 3.
Further characterizations were then performed. First, Fouri-
er Transform Infrared spectroscopy (FT-IR, Figure 3b, 3c, S9)
revealed the exposed S-H band from free ligands at 2563 cm-1.
This peak becomes absent after conjugation with ce-MoS2,
giving indication that the thiol moiety becomes buried on to
the ce-MoS2 surface (Figure 3b).24,25 Presence of the ligands
on the conjugates were also validated by monitoring the C-H
aliphatic bands 2854 and 2930 cm-1.Here, these aliphatic
bands appear on the conjugates at 2864 and 2935 cm-1 (Figure
3c).26 Unique pegylated ligand signature on conjugated ce-
MoS2 surfaces were also verified using X-Ray Photoelectron
Spectroscopy (XPS). For example, ether (C-O-C) bonds char-
acteristic of PEG ligands appeared in all conjugated samples
(286.6 eV, Figure S8).These results further corroborate pres-
ence of PEG ligands on the ce-MoS2, and are consistent with
thiol-PEG functionalized materials.27-29
To expand upon the conjugations, ligand 2 and ligand 3
were synthesized. Here, the conjugates also show appropriate
changes in ζ-potential as well, with ligand 2 producing a ζ-
potential of -29 mV and ligand 3 a ζ-potential of +36 mV.
Overall, ligand 3 conjugates exhibited the greatest colloidal
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Figure 4. (a) Colloidal stability of ce-MoS2 samples after 21
days in water. (b) Colloidal stability of ce-MoS2 functional-
ized with NMe3 terminated thiol at various pH.
With the conjugation assessed, we then evaluate the effect
of residual lithium (Li) from the exfoliation process. Here, ce-
MoS2 purified using the 3X centrifugation process described
by Heising23 produced a Li:Mo ratio of 0.25, consistent with
their report. ce-MoS2 purified using the dialysis process
described here reduced the Li:Mo ratio to 0.02, more than ten-
fold lower (Figure S10).However, the residual Li doesn’t
appear to effect conjugation results radically (Figure S11)
Figure 5. (a) Structure of a single unit of a β-Gal tetramer.
Anionic residues (Asp and Glu) surrounding β-gal’s active site
are highlighted (bottom) (b) Concentration dependence of β-gal
inhibition with various ce-MoS2 conjugate.
We also examined the effect of ligand conjugation on the
hydrogen evolution reaction (HER) process. As previous stud-
ies suggest edges to dominate HER catalysis,30 we expect that
ligand conjugation to suppress HER activity. Indeed, decrease
catalytic activity was clearly observed (Figure 3c, S12). It thus
appears that the thiol ligands can at minimum functionalize the
various edges in ce- MoS2.
strate the possibility to tune ce-MoS2 for selective host-guest
interactions with enzymes. Further development of this
demonstrated concept can thus be utilized for biosensor de-
sign. 9,35,36
In summary, we have demonstrated ligand conjugation of
chemically exfoliated MoS2 sheets through thiol chemistry. In
this manner, we were able to tune the ζ-potential and surface
functionality of ce-MoS2 sheets to enable its broad usage as
artificial receptors for enzymes. Because these aforementioned
assemblies have potential applications in sensing,35,37 ener-
gy,1,30 etc, and because devices using 2D materials can outper-
form their nanoparticles,34,38 it is possible that the functional-
ized ce-MoS2 assemblies may enjoy similar advantages. The
ability to functionalize these sheets through facile thiol chem-
istry suggests that similar chemistry may be applied to other
chemically exfoliated transition metal dichalcogenide sheets
(Figure S11), and can therefore open the window for further
applications and solution processing of these emerging two-
dimensional materials.
We then monitored the changes in colloidal stability with
ligand conjugation. Most observably, native ce-MoS2 irrevers-
ibly precipitated due to restacking within the first 21 days
(Figure 5a).14 Comparably, the conjugates maintained colloidal
stability (ligand 3), or can be readily re-dispersed with shak-
ing (ligand 1a, 2) (Figure 4a). This is likely due PEG ligand
preventing complete restacking. Due to the pH independent
+
nature of the NMe3 group on ligand 3, its conjugates are also
capable of resisting flocculation in acidic media (Figure 4b).
To compare, nativece-MoS2 flocculated at low pH.14 Ligand 3
conjugates, on the other hand were able to maintain colloidal
stability (Figure 4b).
The combination of ζ-potential tailoring and pegylation also
enable the tuning of ce-MoS2 for selective host-guest interac-
tions with biomolecules. As we have recently shown ce-MoS2
to be a promising photothermal agent,31 ligand modifications
shown here can have immediate applications. To demonstrate
this, we show the ligands ability to change ce-MoS2’s function
as an artificial protein receptor. To this end, we use β-
galactosidase (β-gal), a hydrolase enzyme. Here, β-gal, due to
a ring of anionic residues (Asp and Glu) surrounding its active
site does not interact with native ce-MoS2 (Figure 5a).32,33 By
tuning ce-MoS2 for the correct electrostatic host-guest interac-
tions we thus enable selective complexation and inhibition of
this enzyme.34 For this, 62.5 pM of β-gal were incubated with
various concentrations of ce-MoS2-conjugates. After 30
ASSOCIATED CONTENT
Synthetic protocols, experimental procedures, and additional
characterizations are included in the supporting information. This
material is available free of charge at http://pubs.acs.org.
Corresponding Authors
v-dravid@northwestern.edu,
jiaxing-huang@northwestern.edu,
Author Contributions
All authors have approved the final version of the manuscript.
minutes, o-nitrophenyl-β-D-galactopyranoside (ONPG), a
ACKNOWLEDGMENT
chromogenic substrate was added to monitor β-gal activity.
From this experiment, it can be seen that only the ligand 3
conjugate, which is cationic, showed ability to modulate β-gal
activity. Specifically, 50% of β-gal activity can be inhibited by
0.04 µg/ml of the conjugate (Figure 5b). These results demon-
This work was partly funded by the National Cancer Institute
Center for Cancer Nanotechnology Excellence (CCNE) initiative
at Northwestern University Award No. U54CA119341. JH
acknowledges support from National Science Foundation (DMR
CAREER 0955612) and the Alfred P. Sloan Research Foundation.
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(18)
Chen, M.; Chhowalla, M. ACS Nano 2012, 6, 7311.
(19) Divigalpitiya, W. M. R.; Frindt, R. F.; Morrison,
S. R. Science 1989, 246, 369.
(20) Raybaud, P.; Hafner, J.; Kresse, G.; Toulhoat, H.
Phys. Rev. Lett. 1998, 80, 1481.
(21) Joensen, P.; Crozier, E. D.; Alberding, N.;
Frindt, R. F. J. Phys. C 1987, 20, 4043.
Eda, G.; Fujita, T.; Yamaguchi, H.; Voiry, D.;
S. B. was supported by Basic Science Research Program through
the National Research Foundation of Korea funded by the MEST
(Project no. 2012-000181). We thank NU-HTA and NU
NUANCE and NU-QBIC for characterization equipment availabil-
ity and expertise. We also thank A. Yan and Y. Huang for assis-
tance with EM microscopy and M. Rotz and Dr. K. MacRenaris
assistance with ICP-MS. SC thanks US DHS for a graduate fel-
lowship.
1
2
3
4
5
6
7
8
(22) Late, D. J.; Liu, B.; Matte, H. S. S. R.; Rao, C.
N. R.; Dravid, V. P. Adv. Funct. Mater. 2012, 22, 1894.
REFERENCES
(23)
1999, 121, 11720.
(24)
Heising, J.; Kanatzidis, M. G. J. Am. Chem. Soc.
9
(1) Li, Y.; Wang, H.; Xie, L.; Liang, Y.; Hong, G.;
Dai, H. J. Am. Chem. Soc. 2011, 133, 7296.
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
Shi, W.; Sahoo, Y.; Swihart, M. T. Colloid Sur-
(2)
Giacometti, V.; Kis, A. Nat Nano 2011, 6, 147.
(3) Eda, G.; Yamaguchi, H.; Voiry, D.; Fujita, T.;
Chen, M.; Chhowalla, M. Nano Lett. 2011, 11, 5111.
(4) Zhang, H.; Loh, K. P.; Sow, C. H.; Gu, H.; Su,
X.; Huang, C.; Chen, Z. K. Langmuir 2004, 20, 6914.
Radisavljevic, B.; Radenovic, A.; Brivio, J.;
faces A 2004, 246, 109.
(25) Thangadurai, P.; Balaji, S.; Manoharan, P. T.
Nanotechnology 2008, 19, 435708.
(26) Porter, M. D.; Bright, T. B.; Allara, D. L.;
Chidsey, C. E. D. J. Am. Chem. Soc. 1987, 109, 3559.
(27) Harder, P.; Grunze, M.; Dahint, R.; Whitesides,
G. M.; Laibinis, P. E. J. Phys. Chem. B. 1998, 102, 426.
(5)
Liu, K.-K.; Zhang, W.; Lee, Y.-H.; Lin, Y.-C.;
Chang, M.-T.; Su, C.-Y.; Chang, C.-S.; Li, H.; Shi, Y.; Zhang, H.;
Lai, C.-S.; Li, L.-J. Nano Lett. 2012, 12, 1538.
(28)
Wagner, C. D.; Muilenberg, G. E. Handbook of
x-ray photoelectron spectroscopy: a reference book of standard data
for use in x-ray photoelectron spectroscopy; Perkin-Elmer Corp.,
Physical Electronics Division, 1979.
(29) Weisbecker, C. S.; Merritt, M. V.; Whitesides,
G. M. Langmuir 1996, 12, 3763.
(6)
Zhang, Y.; Fang, Y.; Tenne, R.; Wang, C. ACS Nano 2011, 5, 1276.
(7) Medintz, I. L.; Uyeda, H. T.; Goldman, E. R.;
Mattoussi, H. Nat. Mater. 2005, 4, 435.
Wu, H.; Yang, R.; Song, B.; Han, Q.; Li, J.;
(8)
Nakanishi, H.; Walker, D. A.; Bishop, K. J. M.;
(30) Jaramillo, T. F.; Jørgensen, K. P.; Bonde, J.;
Nielsen, J. H.; Horch, S.; Chorkendorff, I. Science 2007, 317, 100.
Wesson, P. J.; Yan, Y.; Soh, S.; Swaminathan, S.; Grzybowski, B. A.
Nat Nano 2011, 6, 740.
(31)
Chou, S. S.; Kaehr, B.; Kim, J.; Foley, B. M.;
(9)
Arvizo, R. R.; Bunz, U. H. F.; Rotello, V. M. Nat Chem 2009, 1, 461.
(10) Yaacobi-Gross, N.; Soreni-Harari, M.; Zimin,
M.; Kababya, S.; Schmidt, A.; Tessler, N. Nat. Mater. 2011, 10, 974.
(11) Rapoport, L.; Fleischer, N.; Tenne, R. J. Mater.
Chem. 2005, 15, 1782.
De, M.; Rana, S.; Akpinar, H.; Miranda, O. R.;
De, M.; Hopkins, P. E.; Huang, J.; Brinker, C. J.; Dravid, V. P. An-
gew. Chem., Int. Ed. 2013, n/a. DOI: 10.1002/anie.201209229
(32) Verma, A.; Simard, J. M.; Worrall, J. W. E.;
Rotello, V. M. J. Am. Chem. Soc. 2004, 126, 13987.
(33) Jacobson, R. H.; Zhang, X. J.; DuBose, R. F.;
Matthews, B. W. Nature 1994, 369, 761.
(12)
Yarar, B.; Kaoma, J. Colloids Surf. 1984, 11,
(34) De, M.; Chou, S. S.; Dravid, V. P. J. Am. Chem.
Soc. 2011, 133, 17524.
429.
(13)
Tahir, M. N.; Zink, N.; Eberhardt, M.; Therese,
(35)
Miranda, O. R.; Chen, H.-T.; You, C.-C.;
H. A.; Kolb, U.; Theato, P.; Tremel, W. Angew. Chem., Int. Ed. 2006,
45, 4809.
(14) Joensen, P.; Frindt, R. F.; Morrison, S. R. Mater.
Res. Bull. 1986, 21, 457.
(15) Schumacher, A.; Scandella, L.; Kruse, N.; Prins,
R. Surf. Sci. 1993, 289, L595.
(16) Zeng, Z.; Yin, Z.; Huang, X.; Li, H.; He, Q.; Lu,
G.; Boey, F.; Zhang, H. Angew. Chem., Int. Ed. 2011, 50, 11093.
Mortenson, D. E.; Yang, X.-C.; Bunz, U. H. F.; Rotello, V. M. J. Am.
Chem. Soc. 2010, 132, 5285.
(36)
Miranda, O. R.; You, C.-C.; Phillips, R.; Kim, I.-
B.; Ghosh, P. S.; Bunz, U. H. F.; Rotello, V. M. J. Am. Chem. Soc.
2007, 129, 9856.
(37) Lee, J.-S.; Ulmann, P. A.; Han, M. S.; Mirkin, C.
A. Nano Lett. 2008, 8, 529.
(38) Chou, S. S.; De, M.; Luo, J.; Rotello, V. M.;
Huang, J.; Dravid, V. P. J. Am. Chem. Soc. 2012, 134, 16725.
(17) Dungey, K. E.; Curtis, M. D.; Penner-Hahn, J. E.
Chem. Mater. 1998, 10, 2152.
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Figure 1. Structural models illustrating ligand conjugation of ce-MoS2 sheets.
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Figure 2. (a) XRD spectra of ce-MoS2. (b) Low and high magnification AFM micrograph of ce-MoS2.
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Figure 3. (a) ζꢀpotential, (b) FTꢀIR spectra focused upon the thiol peak, (c) FTꢀIR spectra showing all peaks
and (d) HER polarization curve before and after ligand conjugation
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Figure 4. (a) Colloidal stability of ce-MoS2 samples after 21 days in water. (b) Colloidal stability of ce-MoS2
functionalized with NMe3 terminated thiol at various pH.
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Figure 5. (a) Structure of a single unit of a βꢀGal tetramer. Anionic residues (Asp and Glu) surrounding βꢀ
gal’s active site are highlighted (bottom) (b) Concentration dependence of βꢀgal inhibition with various ceꢀ
MoS2 conjugate.
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Journal of the American Chemical Society
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ACS Paragon Plus Environment