Multicolor Emitting Block Copolymer-Integrated Graphene Quantum Dots for Colorimetric, Simultaneous Sensing of Temperature, pH, and Metal Ions

Article abstract of DOI:10.1021/acs.chemmater.5b01545

Highly selective optical sensors that are capable of detecting complex stimuli have attracted significant interest in environmental, biomedical, and analytical chemistry applications. In this Article, we report the development of novel and versatile platform for highly efficient, colorimetric multifunctional sensors using block copolymer-integrated graphene quantum dots (bcp-GQDs). In particular, the multisensing behavior is successfully generated simply by grafting blue-emitting, temperature-responsive block copolymers onto green-emitting, 10 nm size GQD that provides luminescent response to pH changes. Thus, the bcp-GQDs showed simultaneous, orthogonal sensing behavior to temperature and pH, as well as dose-dependent responses to different types of metal ions. In addition, the bcp-GQD sensor showed excellent reversibility and dispersion stability in pure water, indicating that our system is an ideal platform for environmental and biological applications. The detailed mechanism of the responsive behavior of the bcp-GQDs was elucidated by measurements of time-resolved fluorescence and dynamic light scattering.

Full text of DOI:10.1021/acs.chemmater.5b01545

Page 1 of 21
Chemistry of Materials
1
2
3
4
5
6
7
8
9
Multi-Color Emitting Block Copolymer-Integrated Graphene Quantum
Dots for Colorimetric, Simultaneous Sensing of Temperature, pH, and
Metal Ions
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
Chan Ho Park, 1 Hyunseung Yang, 1 Junhyuk Lee, 1 Han-Hee Cho, 1 Dahin Kim, 1 Doh C. Lee,
1 Bumjoon J. Kim*,1
1Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science
and Technology (KAIST), Daejeon 305-701, Korea
Keywords
colorimetric sensor, multi-functional sensor, graphene quantum dots, stimuli-responsive
polymer, block copolymer
ACS Paragon Plus Environment

Chemistry of Materials
Page 2 of 21
1
2
3
4
5
ABSTRACT
6
7
8
9
Highly-selective optical sensors that are capable of detecting complex stimuli have attracted
significant interest in environmental, biomedical, and analytical chemistry applications. In this
work, we report the development of novel and versatile platform for highly-efficient,
colorimetric multi-functional sensors using block copolymer-integrated graphene quantum
dots (bcp-GQDs). In particular, the multi-functional sensing behavior is successfully generated
simply by grafting blue emitting, temperature-responsive block copolymers onto green-
emitting, 10-nm size GQD with the GQD providing luminescent response to pH changes. Thus,
the bcp-GQDs showed simultaneous, orthogonal sensing behavior to temperature and pH, as
well as dose-dependent responses to different types of metal ions. In addition, the bcp-GQD
sensor showed excellent reversibility and dispersion stability in pure water, indicating that our
system is an ideal platform for environmental and biological applications. The detailed
mechanism of the responsive behavior of the bcp-GQDs was elucidated by measurements of
time-resolved fluorescence and dynamic light scattering.
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
ACS Paragon Plus Environment

Page 3 of 21
Chemistry of Materials
1
2
3
4
5
INTRODUCTION
6
7
8
9
Fluorescent materials have attracted significant attention for a wide variety of applications,
ranging from optoelectronic devices to chemical and biological sensors.1-4 Particularly,
fluorescent multi-functional sensors, which respond simultaneously and independently to
different stimuli, have been the center of research interest due to their simple detection of
multiple stimuli in a complex environment.4-6 These multi-functional sensing behaviors are
typically achieved by integrating different responsive objects, such as stimuli-responsive small
molecules, polymers, and/or inorganic particles into a single platform.6, 7 However, such
sensors typically require a multistep and complex synthesis of different types of responsive
components.8, 9 Additionally, many functional sensors based on small molecules and polymers
often suffer from poor dispersion in aqueous media and toxicity, which limit their use in
biological and environmental applications.10-12 More importantly, most fluorescent sensors
respond to stimuli by a single photoluminescence (PL) intensity change that often requires an
expensive PL detector to monitor the response effectively.13-15
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
Graphene quantum dots (GQDs), nanometer-sized graphene derivatives, have very
interesting opto-electronic properties due to quantum confinement and edge effects.16-21
Therefore, in contrast to graphene and graphene oxide that do not exhibit strong stimuli-
responsive or luminescent behaviors, GQDs have tunable luminescent properties that depend
on their size as well as pH and the presence of metal ions, making them great candidates for a
multi-sensing platform.18, 22-28 In addition, their surface typically has functional, oxygen-
containing groups that provide excellent water-solubility as well as reactive sites for surface
modification.19 Despite such advantages, the multi-sensing behavior of GQD-based materials
has not been extensively investigated.29, 30 To the best of our knowledge, the colorimetric,
multi-sensing response of the GQD-based sensors has not been demonstrated despite its great
advantage of rapidly readable responses.
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 21
1
2
3
4
5
6
7
8
9
Herein, we describe the development of a colorimetric, multi-sensing platform based on
responsive block copolymer-integrated GQDs (bcp-GQDs) that detect different types of
information simultaneously, including temperature, pH, and various kinds of metal ions. Our
synthetic approach is very simple, involving single-type blue emitting, thermally-responsive
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
poly(7-(4-(acryloyloxy)butoxy)coumarin)-b-poly(N-isopropylacrylamide)
(P7AC-b-
PNIPAAm) polymers grafted to green-emitting, 10-nm GQDs (Scheme 1). A key strategy for
generating colorimetric, multi-sensing behavior is to control the relative amounts of blue
emission from P7AC-b-PNIPAAm and green emission from the GQD core, which are both
strongly dependent on different types of stimuli. The colorimetric sensing response to
temperature change was generated by tuning the distance between the blue and green emitters
and, thus, their Förster resonance energy transfer (FRET). In addition, the luminescent response
of the green-emitting GQD core produced quantitative, colorimetric switching behavior of bcp-
GQDs in response to changes in pH and different types of metal ions. The detailed mechanism
of the responsive behavior of the bcp-GQD sensors was investigated using time-resolved
photoluminescence spectroscopy, dynamic light scattering, and microscopy. To the best of our
knowledge, this is the first colorimetric, multi-functional sensor based on GQDs.
Scheme 1. Structure of block copolymer-grafted graphene quantum dots (bcp-GQDs) and their
sensing behavior.
ACS Paragon Plus Environment

Page 5 of 21
Chemistry of Materials
1
2
3
4
5
RESULTS AND DISCUSSION
6
7
8
9
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
Figure 1. Synthesis of bcp-GQDs
Figure 1 shows the synthetic procedure employed to produce fluorescent P7AC-b-
PNIPAAm block copolymer-grafted GQDs. Green-emitting GQDs were synthesized by the
cleavage of carbon black (CX-72), as reported in a previous study.25, 26 Blue-emitting P7AC-
b-PNIPAAm diblock copolymers were synthesized on the surface of the GQDs by the
‘‘grafting-from’’ method using reversible addition–fragmentation chain transfer (RAFT)
polymerization.31 First, the trithiocarbonate RAFT chain transfer agent was grafted covalently
onto the surface of the pristine GQDs by the N,N'-dicyclohexylcarbodiimide (DCC) coupling
reaction between the hydroxyl group on the GQD surface and the carboxylic acid group of the
RAFT agent.11, 32 The functionalized GQDs were then precipitated, centrifuged, and filtered
several times to remove ungrafted RAFT agent and other chemical residues completely, which
was confirmed using thin-layer chromatography. For convenience, RAFT chain transfer agent-
grafted GQDs are denoted as RAFT-GQDs. The PNIPAAm block was polymerized from the
RAFT-GQDs, followed by the blue emitting P7AC block to produce P7AC-b-PNIPAAm block
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 21
1
2
3
4
5
6
7
8
9
copolymer chains on the GQDs (bcp-GQDs). Since the molecular weight (Mn) of the
PNIPAAm block is a critical parameter that determines the distance between the two
chromophores and the Mn of the P7AC block influences the brightness of the blue emitters, the
Mn of both the PNIPAAm and P7AC blocks were controlled carefully.13 The total Mn of P7AC-
b-PNIPAAm of bcp-GQD was 6.4 kg mol−1 with a polydispersity index (PDI) of 1.16. The Mn
and PDI values of the PNIPAAm block only were 5.9 kg mol−1 and 1.13, respectively. The
areal chain density (δ) of the grafted P7AC-b-PNIPAAm polymers on the GQDs was estimated
to be 0.035 chain nm−2. The δ value was calculated based on the average size of the GQDs
using transmission electron microscopy (TEM) images, and the weight fractions of the GQD
cores and the grafted polymers obtained by thermogravimetric analysis (TGA) (Supporting
Information (SI) Figure S1).33-35 The δ value is comparable to the values reported previously
for other systems involving PNIPAAm brushes on graphene.13, 36
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
The conjugation of the P7AC-b-PNIPAAm polymers to the surface of the GQDs was
confirmed by attenuated total-reflectance Fourier transform infrared spectroscopy (ATR-FTIR)
and X-ray photoelectron spectroscopy (XPS) measurements. As shown in Figure S2a, ATR-
FTIR of RAFT-GQDs showed stretching vibrations of the thiocarbonyl group (C=S) at 1072
cm−1, corresponding to the RAFT agent.37, 38 The amide peaks from the PNIPAAm blocks in
the PNIPAAm-GQDs and bcp-GQDs were observed at 1530, 1640 and 3290 cm−1.38 Compared
to the PNIPAAm-GQDs, the bcp-GQDs exhibited a slightly increased intensity of the C=O
stretching peak at 1722 cm−1 and a decreased intensity of the amide peak due to the additional
C=O groups from the P7AC block (SI Figure S2b). In addition, XPS of the functionalized
GQDs revealed sulfur (S 2p) peak corresponding to the grafted RAFT agent, whereas XPS of
pristine GQDs did not show any signal (SI Figure S2c). The S 2p peak intensity decreased
significantly for the PNIPAAm-GQDs and for the bcp-GQDs, because the portion of sulfur
was diluted by the grafted block copolymers.
ACS Paragon Plus Environment

Page 7 of 21
Chemistry of Materials
1
2
3
4
5
6
7
8
9
We examined the solubility and stability of the bcp-GQDs (SI Figure S3). It was observed
that all of the pristine GQDs, RAFT-GQDs, PNIPAAm-GQDs, and bcp-GQDs were dispersed
successfully in water. As shown in Figure S3, the green emission of the pristine-GQDs, RAFT-
GQDs, and PNIPAAm-GQDs was evident. In stark contrast, the bcp-GQDs showed near white
emission due to the simultaneous blue emission of the P7AC block and green emission of the
GQDs, demonstrating the potential of bcp-GQDs as luminescent sensors that have tunable
fluorescence properties (SI Figure S4). To further confirm the chemical grafting of the block
copolymers on the GQDs, the average sizes and heights of pristine GQDs, RAFT-GQDs, and
bcp-GQDs were measured and compared by high-resolution TEM and atomic force
microscopy (AFM) (SI Figure S5). The average size and height of the GQDs were 11.1 and
0.71 nm, respectively, while the average size and height of the RAFT-GQDs were 11.8 and
0.73 nm, respectively. In contrast, the average size and height of the bcp-GQDs increased
significantly to 26.6 and 3.88 nm, respectively, due to the presence of the grafted polymer
chains on the GQD surface. These results indicated that the P7AC-b-PNIPAAm chains were
successfully grafted from the RAFT agent covalently attached to the surface of the GQDs.
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
Figure 2. (a) PL spectra of the bcp-GQDs; (b) Reversibility test of the PL behavior of bcp-
GQDs with the excitation at 365 nm.
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 21
1
2
3
4
5
6
7
8
9
Figure 2a shows the PL response of the bcp-GQDs in water (pH 7) as a function of
temperature. The concentration of the bcp-GQDs was maintained at the low concentration of
30 ppm to avoid any PL quenching of the P7AC block by other GQD substrates in the solution.
At room temperature, the PL spectra of the bcp-GQDs showed two emission peaks, one at 410
nm from the P7AC block and one at 505 nm from the GQD cores, producing near white
luminescence. When the temperature of the solution increased to 40 ˚C, the intensity of the
blue emission peak at 410 nm decreased suddenly, whereas the intensity at 505 nm increased
significantly, showing green color. To quantify the change in PL intensity in terms of
temperature and to examine the reversibility of the response behavior of the bcp-GQDs, the PL
intensity ratios at emission levels of 505 and 410 nm (I505nm/I410nm) were plotted with
continuous cycles in aqueous media at different temperatures in Figure 2b. When the
temperature was increased from 25 to 40 ˚C, the I505nm/I410nm value significantly increased from
0.91 to 2.27. This change was reproducible over continuous heating-cooling cycles. We
attribute the extraordinary reversibility and stability of the bcp-GQDs to the strong covalent
linkage between the grafted polymers and the GQDs, and to the excellent dispersion behavior
of the GQD substrates in water. Fast response, high reversibility, stability, and visible color
change are crucial for successful application and commercialization of optical sensors.8, 39, 40
The colorimetric response of the bcp-GQD solution as a function of temperature was correlated
with the change in the conformation of the PNIPAAm chain at the lower critical solution
temperature (LCST). Below 32 ˚C, the PNIPAAm chains in the bcp-GQDs become hydrophilic
and stretched in water. Thus, the distance between the two fluorescent units, i.e., the blue-
emitting P7AC block and the green emitting GQDs, should be long enough to suppress the
FRET between them. Above the LCST, the PNIPAAm chains collapse, promoting FRET from
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
ACS Paragon Plus Environment

Page 9 of 21
Chemistry of Materials
1
2
3
4
5
6
7
the higher energy P7ACs to the lower energy GQDs and producing a color change from white
to green.41-43
8
9
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
Figure 3. (a) Reversible behavior of the fluorescence decay of bcp-GQDs between 25 ˚C and
40 ˚C. Both measurements were performed at 410 nm emission with the excitation at 370 nm.
(b) DLS analysis for the sizes of pristine GQDs and bcp-GQDs as a function of temperature.
The FRET efficiency was evaluated by measuring the lifetime of the fluorophores (Figure
3a).44-46 The decay in the fluorescence intensity of the P7AC emission from the bcp-GQDs at
410 nm was investigated by time-resolved fluorescence (TRF) under irradiation at 370 nm in
water.47 The TRF results indicated that the bcp-GQDs were temperature-sensitive and their
fluorescent lifetime decreased significantly at the temperature above the LCST. These results
are summarized in Table S1, and the data were fitted using a double-exponential decay model.
At 25 ˚C, below the LCST of the PNIPAAm spacer, the P7AC emission in the bcp-GQDs had
an average lifetime (τave) of 1.96 ns, with two decay components of τ1= 1.73 ns (population A1=
96.34%) and τ2= 7.91 ns (population A2 = 3.66%). In contrast, at 40 ˚C, above the LCST of
PNIPAAm, the P7AC emission decay process was much faster, with a τave value of 0.79 ns,
with decay components of τ1= 0.52 ns (population A1= 83.87%) and τ2= 2.19 ns (population
A2 = 16.13%). The shorter lifetime of the P7AC emission in the bcp-GQDs was attributed to
an increase in the non-radiative decay rate caused by energy transfer from the P7ACs to the
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 21
1
2
3
4
5
6
7
GQDs. A similar TRF trend after multiple cycles was obtained repeatedly and is consistent
with that of the reversibility test of the static PL spectra (SI Figure S6).
8
9
A deeper insight into the dramatic color responses as a function of temperature was
obtained by examining the change in the size of the bcp-GQDs via dynamic light scattering
(DLS) (Figure 3b). Pristine GQDs had a temperature-independent, hydrodynamic diameter of
12 nm, which is in excellent agreement with the size of the GQDs measured by high resolution
TEM. In stark contrast, the particle sizes of the bcp-GQDs were strongly dependent on
temperature due to the conformational change of the polymer chains on the GQDs. The particle
size was constant at 16 nm above the LCST, showing good agreement with the sum of the GQD
core (~12 nm) and twice the radius of gyration of the PNIPAAm chains (~1.1 nm).48, 49 Under
these temperature conditions, the distance between the P7AC block and GQD core was short
enough to induce strong FRET from P7AC to the GQD as evidenced by the strong green
luminescence of the bcp-GQDs. When the temperature was below the LCST, the
hydrodynamic particle size of the bcp-GQDs was remarkably increased to 45 nm. Under these
conditions, the distance between the P7AC block and GQD core became significantly larger
and suppressed the FRET. Because the hydrodynamic particle size can be overestimated by
DLS measurements due to extensive swelling of the polymers by the solvent,11 the increase in
the particle size is not equal to the increase in the donor-to-acceptor distance. However, it is
worthwhile to note that the trend of the particle size dependence on the temperature change
was consistent with that of the PNIPAAm conformation and the PL spectra in Figure 2. These
observations described that the dramatic temperature-dependent color response of the bcp-
GQDs was induced solely by the FRET effect from the P7AC block to the GQD due to the
changes of PNIPAAm’s conformation in response to temperature.
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
ACS Paragon Plus Environment

Page 11 of 21
Chemistry of Materials
1
2
3
4
5
6
7
8
9
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
Figure 4. (a) The ratio of PL intensity of bcp-GQDs at different pH values; (b) PL spectra of
bcp-GQDs at different pH values from pH 1 to 11 at 25 ˚C.
To demonstrate the use of the bcp-GQD sensor as a multi-sensing platform, the colorimetric
responses of the bcp-GQDs to changes in pH and ion stimuli were investigated. Figure 4 shows
the pH-dependent PL behavior of the bcp-GQDs. The color of the solution distinctly turned
from blue (pH 1) to white (pH 7) to cyan (pH 11) as the pH increased. For example, the
I505nm/I410nm value was 0.20 at pH 1, but it increased to 0.71 at pH 3. At pH 7, I505nm/I410nm value
was highest as 0.94. This is because the emission of the GQD core at 505 nm in the bcp-GQDs
decreased as the solution became more acidic. For the same reason, lower I505nm/I410nm values
were provided as 0.63 at pH 9 and 0.59 at pH 11 than at the neutral condition. Whereas the PL
intensity of the bcp-GQDs at 410 nm remained almost constant irrespective of pH change, the
emission intensity of the GQDs in strong acidic and alkaline conditions decreased considerably
because the pH change can induce protonation or deprotonation of emissive sites (i.e., oxygen
groups and free zigzag sites) in the GQD cores.18, 26, 50 Thus, the relative amounts of green to
blue emissions were tuned in terms of pH value, generating colorimetric behavior. Compared
with traditional pH responsive polymer-based sensors that change their conformation only at a
specific pH value, our bcp-GQDs system has advantages in monitoring a wide range of pH
ACS Paragon Plus Environment

Chemistry of Materials
Page 12 of 21
1
2
3
4
5
6
7
8
9
values with visible color changes.39 Also, we highlight that simultaneous, orthogonal sensing
of changes in temperature and pH can be achieved using our bcp-GQDs (SI Figure S7). The
PL and color changes of bcp-GQDs in different pH conditions (i.e., pH 1-11) were observed in
terms of temperature change.
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
Figure 5. (a) PL spectra of bcp-GQDs at the presence of Cu2+ and Fe3+ at a concentration of
100 μM; (b) Ratio of PL intensity upon the addition of 100 μM of guest metal ions (Ag2+, Cd+,
Au3+, Sn2+, Cu2+, Pb2+, Cr3+, Fe3+, and Pd2+); (c) PL spectra of bcp-GQDs as a function of the
Fe3+ concentration (μM); (d) Plot of I505nm/I410nm of bcp-GQDs as a function of the Fe3+
concentration (The line is a guide for the eye. The PL spectra were measured under irradiation
at 365 nm.)
Of particular interest is that the bcp-GQDs can detect various types of metal ions in a dose-
dependent manner. Figure 5 highlighted that the bcp-GQD system can be applied for the
sensitive detection of metal ions with dose-dependent color distinction. All experiments were
performed in pH 7 aqueous solution at 25 ˚C. Figure 5a shows changes in the PL spectra of
ACS Paragon Plus Environment

Page 13 of 21
Chemistry of Materials
1
2
3
4
5
6
7
8
9
bcp-GQDs in response to Cu2+ and Fe3+. The solution of bcp-GQDs turned from white to a
greenish blue color in the presence of Cu2+ at the concentration of 100 μM, whereas the solution
changed to deep-blue color in the presence of Fe3+ at the same concentration. These phenomena
were caused by the PL response of the GQD core at 505 nm in the presence of different metal
ions. In this regard, we investigated the color response of the bcp-GQD sensor in the presence
of various types of metal ions (i.e., Ag2+, Cd+, Au3+, Sn2+, Cu2+, Pb2+, Cr3+, Fe3+, and Pd2+)
(Figure 5b). The concentration of the metal ions in the solution was fixed at 100 μM. It was
observed that the degree of reduction in the green emission of GQD cores relies on the type of
metal ions, which makes multi-color recognition of bcp-GQDs dependent on the type of metal
ion. Furthermore, the concentration of the metal ions determines the colorimetric response of
the bcp-GQDs. For example, we examined the effect of Fe3+ concentration on the PL intensity
of the bcp-GQD cores at 505 nm, which showed a gradual decrease in the intensity as the Fe3+
concentration increased (Figure 5c). The I505nm/I410nm value decreased linearly with respect to
Fe3+ concentration in a range from 0 to 50 μM, enabling the quantitative measurement of the
Fe3+ concentrations (Figure 5d). These results can be explained by the formation of non-
radiative metal-GQD complexes by the interaction between the GQDs and electrophilic metal
ions, which contributes to additional fluorescence quenching by charge transfer from the
excited GQDs to the metal ions.51-55 For example, Figure S8 shows that the fluorescence decay
of GQD cores in bcp-GQDs became much faster in the presence of the 100 μM concentration
of Fe3+.56 Since the degree of formation of metal-GQD complexes is highly dependent on the
concentration of metal ions and the binding affinity between metal ions and GQDs,57 the bcp-
GQDs showed distinct color responses depending on the concentration and also had different
PL responses for different metal ions (Figure 5b). In addition, the ion sensing behavior of bcp-
GQDs was investigated in the presence of different stimuli of temperature and pH. Figure S9
demonstrates that the bcp-GQDs had simultaneous sensing behavior for temperature and pH,
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
ACS Paragon Plus Environment

Chemistry of Materials
Page 14 of 21
1
2
3
4
5
6
7
8
9
and they also showed responses to different types of metal ions with excellent stability. The
colorimetric, orthogonal response of bcp-GQD sensors towards various stimuli sensing is
potentially advantageous for their use in environmental sensing applications, including tap-
water analysis, cell diagnosis and bio-imaging.
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
CONCLUSIONS
In summary, we developed a novel colorimetric multi-functional sensor using block
copolymer-integrated GQDs through the “grafting from” method. The bcp-GQDs had
simultaneous, orthogonal sensing behavior to temperature and pH, as well as dose-dependent
responses to different types of metal ions with excellent reversibility and stability. All of the
responses can be easily detected by their distinctive colorimetric changes. Our GQD-based
sensing platform can be applied easily in various sensor systems with alternate grafted
molecules, thus providing promising opportunities for use in opto-electronic, environmental,
and biological applications.
METHODS
Materials: Vulcan CX-72 carbon black was purchased from Cabot Corporation. Anhydrous
potassium carbonate (K2CO3, 99.5%), magnesium sulfate (MgSO4, 99%), sodium hydroxide
(NaOH powder, 98%), and hydrochloric acid (HCl, 10 M) were purchased from Daejung
Chemical & Metal Co. Azobisisobutyronitrile (AIBN, 98%) was purchased from Junsei
Chemical Co. and purified by recrystallization from ethanol. 7-hydroxycoumarin and other
materials were purchased from Sigma-Aldrich and N-isopropylacrylamide (NIPAM, 99%)
purified by recrystallization in hexane. Deionized (DI) water was used in all experiments.
Synthesis of 7-(4-(acryloyloxy)butoxy)coumarin (7AC): The 7AC monomer was synthesized
as previously reported.13, 58 Anhydrous K2CO3 (3.48 g, 24.8 mmol) was added into a mixture
of 7-hydroxycoumarin (2 g, 12.4 mmol) and 1,4-dibromobutane (4.42 mL, 37.2 mmol) in
ACS Paragon Plus Environment

Page 15 of 21
Chemistry of Materials
1
2
3
4
5
6
7
8
9
acetone (120 mL). The resulting suspension was refluxed for 24 h. The precipitate was filtered
off, and the solvent was removed. The resulting mixture was diluted with diethyl ether and the
separated organic layer was washed with DI water, dried over MgSO4, and concentrated under
reduced pressure. The residue was purified by means of column chromatography using silica
gel and a mixture of hexane and ethyl acetate as the eluent, affording 7-(4-bromobutoxy)-
coumarin. Then, 7-(4-bromobutoxy)-coumarin (2.38 g, 9 mmol) and excess sodium acrylate
(1.128 g, 12 mmol) were dissolved in ethanol (150 mL). Hydroquinone (0.02 g, 1.8 mmol) was
added, and the solution was refluxed for 36 h. The precipitate was filtered off and washed with
ethanol. After the solvent was removed under reduced pressure, DI water was added, and the
residue was extracted with diethyl ether. The residue was purified by column chromatography
on silica gel with a mixture of hexane and ethyl acetate as the eluent to yield 7AC (1.4 g, 61%)
as a white solid.
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
1H NMR (CDCl3): 7.62 (d, 1H), 7.34 (d, 1H), 6.80 (m, 2H), 6.41 (d, 1H), 6.24 (m, 1H), 6.11
(m, 1H), 5.81 (m, 1H), 4.23 (s, 2H), 4.04 (s, 2H), 1.90 (s, 2H), 1.55 (s, 2H).
Synthesis of trithiocarbonate RAFT chain transfer agent: We synthesized (2-(((butylsulfanyl)-
carbonothioyl)sulfanyl))propanoic acid using a procedure modified from previous reports.11, 59
An aqueous solution of NaOH (50 %, 16.0 g) was added to a mixture of butanethiol (18.0 g,
200 mmol) and DI water (30 mL), followed by the addition of acetone (10 mL) to give a
colorless solution. The solution was stirred at room temperature for 0.5 h. Carbon disulfide (14
mL, 17.6 g, 231 mmol) was added to obtain a clear orange solution. The reaction mixture was
stirred for 0.5 h and then cooled in an ice bath. Then, 2-bromopropionic acid (31.4 g, 205 mmol)
was added dropwise, followed by the addition of NaOH(aq) (50 %, 16.0 g) at a rate such that
the temperature of the bath was kept lower than 30 °C. After the exothermic reaction had
terminated, DI water (30 mL) was added, and the reaction mixture was stirred at room
temperature for 24 h. The reaction mixture was diluted with 50 mLof water. Then, 10 M HCl(aq)
(60 mL) was added to the solution under an ice bath. A yellow oil was obtained, and kept in an
ice bath until the oil solidified. The solid was separated by filtration, washed with cold water,
and dried. Finally, the product was recrystallized from hexane with gentle stirring to give
bright-yellow solid crystals (34.8g, 71.2%).
1H NMR (CDCl3, 500 MHz) δ 9.9 (br s, 1H), 4.87 (q, 1H), 3.37 (t, 2H), 1.66-1.76 (m, 2H),
ACS Paragon Plus Environment

Chemistry of Materials
Page 16 of 21
1
2
3
4
5
1.64 (d, 3H), 1.42-1.49 (m, 2H), 0.94 (t, 3H).
6
7
8
9
Synthesis of GQDs: GQDs were synthesized via chemical oxidation.25, 26 In brief, carbon black
(1 g) was added to a mixture of nitric acid(aq) (100 mL) and DI water (150 mL). The resulting
suspension was refluxed for 48 h. The solution was then cooled to room temperature and
centrifuged (6000 rpm, 20 min). The supernatant was heated to yield a reddish-brown powder.
GQDs were re-dispersed in tetrahydrofuran (THF) and ultra-filtered through a 0.22 μm
microporous membrane, resulting in the fluorescent GQDs.
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
Synthesis of bcp-GQDs: GQDs (0.1 g), trithiocarbonate RAFT agent (0.5 g, 2.1 mmol), DCC
(10 mg, 0.05 mmol) and 4-dimethylaminopyridine (DMAP) (1 mg, 0.01 mmol) were mixed in
THF overnight at room temperature. Then, the mixture was precipitated into diethyl ether and
centrifuged (10000 rpm, 20 min) several times. The resulting material was vacuum-dried, re-
dispersed in dimethylformamide (DMF), and filtered through a 0.45 μm PVDF syringe filter.
Asolution of RAFT-GQDs (100 mg), NIPAAm monomer (0.5 g, 4.4 mmol), and AIBN (6 μmol)
in DMF (5 ml) was added into a glass ampoule for polymerization under vacuum. After
polymerization for 12 h at 65 °C, PNIPAAm-GQDs were precipitated into cold diethyl ether
twice and vacuum-dried. A solution of PNIPAAm-GQDs (0.1 g), 7AC monomer (65 mg, 0.23
mmol), and AIBN (0.5 mg, 4 μmol) in DMF (5 ml) was added into a glass ampoule for
sequential polymerization under vacuum. After reacting for 12 h at 65 °C, the product was
precipitated in cold diethyl ether twice and vacuum-dried.
Characterization: Detailed procedures are described in the Supporting Information
ASSOCIATED CONTENT
Supporting Information
ACS Paragon Plus Environment

Page 17 of 21
Chemistry of Materials
1
2
3
4
5
6
7
8
9
Detailed characterization data: TGA, ATR-FTIR, XPS, TEM, SEM, PL spectra, and
fluorescence decay data. This material is available free of charge via the Internet at
http://pubs.acs.org.
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
AUTHOR INFORMATION
Corresponding Author
*E-mail: bumjoonkim@kaist.ac.kr
ACKNOWLEDGEMENT
This work was supported by Samsung Research Funding Center of Samsung Electronics under
Project Number SRFC-MA1301-07. We thank Rachel Letteri for helpful discussions.
REFERENCES
(1)
fluorescent conjugated polymers. Chem. Rev. 2007, 107, 1339-1386.
(2) Medintz, I. L.; Uyeda, H. T.; Goldman, E. R.; Mattoussi, H., Quantum dot
bioconjugates for imaging, labelling and sensing. Nat. Mater. 2005, 4, 435-446.
(3) Baldo, M. A.; Thompson, M. E.; Forrest, S. R., High-efficiency fluorescent organic
light-emitting devices using a phosphorescent sensitizer. Nature 2000, 403, 750-753.
(4) Schaferling, M., The Art of Fluorescence Imaging with Chemical Sensors. Angew.
Chem. Int. Ed. 2012, 51, 3532-3554.
(5) Li, C. H.; Zhang, Y. X.; Hu, J. M.; Cheng, J. J.; Liu, S. Y., Reversible Three-State
Thomas, S. W.; Joly, G. D.; Swager, T. M., Chemical sensors based on amplifying
Switching of Multicolor Fluorescence Emission by Multiple Stimuli Modulated FRET
Processes within Thermoresponsive Polymeric Micelles. Angew. Chem. Int. Ed. 2010, 49,
5120-5124.
(6)
and imaging. Chem. Soc. Rev. 2010, 39, 3102-3114.
(7) Yan, X. Z.; Wang, F.; Zheng, B.; Huang, F. H., Stimuli-responsive supramolecular
polymeric materials. Chem. Soc. Rev. 2012, 41, 6042-6065.
(8) Hu, J. M.; Liu, S. Y., Responsive Polymers for Detection and Sensing Applications:
Current Status and Future Developments. Macromolecules 2010, 43, 8315-8330.
(9) Kim, H. N.; Guo, Z. Q.; Zhu, W. H.; Yoon, J.; Tian, H., Recent progress on polymer-
based fluorescent and colorimetric chemosensors. Chem. Soc. Rev. 2011, 40, 79-93.
(10) Pietsch, C.; Hoogenboom, R.; Schubert, U. S., Soluble Polymeric Dual Sensor for
Stich, M. I. J.; Fischer, L. H.; Wolfbeis, O. S., Multiple fluorescent chemical sensing
Temperature and pH Value. Angew. Chem. Int. Ed. 2009, 48, 5653-5656.
ACS Paragon Plus Environment

Chemistry of Materials
Page 18 of 21
1
2
3
4
5
6
(11)
Paek, K.; Chung, S.; Cho, C. H.; Kim, B. J., Fluorescent and pH-responsive diblock
copolymer-coated core-shell CdSe/ZnS particles for a color-displaying, ratiometric pH sensor.
Chem. Commun. 2011, 47, 10272-10274.
7
8
9
(12)
Hong, S. W.; Ahn, C. H.; Huh, J.; Jo, W. H., Synthesis of a PEGylated polymeric pH
sensor and its pH sensitivity by fluorescence resonance energy transfer. Macromolecules 2006,
39, 7694-7700.
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
(13)
Fluorescent Block Copolymer-Functionalized Graphene Oxide. Nanoscale 2013, 5, 5720-5724.
(14) Hong, S. W.; Kim, D. Y.; Lee, J. U.; Jo, W. H., Synthesis of Polymeric Temperature
Sensor Based on Photophysical Property of Fullerene and Thermal Sensitivity of Poly(N-
isopropylacrylamide). Macromolecules 2009, 42, 2756-2761.
Yang, H.; Paek, K.; Kim, B. J., Efficient Temperature Sensing Platform Based on
(15)
Qu, Z. B.; Zhou, X. G.; Gu, L.; Lan, R. M.; Sun, D. D.; Yu, D. J.; Shi, G. Y., Boronic
acid functionalized graphene quantum dots as a fluorescent probe for selective and sensitive
glucose determination in microdialysate. Chem. Commun. 2013, 49, 9830-9832.
(16)
Dots as Light Absorbers for Photovoltaics. Nano Lett. 2010, 10, 1869-1873.
(17) Ritter, K. A.; Lyding, J. W., The influence of edge structure on the electronic properties
of graphene quantum dots and nanoribbons. Nat. Mater. 2009, 8, 235-242.
(18) Pan, D. Y.; Zhang, J. C.; Li, Z.; Wu, M. H., Hydrothermal Route for Cutting Graphene
Sheets into Blue-Luminescent Graphene Quantum Dots. Adv. Mater. 2010, 22, 734-738.
(19) Zhu, S. J.; Zhang, J. H.; Tang, S. J.; Qiao, C. Y.; Wang, L.; Wang, H. Y.; Liu, X.; Li,
Yan, X.; Cui, X.; Li, B. S.; Li, L. S., Large, Solution-Processable Graphene Quantum
B.; Li, Y. F.; Yu, W. L.; Wang, X. F.; Sun, H. C.; Yang, B., Surface Chemistry Routes to
Modulate the Photoluminescence of Graphene Quantum Dots: From Fluorescence Mechanism
to Up-Conversion Bioimaging Applications. Adv. Funct. Mater. 2012, 22, 4732-4740.
(20)
Shen, J. H.; Zhu, Y. H.; Yang, X. L.; Li, C. Z., Graphene quantum dots: emergent
nanolights for bioimaging, sensors, catalysis and photovoltaic devices. Chem. Commun. 2012,
48, 3686-3699.
(21)
Gupta, V.; Chaudhary, N.; Srivastava, R.; Sharma, G. D.; Bhardwaj, R.; Chand, S.,
Luminscent Graphene Quantum Dots for Organic Photovoltaic Devices. J. Am. Chem. Soc.
2011, 133, 9960-9963.
(22)
Eda, G.; Lin, Y. Y.; Mattevi, C.; Yamaguchi, H.; Chen, H. A.; Chen, I. S.; Chen, C.
W.; Chhowalla, M., Blue Photoluminescence from Chemically Derived Graphene Oxide. Adv.
Mater. 2010, 22, 505-509.
(23)
for sensing. Mater. Today 2013, 16, 433-442.
(24) Li, L. L.; Wu, G. H.; Yang, G. H.; Peng, J.; Zhao, J. W.; Zhu, J. J., Focusing on
Sun, H. J.; Wu, L.; Wei, W. L.; Qu, X. G., Recent advances in graphene quantum dots
luminescent graphene quantum dots: current status and future perspectives. Nanoscale 2013,
5, 4015-4039.
(25)
Yang, H.; Kang, D. J.; Ku, K. H.; Cho, H. H.; Park, C. H.; Lee, J.; Lee, D. C.; Ajayan,
P. M.; Kim, B. J., Highly Luminescent Polymer Particles Driven by Thermally Reduced
Graphene Quantum Dot Surfactants. ACS Macro Lett. 2014, 3, 985-990.
(26)
Dong, Y. Q.; Chen, C. Q.; Zheng, X. T.; Gao, L. L.; Cui, Z. M.; Yang, H. B.; Guo, C.
X.; Chi, Y. W.; Li, C. M., One-step and high yield simultaneous preparation of single- and
multi-layer graphene quantum dots from CX-72 carbon black. J. Mater. Chem. 2012, 22, 8764-
8766.
(27)
Peng, J.; Gao, W.; Gupta, B. K.; Liu, Z.; Romero-Aburto, R.; Ge, L. H.; Song, L.;
Alemany, L. B.; Zhan, X. B.; Gao, G. H.; Vithayathil, S. A.; Kaipparettu, B. A.; Marti, A. A.;
Hayashi, T.; Zhu, J. J.; Ajayan, P. M., Graphene Quantum Dots Derived from Carbon Fibers.
Nano Lett. 2012, 12, 844-849.
ACS Paragon Plus Environment

Page 19 of 21
Chemistry of Materials
1
2
3
4
5
6
(28)
Kwon, W.; Kim, Y. H.; Lee, C. L.; Lee, M.; Choi, H. C.; Lee, T. W.; Rhee, S. W.,
Electroluminescence from Graphene Quantum Dots Prepared by Amidative Cutting of Tattered
Graphite. Nano Lett. 2014, 14, 1306-1311.
7
8
9
(29)
Liu, X.; Liu, H. J.; Cheng, F.; Chen, Y., Preparation and characterization of multi
stimuli-responsive photoluminescent nanocomposites of graphene quantum dots with
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
hyperbranched polyethylenimine derivatives. Nanoscale 2014, 6, 7453-7460.
(30)
Dong, Y. Q.; Li, G. L.; Zhou, N. N.; Wang, R. X.; Chi, Y. W.; Chen, G. N., Graphene
Quantum Dot as a Green and Facile Sensor for Free Chlorine in Drinking Water. Anal. Chem.
2012, 84, 8378-8382.
(31)
Hong, C. Y.; You, Y. Z.; Pan, C. Y., Synthesis of water-soluble multiwalled carbon
nanotubes with grafted temperature-responsive shells by surface RAFT polymerization. Chem.
Mater. 2005, 17, 2247-2254.
(32)
Paek, K.; Yang, H.; Lee, J.; Park, J.; Kim, B. J., Efficient Colorimetric pH Sensor
Based on Responsive Polymer-Quantum Dot Integrated Graphene Oxide. ACS Nano 2014, 8,
2848-2856.
(33)
Yoo, M.; Kim, S.; Lim, J.; Kramer, E. J.; Hawker, C. J.; Kim, B. J.; Bang, J., Facile
Synthesis of Thermally Stable Core-Shell Gold Nanoparticles via Photo-Cross-Linkable
Polymeric Ligands. Macromolecules 2010, 43, 3570-3575.
(34)
Kwon, T.; Kim, T.; Ali, F. B.; Kang, D. J.; Yoo, M.; Bang, J.; Lee, W.; Kim, B. J.,
Size-Controlled Polymer-Coated Nanoparticles as Efficient Compatibilizers for Polymer
Blends. Macromolecules 2011, 44, 9852-9862.
(35)
Nurunnabi, M.; Khatun, Z.; Nafiujjaman, M.; Lee, D. G.; Lee, Y. K., Surface Coating
of Graphene Quantum Dots Using Mussel-Inspired Polydopamine for Biomedical Optical
Imaging. ACS Appl. Mater. Interfaces 2013, 5, 8246-8253.
(36)
Deng, Y.; Zhang, J. Z.; Li, Y. J.; Hu, J. H.; Yang, D.; Huang, X. Y., Thermoresponsive
graphene oxide-PNIPAM nanocomposites with controllable grafting polymer chains via
moderate in situ SET-LRP. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 4451-4458.
(37)
Boyer, C.; Liu, J.; Bulmus, V.; Davis, T. P.; Barner-Kowollik, C.; Stenzel, M. H.,
Direct synthesis of well-defined heterotelechelic polymers for bioconjugations.
Macromolecules 2008, 41, 5641-5650.
(38)
Yang, Y. F.; Song, X. H.; Yuan, L.; Li, M.; Liu, J. C.; Ji, R. Q.; Zhao, H. Y., Synthesis
of PNIPAM Polymer Brushes on Reduced Graphene Oxide Based on Click Chemistry and
RAFT Polymerization. J. Polym. Sci., Part A: Polym. Chem. 2012, 50, 329-337.
(39)
Stuart, M. A. C.; Huck, W. T. S.; Genzer, J.; Muller, M.; Ober, C.; Stamm, M.;
Sukhorukov, G. B.; Szleifer, I.; Tsukruk, V. V.; Urban, M.; Winnik, F.; Zauscher, S.; Luzinov,
I.; Minko, S., Emerging applications of stimuli-responsive polymer materials. Nat. Mater. 2010,
9, 101-113.
(40)
Wu, T.; Zou, G.; Hu, J. M.; Liu, S. Y., Fabrication of Photoswitchable and
Thermotunable Multicolor Fluorescent Hybrid Silica Nanoparticles Coated with Dye-Labeled
Poly(N-isopropylacrylamide) Brushes. Chem. Mater. 2009, 21, 3788-3798.
(41)
Jares-Erijman, E. A.; Jovin, T. M., FRET imaging. Nat. Biotechnol. 2003, 21, 1387-
1395.
(42)
Clapp, A. R.; Medintz, I. L.; Mauro, J. M.; Fisher, B. R.; Bawendi, M. G.; Mattoussi,
H., Fluorescence resonance energy transfer between quantum dot donors and dye-labeled
protein acceptors. J. Am. Chem. Soc. 2004, 126, 301-310.
(43)
Huang, P. J. J.; Liu, J. W., DNA-Length-Dependent Fluorescence Signaling on
Graphene Oxide Surface. Small 2012, 8, 977-983.
ACS Paragon Plus Environment

Chemistry of Materials
Page 20 of 21
1
2
3
4
5
6
7
8
9
(44)
Clapp, A. R.; Medintz, I. L.; Fisher, B. R.; Anderson, G. P.; Mattoussi, H., Can
luminescent quantum dots be efficient energy acceptors with organic dye donors? J. Am. Chem.
Soc. 2005, 127, 1242-1250.
(45)
Self-assembled nanoscale biosensors based on quantum dot FRET donors. Nat. Mater. 2003,
2, 630-638.
Medintz, I. L.; Clapp, A. R.; Mattoussi, H.; Goldman, E. R.; Fisher, B.; Mauro, J. M.,
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
(46)
Dulkeith, E.; Morteani, A. C.; Niedereichholz, T.; Klar, T. A.; Feldmann, J.; Levi, S.
A.; van Veggel, F. C. J. M.; Reinhoudt, D. N.; Moller, M.; Gittins, D. I., Fluorescence
quenching of dye molecules near gold nanoparticles: Radiative and nonradiative effects. Phys.
Rev. Lett. 2002, 89, 203002.
(47)
Jones, G.; Jackson, W. R.; Choi, C.; Bergmark, W. R., Solvent Effects on Emission
Yield and Lifetime for Coumarin Laser-Dyes - Requirements for a Rotatory Decay Mechanism.
J. Phys. Chem. 1985, 89, 294-300.
(48)
under Attractive Cosolvent Conditions. Macromolecules 2013, 46, 1231-1238.
(49) Xue, C. Y.; Choi, B. C.; Choi, S.; Braun, P. V.; Leckband, D. E., Protein Adsorption
Modes Determine Reversible Cell Attachment on Poly(N-isopropyl acrylamide) Brushes. Adv.
Funct. Mater. 2012, 22, 2394-2401.
Heyda, J.; Muzdalo, A.; Dzubiella, J., Rationalizing Polymer Swelling and Collapse
(50)
Radovic, L. R.; Bockrath, B., On the chemical nature of graphene edges: Origin of
stability and potential for magnetism in carbon materials. J. Am. Chem. Soc. 2005, 127, 5917-
5927.
(51)
on Colloidal Graphene Quantum Dots. J. Am. Chem. Soc. 2012, 134, 16095-16098.
(52) Ran, X.; Sun, H. J.; Pu, F.; Ren, J. S.; Qu, X. G., Ag Nanoparticle-decorated graphene
quantum dots for label-free, rapid and sensitive detection of Ag+ and biothiols. Chem. Commun.
2013, 49, 1079-1081.
(53)
Graphene-Based Nanocomposites. Small 2009, 5, 2253-2259.
(54) Liu, Y. Y.; Kim, D. Y., Ultraviolet and blue emitting graphene quantum dots
synthesized from carbon nano-onions and their comparison for metal ion sensing. Chem.
Commun. 2015, 51, 4176-4179.
Yan, X.; Li, Q. Q.; Li, L. S., Formation and Stabilization of Palladium Nanoparticles
Pasricha, R.; Gupta, S.; Srivastava, A. K., A Facile and Novel Synthesis of Ag-
(55)
Ananthanarayanan, A.; Wang, X. W.; Routh, P.; Sana, B.; Lim, S.; Kim, D. H.; Lim,
K. H.; Li, J.; Chen, P., Facile Synthesis of Graphene Quantum Dots from 3D Graphene and
their Application for Fe3+Sensing. Adv. Funct. Mater. 2014, 24, 3021-3026.
(56)
probes in Au@C-dot nanobeacons for fluorescent turn-on detection of biothiols. Nanoscale
2015, 7, 1802-1808.
(57)
Facile Microwave Avenue to Electrochemiluminescent Two-Color Graphene Quantum Dots.
Adv. Funct. Mater. 2012, 22, 2971-2979.
Mandani, S.; Sharma, B.; Dey, D.; Sarma, T. K., Carbon nanodots as ligand exchange
Li, L. L.; Ji, J.; Fei, R.; Wang, C. Z.; Lu, Q.; Zhang, J. R.; Jiang, L. P.; Zhu, J. J., A
(58)
Feng, P.; Zhu, J.; Cheng, Z. P.; Zhang, Z. B.; Zhu, X. L., Reversible addition-
fragmentation chain transfer polymerization of 7-(4-(acryloyloxy)butoxy)coumarin. Polymer
2007, 48, 5859-5866.
(59)
of Thermally Stable Au Nanoparticles with Highly Grafted Polymer Shell and Control of Their
Behavior in Polymer Matrix. J. Polym. Sci., Part A: Polym. Chem. 2011, 49, 3464-3474.
Lim, J.; Yang, H.; Paek, K.; Cho, C. H.; Kim, S.; Bang, J.; Kim, B. J., "Click" Synthesis
ACS Paragon Plus Environment

Page 21 of 21
Chemistry of Materials
1
2
3
4
5
6
7
8
Table of Contents
9
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
Multi-Color Emitting Block Copolymer-Integrated Graphene Quantum
Dots for Colorimetric, Simultaneous Sensing of Temperature, pH, and
Metal Ions
Chan Ho Park, Hyunseung Yang, Junhyuk Lee, Han-Hee Cho, Dahin Kim, Doh C. Lee,
Bumjoon J. Kim*
*E-mail: bumjoonkim@kaist.ac.kr
ACS Paragon Plus Environment