Valence-tautomeric infinite coordination polymer nanoparticles for encapsulation of rhodamine B and its potential application for colorimetric and fluorescence dual mode sensing of hypochlorite

Article abstract of DOI:10.1039/c5ra17114h

In this work, we for the first time developed a visual and fluorescent dual probe for hypochlorite (ClO^-) based on stimuli-responsive valence-tautomeric infinite coordination polymer (ICP) nanoparticles encapsulated with a fluorescent dye, i.e.

Full text of DOI:10.1039/c5ra17114h

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Valence-tautomeric infinite coordination polymer nanoparticles
for encapsulation of Rhodamine B and its potential application for
colorimetric and fluorescent dual mode sensing of hypochlorite
Received 00th January 20xx,
Accepted 00th January 20xx
Xiaolei Zhang,a Jingjing Deng,a* Guoyue Shib and Tianshu Zhoua*
DOI: 10.1039/x0xx00000x
In this work, we for the first time developed a visual and fluorescent dual probe for hypochlorite (ClO-) based on stimuli-
responsive valence-tautomeric infinite coordination polymer (ICP) nanoparticles encapsulated with a fluorescent dye, i.e.,
rhodamine B (RhB). In the absence of ClO-, the as-formed RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles is well
dispersed and quite stable in aqueous solution. However, the addition of ClO- into the dispersion of RhB@{Co(3,5-
dbsq)(3,5-dbcat)(bix)} destroys {Co(3,5-dbsq)(3,5-dbcat)(bix)} network structure, resulting in the release of RhB from ICP
nanoparticles into the solvent. As a consequence, the color of the dispersion changed from purple to orange-red and, at
the meantime, the fluorescence of RhB turns on, which constitutes a new mechanism for colorimetric and fluorescent
dual-model sensing of ClO-. With the method demonstrated here, the ClO- in tap water can be easily visualized by the
naked eyes and detected quantitatively through double channels. This study not only offers a new method for on-spot
visible detection of ClO- in environmental samples, but also provides a strategy for designing dual mode sensing
www.rsc.org/
mechanisms
based
on
stimulus
response
of
valence-tautomeric
ICP
nanomaterials.
requirements from on-spot practical applications for effective
control of the drinking water quality, monitoring microbial
Introduction
population dynamics and understanding of the pathology of
Nowadays, growing public concern has invigorated interest in
detection and quantification of various contaminants in
drinking water.1,2 Hypochlorite (ClO−) and its protonated form
hypochlorous acid (HClO) can be easily encountered in our
daily lives owing to its extensive applications such as drinking
water disinfection, cooling water treatment and household
bleaching, etc.3,4 In water treatment, the concentration of free
residual chlorine must be strictly controlled, because the low
level cannot kill pathogenic bacteria and cause many hazards
of an insufficient disinfection while the excessive intake and
diseases substantially necessitate
a new method for
monitoring ClO− both in method simplicity and sensitivity.25,26
Optical probes based on colorimetric and fluorescent
responses are good candidates for realizing this goal. Because
they not only enable the visualization of the target simply with
bare eyes, but also validate a quantitative fluorescence assay
in a simple and rapid feature.27-30 However, most of the
traditional probes for dual assay of ClO− are prone to suffer the
influence of the background fluorescence, solvent dependence
and time-consuming synthesis.31,32 So a novel material for ClO−
based on both color and fluorescence changes with excellent
performance are still urgently needed. As a newly emerging
fascinating nanomaterial, infinite coordination polymer (ICP)
nanoparticles constructed from metal ions and organic
bridging ligands, have activated growing interests because of
their highly structural tailorability and excellent adaptive
capability of guest encapsulation, which make them
particularly attractive for dual-modal detection since the
network and guest molecule could be rationally designed,
respectively.33-36 Herein, we employed a new strategy for the
detection of ClO− based on stimulus response of valence-
tautomeric {Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles
encapsulated with RhB (RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)})
which could provide dual signal responses of both colorimetric
and fluorescent outputs (Scheme 1).
over-production of ClO− can both elicit adverse health e
ffects
on human.5-7 On the other hand, as one of the biologically
important reactive oxygen species (ROS),8-11 the excessive
generation of ClO− can cause many diseases including
cardiovascular diseases, neuron degeneration, rheumatoid
arthritis and even cancer.12-15 Thus, development of a direct,
sensitive, and selective method for hypochlorite residues in
tap water is of great importance. Towards this end, several
elegant methods have been developed for ClO− determination,
such as colorimetric, fluorescent, electrochemical and
chromatographic methods and so forth. 16-24 However, the high
a.School of Ecological and Environmental Sciences, East China Normal University,
500 Dongchuan Road, Shanghai 200241, China. E-mail: tszhou@des.ecnu.edu.cn,
jjdeng@des.ecnu.edu.cn Fax: +86-21-54341277, Tel: +86-21-54341277
b.Department of Chemistry, East China Normal University, 500 Dongchuan Road,
Shanghai 200241, China.Address here.
†
DOI: 10.1039/x0xx00000x
Electronic
Supplementary
Information
(ESI)
available.
See
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Reagents and Materials.
α,α′-dichloro-p-xylene,
3,5-diterbutylbenzoquinone,
3,5-
diterbutylcatechol were purchased from J
＆K. (Beijing, China).
Cobalt acetate (Co(CH3COO)2·4H2O) was obtained from
Aladdin Chemical Co. (Shanghai, China). Imidazole, sodium
hydrogen phosphate, potassium dihydrogen phosphate,
sodium hypochlorite, rhodamine B and potassium carbonate
were from Sinopharm Chemical Reagent Co. (Shanghai, China).
All chemicals were analytical grade reagents at least and used
without further purification. All aqueous solutions were
prepared with Milli-Q water (18.2 MΩ.cm) and all experiments
were carried out at room temperature unless otherwise noted.
Synthesis of bix.
1,4-bis(imidazol-1-yl-methyl)benzene (bix) was synthesized as
reported previously.37 Briefly, a solution containing imidazole
(3.16 g, 46.4 mmol) and α, α′ꢀdichloro-p-xylene (0.78 g, 4.46
mmol) in methanol (50 mL) was refluxed for 18 h. Removal of
methanol by evaporation gave a yellow syrup that was
recrystallized from an aqueous solution of K2CO3 (6.13 g, 100
mL) to yield crystalline bix dehydrate.
Scheme 1. A) Schematic illustration of the formation of RhB@{Co(3,5-dbsq)(3,5-
dbcat)(bix)} ICP nanoparticles based on {Co(3,5-dbsq)(3,5-dbcat)} units through bix
ligands with RhB entrapped. B) Schematic illustration of the colorimetric and
fluorescent sensing of ClO- based on the stimuli-responsive RhB@{Co(3,5-dbsq)(3,5-
dbcat)(bix)} ICP nanoparticles with released RhB as the signal readout.
Synthesis of {Co(3,5-dbsq)(3,5-dbcat)(bix)} particles and
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} nanoparticles
The valence-tautomeric ICP nanoparticles constructed with
{Co(3,5-dbsq)(3,5-dbcat)} (3,5-dbsq- and 3,5-dbcat2- are the
semiquinonate radical and catecholate forms of 3,5-di-tert-
butyl-1,2-benzoquinone (3,5-dbq), respectively) and bix (1,4-
bis(imidazol-1-yl-methyl)benzene) ligand, in which fluorescent
dye (i.e.,RhB) is used as a guest to form the RhB@{Co(3,5-
dbsq)(3,5-dbcat)(bix)} ICP nanoparticles. By reversible
intramolecular transfer involving the metal ion and the redox-
active ligand, the network of {Co(3,5-dbsq)(3,5-dbcat)}
interconvert reversibly between two valence tautomers—low-
spin ls-[CoIII(3,5-dbsq)(3,5-dbcat)] and high-spin hs-[CoII(3,5-
dbsq)2]. The network of {Co(3,5-dbsq)(3,5-dbcat)} ICP
nanoparticles shows blue color, meantime, the trapped RhB
shows magenta color. Accordingly, the RhB@{Co(3,5-
dbsq)(3,5-dbcat)(bix)} ICP nanoparticles exhibit a purple color
and weak emission of RhB in water. Upon the presence of ClO-,
the redox-active ligand 3,5-dbsq, 3,5-dbcat were oxidized to
3,5-dbq (yellow), resulting in the destruction of {Co(3,5-
dbsq)(3,5-dbcat)(bix)} network and the release of
encapsulated RhB into solution (Figure S1). As a result,
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles display
the mixed color of 3,5-dbq and RhB (orange-red) and turn on
the fluorescence of RhB, which provides a straightforward
basis for the colorimetric and fluorescent dual assay for ClO-.
As we know, this is the first example of ClO- detection based
on stimuli-responsive ICP nanoparticles from colorimetric and
fluorescent double signal. With the help of a UV-lamp (365
nm), this method can even possess on-site visible features in
daytime and night easily, which could be further developed for
simple environmental applications.
{Co(3,5-dbsq)(3,5-dbcat)(bix)}
ICP
nanoparticles
were
synthesized with procedures reported previously.38 The
Co(3,5-dbsq)(3,5-dbcat)(bix) nanoparticles show adaptive
encapsulation property towards some water-soluble dyes
during the self-assembly process. Herein, RhB, was chosen as
the guest molecular. Encapsulation of RhB into ICPs was
performed by the following procedures. An aqueous solution
of Co(CH3COO)2·4H2O (120 mg, 0.5 mmol) was added to a
ethanol solution (10 mL) of bix (121 mg, 0.5 mmol) and 3,5-
diterbutylcatechol (110 mg, 0.5 mmol). Then 50 mL H2O was
added into the reaction mixture to produce a purple
precipitatation consisting of RhB functionalized valence-
tautomeric ICPs.
Colorimetric and fluorescent hypochlorite Sensing
The stock solutions of hypochlorite were prepared in PBS
buffer solution (2 mM, pH 7.0) to cancel out the pH effect.
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles (0.8 mg)
were dispersed into PBS buffer solution (2 mM, pH 7.0, 2000
µL) containing different concentrations of NaClO and the final
concentrations of NaClO were 0 µM, 1 µM, 5 µM, 10 µM, 50
µM, 100 µM, 200 µM, 400 µM, 600 µM and 800 µM. After 3
min, the resulting mixtures were photographed in the ambient
light and excited by a 365 nm UV-lamp in the dark respectively
with a digital camera, and used UV-Vis spectrophotometer and
fluorescence spectrophotometer for colorimetric and
fluorescent detection, respectively.
Colorimetric and fluorescent sensing of hypochlorite in tap water.
The RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles (0.8
mg) dispersed in tap water (2000 μL) which containing
Experimental
2 | J. Name., 2012, 00, 1-3
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different concentrations of ClO- (500 μM, 0 μL, 2 μL, 10 μL, 20 at 554 nm in UV-Vis spectra (Figure 1C). When excited at 535
μL, 40 μL, 80 μL). The control group was prepared by adding nm, the RhB functionalized ICP nanoparticles emits weak
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles (0.8 mg) fluorescence at 578 nm (Figure 1D, red curve), thus may be
into Milli-Q water (2000 μL). The concentrations of ClO- were ascribed to the suppression of {Co(3,5-dbsq)(3,5-dbcat)(bix)}
determined through both UV-Vis and fluorescence ICP network (Figure 1D). These results demonstrated the
spectrophotometer. Beyond that, the mixtures were successful formation of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)}
photographed in ambient light and under UV-lamp nanoparticles, which combined the inherent properties of both
respectively.
{Co(3,5-dbsq)(3,5-dbcat)(bix)} network and the trapped RhB.
Results and discussion
Mechanistic Investigation on Colorimetric and Fluorescent
Hypochlorite Assay
Figure 2. A) UV-Vis spectra of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} nanoparticles in PBS
buffer without (black curve) and with (red curve) the presence of ClO− (400 µM). Inset:
Photographs of the dispersion without (vial 1) and with (vial 2) the addition of 400 µM
ClO−. B) Fluorescent emission spectra of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)}
nanoparticles dispersing in PBS buffer without (balck curve) and with (red curve) the
addition of 400 µM ClO− (λx=535 nm). Inset: Photographs of the dispersion without (vial
1) and with (vial 2) the addition of 400 µM ClO− under 365 nm UV lamp. SEM image of
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles without (C) and with the addition
of 400 µM ClO− (D) dispersed in Milli-Q water.
Figure 1. SEM image of {Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles (A) and
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles (B) dispersed in Milli-Q
water. Inset, photographs of the {Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles
(A) and RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP (B). C) UV-Vis spectra of the
{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles (black curve) and RhB@{Co(3,5-
dbsq)(3,5-dbcat)(bix)} (red curve) nanoparticles dispersed in PBS buffer solution.
As displayed in Figure 2A, the addition of ClO- (80 µL, 4 mM)
into PBS buffer containing RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)}
D) Fluorescent emission spectra of {Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP ICP nanoparticles (0.8 mg) obviously lead to a color change of
nanoparticles (black curve) and RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)}
the dispersion from purple to orange-red, accompany with the
production of a new absorbance peak at 411 nm (A411) (red
arrow), and the decrease of the absorbance peak of RhB at 554
nm (A554) (blue arrow). Meanwhile, such a procedure also
leads to a change in fluorescence channel. Upon the addition
of ClO-, the fluorescent spectrum shows an increase at 578 nm
clearly (Figure 2B, red arrow). To further study the destruction
of {Co(3,5-dbsq)(3,5-dbcat)(bix)}, the SEM images have been
investigated. With the addition of ClO-, the morphology of ICP
nanoparticles changed from smooth spheres to irregular
shape, some of the ICP nanoparticles aggregated and some of
the particles collapsed (Figure 2C, D). This phenomenon could
be due to the oxidation of ClO- convert the redox-active ligand
into 3,5-dbq, leading to the destruction of {Co(3,5-dbsq)(3,5-
dbcat)(bix)} network and thereby the released RhB into the
solution. The ratio of A411 to A554 (A411/A554) and fluorescent
intensity of released RhB (I578) could be considered as an
nanoparticles (red curve) dispersed in PBS buffer.
The {Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles were
prepared by adding cobalt acetate aqueous solution into
ethanol solution containing 3,5-dbcat and bix through self-
assembly and the formed blue precipitation was characterized
with scanning electron microscopy (SEM). SEM images of the
resulting blue dispersion demonstrated the formation of
spherical particles with the average size of 61.4±10.1 nm
(Figure 1A). As shown in Figure 1B, the synthetic RhB@{Co(3,5-
dbsq)(3,5-dbcat)(bix)} ICP nanoparticles have almost the same
shape and size (diameter of 58.2±10.2 nm) as {Co(3,5-
dbsq)(3,5-dbcat)(bix)} ICP particles, suggesting that the
encapsulation of RhB does not change the morphology of
{Co(3,5-dbsq)(3,5-dbcat)(bix)} network. However, the color of
ICP nanoparticles changed from blue to purple (Figure 1B,
inset), accompanying with the unique absorption peak of RhB
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indicator for the degree of destruction of RhB@{Co(3,5- 8.5 did not result in an obvious change in the fluorescent
dbsq)(3,5-dbcat)(bix)} ICP nanoparticles caused by the intensity and different concentration of hypochlorite induced
oxidation of ClO-. Thus, the colorimetric and fluorescence the slight pH change in PBS buffer, which did not affect our
responding to ClO- can be realized as demonstrated below. measurement. Figure S3 C, D, shows that the fluorescent
Here, we need to mention, to further investigate the decrease spectra increased gradually with the reaction time until 100 s.
of the absorbance peak of RhB at 554 nm, transmittance (
spectra of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP the optimized reaction time in the sequent experiment.
nanoparticles were detected. As shown in Figure S2, the of Under the optimal conditions, the sensitivity of the
T)
To make sure the reaction adequately, 3 min was chosen as
T
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles at 554 colorimetric and fluorescent sensing of ClO− was evaluated as
nm increased. According to Lambert-Beer law, the absorbance depicted in Figure 3 and S4. The addition of various
spectrum of light absorption is defined as the logarithm of the concentrations of ClO− to the dispersion gradually turns the
ratio of the incident light intensity I0 to the transmitted light color from purple to orange-red in ambient light,
intensity
nanoparticles upon addition of hypochlorite, the reflection of the dispersion; with increasing the concentration of ClO−, A411
ICP nanoparticles decreased, thus increasing transmittance of increases, while 554 decreases. The ratio of A411 554 increases
RhB inside the blue shell ( t of RhB entrapped increased). As within a concentration range from 1 μM to 400 μM (A411 A554
a result, the
It, as shown formula 1. With the destruction of ICP accompanying with a dramatic change in the UV-Vis spectra of
A
/A
I
,
T
/
=
A
554 decreased.39-44 Consequently, the ratio of the 0.404+0.00347 C/μM, R2 = 0.998) (Figure 3A). Meanwhile, the
A411 to A554 was further developed as an indicator for the addition of ClO− also leads to increase of fluorescent intensity
destruction of the RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP at 578 nm, which shows a linear response range from 1 μM to
nanoparticles.
400 μM (I
=552.191+3.704 C/μM, R2=0.995) (Figure 3B). Since
our colorimetric channel was ratiometric, thus high sensitivity
could be achieved by the amplified signal readout through
simultaneous readings of two wavelengths. As a result, the
working concentration range of double channel was almost
the same. 27 The basal level of ClO- in environmental systems is
on the micromolar scale which just falls within the linear range
of the present analytical method,40-43 thus confirming that the
strategy developed in this study is able to realize the dual
channel detection of ClO- in aquatic environment.
A
A
= lg(Io
/
I
t) = lg(1/
T
)
(1)
: Absorbance
I
o: Incident Light
I
t: Transmission Light T：
Transmittance
Sensitivity and Selectivity
By using ClO- as the oxidant, we next studied the selectivity
of this double signal-based method. Various environmentally
relevant ions and oxidants were taken into account.49 As
illustrated in Figure 4, the separate addition of each kind of
A)
B)
10 50
10 50
5
5
100
100
1
1
200
200
0
0
400
400
-
-
anion (200 µL, 2 mM) including SO42-, Ac-, CO32-, NO2 , NO3 , I-,
+
NH4 , Cl-, Ca2+ and Mg2+ into the dispersion of PBS buffer
1.6
1.2
0.8
0.4
2000
1600
1200
800
2.0
1.6
1.2
0.8
2000
containing RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} nanoparticles
(0.8 mg, 1800 µL) did not result in an obvious change either in
the color (Figure 4A) or in the fluorescent intensity (Figure 4B),
however, the addition of ClO- (200 µL, 2 mM) induced an
obvious color change (from purple to orange-red) and a
significant enhancement of fluorescent intensity of the
dispersion. To further explore the selectivity of this
colorimetric and fluorescent method toward ClO−, the
1500
1000
500
0
400
0
100 200 300 400
0 100 200 300 400
NaClO(μM)
NaClO (μM)
570 600 630 660 690
350 400 450 500 550 600
absorption ratio of A411/A554 and the fluorescent intensity of
Wavelength (nm)
Wavelength (nm)
the dispersion were shown by the red bar in Figure 4C and 4D.
These results substantially demonstrate the present method
has a high selectivity against these potential interferences in
environmental water. This property, along with the good
Figure 3. A) UV/Vis spectra and photographs (Upper) of RhB@{Co(3,5-dbsq)(3,5-
dbcat)(bix)} nanoparticles in PBS buffer with the presence of different concentrations
of ClO-. Inset: Plot of A411/A554 against ClO- concentration. Each point was the average of
three independent experiments. Error bars indicate standard deviations (n = 3). B)
Fluorescence spectra and photographs (Upper) of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} linearity, substantially enables the utilization of the stimuli-
nanoparticles in PBS buffer with the presence of different concentrations of ClO-. Inset:
responsive
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)}
ICP
nanoparticles for ClO- detection, and essentially offers a
technically simple yet rapid approach to direct sensing of ClO-
in tap water.
I
578 as a function of the concentration of hypochlorite ions when excited at 535nm.
To optimize the conditions before detection, we considered
the pH range and the time course of the fluorescence response
of this dual probe upon addition of ClO−. As demonstrated in
Figure S3 A, B, the RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)}
nanoparticles in PBS buffer with different pH valve from 7.0 to
4 | J. Name., 2012, 00, 1-3
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B)
A)
1.6
1.2
0.8
0.4
0.0
A)
B)
2.0
Tap
H2O
800
H2O
ClO-
water
Tap water
ClO-
1050
700
350
0
ClO-
1.6
1.2
0.8
0.4
0.0
600
400
200
0
Tap
water
ClO-
H2O
ClO-
Other ions
Other ions
H2O
Tap water
ClO-
350 400 450 500 550 600
540
570
600
630
660
Wavelength (nm)
Wavelength (nm)
350 400 450 500 550 600
540
570
600
630
660
C)
D)
1.6
1.2
0.8
0.4
0.0
Wavelength (nm)
Wavelength (nm)
C)
D)
-
NO
3
-
I-
NH4
NO2
+
2-
CO3
Cl-
0.8
Ac-
2-
0.9
Ca2+
Mg2+
ClO-
600
SO4
0
△
△
△
△
450
300
150
0.4
0.0
0.6
0.3
0.0
△
△
△
△
△
△
△
△
Figure 4. UV-Vis spectra (A) and fluorescence spectra (B) of RhB@{Co(3,5-dbsq)(3,5-
dbcat)(bix)} ICP nanoparticles in PBS buffer with the presence of various relevant ions
at a concentration of 200 µM. C) Values of △A411/A554 obtained from UV-Vis spectra
and photographs (inset) of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles
dispersion responses to various ions. Error bars show the standard deviations (n = 3). D)
Values of △I/I0 obtained from fluorescence spectra and photographs (inset) of
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles dispersion responses to various
ions when excited by a 365nm UV lamp. Error bars show the standard deviations (n = 3).
0
50
100 150 200
0
50
100 150 200
NaClO (μmol)
50.9 uM
NaClO (μmol)
51.4 uM
Figure 5. UV-Vis spectra of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles in
Milli-Q water (vial 1, black curve), tap water (vial 2, red curve), tap water spiked with
ClO-, respectively. Inset: Photographs of RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP
nanoparticles in Milli-Q water (black curve), tap water (red curve), tap water spiked
with ClO- (violet curve). B) Fluorescence spectra of the dispersion in Milli-Q water (black
curve), tap water (red curve), tap water spiked with ClO-, respectively. Inset:
Photographs of the dispersion in the Milli-Q water (vial 1, black curve), tap water (vial 2,
red curve), tap water spiked with ClO- (violet curve) when excited by a 365 nm UV lamp.
C) Plot of △A411/A554 (A411/A554 (tap water) - A411/A554 (Milli-Q water)) against the ClO-
Colorimetric and Fluorescent Sensing of ClO- in Tap water
To demonstrate the validity of our colorimetric and fluorescent
method for sensing of ClO- in tap water, we applied a standard
addition method to compensate matrix effects and obtained
stability and accuracy also.50 RhB@{Co(3,5-dbsq)(3,5-
dbcat)(bix)} ICP nanoparticles were first dispersed in tap water,
and then different amounts of ClO- were spiked into the tap
water to estimate the ClO- level in the sample. As a
comparison, the RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP
nanoparticles were also dispersed in Milli-Q water (without
ClO- as control). The results are shown in Figure 5, where the
ClO- in tap water could be determined both by color change
(from purple to orange-red, Figure 5A, inset) and the
enhancement of fluorescent intensity (Fig. 5B, inset) with the
help of a 365 nm UV lamp by naked eyes. Moreover, It was
concentration. Error bars show the standard deviations (n = 3). D) Plot of
water)-I578(Milli-Q water)) against the ClO- concentration. Error bars show the standard
△I (I578 (tap
deviations (n = 3).
Conclusions
On the basis of the stimulus-response of valence-tautomeric
RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles, we
have for the first time demonstrated a simple and yet effective
colorimetric and fluorescent dual probe for ClO−. The dual
signal response and excellent analytical properties of this
method validate it is a reliable approach for accurate
determination of ClO− in tap water, and this method could be
further developed as test paper for on-site ClO- detection,
which is of great importance in drinking water safety.
Moreover, this colorimetric and fluorescent dual system offers
a new strategy and great promise for other pollutant
molecules detection by rational designing the nanostructures
of novel infinite coordination polymer nanoparticles.
found that the ratio of A411
linear response to ClO- spiked into tap water and the
regression equation is A411 554 = 0.20599 + 0.00401 =
/μM, R2
/A554 from UV-Vis spectra provides a
/A
C
0.997 (Figure 5C). Similarly, the fluorescent intensity at 578 nm
from fluorescent spectra also shows a linear response towards
ClO- spiked into tap water and the regression equation is
I =
118. 36025 + 2.32278 C
/μM, with R2= 0.993 (Figure 5D).By
using the standard addition method mentioned above, we
estimated that the concentration of ClO- in the tap water is
51.4 μM and 50.9 μM by colorimetric channel and fluorescent
channel, respectively, which showed great consistency with
each other (Figure 5C,D) and data reported previously.51 These
properties validate the reliability of this colorimetric and
fluorescent method based on stimuli-responsive RhB@{Co(3,5-
dbsq)(3,5-dbcat)(bix)} ICP nanoparticles in real sample
detection.
Acknowledgements
This work is supported by the National Natural Science
,
Foundation of China (No. 21277048
21505046).
Notes and references
This journal is © The Royal Society of Chemistry 20xx
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Table of Contents:
The colorimetric and fluorescent ClO- sensing based on the stimulus response of
valence-tautomeric RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles.
Highlights:
ꢀ Valence-tautomeric RhB@{Co(3,5-dbsq)(3,5-dbcat)(bix)} ICP nanoparticles were
synthesized as colorimetric and fluorescent dual probe.
ꢀ This dual probe shows high selectivity and sensitivity for ClO- assay.
ꢀ This dual probe could be applied for monitoring ClO- in tap water directly.
ꢀ This method offered a new strategy for other contaminants detection based on
novel ICP nanoparticles.