Self-assembled tetraphenylethylene macrocycle nanofibrous materials for the visual detection of copper(ii) in water

Article abstract of DOI:10.1039/c3tc32373k

A tetraphenylethylene (TPE) Schiff base macrocycle with an aggregation-induced emission (AIE) effect was synthesized by the condensation reaction of the TPE dialdehyde and 1,2-benzenediamine. The macrocycle could aggregate into nanofibers in an aqueous solution to give a stable and fluorescent suspension. The fluorescent nanofibers showed a highly selective response to copper ions in an aqueous solution with the detection sensitivity up to a nanomolar level. Meanwhile, the emission of the nanofibers displayed a very large Stokes shift up to 260 nm because of the AIE effect, which brought the emission into the red area and avoided background interference. Therefore, the macrocycle probe showed great potential for the detection of Cu(ii) in real water samples including pork juice-containing water. In addition, the macrocycle reacted with Cu(ii) to give a color change and so the copper ion can be detected at the 10 μM level by the naked eye.

Full text of DOI:10.1039/c3tc32373k

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Materials Chemistry C
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Self-assembled tetraphenylethylene macrocycle
nanofibrous materials for the visual detection of
copper(II) in water†
Cite this: J. Mater. Chem. C, 2014, 2,
2353
Hai-Tao Feng,a Song Song,a Yi-Chang Chen,a Chang-Hong Shenb
a
*
and Yan-Song Zheng
A tetraphenylethylene (TPE) Schiff base macrocycle with an aggregation-induced emission (AIE) effect was
synthesized by the condensation reaction of the TPE dialdehyde and 1,2-benzenediamine. The macrocycle
could aggregate into nanofibers in an aqueous solution to give a stable and fluorescent suspension. The
fluorescent nanofibers showed a highly selective response to copper ions in an aqueous solution with
the detection sensitivity up to a nanomolar level. Meanwhile, the emission of the nanofibers displayed a
very large Stokes shift up to 260 nm because of the AIE effect, which brought the emission into the red
area and avoided background interference. Therefore, the macrocycle probe showed great potential for
the detection of Cu(II) in real water samples including pork juice-containing water. In addition, the
macrocycle reacted with Cu(II) to give a color change and so the copper ion can be detected at the 10
mM level by the naked eye.
Received 30th November 2013
Accepted 20th December 2013
DOI: 10.1039/c3tc32373k
www.rsc.org/MaterialsC
although the selectivity is high.12–15 Therefore, developing an
excellent method for the detection of copper ions is still a
challenge.
During the last decade, a new class of organic compounds
Introduction
Copper is an essential trace element for all living systems,1,2 but
an excess of the unbound copper ion is very harmful.3,4 There-
fore, detection of the copper ion always attracts intensive and
extensive interest.5,6 Especially in recent years, a large number
of reports about analysis methods for this metal ion have been
documented, including those based on organic dyes coordi-
nating to copper ions,7–13 reactions catalyzed by copper ions,14–23
and nanoparticles absorbing copper ions.24 By these extensive
efforts, both the selectivity and sensitivity for the detection of
copper ions have been improved very much. The analytical
method based on inorganic nanoparticles not only has meth-
odological novelty, but also exhibits high sensitivity at the nM
level, however the selectivity is generally not high.24–29 Moreover,
the nanoparticles easily aggregate during storage and trans-
portation. If the nanoparticles are prepared on site, this is
difficult to repeat because the experimental preparation needs
multiple reaction components and strict reaction conditions.
Other methods also have some shortcomings such as low
sensitivity, low selectivity or low practicality. For example, many
reported Schiff base chemosensors have a low sensitivity at the
micromolar level or can be only used in organic solvents
with an aggregation-induced emission (AIE) effect has been
enormously expanded due to the great potential that such
compounds have displayed, not only in efficient organic light
emission diodes, but also in highly selective and stable uo-
rescence sensors for biological and chemical analytes,
including metal ions.30–34 By coordination or intermolecular
connections induced with copper ions, AIE molecules, such as
tetraphenylethylene (TPE) and its derivatives, can aggregate and
emit strong uorescence, which could be used to selectively
detect copper ions.35 However, the reported detection of copper
ions using AIE probes was implemented in an organic solvent
and the sensitivity was not high. The reason for this problem is
that the aggregation of the AIE molecules in an organic solvent
induced by analytes needs a relatively large concentration. If the
AIE molecules aggregate beforehand by the addition of a non-
solvent of the AIE compound into the solution, an intense
uorescent emission will appear at a very low concentration,
which can signicantly raise the detection sensitivity. Usually,
an organic AIE molecule is insoluble in water and an aqueous
suspension or colloid of the AIE molecules with strong uo-
rescence at very low concentration can be used to sensitively
detect analytes in water. This kind of suspension or colloid is
very similar to inorganic nanoparticles or quantum dots in
water,24–29 but it can be easily prepared on site just by the
addition of water into the solution of the AIE compound in an
organic solvent that is miscible with water. This will avoid the
aSchool of Chemistry and Chemical Engineering, Huazhong University of Science and
Technology, Wuhan 430074, China. E-mail: zyansong@hotmail.com
bSchool of Chemistry and Materials Science, South Central University for Nationalities,
Wuhan 430074, China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3tc32373k
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problem of stability and repeatability in the storage and prep-
aration of the inorganic nanoparticles as well as the toxicity of
heavy metals. In this regard, here we report a TPE Schiff base
macrocycle with an AIE effect that can form uorescent nano-
bers in aqueous media, which can be selectively quenched by
copper ions with a detection sensitivity up to the nM level.
Meanwhile, the nanobers emit red light due to the AIE effect
and have shown a potential for the detection of Cu(II) in real
water samples including pork juice-containing water.
Fig. 1 Change in the fluorescence spectra of 3 (2.0 ꢀ 10ꢁ6 M) with a
change of the water fraction in THF. lex ¼ 365 nm; ex/em slits ¼ 10/10
nm (the same slit widths were used for all other experiments below).
Inset: curve of fluorescence intensity at 595 nm vs. water fraction.
Results and discussion
Synthesis and AIE effect of TPE Schiff base macrocycle 3
The TPE Schiff base macrocycle 3 was synthesized according to
the synthetic route shown in Scheme 1. The known compound 1
with an AIE effect was treated with hexamethylenetetramine in
triuoroacetic acid to give the dialdehyde 2. By a condensation
reaction of the dialdehyde 2 with 1,2-diaminobenzene, the TPE
Schiff base macrocycle 3 was easily obtained by recrystallization
from chloroform and methanol in a 94% yield. It is well known
that imine groups including Schiff bases and hydrazones have a
strong tendency to bind copper ions.7–15 As macrocycle 3 bears
four imine groups in a cycle, it will have the possibility to
display a good affinity and selectivity to copper ions.
As expected, while the dilute solution of 3 in THF or chlo-
roform had almost no uorescence, its solid was red light-
emitting under UV illumination. When the non-solvent water
was added into the solution of 3 in THF, aggregation occurred
and the resultant suspension showed strong uorescence. With
the increasing volume percent of water in THF from 0% to 90%
(Fig. 1), the uorescence intensity of 3 increases. At 90% water,
the uorescence intensity of the resultant suspension was six
times higher than that of the solution of 3 in pure THF. This
result indicated that macrocycle 3 was an AIE compound.
Moreover, a very large Stokes shi up to 260 nm was observed
(absorption maximum wavelength 335 nm and emission
maximum wavelength 595 nm), which would be helpful for the
practical application of the uorescent probes in biological
imaging and sensing since long-wavelength emissions have the
advantages of minimal photodamage to biological samples,
deep tissue penetration, and minimal background interference
from living systems.
Physical and electrochemistry properties of macrocycle 3
It was shown by FE-SEM images (Fig. 2A and B) that the
suspension of 3 in a mixed solvent of water and THF (9 : 1,
volume ratio, the related solvent ratio below is also the volume
ratio) was composed of nanobers with a diameter of 100–200
nm. TEM images conrmed the brous structure of the
suspension (Fig. 2C and D) with a diameter of about 150 nm,
which was in accordance with the FE-SEM measurement. Due to
the tiny nanobrous structure, the suspension in a mixed
solvent of water and THF (9 : 1) was very stable and no precip-
itates were observed aer it was le standing for more than one
week. A dynamic light scattering (DLS) diagram (Fig. S3†) also
showed that the particles in the suspension had a diameter of
about 120 nm.
A cyclic voltammetry (CV) measurement of 3 was carried out
in CH2Cl2 by making use of an Ag/AgCl reference electrode. As
Fig. 2 FE-SEM image (A and B) and TEM image (C and D) of a
suspension of 3 (0.1 mM) in a mixed solvent of water and THF (9 : 1).
Scheme 1 Synthesis of fluorescence sensor 3.
2354 | J. Mater. Chem. C, 2014, 2, 2353–2359
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shown in Fig. 3, compound 3 showed an irreversible oxidation
peak at Eox ¼ +0.82 V. The experiments were calibrated with the
ferrocene/ferrocenium (Fc/Fc+) redox system, and the onset
oxidation potentials were used to determine the HOMO levels
based on the internal standard Fc value of ꢁ4.8 eV with respect
to the vacuum level.36 Since the onset oxidation potential of Fc
relative to the Ag/AgCl reference electrode is 0.384 eV, the
HOMO levels of compound 3 can be estimated using the
equation EHOMO ¼ ꢁ[4.8 ꢁ 0.384 + Eoonx set] eV z ꢁ[4.4 + Eooxnset] eV
according to the literature.37 Therefore, the HOMO level of 3 was
estimated to be ꢁ5.22 eV. With the low HOMO level, compound
3 will be an ideal electron donor when it reacts with metal ions
bearing positive charge(s).
Selective and sensitive interaction of compound 3 with Cu(II)
Initially, the response of 5 mM 3 to metal ions (13 mM) was
measured by a UV-Vis absorption spectrum in a mixed solvent
of water and THF (2 : 1). As shown in Fig. 4A, the solution of 3
exhibited almost no absorption at about 450 nm, but the
addition of copper ions led to a strong absorption at this
Fig. 4 (A) UV-Vis spectra of 3 in the presence of different metal ions in
wavelength while the absorption at 335 nm decreased rapidly. H2O–THF 2 : 1 ([3] ¼ 5.0 ꢀ 10ꢁ6 M, [metal] ¼ 1.3 ꢀ 10ꢁ5 M). (B) (I)
Other metal ions, including Fe2+, Co2+, Ni2+, Zn2+, Cd2+, Hg2+
,
Photos of 3 in H2O–THF 2 : 1 under daylight and (II) photos of 3 in
H2O–THF 9 : 1 under 365 nm light after addition of the metal ion ([3] ¼
1.0 ꢀ 10ꢁ5 M, [metal] ¼ 2.0 ꢀ 10ꢁ5 M).
Mn2+, Ag+, Cr3+, Pb2+, Al3+, Ca2+, Mg2+, K+ and Na+ ions, did not
lead to an obvious change of the UV-Vis spectrum of 3. At
about 1.0 ꢀ 10ꢁ5 M, the mixture of 3 with copper ions resulted
in an intense yellow brown colour, but the other transition
metal ions did not show any colour change (Fig. 4B-I). The U.S.
Environmental Protection Agency (EPA) has set the maximum
allowable level of copper in drinking water at 2.0 ꢀ 10ꢁ5 M,
therefore, in the presence of probe 3, it can be seen with the
naked eye whether the level of copper ions has exceeded the
standard.
the new absorption at 450 nm had a red shi of 115 nm;
therefore, a colour change from colourless to yellow could be
seen. The formation of the isosbestic points and the colour
To investigate the effect of the copper ion concentration, a
UV-Vis titration of 3 with copper ions was carried out in H2O–
THF 2 : 1. As shown in Fig. 5A, with an increase of copper ions,
the absorption at 335 nm gradually decreased but two new
absorptions of 3 at 450 nm and 305 nm gradually increased. As a
result, two distinct isosbestic points at 381 nm and 316 nm were
formed. Aer 4.8 equivalent of the copper ions were added,
more copper ions did not lead to a further change of the
absorption intensity. Comparing to the absorption at 335 nm,
Fig. 5 (A) Change in the UV-Vis spectra of 3 in H2O–THF 2 : 1 with
copper ions. Inset, curve of absorbance vs. concentration of the
copper ion. (B) Job's plot for determining the binding ratio of 3 to Cu2+
Fig. 3 Cyclic voltammograms of 3 (1 mM) in CH2Cl2 containing in H2O–THF 2 : 1. [3] ¼ 5.0 ꢀ 10ꢁ6 M, [Cu2+] ¼ 0.13, 0.27, 0.40, 0.53,
Bu4NPF6 (0.01 M) as the supporting electrolyte at room temperature. 0.67, 0.80, 0.93, 1.07, 1.20, 1.33, 1.47, 1.60, 1.73, 1.87, 2.0, 2.13, 2.27,
Scan rate, 100 mV sꢁ1
.
2.40, 2.53, 2.67/10ꢁ5 M.
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change ambiguously demonstrated that a stable complex of 3 of Cu(II) while the solution of 3 when mixed with two equiva-
with Cu(II) was produced. lents of other metal ions still emitted red light under a portable
From a Job's plot (Fig. 5B), the complex of 3 with Cu(II) had UV lamp (Fig. 4B-II).
a 1 : 2 binding ratio of 3 vs. Cu(II). The association constant of
With an increase in the concentration of copper ions, the
the complex and the molar extinction coefficient were calcu- uorescence intensity of 3 at 595 nm decreased gradually
lated to be (1.6 ꢂ 0.25) ꢀ 1011 Mꢁ2 and (1.6 ꢂ 0.01) ꢀ 104, (Fig. 7). When a 2.5 equivalent of copper ions was added, the
respectively, by the nonlinear curve tting of the absorbance at emission was almost completely quenched, which was in
450 nm with the concentration of copper ions. It was also accordance with the 1 : 2 binding ratio of 3 vs. Cu(II) from the
noted that only 1.3 mM Cu(II) could lead to an obvious increase UV-Vis titration. Noticeably, even in the presence of 5.0 ꢀ 10ꢁ9
of the absorption intensity at 450 nm, therefore, probe 3 has M copper ions, the uorescence intensity of 3 displays an
an ability to detect copper ions at the micromole level by a UV- obvious decrease. By using this set of uorescence titration
Vis spectrometer.
data, a 1.1 nM detection limit could be determined (Fig. S4†).
On the other hand, the uorescence response of 2 mM of 3 to Moreover, in the range 5.0 ꢀ 10ꢁ9 M to 2.0 ꢀ 10ꢁ5 M, the
different metal ions (5 mM) was investigated in H2O–THF 9 : 1. relationship of the logarithm of copper concentration vs. the
As shown in Fig. 6A, while other metal ions generally led to a uorescence intensity was a straight line, which was benecial
little increase of the uorescence intensity, the copper ion for the quantitative analysis of the copper ion. Recently, it was
obviously quenched the uorescence of 3. The uorescence reported that a dinuclear Ru complex bearing a 2,6-diimidazo-
intensity ratio of 3 without and with the copper ions was up to lepyridine coordination position had a detection limit of 33.3
sixfold. Even in the presence of other metal ions (5 mM), copper nM for Cu(II),7 and a water-soluble Schiff base probe could
ions could also efficiently quench the uorescence of 3 (Fig. 6B), detect copper ions at a concentration of 1 ppm (about 40 mM).8
indicating a very high selectivity for the copper ion. Using Rhodamine hydrazide-based uorescent copper probes gener-
quinine bisulfate in 1 N H2SO4 as the standard, the uorescence ally displayed ten to a hundred nM detection limit.14–17 Some
quantum yield of a mixture of the suspension of 3 and 2.5 reports13,16,24 compare a large number of analytical methods for
equivalent of Cu(II) was measured to be 0.20%, but that of the Cu(II) and show that it is very rare for Cu(II) probes to have a
suspension of 3 was 8.4%, further indicating that the uores- detection limit of a nM level while keeping a high selectivity.
cence of the nanobers from the aggregation of 3 could be
efficiently quenched by the copper ion. At 1.0 ꢀ 10ꢁ5 M, the red
Measurement of copper ion in real water by compound 3
uorescence of 3 disappeared in the presence of two equivalents
In order to explore the practical applicability of the uorescent
macrocycle 3 to natural systems, real water samples including
river water, lake water, tap water, and pork juice-containing
water were tested. The river water and lake water were taken
from the Yangzi River and the East Lake in Wuhan, respectively,
and the water containing pork juice was prepared from normal
pork. Aer the distilled water in the mixed solvent of water–THF
9 : 1 was replaced by Yangzi River water, the uorescence
intensity of 2 mM of 3 decreased with the concentration of
copper ions, and showed a straight line between the logarithm
of the copper concentration and the intensity, indicating that
this uorescence probe could be used to detect Cu(II) in
Fig. 6 (A) Fluorescence spectra of 3 in the presence of various metal
ions. (B) Fluorescence intensity of 3 at 595 nm in the presence of a Fig. 7 Fluorescence spectrum change of 3 with copper ion in H2O–
single metal ion (black bar) and in the mixture of Cu2+ and other metal THF 9 : 1. [3] ¼ 2.0 ꢀ 10ꢁ6 M; [Cu2+] ¼ 0, 0.0050, 0.010, 0.020, 0.050,
ions (grey bar). Solvent: H2O–THF ¼ 9 : 1; [3] ¼ 2.0 ꢀ 10ꢁ6 M; [metal] ¼ 0.10, 0.20, 0.50, 0.80, 1.0, 2.0, 5.0, 10, 20/10ꢁ6 M. Inset: curve of
5.0 ꢀ 10ꢁ6 M.
fluorescence intensity at 595 nm vs. logarithm of Cu(II) concentration.
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river water (Fig. S5A†). In a similar way, the copper ion in lake not obey the Stern–Volmer quenching equation (I0/I ¼ 1 + K
water and tap water could be also detected by this probe [Cu]). Therefore, the uorescence quenching is static
(Fig. S5B and C†).
quenching. The formation of the 3–2Cu2+ complex and the
a
Moreover, the copper ion in pork juice-containing water intramolecular charge transfer (ICT) from copper to the TPE
could also be detected by probe 3. As shown in Fig. 8A, when unit should be the main reason why copper ions can quench the
copper ions (2.0 ꢀ 10ꢁ5 M) were gradually added to a mixture of emission. During the UV-Vis titration of 3 with copper ions, the
3 (1.0 ꢀ 10ꢁ5 M) in pork juice-containing water, the uores- formation of isosbestic points, color change, and a very large
cence intensity of 3 decreased by degrees. Even at a low association constant of the 3–2Cu(II) complex also demon-
concentration of 0.05 mM Cu(II), the uorescence intensity of 3 strated that compound 3 and copper ions were easy to bind
showed a signicant decrease. The change of the intensity with together. In addition, the cyclic voltammetry (CV) measurement
the logarithm of the copper concentration was also a straight of 3 also disclosed that the Schiff base 3 was a good electron
line. In addition, a color change aer the addition of the copper donor, which can display an ability to coordinate positive
ion (20 mM) could be seen by the naked eye both under a UV copper ions, so that it was reasonable for charge transfer to
lamp and in daylight (Fig. 8B). These results indicated that occur between compound 3 and the copper ion.
probe 3 was interfered with very little by biological substances
The aggregation of 3 in a mixture of water and THF formed
which display an unstable emission at about 440 nm. The nanobers. Although the nanobers were in the solid state, they
potential of 3 in the detection of copper ions in living issues were easy to react with copper ions due to their tiny size and
can be ascribed to the large Stokes shi which results from the high binding force to Cu(II). Because of a macrocyclic frame-
AIE effect.
work, the room between the two neighboring imine groups just
accommodated one copper ion, therefore, the selectivity was
very high.
Quenching mechanism of uorescence nanobers of 3 by
Cu(II)
In the uorescence titration of probe 3 with copper ions (Fig. 7
and 8A), the relationship of the uorescent intensity of 3 vs. the
logarithm of Cu(II) concentration was linear, but the plot of I0/I
(I0 and I, uorescence intensity of 3 without and with copper
ions) vs. Cu(II) concentration was not a straight line. This indi-
cated that the uorescence quenching of 3 by copper ions did
Experimental section
Materials and measurements
All reagents and solvents were chemical pure (CP) grade or
analytical reagent (AR) grade and were used as received unless
otherwise indicated.
Pork juice-containing water: normal and fresh pork (7.5 g)
was mashed into a paste, to which distilled water (20 mL) was
added. Aer stirring vigorously for 0.5 h, the mixture was le
standing for 4 h followed by ltering through lter paper. The
ltrate with a little turbidity was stored in a freezer as pork juice-
containing water.
Synthesis of compound 2
1,1-Diphenyl-2,2-di(p-hydroxylphenyl) ethylene 1 (0.50 g, 1.37
mmol) was added to a solution of hexamethylenetetramine
(1.92 g, 13.7 mmol) in triuoroacetic acid (30 mL) under
vigorous stirring. Aer the reaction mixture was reuxed for 4 h,
it was quenched with water (30 mL) and extracted with CH2Cl2
(3 ꢀ 20 mL). The combined organic phase was washed with
saturated Na2CO3 (20 mL), water (20 mL) and brine (20 mL) in
order. Upon drying over anhydrous Na2SO4, the solution was
evaporated to dryness under reduced pressure. The residue was
puried by column chromatography to give 2 as a pale yellow
solid (0.37 g, 64%). M.p. ¼ 184.4–184.9 ꢃC. 1H NMR (400 MHz,
CDCl3) d ¼ 6.76 (d, J ¼ 9.2 Hz, 2H), 7.02–7.04 (m, 4H), 7.12–7.16
(m, 6H), 7.19–7.22 (m, 4H), 9.60 (s, 2H), 10.95 (s, 2H). 13C NMR
(CDCl3, 100 MHz) d ¼ 196.36, 160.42, 142.95, 141.96, 139.95,
136.83, 136.37, 134.88, 131.12, 128.12, 126.99, 120.28, 117.32. IR
(KBr) n ¼ 3308, 3181, 3100, 3074, 3048, 1665, 1615, 1581, 1478,
1441, 1371, 1317, 1285, 1207, 1162, 1071, 1029, 1006, 928, 885,
842 cmꢁ1. MALDI/DHB HRMS m/z calcd for C28H20O4 420.14
Fig. 8 (A) Fluorescence spectrum change of 3 with copper ions in
pork juice-containing water and THF 9 : 1. [3] ¼ 5.0 ꢀ 10ꢁ6 M; [Cu2+] ¼
0, 0.050, 0.10, 0.50, 1.0, 2.0, 5.0, 10, 20/10ꢁ6 M. Inset: curve of fluo-
rescence intensity with the logarithm of Cu(II) concentration. (B)
Photos of 3 in pork juice-containing water and THF 9 : 1 under 365 nm
light (I) and in daylight (II). [3] ¼ 1.0 ꢀ 10ꢁ5 M; [Cu2+] ¼ 2.0 ꢀ 10ꢁ5 M. [M], found 420.13 [M].
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Synthesis of compound 3
To a solution of 2 (0.10 g, 0.24 mmol) in ethanol (15 mL) 1,2-
benzenediamine (0.026 g, 0.24 mmol) was added under
vigorous stirring, then a catalytic amount of acetic acid was
added, which was allowed to reux for 4 h. The resultant orange
precipitates were ltered and recrystallized by chloroform and
methanol to give 3 as light yellow powder (0.11 g, 94%). M.p.>
300 ꢃC. 1H NMR (400 MHz, CDCl3) d ¼ 6.74 (d, J ¼ 8.64 Hz, 4H),
6.99 (d, J ¼ 2 Hz, 4H), 7.06–7.08 (m, 8H), 7.13–7.19 (m, 19H),
7.28–7.30 (m, 3H), 8.31 (s, 4H), 12.83 (s, 4H). 13C NMR (CDCl3,
100 MHz) d ¼ 160.18, 144.14, 140.21, 137.21, 135.67, 134.28,
135.51, 131.34, 131.27, 128.17, 128.08, 127.38, 126.55, 118.50,
117.44, 116.96. IR (KBr) n ¼ 3055, 3022, 1656, 1618, 1579, 1483,
1442, 1354, 1282, 1226, 1206, 1169, 1126, 1111, 974, 834, 752,
699 cmꢁ1. MALDI/DHB HRMS m/z calcd for C68H48N4O4 984.37
[M], found 985.37 [(M + 1)].
¨
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Chem. Soc., 2012, 134, 16000.
Conclusions
In conclusion, a TPE Schiff base macrocycle 3 with an AIE effect
was synthesized. It was found that the uorescent nanobers
formed by aggregation of the macrocycle 3 showed great
potential for the highly selective and sensitive detection of
copper ions in pure and real water, especially in living tissue-
containing water. This kind of new uorescence probe for Cu(II)
can easily be prepared on site just by the addition of water to the
solution of 3 in THF, which overcomes the difficulty of the on
site preparation of inorganic quantum dots by other methods
and the toxicity of heavy metal ions, showing a potential for
practical applications. In addition, this research result also
demonstrated that the selectivity could be improved by a mac-
rocycle and the sensitivity could be promoted by an AIE effect,
which has a general meaning for the design of new macrocycle
probes with AIE effects to detect other analytes.
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Acknowledgements
This research work was supported by the National Natural
Science Foundation of China (no. 21072067) and the Analytical
and Testing Centre at Huazhong University of Science and
Technology.
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