Analysis of aqueous systems using all-inorganic perovskite CsPbBr3 quantum dots with stable electrochemiluminescence performance using a closed bipolar electrode

Article abstract of DOI:10.1016/j.elecom.2019.106559

All-inorganic perovskite CsPbX₃ (X = Cl, Br, I) quantum dots (QDs) have emerged as a new class of semiconductor nanocrystals, but the stability of CsPbX₃ QDs in polar solvents is still a significant challenge. Since most targets in analytical chemistry, especially for biological detection, exist in an aqueous medium, this weakness seriously hampers practical analytical applications of CsPbX₃ QDs. In this work, we introduce a closed bipolar electrode (BPE) to extend the application of perovskite QDs to aqueous systems. Based on the principle of conservation of charge in the electrode reactions at opposite ends of the BPE, the concentration of H₂O₂ in an aqueous medium can be detected by measuring the ECL intensity of CsPbBr₃ QDs in an organic solution. Thus, for the first time, H₂O₂ in an aqueous system has been successfully analyzed using all-inorganic perovskite CsPbBr₃ QDs with stable electrochemiluminescence performance combined with a closed bipolar electrode chip.

Full text of DOI:10.1016/j.elecom.2019.106559

Electrochemistry Communications 108 (2019) 106559
Contents lists available at ScienceDirect
Electrochemistry Communications
journal homepage: www.elsevier.com/locate/elecom
Analysis of aqueous systems using all-inorganic perovskite CsPbBr quantum
3
dots with stable electrochemiluminescence performance using a closed
bipolar electrode
Nan Hao , Jinwen Lu , Zhen Dai , Jing Qian , Jiadong Zhangb,⁎, Yingshu Guod,⁎, Kun Wanga,c,⁎
b
c
a
a
a
a
a
School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, PR China
National & Local Joint Engineering Research Center for Deep Utilization Technology of Rock-salt Resource, Huaiyin Institute of Technology, Huai'an 223003, PR China
Key Laboratory of Sensor Analysis of Tumor Marker, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science and
Technology, Qingdao 266042, PR China
d
Collaborative Innovation Center of Tumor Marker Detection Technology, Equipment and Diagnosis-Therapy Integration in Universities of Shandong, Shandong Province
Key Laboratory of Detection Technology for Tumor Markers, School of Chemistry and Chemical Engineering, Linyi University, Linyi 276005, PR China
A R T I C L E I N F O
A B S T R A C T
Keywords:
All-inorganic perovskite CsPbX
3
(X = Cl, Br, I) quantum dots (QDs) have emerged as a new class of semi-
Electrochemiluminescence
Bipolar electrode
Perovskite
conductor nanocrystals, but the stability of CsPbX QDs in polar solvents is still a significant challenge. Since
3
most targets in analytical chemistry, especially for biological detection, exist in an aqueous medium, this
weakness seriously hampers practical analytical applications of CsPbX QDs. In this work, we introduce a closed
3
3
CsPbBr QDs
bipolar electrode (BPE) to extend the application of perovskite QDs to aqueous systems. Based on the principle of
conservation of charge in the electrode reactions at opposite ends of the BPE, the concentration of H in an
aqueous medium can be detected by measuring the ECL intensity of CsPbBr QDs in an organic solution. Thus,
for the first time, H in an aqueous system has been successfully analyzed using all-inorganic perovskite
CsPbBr
O
2 2
3
2 2
O
3
QDs with stable electrochemiluminescence performance combined with a closed bipolar electrode chip.
1
. Introduction
In recent years, all-inorganic cesium lead halide (CsPbX
polymer nanospheres, and this material was successfully used in live
cell imaging [9]. The application of CsPbBr QDs in the analysis field is
3
3
, X = Cl,
still in its infancy, although there have been some research efforts in
this area [8,10–14].
Br, I) perovskite quantum dots (QDs) have attracted great attention due
to their superior optical/electronic performance, including their high
fluorescence quantum yield (QY), narrow spectral width, composition-
dependent tunable bandgap and defect-resistance photophysical prop-
erties [1–4]. They have been widely applied in optoelectronic and
photovoltaic devices. However, despite these remarkable properties,
all-inorganic perovskite QDs are also highly hygroscopic in a polar
solvent or a high-humidity environment due to their ionic crystal
characteristics. This weakness severely limits their practical applica-
tions in analytical chemistry because the majority of targets, especially
for biological detection, exist in an aqueous medium [5–7]. Up to now,
the main approach to improving the stability has been to encapsulate
Electrochemiluminescence (ECL), which has high sensitivity, good
selectivity, wide linear range and other characteristics, has become a
subject of interest to analytical chemists [15–18]. The ECL performance
of perovskite nanocrystals (NCs) as novel emitters has been explored.
Previous research has studied the co-reactant and annihilation ECL
approaches and shown that the ECL spectra of perovskite NCs was
nearly the same as their photoluminescence spectra [12,19]. Zhu’s
group proposed that high-quality CsPbBr QD film produced intense
3
and stable ECL [14], with an ECL efficiency five times higher than the
2
+
classical Ru(bpy)
cause CsPbBr QDs are unstable in polar solvents due to their in-
trinsically ionic nature, ECL detection was conducted in organic re-
3
/tri-n-propylamine (TPA) system. However, be-
3
CsPbX QDs within matrices for better water resistance. For instance,
3
Wang et al. [8] constructed a CsPbBr
3
QD electrospun fiber membrane
agents, which means that the practical application of CsPbBr QDs to
3
sensor, which uses the fluorescence resonance energy transfer (FRET)
method for sensitive detection of rhodamine 6G (R6G). Li’s group en-
the analysis of aqueous systems remains a challenge. Bipolar electrodes
(BPE) are an effective tool in ECL sensing, as they convert the elec-
trochemical reaction signal into a measurable optical signal, and
capsulated CsPbBr QDs within poly(methyl methacrylate) (PMMA)
3
⁎
Corresponding authors.
E-mail addresses: jiadongzhang@hyit.edu.cn (J. Zhang), yingshug@126.com (Y. Guo), wangkun@ujs.edu.cn (K. Wang).
https://doi.org/10.1016/j.elecom.2019.106559
Received 1 September 2019; Received in revised form 18 September 2019; Accepted 18 September 2019
Available online 17 October 2019
1
388-2481/ © 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license
(
http://creativecommons.org/licenses/BY-NC-ND/4.0/).

N. Hao, et al.
Electrochemistry Communications 108 (2019) 106559
overcome the problem of contact between the electroactive material
and the ECL indicator [20–22]. When a certain driving potential is
applied, an overpotential is produced at the interface between the so-
lution and the BPE, which leads to oxidation and reduction reactions at
opposite ends of the BPE [23]. According to the principle of charge
conservation, the currents generated by oxidation and reduction are
equal, so researchers often associate the reduction reaction occurring at
the cathode with the ECL intensity generated at the anode, which is
then used for quantitative detection [24,25]. It is therefore reasonable
to experiment with a closed BPE in conjunction with perovskite QDs, in
order to extend their analytical use to aqueous systems.
at 600 V with a triple amplification stage. For greater accuracy, each
reaction cell was rinsed several times using a syringe before measure-
ment.
3. Results and discussion
3.1. Design principle of the experiment
As a proof of concept experiment, hydrogen peroxide was selected
as the target molecule [30]. Various concentrations of H O solution
2
2
were added to the sensing (cathode) cell and an ECL luminescence re-
In this work, we constructed a novel closed BPE ECL sensing plat-
form to detect a target in aqueous solution using the excellent lumi-
nescence performance of perovskite QDs. Based on the principle of
charge conservation, the concentration of hydrogen peroxide in an
aqueous solution in the cathode reaction cell was successfully de-
agent (CsPbBr QD/EA) was added to the reporting (anode) cell
3
(Scheme 1a). EA containing a certain concentration of tetra-n-buty-
lammonium hexafluorophosphate (TBAPF ) was necessary as both
6
electrolyte solution and co-reactant. According to the work of Zhu and
Bard, EA participates in the luminescence process of CsPbBr as a co-
3
termined by recording the ECL intensity of CsPbBr
3
/ethyl acetate (EA)
ECL system avoids interference between
reactant. When a voltage was applied to the anode of the BPE, inter-
•
+•
at the anode. This BPE-CsPbBr
3
mediate radicals CH CO and [CsPbBr ] were produced by the oxi-
3
3
the polar solvents and an organic ECL reporting reagent, and achieves
the goal of using perovskite QDs in the analysis of aqueous systems.
This simple strategy overcomes the limitation imposed by the intrinsic
instability of perovskite QDs in an aqueous medium, and may open a
new direction for the application of all-inorganic perovskite QDs for
ECL-based detection of targets in polar solvents.
dation of EA and CsPbBr respectively. Then the unstable excited
3
,
•
substances, [CsPbBr ]*, generated from the combination of CH CO and
3
3
+•
[CsPbBr ] , finally emitted photons back to the ground state to
3
achieve luminescence [14,31]. The above ECL mechanism can be
summarized by the following four reactions:
CsPbBr
CH
3
− e− → [CsPbBr
3
]+•
(1)
(2)
(3)
(4)
COOC
2
H
5
− e− → CH
3
CO + products
]* + products
•
2
. Experimental
.1. Preparation of CsPbBr
Details of materials and reagents are provided in the Supporting
3
[
[
CsPbBr
CsPbBr
3
]+• + CH
3
CO → [CsPbBr
+ hν
•
3
2
3
QDs
3
]* → CsPbBr
3
Information. Samples of CsPbBr
3
QDs were synthesized following the
When a sufficiently high voltage is applied to the BPE, the potential
difference between the BPE and the solution drives the oxidation and
reduction reactions. The oxidation of CsPbBr QDs/EA at the anode and
method reported previously [1,14,26]. As shown in Fig. S1, the pre-
cursors of Cs oleate and Pb oleate must be prepared before the synthesis
3
of the CsPbBr
3
QDs. Briefly, 1 mL oleic acid (OA) and 1 mL oleylamine
the reduction of
H
2
O
2
at the cathode occur simultaneously
(
OLA) were added to a mixture containing 10 mL octadecene (ODE) and
(Scheme 1b). According to the principle of charge conservation, the
0
.069 g of PbBr
. The solid was completely dissolved and heated to 160 °C.
CO
) was added and the
2
after degassing for one hour and heated to 120° C
currents generated by oxidation and reduction are equal. The con-
under N
2
centration of H
2
O may therefore be indirectly detected by measuring
2
Then, 0.8 mL Cs oleate solution (formed by heating 0.407 g Cs
2
3
,
the ECL intensity of CsPbBr
3.2. Characterization of CsPbBr
To demonstrate the successful preparation of CsPbBr
3
QD/EA at the anode.
2
0 mL ODE and 1250 μL OA to 160 °C under N
2
reaction vessel transferred to an ice water bath after 5 s to stop the
reaction.
3
QDs
3
QDs, TEM,
2.2. Fabrication of the ITO-based closed BPE device
XRD, UV–vis and PL spectra were recorded. The CsPbBr QDs dispersed
3
in n-hexane appeared yellow-green under visible light (Fig. 1A), and
The closed bipolar electrode used in this experiment was fabricated
emitted a bright green light when irradiated by ultraviolet light
in two main steps. Firstly, ITO glass with a striped pattern was fabri-
cated by pattern etching [27]. The ITO surface was first cleaned using
acetone, ethanol, and high purity water in turn. The striped pattern
screen was then held on the printing table through the use of a vacuum,
and a special ITO printing ink was used to print the pattern on the
surface of the ITO glass. Then, the printed ITO glass was air-dried,
immersed in an acidic etching solution and etched in a shaker at 37 °C
for 15 min. Finally, 10% NaOH was used to clean the remaining ink
from the ITO glass. The second step was simply to form a pair of micro-
reaction cells (length 4 mm, width 2 mm) with poly(ethylene ter-
ephthalate) (PET) membrane, following the etched pattern [28,29].
(365 nm), indicating that the CsPbBr
3
QDs have a high photo-
luminescence quantum yield (PLQY). Previous reports have shown that
the PLQY of CsPbBr QDs is as high as 90% [32]. The UV–visible and PL
spectra of the CsPbBr QDs are shown in Fig. 1B. It is clear that the
CsPbBr
3
3
3
QDs exhibit a maximum absorption peak at around 515 nm
and a sharp emission peak at around 519 nm (excitation wavelength
350 nm), which is consistent with a previous report [11]. Uniform cubic
CsPbBr nanocrystals about 9 nm in size could be observed in the TEM
3
image (Fig. 1C) [33,34]. The XRD pattern (Fig. 1D) indicates that well-
defined diffraction peaks can be assigned to the orthorhombic phase of
CsPbBr
3
[35,36]. Measurement and scanning XPS data for the CsPbBr
3
QDs are shown in Fig. S2a, and the results are in line with expectations.
.3. ECL behavior of CsPbBr QDs in an organic medium
After successfully synthesizing CsPbBr QDs, we first explored the
2.3. Quantitative determination of H
O
2 2
3
3
As shown in Scheme 1a, a solution of H
2
O (0.1 M PBS, pH 7.4) was
2
added to the sensing microcell. N-hexane solution containing 0.05 M
CsPbBr QDs was added to the reporting microcell and evaporated to
form a CsPbBr QD film, with the continuous addition of 0.05 M tetra-n-
3
3
ECL properties of CsPbBr QDs in the organic phase. The experiment
was conducted with a traditional three-electrode system. A glassy
carbon electrode (GCE) was modified with a CsPbBr QDs film and used
as the working electrode. It can be seen from Fig. S3 that a CsPbBr QD
film scraped and coated in EA several times maintained a dense
3
3
butylammonium hexafluorophosphate (TBAPF
6
) in EA. The CV scan-
3
ning potential window was chosen to be 0 to 1.25 V, and the scanning
rate was 0.1 V/s. The ECL signals were collected using a PMT operated
3
2

N. Hao, et al.
Electrochemistry Communications 108 (2019) 106559
Scheme 1. Schematic diagram of the CsPbBr
3
QD-based BPE-H
2
2
O sensing system.
accumulation and showed a significantly reduced grain size. EA con-
taining 0.05 M TPABF was used as the electrolyte solution, and the
potential window was 0 to 1.25 V, with a scanning rate of 0.1 V/s. As
shown in Fig. 2A, a GCE modified with CsPbBr QDs displayed sig-
3
6
nificant and steady anodic ECL, which is consistent with previous work
by Wang and Zhang [12,14]. As shown in Fig. S4, a significant ECL
Fig. 1. (A) Photographs of CsPbBr
3
QDs. (B) UV–vis and PL spectra of CsPbBr
3
QDs. (C) TEM image of CsPbBr
3
QDs. (D) XRD patterns of CsPbBr QDs.
3
3

N. Hao, et al.
Electrochemistry Communications 108 (2019) 106559
Fig. 2. ECL vs time curve of a GCE modified with CsPbBr
3
QD film in (A) EA containing 0.05 M TBAPF
6
; (B) N
2
-saturated 0.1 M PBS; (C) ECL vs time curve of CsPbBr
3
QDs in BPE containing 10 mM H
2
O
2
(red line: N -saturated 0.1 M PBS) in the cathode cell. (For interpretation of the references to colour in this figure legend, the
2
reader is referred to the web version of this article.)
signal was detected around 1.2 V. The cyclic voltammograms (CV)
showed no obvious peak. It can be seen from Fig. 2B that when the
were analyzed using the same ITO-based closed BPE device. The linear
relationship between the concentration of H and the ECL intensity
of CsPbBr QDs/EA is shown in Fig. 3A. As the concentration of H
increased, the electron transfer on the BPE increased, producing a great
increase in ECL intensity. As observed, a higher concentration of H
causes a higher ECL intensity, as increased H reduction in the sen-
sing cell induces increased oxidation of CsPbBr QDs/EA due to the
need for charge balance [20,29]. There was a linear relationship be-
2 2
O
CsPbBr
3
QD GCE was immersed in the aqueous solution under the same
3
2 2
O
conditions, an ECL signal could again be observed, but this decreased
very rapidly due to the extreme instability of the CsPbBr
polar solvent [5].
3
QDs in the
O
2 2
O
2 2
3
2
3.4. BPE-H O
2
ECL sensing performance of CsPbBr QDs
3
tween ECL intensity and
H
2
O
2
concentration within the range
1
–200 mM, with a detection limit of 0.05 mM (Fig. 3B).
Optimizing the driving voltage (Etot) played an important role in the
BPE-ECL measurement. 3.1 V was selected as Etot to obtain a strong ECL
signal (see Fig. S5). Before any further experiments were conducted, the
4
. Conclusion
ECL performance of CsPbBr QDs on the ITO-based closed BPE device
3
should be investigated. A 0.1 M PBS solution containing 10 mM H
was added to the sensing microcell and an EA solution containing
.05 M TBAPF was added to the reporting microcell modified with
CsPbBr QD film. When the driving voltage was applied, a strong and
stable ECL signal was observed (Fig. 2C), which was attributed to the
oxidation of CsPbBr QDs/EA at the anode electrode surface. Compared
with PBS (red line), the ECL intensity increased about five-fold after
adding H to the cathode cell, which indicated that H had par-
ticipated in and promoted the oxidation reaction of CsPbBr QDs. This
result indicated that the BPE-H ECL system using CsPbBr QDs as
the emitter in this work could be used in further experiments.
2
O
2
In summary, a novel BPE-ECL sensor based on all-inorganic per-
ovskite CsPbBr
3
QDs has been successfully constructed. CsPbBr QDs
3
0
6
were synthesized according to a well-established method and served as
the electrochemiluminescent material. A home-made closed bipolar
electrode chip was successfully fabricated, and the concentration of
3
3
H
2
O
2
was indirectly detected by measuring the ECL intensity of CsPbBr
3
QDs/EA at the anode. This BPE-ECL device successfully used the all-
2
O
2
2 2
3
O
inorganic perovskite CsPbBr QDs for the quantitative determination of
3
H
2
O in an aqueous system. In addition, this first application of the
2
2
O
2
3
electrochemiluminescence of all-inorganic perovskite QDs in a bipolar
electrode may open a new direction for us to explore and overcome the
problem that has limited the application of perovskite halide materials.
3.5. Sample detection
Under the optimum conditions, different concentrations of H
2 2
O
4

N. Hao, et al.
Electrochemistry Communications 108 (2019) 106559
Fig. 3. (A) ECL intensity of CsPbBr
3
QDs in BPE containing different concentrations of H
2
O
2
: (a) 1 mM, (b) 5 mM, (c) 10 mM, (d) 20 mM, (e) 50 mM, (f) 100 mM, (g)
2
00 mM. (B) Corresponding linear relationship between the concentration of H
2
O
2
and the ECL intensity of the CsPbBr QDs.
3
Acknowledgments
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This work was supported by National Natural Science Foundation of
China (Nos. 21876068, 21605055 and 21675066), the Open Fund
Program of Jiangsu Provincial Engineering Laboratory for Advanced
Materials of Salt Chemical Industry (SF201703), and the Foundation of
Key Laboratory of Sensor Analysis of Tumor Marker, Ministry of
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