One-pot development of water soluble copper nanoclusters with red emission and aggregation induced fluorescence enhancement

Article abstract of DOI:10.1039/c6ra01499b

One-pot synthesis of water-soluble Cu NCs using DHLA protection ligands by different reducing reagents including NaBH₄, N₂H₄ and THPC was developed. Furthermore, it was found that the as prepared Cu NCs using THPC as a reducing reagent describe fluorescence enhancement in the presence of Zn²⁺ and Al³⁺. It is proposed that the binding of Zn²⁺ and Al³⁺ to OH on the copper core of Cu NCs promotes the formation of CuNC-OH-Zn-OH-Cu NCs and CuNC-OH-Al-OH-Cu NCs aggregates respectively, which enables aggregation induced fluorescence enhancement. Additionally, it was found that the fluorescence enhancement were partly reversible by the introduction of an alkaline buffer solution and Zn²⁺.

Full text of DOI:10.1039/c6ra01499b

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One-pot Development of Water Soluble Copper Nanoclusters with
Red Emission and Aggregation Induced Fluorescence
Enhancement
Received 00th January 20xx,
Accepted 00th January 20xx
Dan Li, Zhenhua Chen*, Zhanghui Wan, Tiezhu Yang, Hao Wang and Xifan Mei*
DOI: 10.1039/x0xx00000x
www.rsc.org/
One-pot synthesis of water-soluble Cu NCs using DHLA protection ligands by different reducing reagents including NaBH4,
N2H4 and THPC were developed. Furthermore, it was found the as prepared Cu NCs using THPC as a reducing reagent
describe fluorescence enhancement in the presence of Zn2+ and Al3+. It is proposed that the binding of Zn2+ and Al3+ to OH
on the copper core of Cu NCs promotes the formation of CuNC-OH-Zn-OH-Cu NCs and CuNC-OH-Al-OH-Cu NCs aggregates
respectively, which enables aggregation induced fluorescence enhancement. Additionally, it was found the fluorescence
enhancement were partly reversible by the introduction of alkaline buffer solution and Zn2+
.
NCs and applied them for cancer cell imaging. Besides protein,
Introduction
GSH peptide (glutathione) has been used as a template for
19, 20
preparation of water soluble Cu NCs.
The obtained
nanoclusters could be further applied for cell study. These
products for Cu NCs are well applied, but the sizes are
relatively big when big molecules are used. On the other hand,
fewer works contribute to the fabrication of water soluble Cu
NCs with red emission using small molecules, which will
possess the properties such as smaller size, easier separation
and low cost. For small molecules, dihydrolipoic acid (DHLA)
has been found as effective ligands for one-pot fabrication of
water soluble Au NCs and Ag NCs with red emission, but it has
only been employed for the preparation of Cu NCs with green
Recently, the synthesis and application of water soluble noble
metal nanoclusters have drawn wide attentions in the area of
green sensing and bio-imaging due to their low toxicity and
excellent fluorescence behaviors such as photo stability and
large stoke shift. 1-3 Though the fabrication protocols for water
soluble Gold (Au NCs) and silver nanoclusters (Ag NCs) have
been widely reported, less significant research activity has
been contributed to the design of water soluble copper
4-6
nanoclusters (Cu NCs). However, Cu NCs may provide more
cost effective sources for applications in various areas.
21, 22
and orange emission in the absence of additional ligand.
Meanwhile, most reported water soluble Cu NCs describe blue
4, 7-13
In this work, we for the first time develop several strategies for
one-pot synthesis of water soluble Cu NCs stabilized by DHLA
with red emission based on the introduction of various kinds of
reducing reagents. Furthermore, fluorescence enhancement
was described in the presence of amphoteric metal ions such
as Zn2+ and Al3+. The enhancement was found to be partly
reversible by the introduction of metal ions such as Zn2+ and
alkaline buffer solution, which will be promising for future
applications.
or green emission at short wavelength.
In the area of
sensing or bio-applications, red emission is more expected due
to the low energy, which will hardly harm living organisms.
Besides, humans’ eyes are sensitive to red color. Some papers
reported the strategies for fabrication of Cu NCs with red
emission, but the as prepared nanoclusters are not water
14, 15
soluble.
Until now, only several papers reported the
synthesis of water soluble Cu NCs with red emission, most of
which have been using protein, peptide or the combination of
16-20
polymer as templates.
For instance, Lin developed BSA
18
Experimental
protein protected Cu NCs with red emission.
The as
prepared Cu NCs can be well applied in cell imaging and pH
sensing. Li employed Transferrin protein for synthesis of Cu
Reagents and Instruments
(±)-α-Lipoic acid (>99%), Copper Sulfate (CuSO4, >99%), Sodium
hydroxide (NaOH,>99%), Sodium borohydride (NaBH4, >98%)
were purchased from Sigma Aldrich. Other metal salts are all
of analytical grades. All the reagents for preparation of Cu NCs
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were used as received without further purification. Deionized comparison, the as prepared colloid was directly used without
water (> 18 M ) was used through the experiment. the separation of NaCl or other residual ions. The final solution
Fluorescence spectra were recorded on FS-2 would be stored at 4 °C.
spectrophotometer (SCINCO). Transmission electron
Ω
a
microscope (TEM) and Energy Dispersive Spectrometer (EDS) For material characterizations including TEM, XPS and future
images were obtained on a Hitachi transmission electron applications in some media such as bio-culture, the as
microscope using a JEM-1400 microscope (JEOL, Tokyo, Japan) obtained DHLA-Cu NCs colloid would be dialyzed against
operated at 120 kV. UV-Vis absorption spectra were deionized water using a 3 kDa cut-off dialysis bag for 24 h to
performed on a UV-1600 spectrometer (Shanghai). XPS spectra remove the unreacted small molecules and free ions.
were obtained on Escalab 250 X-ray photoelectron
spectroscope.
Fluorescence enhancement experiments
Synthesis of Cu NCs-1 using NaBH4
To investigate the fluorescence behaviours of Cu NCs in the
presence various metal ions, the following cations including
+
In a typical procedure, 18.0 mg of (±)-α-Lipoic acid was Co2+, Mg2+, NH4 , Mn2+, Pb2+, Cu2+, Fe3+, Ca2+, Hg2+, Al3+, Ag+ and
dispersed in 8.0 mL of water. To the mixture, 200 μL of 1 M Zn2+ were introduced. 2 mL of various metal ion solutions (400
NaOH solution was added to decompose (±)-α-lipoic acid to μM) were mixed with 100 µL of Cu NCs solution to investigate
DHLA. Then, 100 μL of 0.1 M CuSO4 solution was combined. 3 the enhancement. Besides, Zn2+ solutions at different
minutes later, 100 μL of 100 mM NaBH4 (100 mM) was added. concentrations including 0, 25, 50, 150, 250, 350, 400 and 500
The color changed to yellow within several minutes. After that, μM were also studied. The fluorescence spectra of the
1 mL of 100 mM NaBH4 solution was combined. The mixture mixtures were recorded.
was allowed to stir for several minutes. Next, 500 μL of 100
mM CuSO4 was combined. The mixtures were placed overnight. Results and discussion
The final solution was stored at 4 °C.
Characterization of Cu NCs
Synthesis of Cu NCs-2 using N2H4
Initially, (±)-α-lipoic acid was decomposed by NaOH to DHLA
In a typical procedure, 18.0 mg of (±)-α-lipoic acid was ligand. The complex for DHLA-Au3+ or DHLA-Ag+ are completely
dispersed in 8.0 mL of water. 200 µL of 1 M NaOH was added dissolved in water. However, after the addition of Cu2+, the
to decompose (±)-α-lipoic acid to DHLA. Then, aqueous precipitates had been observed due to the formation of DHLA-
solution of CuSO4 (100 µL, 100 mM) was added to DHLA Cu2+, Cu(OH)2, and other complex such as DHLA-Cu(OH)x. After
solution with vigorous stirring at room temperature. 1 min that, when the reducing reagents including NaBH4, N2H4 or
later, 100 µL of N2H4 (80%) was introduced. The fluorescence THPC were introduced, the as formed products of Cu NCs will
can be observed after several minutes. After that, the mixture be soluble in water since the precipitates are soon be reduced
was allowed to stir for 1 hour. The final solution was stored at to Cu0 based on the colour change and the dissolve of the
4 °C.
aggregates. The characterizations for the fluorescence spectra
of Cu NCs are described in Fig. S1 - Fig. S5. It can be concluded
from Fig. S1 to Fig. S4 that the introduction of all the reducing
reagents resulted in the formation of fluorescent Cu NCs with
Synthesis of Cu NCs-3 using THPC
In a typical procedure, 18.0 mg of (±)-α-Lipoic acid was red emission. The emission wavelength ranged from 605 nm to
dispersed in 8.0 mL of water. 200 µL of 1 M NaOH was added 680 nm (Fig. S5). However, after the investigation of the
to decompose (±)-α-lipoic acid to DHLA. Then, aqueous stability (see Fig. S6), it is found that the as formed Cu NCs-1
solution of CuSO4 (100 µL, 100 mM) was added to the DHLA lost the fluorescence within 12 hours. This indicated Cu NCs-1
solution with vigorous stirring at room temperature. After that, was too unstable to be employed for further applications. It is
20 µL of THPC was introduced. The mixture was placed well acknowledged that water soluble Cu0 tend to be oxidized
23
overnight. The final solution was stored at 4 °C.
in the presence of air. The strong reducing reagent, NaBH4
will decompose in water so fast that the residual NaBH4 can’t
stop Cu0 from further oxidation. Therefore, the as formed Cu
NCs-1 will not be stable after the decomposition of NaBH4. In
Synthesis of Cu NCs-4 using THPC in the presence of NaCl
In a typical procedure, 18.0 mg of (±)-α-lipoic acid was the presence of additional Cu2+, the forward reaction of the
dispersed in 8.0 mL of water. 200 µL of 1 M NaOH was added following equation can be inhibited due to the common ion
to decompose (±)-α-lipoic acid to DHLA. Then, aqueous effect.
solution of CuSO4 (100 µL, 100 mM) was added to DHLA
air
solution with vigorous stirring at room temperature. After that,
→
Cu0
Cu2+
←
1.0 M of NaCl was combined to facilitate the capping of DHLA.
1 min later, 20 µL of THPC was introduced. After that, the
mixture was placed overnight. For the fluorescence
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Thus, unlike other methods, 500 μL of CuSO4 (100 mM) was emission peaks at 362 nm and 627 nm with a quantum yield of
used during the synthesis process. In the presence of 2.8% using Acridine Yellow as a reference (Fig. 1b). To test
additional Cu2+, fluorescent Cu NCs-1 can be obtained. In whether the observed fluorescence was caused by the
previous paper, the phenylethanethiol protected Cu NCs can reaction between DHLA and the reducing reagent, the
only be stable for 2 hours by using NaBH4 as a reducing emission spectra were recorded for DHLA of the same
24
reagent. The stability is similar to our Cu NCs. This reveals condition that has been used to synthesize Cu NCs-4, but no
the as formed Cu NCs-1 will not be suitable for further fluorescence was observed. This indicated the formation of
applications, which is similar to the paper. Meanwhile, the fluorescent Cu NCs. Size information of Cu NCs-4 was studied
introduction of N2H4 resulted in the formation of other by TEM. As shown in Fig. 1c and Fig. 1d, the TEM image and
unstable nanoclusters (Cu NCs-2) next to Cu NCs-1. Compared the size distribution diagram indicated that the average
to NaBH4, N2H4 was a weaker reducing reagent, which diameter of the Cu NCs was ca. 1.6 nm. Additionally, XPS
wouldn’t decompose so fast. Thus, it has been used for characterization was carried out to determine the oxidation
synthesis of relative more stable Cu NCs by using BSA protein state of copper in Cu NCs-4. As shown in Fig. 1e, two peaks
18
as a template. Notwithstanding, the residual N2H4 are not located at 931.9 eV and 951.7 eV are observed, which can be
enough to protect Cu NCs-2 from fast decomposition based on assigned to the binding energies of the 2p3/2 and 2p1/2
Fig. S6. This reveals that Cu0 can’t be protected just by the electrons of Cu(0), respectively. The absence of Cu2p3/2
residual reducing reagent.
satellite peak around 942.0 eV reveals that no Cu(II) electrons
are present. Notwithstanding, the binding energy of Cu(0) is
On the other hand, THPC was a weak reducing reagent, which just 0.1 eV away from that of Cu(I) according to the papers. 5, 12
enabled the slow formation of Cu NCs. THPC can not only act Therefore the valence state of copper for the obtained Cu NCs-
as a reducing reagent, but also it will play a role as the 4 most likely lies between 0 and 1, which is similar to previous
20, 28
complexing and protection reagent that describes steric effect. reported Cu NCs.
25
Moreover, it can be seen from Fig 1f
It can be seen from Fig. S6 that Cu NCs-3 are more stable that the presence of C, S and O belongs to the protecting
than Cu NCs-2 and Cu NCs-1. Therefore, using THPC as a ligand, DHLA. In summary, the optical behaviour, TEM and XPS
reducing reagent was further investigated. It is reported that study all confirm the formation of DHLA protected Cu NCs.
NaCl aging will maximize the loading of thiolated single strand
DNA on gold nanoparticles.26 Since DHLA is also a thiolated
ligand, it can be concluded that NaCl aging will also facilitate
the modification. As well as this, it was reported the
fluorescence of thiolated ligand (11-mercaptoundecanoic acid)
protected gold nanodots was enhanced about 13 times in the
b
a
2.5
2.0
1.5
1.0
0.5
0.0
Excitation
Emission
1.0
0.8
0.6
0.4
0.2
0.0
27
presence of NaCl. Enlightened by these phenomena, NaCl
was introduced in the formation process of Cu NCs so that to
facilitate the loading of DHLA on copper core. Then, it was
found that Cu NCs-4 exhibited higher maxim emission intensity
(see Fig. S7). The detail of NaCl effect is beyond the scope of
this study, which will be discussed in the future. At the same
time, we found that there was no big difference for the
stability of the fluorescence for Cu NCs-3 and Cu NCs-4. In
addition, the maxim fluorescence emission intensity was
compared for all the obtained Cu NCs, see Fig. S7. It can be
observed that Cu NCs-4 describes advantages over other
nanoclusters. Based on the comparison of the fluorescence
properties, Cu NCs-4 was selected for further investigation.
Furthermore, the stability of Cu NCs-4 was investigated under
350 400 450 500 550 600
Wavelength (nm)
200 300 400 500 600 700 800
Wavelength (nm)
d
40
30
20
10
0
1.2
1.6
Size (nm)
2.0
2.4
f
e
3000
15.0k
10.0k
5.0k
0.0
Cu2p
2500 931.9 eV
4
℃ in the refrigerator, see Fig. S8. It can be seen that the
2000
1500
1000
500
0
C1S
951.7 eV
O1s
fluorescence intensity decreased more slowly compared to that
at room temperature. Thus, for further protection of Cu NCs-4
from oxidation, lower temperature should be applied.
Na1s
S2p
930
940
Binding energy (eV)
950
960
0
200 400 600 80010001200
Binding Energy (eV)
The properties of the as-prepared Cu NCs-4 were characterized
and described in Fig. 1. Based on the UV-Vis spectrum (Fig. 1a),
no peak can be observed for normal size copper nanoparticles
(around 520 - 560 nm). This is not surprising that ultra-small
Fig. 1 UV-Vis absorption (a), fluorescence excitation, emission spectra (b),
TEM (c), the corresponding size distribution (d) and XPS characterization for
Cu2p (e), as well as XPS survey (f) of the as prepared Cu NCs-4.
nanoclusters can’t support surface plasmon resonance (SPR),
5
which are similar to previous reported Cu NCs.
The
fluorescence spectra of Cu NCs-4 had the maxim excitation and
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and thus the fluorescence can be monitored. As well as this,
compared to the Al3+ aggregation product (Fig. 3d), it can be
observed the Zn2+ aggregation product are more dispersed at higher
magnifications (Fig. 3b). Large aggregates are present in Al3+
aggregation product. This reveals that some Al(OH)3 may coexist as
well as the assembled aggregates for nanoclusters. This is in
agreement with the fluorescence measurement that the
The fluorescence behaviour of the as obtained products is
demonstrated in Fig. S9. It can be observed from Fig. S9b that the
maxim fluorescence intensity is obtained with 20 μL of THPC. For
further increasing the amounts of THPC, the fluorescence intensity
will decrease. If too much of THPC was used, the colour of the
reactants would never change. Meanwhile, no fluorescence can be
detected, which means no Cu NCs are formed. Thus, THPC only acts
as a complexing reagent at high concentrations.
enhancement is higher for Cu NCs in the presence of Zn2+
.
To test the effect of cations on the influence for the fluorescence of
Cu NCs-4, the fluorescence emission spectra in the presence of
various cations are investigated and described in Fig. 2. Among
these cations, the fluorescence for Cu NCs-4 solution describe
insignificant change in the presence of Co2+, Mg2+, NH4+, Mn2+, Pb2+
,
Ni2+, Ca2+, Ba2+. The fluorescence of Cu NCs-4 will be quenched in
the presence of heavy metal ions such as Cu2+, Ag+, Hg2+, Fe3+ at the
studied conditions. However, amphoteric metal ions such as Zn2+
and Al3+ demonstrated enhancement for the fluorescence of Cu
NCs-4. Especially, the fluorescence response in the prescience of
Zn2+ is 2 times higher than that of Cu NCs-4 in the absence of Zn2+
.
Both Al3+ and Zn2+ can combine with OH groups as well as attaching
on the surface of Cu NCs to promote the formation of aggregates.
This is similar to the phenomena that Zn2+ can bind with Au NCs
29
through the interaction with OH.
Then, the fluorescence
enhancement was caused by the aggregation of Cu NCs-OH-Zn-OH-
Cu NCs and Cu NCs-OH-Al-OH-Cu NCs respectively. It is worth noted
that the fluorescence enhancement induced by Zn2+ was more
significant compared to Al3+.The solubility product constant for
Al(OH)3 is much smaller than that for Zn(OH)2. Thus, besides the
fluorescent aggregates, the addition of Al3+ will result in
considerable chance for formation of Al(OH)3 that cover on the
surface of Cu NCs, which will inhibit the fluorescence measurement.
On the other hand, relative less amounts of Zn(OH)2 was formed on
the surface at our studied condition. Then, relatively large exposure
area was left for the fluorescent aggregates (Cu NCs-OH-Zn-OH-Cu
NCs). The larger exposed surface area will lead to a greater
enhancement of fluorescence for Zn2+ at our studied concentrations.
Fig.3 TEM images for Cu NCs-4 in the presence of Zn2+ (a, lower
magnification, b, higher magnification) and Al3+ (c, lower magnification, d,
higher magnification).
XPS analysis for the aggregates of Cu NCs-4 after the interaction
with Zn2+ and Al3+ are described in Fig. S10 and Fig. S11 respectively.
Cu2p described a spectrum with much weaker intensity for Fig.
S10a, indicating that the surface of Cu NCs was partly covered by
some hydroxides. Then, relatively small ratio of Copper could be
detected by XPS. Meanwhile, the XPS study for Al3+ binding
products demonstrate even weaker peaks for Cu2p (Fig. S11a),
which means relative small surface area of Cu NCs was exposed
compared to Zn2+ binding product. Furthermore, the EDS studies for
the relative dispersed part of the products are described in Fig. S12.
According to the EDS mapping (Fig. S12a) studies, less amounts of
Al are also detected for the binding products of nanoclusters. On
the other hand, Zn plays a more important role for the Zn binding
nanoclusters based on the EDS study. Thus, it can be revealed that
considerable ratio of Al exist in the form of Al(OH)3 rather than
binding with Cu NCs. This is also in agreement with the lower
enhancement factor for the fluorescence of Cu NCs-4 in the
b3.0
a
4
3
2
1
0
Zn2+
Sensor
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
500 550 600 650 700 750
Wavelenth (nm)
presence of Al3+
.
Fig.2 Fluorescence emission spectra (a) and intensity enhancement (b) of Cu
NCs-4 in the presence of different cations (400 μM).
The enhancement of the fluorescence intensity for Cu NCs-4 in the
presence of Zn2+ and Al3+ at different pH values are investigated,
see Fig. S13 and Fig. S14 respectively. It can be seen from Fig. 13 b
that the fluorescence intensity of Cu NCs-4 in the presence of Zn2+
increased more significantly than Cu NCs-4 in the absence of Zn2+
from pH 4 to PH 7. Thus the enhancement keeps increasing until
To directly view Cu NCs-4 in the presence of Zn2+ and Al3+, the TEM
analysis was performed, and the results are displayed in Fig. 3. The
aggregates are observed at lower magnifications (Fig. 3a and Fig.
3c). However, it can be seen from Fig. 3b and Fig. 3d that ultra-small
particles can still be observed at higher magnifications. This
indicates the aggregates may be assembled by ultra-small clusters
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pH 7. However, when pH is higher than 8, the fluorescence intensity Zn2+ is described in Fig. 5. Initially, OH groups are stably bound to
for Cu NCs-4 in the presence of Zn2+ decreased due to the the copper core on the surface of Cu NCs. After the addition of Zn2+
,
dissolution of the dissolution of the aggregates. Meanwhile, when Cu NCs will bind together through Zn-OH interactions, leading to
pH is as high as 10, the easier oxidation of Cu NCs caused the the aggregation of the clusters. As well as this, the aggregation can
decrease of the fluorescence of Cu NCs-4 in the absence of Zn2+. In be re-dispersed in alkaline buffer solution since Zn2+ is amphoteric
the presence of Zn2+, the formation of Zn(OH)2 may possibly block metal ion. Furthermore, both Al can also bind with -OH. Thus, the
photo measurement of the fluorescence. Thus, more significantly mechanisms for their fluorescence enhancement behaviours are
decrease for the fluorescence intensity has been observed. On the quite similar.
other hand, for Cu NCs-4 in the presence of Al3+ (see Fig. S14), it can
be seen that the decrease for the fluorescence is even more
significantly compared to Cu NCs-4 in the presence of Zn2+ at pH 10
due to the easier formation of Al(OH)3 than Zn(OH)2.
Finally, a series of concentrations of Zn2+ were introduced for
investigation of the fluorescence enhancement of Cu NCs-4. Fig. 4
displays the fluorescence response of Cu NCs-4 and the
fluorescence intensity change as a function of Zn2+ concentration. It
can be seen from Fig. 4a that the fluorescence intensity was rapidly
enhanced with the increase of the concentration for Zn2+ with a
linear relationship in the range from 50 - 400 µM. The linear
equation is fitted as
Y = 0.216X + 0.0048, with correlation
coefficient of 0.995, where Y indicates the fluorescence intensity
enhancement (F-F0) at 623 nm, X is the concentration of Zn2+. After
400 μM of Zn2+ was combined, the aggregates can be separated by
centrifugation at 400 rpm. After that, the collected products can be
re-dispersed in pH 8.0 phosphate buffer solutions. Then, the
intensity change (F-F0) is recorded, where F and F0 are the
fluorescence intensity of the new mixture and original Cu NCs-4
solution respectively. It can be seen from Fig. 4b that the
fluorescence (1’) is not enhanced after the aggregates are re-
dispersed in buffer solution. On the other hand, the fluorescence
will be enhanced again (1) after further addition of Zn2+. However,
the enhancement was not as high as the initial enhancement. This is
possibly because the partly formation of Zn(OH)2 that can’t be
dissolved in buffer solution. It can be concluded that the
fluorescence is only enhanced when the aggregates are present.
This further confirmed the aggregation induced fluorescence
enhancement assumption.
Fig. 5 Scheme for the mechanism of the aggregation induced fluorescence
enhancement for Cu NCs in the presence of Zn2+.
Conclusions
Water soluble Cu NCs with red emission has been successfully
synthesized by one-pot methods using DHLA as the protection
ligand based on the introduction of various types of reducing
reagents. Aggregation induced fluorescence enhancement is
described for Cu NCs in the presence of Zn2+ and Al3+. The
fluorescence enhancement is partly reversible by simply re-
dispersing the aggregates in buffer solution and the addition of
additional Zn2+. We believe that our study can serve as a
simple method for fabrication of Cu NCs and the applications
for fluorescence enhancement.
a
b
2.0
4
3
2
1
0
Acknowledgements
1
2
3
4
5
2
1
0
500 ꢀΜ
1.5
1.0
0.5
0.0
This work is supported by Excellent Talents program of
Liaoning Provincial Universities (No. LJQ2013089), National
Natural Science Foundation of China (No. 51202199 and No.
81471854), Natural Science Foundation of Liaoning Province
(No.2014022038), Liaoning Medical University Principal Fund
(No. XZJJ20130104-01), Liaoning Medical University Principal
Fund-Aohong Boze Students Researching Training Program
(No. 2014D22).
0
0
200 400
C ( M)
ꢀ
1'
2'
3'
4'
5'
B
Zn
B
Zn
B
Zn
B
Zn
B
Zn
500 550 600 650 700 750
Wavelength (nm)
Fig. 4 (A) Fluorescence emission spectra of Cu NCs-4 solution in the presence
of different concentrations of Zn2+ (a). Inset: the fluorescence emission
intensity change as a function of Zn2+. (b) Reversibility of the fluorescence
emission intensity change through consecutive disperse of the aggregates in
phosphate buffer solution and addition of Zn2+ (B indicated 10 mM of
phosphate buffer solution, pH = 8.0).
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product, the mechanism for the enhancement of fluorescence by
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DOI: 10.1039/C6RA01499B
One-pot Development of Water Soluble Copper Nanoclusters with
Red Emission and Aggregation Induced Fluorescence Enhancement
Dan Li, Zhenhua Chen*, Zhanghui Wan, Tiezhu Yang, Hao Wang and Xifan Mei*
The binding of Zn2+ and Al3+ to OH on the copper core of Cu NCs promotes the formation of Cu NC-OH-Zn-OH-Cu NCs and Cu
NC-OH-Al-OH-Cu NCs aggregates, which enables aggregation induced fluorescence enhancement.