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Dual-signals electrochemiluminescence ratiometry based the synergic effect between luminol and CdSe quantum dots for direct detection of hydrogen peroxide
Journal of Electroanalytical Chemistry 815 (2018) 61–67
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Dual-signals electrochemiluminescence ratiometry based the synergic effect between luminol and CdSe quantum dots for direct detection of hydrogen peroxide
T
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Yunxia Hu, Chaomin Chen, Yuan Liu, Sui Wang , Zhiyong Guo, Yufang Hu Faculty of Materials Science and Chemical Engineering, State Key Laboratory Base of Novel Functional Materials and Preparation Science, Ningbo University, Ningbo 315211, People's Republic of China
A R T I C L E I N F O
A B S T R A C T
Keywords: Electrochemiluminescence Ratiometric strategy CdSe quantum dots Luminol Synergic effect Hydrogen peroxide
In the present work, a dual signals electrochemiluminescence (ECL) ratiometric strategy was designed based on the synergic effect of the catalysis effect and ECL resonance energy transfer. It was found that CdSe quantum dots (CdSe QDs) can catalyze the oxidation of luminol to promote the signal intensity of luminol at 0.45 V. At the same time, a stronger cathodic ECL peak at −0.75 V from CdSe QDs was observed, which could be attributed to the resonance energy transfer between luminol as a donor and CdSe QDs as an acceptor. Moreover both signals from two different potentials increased with the increase hydrogen peroxide concentration. On the basis of the above results, an enzyme-free ECL sensor was fabricated by immobilization of coating CdSe QDs on Au-graphite oxide (GO-Au) composites modified glassy carbon electrode (GCE), and luminol solution as probe solution, which was used to detect rapidly and sensitively hydrogen peroxide in the range of 0.5–500 μM with a detection limit of 0.5 μM based on the ration of two signals. The sensor exhibited good reproducibility and sensitivity, suggesting that the simple method will be promising in the detection of active oxygen in environmental samples.
1. Introduction It is well known that electrochemiluminescence (ECL) has been gained considerable attention due to outstanding characteristic such as simplicity, high sensitivity, easy controllability and low background [1–3]. Quantum dots (QDs), as a kind of luminescence specie, have been verified by Bard's group on the ECL properties of the silicon QDs [4]. Recently, QDs-based ECL analytical methods have been widely explored due to their unique size-dependent luminescence, high quantum field, optical, and electrochemical properties [5,6]. However, the ECL signal intensity of QDs is usually much lower than that of luminol or Ru(bpy)32+, which limits their wide application. Therefore, it is necessary to develop effective approach to improve QDs ECL for a wider range of applications. Resonance energy transfer has been obtained growing attention as a powerful approach for enhancement of ECL in analysis of target detection, and three kinds of resonance energy transfer have been widely used, such as chemiluminescence resonance energy transfer [7], fluorescence resonance energy transfer [8], and bioluminescence resonance energy transfer [9]. However, in the past ECL resonance energy transfer has been paid less concern. Recently, searches have been gradually done based on the ECL resonance energy
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Corresponding author. E-mail address: [email protected] (S. Wang).
https://doi.org/10.1016/j.jelechem.2018.03.008 Received 4 November 2017; Received in revised form 5 March 2018; Accepted 5 March 2018 Available online 06 March 2018 1572-6657/ © 2018 Elsevier B.V. All rights reserved.
transfer involving Ru(bpy)32+, quantum dots and luminol [10–13]. These searches indicated that ECL resonance energy transfer could happen between the traditional luminescent reagents and QDs. In addition to QDs have the ECL performance, they also could display a good catalytic property on chemiluminescence reactions [14], and the catalytic applications of QDs were relatively less reported on ECL studies [15]. Therefore, it's beautiful to use the catalytic property of QDs while in improving the ECL signals of them. Hydrogen peroxide (H2O2), as a strong oxidant, which may make the body's antioxidant capacity decline by the loss of the body of antioxidants, and further lead to various diseases such as cancer, cardiovascular diseases, and Alzheimer's disease [16–18]. Therefore, it is necessary to detecting quickly and efficiently hydrogen peroxide. At present, several analytical methods have been designed for H2O2 detection, including the UV absorption [19], fluorescence [20], colorimetric assays [21,22], electrochemistry [23], chemiluminescence [24], and so on. However, these methods either time-consuming or require the expensive equipment and harmful fluorescence substance. Moreover, these approaches were mainly based on the variation of single signal, which may introduce false positive or negative errors due to the instrumental or environmental factors [25]. Therefore, developing a
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nanomaterials were characterized using Hitachi SU-70 scanning electron microscope (SEM, Hitachi, Tokyo, Japan) and Transmission electron microscopy (TEM, JEM-1011, Japan). The size distribution was obtained from the Zetasizer ZS90 (Malvern, Malvern, England). UV–vis spectra were measured with a TU-1901 (Beijing Puxi). The fluorescence spectra were measured with Hitachi F-4600 of Hitachi company. The UV lamp (365 nm). The dynamic light scattering (DLS) was taken on a Malvern Zetasizer Nano ZS 90 (UK). .
dual signals strategy requiring ordinary instrumentation yet detecting quickly H2O2 is very essential. Since Xu's group first reported the dual signals ECL ratiometric sensing approach based on CdS nanocrystal and luminol as two different ECL emitters [26], the ECL ratiometric sensors reply on the ratio of two ECL signals have been gotten more and more attention in chemical analysis, and most of them were designed based on the ECL resonance energy transfer between two different emitters such as peroxydisulfate/oxygen(O2/S2O82−) and amino-terminates perylene derivative (PTC-NH2) [27], g-C3N4 nanosheets and Ag–PAMAM–luminol nanocomposites [28], CdS QDs and Ru(bpy)32+ [12,29]. Herein, a dual-signals ECL ratiometry was built based resonance energy transfer between luminol and CdSe QDs. Currently, nanocomposites have gotten promising application in different field. Graphene oxide (GO), as a kind of two-dimensional carbon material with a single atomic layer, can offer a platform for the fixation of organic and inorganic molecules due to its large surface area and high π-π conjunction. However, the surface of GO has oxygenated functional groups such as hydroxyl and carboxyl, so the conductivity of it is poorer. So graphene oxide can be decorated with mental nanoparticles to promote efficiently electrical conductivity. Au nanoparticles can greatly expedite the electron transfer and promote the ECL reaction, thus the GO-Au composites can act as a suitable substrate to load more labels. In this work, we prepared the GO-Au composites to modify the glassy carbon electrode, then CdSe QDs fixed on the GO-Au composites modified electrode, luminol solution as probe solution in the presence of H2O2. It was observed CdSe QDs could effectively catalyze the reaction of luminol-hydrogen peroxide to enhance the luminol ECL signal, and a stronger cathodic ECL peak of CdSe QDs was obtained due to the resonance energy transfer between luminol and QDs. Both signals from two different potentials increased with the increase hydrogen peroxide concentration, thus a dual-signals ECL ratiometric strategy was developed for the detection H2O2 based on the collaborative effect of the catalysis effect and ECL resonance energy transfer.
2.3. Preparation of the GO-Au composites Graphene oxide was prepared from natural graphite power using a modification of Hummers method [30]. In a brief, 0.5 g graphite power, 0.5 g sodium nitrate and 23 mL concentrated sulfuric acid were injected into a round-bottomed flask placed in an ice bath, and the mixed solution was stirred vigorously. After the sodium nitrate was dissolved completely, 3 g solid potassium permanganate was added slowly to the solution and reacted for 2 h. When the solution was dispersed homogeneously, the mixture was transferred to a water bath (35 °C) and stirred vigorously for 1 h. When the temperature of suspension increased to 95 °C, adding 140 mL ultrapure water to the above solution kept the temperature blow 40 °C, followed by slow addition of 3 mL 30% H2O2 solution. After the color of the solution turned from dark brown to yellow, the solution was centrifuged and washed with 0.1 M HCl to dislodge metal ion, then the excessive acid was removed with ultrapure water. The suspension was repeatedly centrifuged and redissolved with ultrapure water until the pH was 6.0. The purified product was dried in a vacuum at room temperature. The resulted GO sample was dispersed in ultrapure water (1 mg/mL) by ultra-sonication for 1 h and centrifuged at 3000 rpm for 10 min and the upper solution was used. GO-Au was prepared as follow. 2 mL 1 mg/mL GO dispersion, 4 mL 1% HAuCl4 and 10 mL ultrapure water were added to a 50 mL roundbottom flask and ultra-sonicated for 1 h. Then sodium citrate (500 μL, 2 M) added to the above solution being refluxed for 4 h at 80 °C. Finally, the product was obtained by centrifugation washed with ultrapure water, and then GO-Au was dispersed in ultrapure water and stored in refrigerator for future use.
2. Experimental 2.1. Reagents and materials Selenium power (> 99.95%), Isopropyl alcohol and 30% H2O2, potassium per-manganate (KMnO4), sulfuric acid (H2SO4, 95%–98%), hydrochloric acid (HCl, 36%–38%), graphite powder (≥99.85%), and sodium nitrate (NaNO3, ≥99%) were purchased from Sinopharm Group Chemical Reagent Co., Ltd. Cadmium dichloride hemipentahydrate (CdCl2·2.5H2O,99.0%), graphite power, sodium citrate and sodium sulfite (97.0%) were supplied from Aladdin Reagent Co., Ltd. (Shanghai, China). Luminol, gold chloride (HAuCl4) and 3-mercaptopropionic acid were obtained from Sigma-Aldrich (St. Louis, MO, USA). All other reagents are of analytical grade or above and used without further purification. 0.1 M Carbonate buffer solution (CBS) was prepared using 0.1 M NaHCO3 and 0.1 M NaCO3, and the pH of which was 9.9 unless otherwise stated. Ultrapure water used for the solutions was purified by the Milli-Q system (≥18 MΩ, Milli-Q, Millipore, Billerica, MA, USA)
2.4. Synthesis of CdSe QDs CdSe QDs were prepared referring to the reported literature procedures [31]. Firstly, 0.8 g sodium sulfite was added to a 100 mL roundbottom flask containing 50 mL ultrapure water. The solution was stirred under nitrogen atmosphere for 30 min, and heated to 90 °C. Then 0.08 g selenium power was added quickly to the above mixture, and refluxed for 5 h under nitrogen protection. When the selenium power was dissolved completely, the yellow clear Na2SeSO3 solution was received. Secondly, CdCl2 solution was obtained by dissolving 37 mg CdCl2·2.5H2O in 50 mL ultrapure water, then 34.6 μL 3-mercaptopropionic acid was added to the CdCl2 solution and adjusted pH to 9.0 with 0.1 M NaOH. Then Na2SeSO3 solution was injected into the mixture. After the solution was heated at 100 °C for 10 min, 3.70 mL N2H4·H2O was added and refluxed for 10 h at 130 °C. The crude products were separated by centrifugation to obtain CdSe QDs, which were purified three times with Isopropyl alcohol and ultrapure water successively by centrifugation at 12000 rpm for 10 min. Finally, the resulted products were diapered in ultrapure water and stored at 4 °C for future use.
2.2. Apparatus A laboratory-built ECL detection system was used. The ECL detection was performed with BPCL Ultra-Weak Luminescence Analyzer (Institute of biophysics, Chinese Academy of sciences, Beijing, China) and a CHI1110B Electrochemical Analyzer (Shanghai Chenhua Instrument Co., Ltd., Shanghai, China). A three-electrode system containing a bare or modified glassy carbon electrode (GCE, Φ = 3 mm) as working electrode, a platinum wire electrode as counter electrode and an Ag/AgCl (3 M KCl) electrode as reference electrode, was used. The voltage of the photomultiplier tube was −650 V. The morphologies of
2.5. Measurement procedure Firstly, the glassy carbon electrodes (GCE) were carefully polished to a mirror with 0.05, 0.3, and 1.0 μm α-Al2O3 power, and then cleaned ultrasonically with ethanol and ultrapure water successively. Next, GCE were rinsed thoroughly with ultrapure water and dried in nitrogen 62
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Scheme 1. Schematic illustration for detecting H2O2 using CdSe QDs and luminol.
atmosphere blowing. Then, 7 μL GO-Au composites were dropped on the surface of GCE. After the electrodes were dried naturally at the room temperature, 7 μL CdSe QDs were spread on the above electrodes surface and dried to obtain the sensor. For the ECL detection, the modified electrodes were immersed into 0.1 M pH 9.9 CBS containing 0.5 mM luminol and different concentration H2O2·The electrodes were scanned from 0.6 V to −1.6 V with a scan rate of 100 mV/s. The whole process was outlined in Scheme 1.
spherical structure of particle with a diameter of 30–80 nm were load the surface of GO, suggesting the GO-Au composite were produced successfully. Fig. 3C showed the TEM image of CdSe QDs, where the average diameter was about 8 nm. Furthermore, the dynamic light scattering (DLS) exhibited the hydrodynamic diameter of QDs (Fig. 1D). It shows that the hydrodynamic diameter of CdSe QDs was distributed in range from 5 nm to 10 nm, and the average diameter size was 7.5 nm. The color of the prepared CdSe QDs was light yellow under the natural light, while the color changed to fuchsia after illumination under a UV lamp, which indicating the produced QDs possess luminescence property (Fig. 1D, Inset).
3. Results and discussion 3.1. Characterization of different material
3.2. Electrochemical behaviors of luminio-H2O2 system at CdSe QDs/GOAu/GCE
Fig. 1A presented the scanning electron microscopy (SEM) images of GO. It can be found that GO shows a large specific surface area, wrinkled and uniform lamellar structure with no aggregation. The SEM image of GO-Au composite (Fig. 1B) showed some approximate
To characterize the fabrication of the sensor, the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were
Fig. 1. SEM images of (A) GO, (B) GO-Au composite, and (C) TEM of CdSe QDs, (D) the sizes distribution of CdSe QDs (Inset: the photo of CdSe QDs under natural light and UV lamp. Left to right).
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light signal increased approximately 100 fold compared with curve c, and the intensity of luminol electrochemiluminescence increased > 2 fold compared with GO-Au/GCE was placed in CBS with H2O2 and luminol. As described above, it suggested CdSe QDs could effectively catalyze the reaction of luminol‑hydrogen peroxide system to enhance the luminol electrochemiluminescence signal, but also revealed the extremely strong CdSe QDs electrochemiluminescence intensity possibly was caused by the resonance energy transfer between QDs and luminol. In order to further verify that there was resonance energy transfer between luminol and QDs, the UV–vis (Fig. 3B) and fluorescence spectra (Fig. 3C) were measured. Fig. 2B exhibited two absorption peaks of luminol at 300–400 nm, and a wide absorption band of CdSe QDs at ~530 nm. When CdSe QDs were mixed with luminol, the absorption peaks of QDs and luminol still occurred at ~530 nm, 300–400 nm, respectively. It revealed there was no new material in the mixture, so luminol was not reacted with CdSe QDs. As shown in Fig. 3C, the maximum emission peak of luminol appeared at ~470 nm, the maximum emission peak of QDs was seen at ~610 nm. When CdSe QDs were mixed with luminol, the FL intensity of CdSe QDs increased while the FL intensity of luminol decreased, suggesting luminol can transfer its energy to CdSe QDs. The absorption of CdSe QDs (530 nm) overlaps with the emission peak of the luminol (470 nm) (Fig. 3D), indicating also there was resonance energy transfer between them.
Fig. 2. Cyclic voltammograms (CVs) of GO-Au/GCE, CdSe QDs/GO-Au/GCE in the CBS containing H2O2 with the absence and presence of luminol. CBS: 0.1 M; H2O2: 0.30 mM; Luminol: 0.5 mM.
carried. As shown in Fig. S1, the results indicated GO-Au composites can accelerate the electron transfer and the CdSe QDs were successfully modified on the GO-Au/GCE. Cyclic voltammograms (CVs) of the GO-Au/GCE and CdSe QDs/GOAu/GCE were relatively obtained in CBS containing H2O2 with the absence and presence of luminol as shown in Fig. 2. There is no cyclic voltammetry (CV) peak at the GO-Au/GCE in CBS containing H2O2. After luminol solution was injected into CBS containing H2O2, an oxidation peak at the potential of approximately 0.45 V, which could be attributed to the oxidation of luminol. When CdSe QDs/GO-Au/GCE was immersed into 0.1 M pH 9.9 CBS containing H2O2 with the absence of luminol, a cathodic CV peak at about −0.75 V could be found which indicated the reduction of CdSe QDs. In the presence of luminol, we could observe two stronger CV peak at roughly −0.75 V and 0.45 V, respectively. Compared with the GO-Au/GCE in the CBS containing luminol and H2O2 and CdSe QDs/GO-Au/GCE in the CBS containing H2O2 with the absence of luminol, When CdSe QDs/GO-Au/GCE was immersed into 0.1 M pH 9.9 CBS containing H2O2 with the presence of luminol, the cathodic CV peak of CdSe QDs at −0.75 V and the anodic CV peak of luminol at 0.45 V were increased simultaneously. This showed that CdSe QDs can catalyze the oxidation of luminiol, but also indicated luminol also play a role in promoting reduction of CdSe QDs.
3.4. Instruction of electrochemiluminescence mechanisms It well known that the electrochemiluminescence intensity of luminol would become stronger with the presence of H2O2 in alkaline condition. Due to the production of O2%− and OH% can stimulate the formation of excited state of luminol. The corresponding of mechanism of the electrochemiluminescence process can be shown as follows [32]:
(1)
(2)
3.3. Electrochemiluminescence resonance energy transfer between Luminol and CdSe QDs
(3) In fact, the chemical reaction rate of the luminol‑hydrogen peroxide system is slower, which produce weaker chemiluminescence signal. Certain nanoparticles can catalyze the luminescent reaction to enhance luminol electrochemiluminescence signal. Because CdSe QDs as a kind of nanoparticle can catalyze the oxidation of luminol, a stronger luminol electrochemiluminescence signal was obtained. As shown in Fig. 3A, the electrochemiluminescence behaviors were discussed comparatively. It could be seen that an extremely weak signal was obtained at the CdSe QDs/GO-Au/GCE in CBS containing H2O2 with the absence of luminol (Fig. 3A, Inset). In the presence of luminol, the GO-Au/GCE was placed in CBS with H2O2, a strong electrochemiluminescence peak from luminol could be observed (Fig. 3A, curve b), which should be assigned to the reaction between oxidized luminol and Superoxide anion. When the CdSe QDs/GO-Au/GCE was immersed in CBS containing luminol without H2O2, CdSe QDs of the electrochemical luminescence signal became stronger compared with curve a, which indicated that resonance energy transfer probably existed between CdSe QDs and luminol. As shown in curve d, When H2O2 solution as a coreactant was added to CBS containing luminol, the intensity of CdSe QDs
(4)
(5)
(6) 64
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Fig. 3. (A) ECL signal responses for different reaction sytems (a) CdSe QDs + H2O2; (b) luminol + H2O2; (c) CdSe QDs + luminol; (d) CdSe QDs + luminol + H2O2 (inset: a). (B) The UV–vis absorption spectra of CdSe QDs, luminol, luminol + CdSe QDs. (C) The Fluorescence spectra of CdSe QDs, luminol, luminol + CdSe QDs. (D) The UV–vis absorption spectra of CdSe QDs and the Fluorescence spectra of luminol.
which was much stronger than luminol. So it is potential to design a dual-signal electrochemiluminescence system to realize the detection of analyte.
When CdSe QDs/GO-Au/GCE was immersed into 0.1 M pH 9.9 CBS containing H2O2 with the absence of luminol, CdSe QDs produced a very weak electrochemical luminescence signal. The signal can be assigned to the reduced CdSe%− was reacted with H2O2, the process can be performed as follow [33]: +e−
3.5. Optimization of experimental conditions
CdSe QDs ⎯⎯⎯→ CdSe⋅−
(7)
2CdSe⋅− + H2 O2 → 2CdSe∗ + 2OH−
(8)
CdSe∗ → CdSe QDs + hv
(9)
In order to obtain a high-performance ECL response, the effects of pH value of electrolyte solution and scan rate on ECL intensity were investigated by detecting H2O2 at the concentration of 300 μM. Fig. 4A showed the effect of pH value from 5.7 to 13 on ECL signal. As shown in curve a, with the increase of pH from 5.7 to 8.4, the CdSe QDs ECL intensity increased dramatically, and then tended to be stable up to pH 10.8. When pH value continued to increase, ECL intensity would be reduced. It can be seen in curve b that the luminol ECL intensity increased gradually with the increase of pH value from 5.7 to 9.9, and then decreased at higher pH up to pH 13. The luminol ECL intensity reached to maximum at pH 9.9. Therefore, pH 9.9 was chosen as the optimal condition in the experiment. The scan rate could influence the ECL intensity due to the ECL efficiency notably depended on the rate of yield and quench of the excited state. With the increase of scan rate, the CdSe QDs ECL intensity gradually increased and reached to a stable value at the scan rate of 0.10 V/s (Fig. 4B, curve a), suggesting the emitted photons of CdSe QDs reached to the maximum state. The catalytic reaction of H2O2 and CdSe QDs played an important role in the process of electrochemical luminescence of luminol, so the effect of scan rate on the luminol ECL signal mainly came from the rate of H2O2 and luminol diffusing to the surface of the electrode. It can be observed that the ECL intensity of luminol came to the maximum value at the scan rate of 0.1 V/s (Fig. 4B, curve b). From the above result, 0.1 V/s was selected the optimal scan rate value.
When CdSe QDs, luminol and H2O2 existed simultaneously, the light signals of CdSe QDs and luminol were both enhanced. This can be attributed to the catalytic effect of CdSe QDs and the resonance energy transfer between luminol and QDs. The response mechanism can be described as follows: According to the above reaction equations, it can be found that Eq. (8) can promote Eq. (3) to produce more O2%−. So the combination of Eqs. (3) and (8) obtain Eq. (10): (10)
(11)
CdSE∗ → CdSe QDs + hv
(12)
The Eq. (10) showed that CdSe QDs have electrocatalytic effect on luminol-H2O2 system. Moreover, Eq. (11) revealed the excited state of luminol could transfer energy to CdSe QDs. Therefore, CdSe QDs can play a role of catalyst to improve luminol luminescence signal, but also act as an electrochemiluminescence acceptor to produce a strong signal,
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Fig. 4. Effect of (A) pH of ECL detection solution and (B) scan rate value.
method has much lower limit of detection and wider liner response range, which can be attributed to following reasons: (1) The GO has large surface and greatly improved the loading capacity of CdSe QDs, meanwhile, GO-Au can enhanced the ECL intensity due to their good conductivity; (2) a dual- signals ECL ratiometric strategy was developed based on the synergic effect of the catalysis effect and ECL resonance energy transfer. Therefore, the proposed method has a good sensitivity to detecting H2O2. To evaluate the selectivity of the prepared method towards H2O2, the effect of coexisting substances like K+, Na+, Ca2+, Mg2+, Pb2+, ethanol, methanol, acetone and glucose were performed on the determination 300 μM H2O2. As shown in Fig. S2, it can be seen that the coexisting substances almost didn't affect the detection of H2O2.
3.6. H2O2 determination Under the optimal experiment conditions, as shown in Fig. 5A, the anodic ECL intensity from luminol and the cathodic ECL intensity of CdSe QDs both increased with the increase of H2O2 concentration. It can be seen from Fig. 5B, a good linear relationship between the H2O2 concentration and the ratio of cathodic to anodic ECL intensity (ICdSe QDs/ILuminol) can be obtained in the concentration range from 0.5 to 500 μM. The regression equation was y = 0.00133x + 0.89177, with a correlation coefficient R of 0.9972, the limit of detection (LOD) of this method was 0.5 μM. In addition, Fig. 5C and Fig. 5D shows the relationship between H2O2 concentration and ECL intensity of CdSe QDs and luminol. The regression equations were y1 = 23.52676x1 + 1847.02721 with the R1 of 0.9720 and y2 = 14.13575x2 + 2201.43747 with the R2 of 0.9421. It is obvious that the correlation coefficient of ratiometry was increased (R > R1 > R2), indicating the accuracy was enhanced based on the ratiometric method. This work of liner response range and limit of detection were compared with previous reference. As presented in Table S1, this
3.7. Analysis of hydrogen peroxide in spiked water samples The application of the proposed method for real water samples was investigated by the spike recovery experiment. The real river samples spiked with different concentrations of H2O2 standard solution were
Fig. 5. (A) ECL signals from CdSe QDs and luminol for the direct detection of H2O2 at the different concentration (0.5, 50, 100, 300, 400, 500 μM); (B) The calibration curve between H2O2 concentration and the ratio of CdSe QDs to luminol ECL peak intensity; (C) Relationship between the CdSe QDs ECL intensity to the concentration of H2O2; (D) Relationship between the luminol ECL intensity to the concentration of H2O2.
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Table 1 Analysis of hydrogen peroxide in spiked water samples. [7] Samples
Spiked (μM)
Detected (μM)
RSD (%)
Recovery (%)
Tap water
0 100 300 500 0 100 300 500
0 93 ± 3.3 307 ± 13.5 438 ± 14.7 0 98 ± 5.7 313 ± 19.3 425 ± 15.7
– 3.5 4.5 3.4 – 5.8 6.4 3.5
– 93.0 102.3 87.6 – 98.0 104.3 90.4
Spring water
[8]
[9]
[10]
[11]
detected and the experimental results were listed in Table 1. As performed in Table 1, H2O2 was not detected in tap water and spring water. The quantitative spike recoveries of H2O2 were 87.6%–104.3% and the relative standard deviation (RSD) was 3.4%–6.4% for the real water samples, indicating that this approach was acceptable and applicable for H2O2 detection in real sample.
[12]
[13]
4. Conclusions
[14]
In a word, a dual signals electrochemiluminescence ratiometric strategy was designed for hydrogen peroxide direct detection. Luminol ECL signal could be enhanced due to the catalytic impact of CdSe QDs on the oxidation of luminol, meanwhile a stronger cathodic ECL signal from CdSe QDs was generated because of the excited state of luminol can transfer its energy to CdSe QDs. Therefore, an enzyme-free ECL sensor was constructed based on both signals at two different potentials increased with the increase of H2O2 concentration. And a linear relationship between the H2O2 concentration from 0.5 to 500 μM and the ratio of cathodic to anodic ECL intensity (ICdSe QDs/ILuminol) was achieved. This method exhibited good sensitivity and reproducibility, and it will be promising for the detection of active oxygen in environmental samples.
[15]
[16] [17]
[18] [19]
[20] [21]
Acknowledgements
[22]
Financial support from the National Natural Science Foundation of China (41576098, 81773483), the Science and Technology Department of Zhejiang Province of China (2016C33176, LGF18B070002) and Natural Science Foundation of Ningbo (2012C50043, 2017A610231, 2017A610228) are gratefully acknowledged. This research was also sponsored by K.C. Wong Magna Fund in Ningbo University.
[23]
[24]
[25]
Appendix A. Supplementary data
[26]
Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jelechem.2018.03.008.
[27]
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Contents lists available at ScienceDirect
Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem
Dual-signals electrochemiluminescence ratiometry based the synergic effect between luminol and CdSe quantum dots for direct detection of hydrogen peroxide
T
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Yunxia Hu, Chaomin Chen, Yuan Liu, Sui Wang , Zhiyong Guo, Yufang Hu Faculty of Materials Science and Chemical Engineering, State Key Laboratory Base of Novel Functional Materials and Preparation Science, Ningbo University, Ningbo 315211, People's Republic of China
A R T I C L E I N F O
A B S T R A C T
Keywords: Electrochemiluminescence Ratiometric strategy CdSe quantum dots Luminol Synergic effect Hydrogen peroxide
In the present work, a dual signals electrochemiluminescence (ECL) ratiometric strategy was designed based on the synergic effect of the catalysis effect and ECL resonance energy transfer. It was found that CdSe quantum dots (CdSe QDs) can catalyze the oxidation of luminol to promote the signal intensity of luminol at 0.45 V. At the same time, a stronger cathodic ECL peak at −0.75 V from CdSe QDs was observed, which could be attributed to the resonance energy transfer between luminol as a donor and CdSe QDs as an acceptor. Moreover both signals from two different potentials increased with the increase hydrogen peroxide concentration. On the basis of the above results, an enzyme-free ECL sensor was fabricated by immobilization of coating CdSe QDs on Au-graphite oxide (GO-Au) composites modified glassy carbon electrode (GCE), and luminol solution as probe solution, which was used to detect rapidly and sensitively hydrogen peroxide in the range of 0.5–500 μM with a detection limit of 0.5 μM based on the ration of two signals. The sensor exhibited good reproducibility and sensitivity, suggesting that the simple method will be promising in the detection of active oxygen in environmental samples.
1. Introduction It is well known that electrochemiluminescence (ECL) has been gained considerable attention due to outstanding characteristic such as simplicity, high sensitivity, easy controllability and low background [1–3]. Quantum dots (QDs), as a kind of luminescence specie, have been verified by Bard's group on the ECL properties of the silicon QDs [4]. Recently, QDs-based ECL analytical methods have been widely explored due to their unique size-dependent luminescence, high quantum field, optical, and electrochemical properties [5,6]. However, the ECL signal intensity of QDs is usually much lower than that of luminol or Ru(bpy)32+, which limits their wide application. Therefore, it is necessary to develop effective approach to improve QDs ECL for a wider range of applications. Resonance energy transfer has been obtained growing attention as a powerful approach for enhancement of ECL in analysis of target detection, and three kinds of resonance energy transfer have been widely used, such as chemiluminescence resonance energy transfer [7], fluorescence resonance energy transfer [8], and bioluminescence resonance energy transfer [9]. However, in the past ECL resonance energy transfer has been paid less concern. Recently, searches have been gradually done based on the ECL resonance energy
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Corresponding author. E-mail address: [email protected] (S. Wang).
https://doi.org/10.1016/j.jelechem.2018.03.008 Received 4 November 2017; Received in revised form 5 March 2018; Accepted 5 March 2018 Available online 06 March 2018 1572-6657/ © 2018 Elsevier B.V. All rights reserved.
transfer involving Ru(bpy)32+, quantum dots and luminol [10–13]. These searches indicated that ECL resonance energy transfer could happen between the traditional luminescent reagents and QDs. In addition to QDs have the ECL performance, they also could display a good catalytic property on chemiluminescence reactions [14], and the catalytic applications of QDs were relatively less reported on ECL studies [15]. Therefore, it's beautiful to use the catalytic property of QDs while in improving the ECL signals of them. Hydrogen peroxide (H2O2), as a strong oxidant, which may make the body's antioxidant capacity decline by the loss of the body of antioxidants, and further lead to various diseases such as cancer, cardiovascular diseases, and Alzheimer's disease [16–18]. Therefore, it is necessary to detecting quickly and efficiently hydrogen peroxide. At present, several analytical methods have been designed for H2O2 detection, including the UV absorption [19], fluorescence [20], colorimetric assays [21,22], electrochemistry [23], chemiluminescence [24], and so on. However, these methods either time-consuming or require the expensive equipment and harmful fluorescence substance. Moreover, these approaches were mainly based on the variation of single signal, which may introduce false positive or negative errors due to the instrumental or environmental factors [25]. Therefore, developing a
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nanomaterials were characterized using Hitachi SU-70 scanning electron microscope (SEM, Hitachi, Tokyo, Japan) and Transmission electron microscopy (TEM, JEM-1011, Japan). The size distribution was obtained from the Zetasizer ZS90 (Malvern, Malvern, England). UV–vis spectra were measured with a TU-1901 (Beijing Puxi). The fluorescence spectra were measured with Hitachi F-4600 of Hitachi company. The UV lamp (365 nm). The dynamic light scattering (DLS) was taken on a Malvern Zetasizer Nano ZS 90 (UK). .
dual signals strategy requiring ordinary instrumentation yet detecting quickly H2O2 is very essential. Since Xu's group first reported the dual signals ECL ratiometric sensing approach based on CdS nanocrystal and luminol as two different ECL emitters [26], the ECL ratiometric sensors reply on the ratio of two ECL signals have been gotten more and more attention in chemical analysis, and most of them were designed based on the ECL resonance energy transfer between two different emitters such as peroxydisulfate/oxygen(O2/S2O82−) and amino-terminates perylene derivative (PTC-NH2) [27], g-C3N4 nanosheets and Ag–PAMAM–luminol nanocomposites [28], CdS QDs and Ru(bpy)32+ [12,29]. Herein, a dual-signals ECL ratiometry was built based resonance energy transfer between luminol and CdSe QDs. Currently, nanocomposites have gotten promising application in different field. Graphene oxide (GO), as a kind of two-dimensional carbon material with a single atomic layer, can offer a platform for the fixation of organic and inorganic molecules due to its large surface area and high π-π conjunction. However, the surface of GO has oxygenated functional groups such as hydroxyl and carboxyl, so the conductivity of it is poorer. So graphene oxide can be decorated with mental nanoparticles to promote efficiently electrical conductivity. Au nanoparticles can greatly expedite the electron transfer and promote the ECL reaction, thus the GO-Au composites can act as a suitable substrate to load more labels. In this work, we prepared the GO-Au composites to modify the glassy carbon electrode, then CdSe QDs fixed on the GO-Au composites modified electrode, luminol solution as probe solution in the presence of H2O2. It was observed CdSe QDs could effectively catalyze the reaction of luminol-hydrogen peroxide to enhance the luminol ECL signal, and a stronger cathodic ECL peak of CdSe QDs was obtained due to the resonance energy transfer between luminol and QDs. Both signals from two different potentials increased with the increase hydrogen peroxide concentration, thus a dual-signals ECL ratiometric strategy was developed for the detection H2O2 based on the collaborative effect of the catalysis effect and ECL resonance energy transfer.
2.3. Preparation of the GO-Au composites Graphene oxide was prepared from natural graphite power using a modification of Hummers method [30]. In a brief, 0.5 g graphite power, 0.5 g sodium nitrate and 23 mL concentrated sulfuric acid were injected into a round-bottomed flask placed in an ice bath, and the mixed solution was stirred vigorously. After the sodium nitrate was dissolved completely, 3 g solid potassium permanganate was added slowly to the solution and reacted for 2 h. When the solution was dispersed homogeneously, the mixture was transferred to a water bath (35 °C) and stirred vigorously for 1 h. When the temperature of suspension increased to 95 °C, adding 140 mL ultrapure water to the above solution kept the temperature blow 40 °C, followed by slow addition of 3 mL 30% H2O2 solution. After the color of the solution turned from dark brown to yellow, the solution was centrifuged and washed with 0.1 M HCl to dislodge metal ion, then the excessive acid was removed with ultrapure water. The suspension was repeatedly centrifuged and redissolved with ultrapure water until the pH was 6.0. The purified product was dried in a vacuum at room temperature. The resulted GO sample was dispersed in ultrapure water (1 mg/mL) by ultra-sonication for 1 h and centrifuged at 3000 rpm for 10 min and the upper solution was used. GO-Au was prepared as follow. 2 mL 1 mg/mL GO dispersion, 4 mL 1% HAuCl4 and 10 mL ultrapure water were added to a 50 mL roundbottom flask and ultra-sonicated for 1 h. Then sodium citrate (500 μL, 2 M) added to the above solution being refluxed for 4 h at 80 °C. Finally, the product was obtained by centrifugation washed with ultrapure water, and then GO-Au was dispersed in ultrapure water and stored in refrigerator for future use.
2. Experimental 2.1. Reagents and materials Selenium power (> 99.95%), Isopropyl alcohol and 30% H2O2, potassium per-manganate (KMnO4), sulfuric acid (H2SO4, 95%–98%), hydrochloric acid (HCl, 36%–38%), graphite powder (≥99.85%), and sodium nitrate (NaNO3, ≥99%) were purchased from Sinopharm Group Chemical Reagent Co., Ltd. Cadmium dichloride hemipentahydrate (CdCl2·2.5H2O,99.0%), graphite power, sodium citrate and sodium sulfite (97.0%) were supplied from Aladdin Reagent Co., Ltd. (Shanghai, China). Luminol, gold chloride (HAuCl4) and 3-mercaptopropionic acid were obtained from Sigma-Aldrich (St. Louis, MO, USA). All other reagents are of analytical grade or above and used without further purification. 0.1 M Carbonate buffer solution (CBS) was prepared using 0.1 M NaHCO3 and 0.1 M NaCO3, and the pH of which was 9.9 unless otherwise stated. Ultrapure water used for the solutions was purified by the Milli-Q system (≥18 MΩ, Milli-Q, Millipore, Billerica, MA, USA)
2.4. Synthesis of CdSe QDs CdSe QDs were prepared referring to the reported literature procedures [31]. Firstly, 0.8 g sodium sulfite was added to a 100 mL roundbottom flask containing 50 mL ultrapure water. The solution was stirred under nitrogen atmosphere for 30 min, and heated to 90 °C. Then 0.08 g selenium power was added quickly to the above mixture, and refluxed for 5 h under nitrogen protection. When the selenium power was dissolved completely, the yellow clear Na2SeSO3 solution was received. Secondly, CdCl2 solution was obtained by dissolving 37 mg CdCl2·2.5H2O in 50 mL ultrapure water, then 34.6 μL 3-mercaptopropionic acid was added to the CdCl2 solution and adjusted pH to 9.0 with 0.1 M NaOH. Then Na2SeSO3 solution was injected into the mixture. After the solution was heated at 100 °C for 10 min, 3.70 mL N2H4·H2O was added and refluxed for 10 h at 130 °C. The crude products were separated by centrifugation to obtain CdSe QDs, which were purified three times with Isopropyl alcohol and ultrapure water successively by centrifugation at 12000 rpm for 10 min. Finally, the resulted products were diapered in ultrapure water and stored at 4 °C for future use.
2.2. Apparatus A laboratory-built ECL detection system was used. The ECL detection was performed with BPCL Ultra-Weak Luminescence Analyzer (Institute of biophysics, Chinese Academy of sciences, Beijing, China) and a CHI1110B Electrochemical Analyzer (Shanghai Chenhua Instrument Co., Ltd., Shanghai, China). A three-electrode system containing a bare or modified glassy carbon electrode (GCE, Φ = 3 mm) as working electrode, a platinum wire electrode as counter electrode and an Ag/AgCl (3 M KCl) electrode as reference electrode, was used. The voltage of the photomultiplier tube was −650 V. The morphologies of
2.5. Measurement procedure Firstly, the glassy carbon electrodes (GCE) were carefully polished to a mirror with 0.05, 0.3, and 1.0 μm α-Al2O3 power, and then cleaned ultrasonically with ethanol and ultrapure water successively. Next, GCE were rinsed thoroughly with ultrapure water and dried in nitrogen 62
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Scheme 1. Schematic illustration for detecting H2O2 using CdSe QDs and luminol.
atmosphere blowing. Then, 7 μL GO-Au composites were dropped on the surface of GCE. After the electrodes were dried naturally at the room temperature, 7 μL CdSe QDs were spread on the above electrodes surface and dried to obtain the sensor. For the ECL detection, the modified electrodes were immersed into 0.1 M pH 9.9 CBS containing 0.5 mM luminol and different concentration H2O2·The electrodes were scanned from 0.6 V to −1.6 V with a scan rate of 100 mV/s. The whole process was outlined in Scheme 1.
spherical structure of particle with a diameter of 30–80 nm were load the surface of GO, suggesting the GO-Au composite were produced successfully. Fig. 3C showed the TEM image of CdSe QDs, where the average diameter was about 8 nm. Furthermore, the dynamic light scattering (DLS) exhibited the hydrodynamic diameter of QDs (Fig. 1D). It shows that the hydrodynamic diameter of CdSe QDs was distributed in range from 5 nm to 10 nm, and the average diameter size was 7.5 nm. The color of the prepared CdSe QDs was light yellow under the natural light, while the color changed to fuchsia after illumination under a UV lamp, which indicating the produced QDs possess luminescence property (Fig. 1D, Inset).
3. Results and discussion 3.1. Characterization of different material
3.2. Electrochemical behaviors of luminio-H2O2 system at CdSe QDs/GOAu/GCE
Fig. 1A presented the scanning electron microscopy (SEM) images of GO. It can be found that GO shows a large specific surface area, wrinkled and uniform lamellar structure with no aggregation. The SEM image of GO-Au composite (Fig. 1B) showed some approximate
To characterize the fabrication of the sensor, the electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were
Fig. 1. SEM images of (A) GO, (B) GO-Au composite, and (C) TEM of CdSe QDs, (D) the sizes distribution of CdSe QDs (Inset: the photo of CdSe QDs under natural light and UV lamp. Left to right).
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light signal increased approximately 100 fold compared with curve c, and the intensity of luminol electrochemiluminescence increased > 2 fold compared with GO-Au/GCE was placed in CBS with H2O2 and luminol. As described above, it suggested CdSe QDs could effectively catalyze the reaction of luminol‑hydrogen peroxide system to enhance the luminol electrochemiluminescence signal, but also revealed the extremely strong CdSe QDs electrochemiluminescence intensity possibly was caused by the resonance energy transfer between QDs and luminol. In order to further verify that there was resonance energy transfer between luminol and QDs, the UV–vis (Fig. 3B) and fluorescence spectra (Fig. 3C) were measured. Fig. 2B exhibited two absorption peaks of luminol at 300–400 nm, and a wide absorption band of CdSe QDs at ~530 nm. When CdSe QDs were mixed with luminol, the absorption peaks of QDs and luminol still occurred at ~530 nm, 300–400 nm, respectively. It revealed there was no new material in the mixture, so luminol was not reacted with CdSe QDs. As shown in Fig. 3C, the maximum emission peak of luminol appeared at ~470 nm, the maximum emission peak of QDs was seen at ~610 nm. When CdSe QDs were mixed with luminol, the FL intensity of CdSe QDs increased while the FL intensity of luminol decreased, suggesting luminol can transfer its energy to CdSe QDs. The absorption of CdSe QDs (530 nm) overlaps with the emission peak of the luminol (470 nm) (Fig. 3D), indicating also there was resonance energy transfer between them.
Fig. 2. Cyclic voltammograms (CVs) of GO-Au/GCE, CdSe QDs/GO-Au/GCE in the CBS containing H2O2 with the absence and presence of luminol. CBS: 0.1 M; H2O2: 0.30 mM; Luminol: 0.5 mM.
carried. As shown in Fig. S1, the results indicated GO-Au composites can accelerate the electron transfer and the CdSe QDs were successfully modified on the GO-Au/GCE. Cyclic voltammograms (CVs) of the GO-Au/GCE and CdSe QDs/GOAu/GCE were relatively obtained in CBS containing H2O2 with the absence and presence of luminol as shown in Fig. 2. There is no cyclic voltammetry (CV) peak at the GO-Au/GCE in CBS containing H2O2. After luminol solution was injected into CBS containing H2O2, an oxidation peak at the potential of approximately 0.45 V, which could be attributed to the oxidation of luminol. When CdSe QDs/GO-Au/GCE was immersed into 0.1 M pH 9.9 CBS containing H2O2 with the absence of luminol, a cathodic CV peak at about −0.75 V could be found which indicated the reduction of CdSe QDs. In the presence of luminol, we could observe two stronger CV peak at roughly −0.75 V and 0.45 V, respectively. Compared with the GO-Au/GCE in the CBS containing luminol and H2O2 and CdSe QDs/GO-Au/GCE in the CBS containing H2O2 with the absence of luminol, When CdSe QDs/GO-Au/GCE was immersed into 0.1 M pH 9.9 CBS containing H2O2 with the presence of luminol, the cathodic CV peak of CdSe QDs at −0.75 V and the anodic CV peak of luminol at 0.45 V were increased simultaneously. This showed that CdSe QDs can catalyze the oxidation of luminiol, but also indicated luminol also play a role in promoting reduction of CdSe QDs.
3.4. Instruction of electrochemiluminescence mechanisms It well known that the electrochemiluminescence intensity of luminol would become stronger with the presence of H2O2 in alkaline condition. Due to the production of O2%− and OH% can stimulate the formation of excited state of luminol. The corresponding of mechanism of the electrochemiluminescence process can be shown as follows [32]:
(1)
(2)
3.3. Electrochemiluminescence resonance energy transfer between Luminol and CdSe QDs
(3) In fact, the chemical reaction rate of the luminol‑hydrogen peroxide system is slower, which produce weaker chemiluminescence signal. Certain nanoparticles can catalyze the luminescent reaction to enhance luminol electrochemiluminescence signal. Because CdSe QDs as a kind of nanoparticle can catalyze the oxidation of luminol, a stronger luminol electrochemiluminescence signal was obtained. As shown in Fig. 3A, the electrochemiluminescence behaviors were discussed comparatively. It could be seen that an extremely weak signal was obtained at the CdSe QDs/GO-Au/GCE in CBS containing H2O2 with the absence of luminol (Fig. 3A, Inset). In the presence of luminol, the GO-Au/GCE was placed in CBS with H2O2, a strong electrochemiluminescence peak from luminol could be observed (Fig. 3A, curve b), which should be assigned to the reaction between oxidized luminol and Superoxide anion. When the CdSe QDs/GO-Au/GCE was immersed in CBS containing luminol without H2O2, CdSe QDs of the electrochemical luminescence signal became stronger compared with curve a, which indicated that resonance energy transfer probably existed between CdSe QDs and luminol. As shown in curve d, When H2O2 solution as a coreactant was added to CBS containing luminol, the intensity of CdSe QDs
(4)
(5)
(6) 64
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Fig. 3. (A) ECL signal responses for different reaction sytems (a) CdSe QDs + H2O2; (b) luminol + H2O2; (c) CdSe QDs + luminol; (d) CdSe QDs + luminol + H2O2 (inset: a). (B) The UV–vis absorption spectra of CdSe QDs, luminol, luminol + CdSe QDs. (C) The Fluorescence spectra of CdSe QDs, luminol, luminol + CdSe QDs. (D) The UV–vis absorption spectra of CdSe QDs and the Fluorescence spectra of luminol.
which was much stronger than luminol. So it is potential to design a dual-signal electrochemiluminescence system to realize the detection of analyte.
When CdSe QDs/GO-Au/GCE was immersed into 0.1 M pH 9.9 CBS containing H2O2 with the absence of luminol, CdSe QDs produced a very weak electrochemical luminescence signal. The signal can be assigned to the reduced CdSe%− was reacted with H2O2, the process can be performed as follow [33]: +e−
3.5. Optimization of experimental conditions
CdSe QDs ⎯⎯⎯→ CdSe⋅−
(7)
2CdSe⋅− + H2 O2 → 2CdSe∗ + 2OH−
(8)
CdSe∗ → CdSe QDs + hv
(9)
In order to obtain a high-performance ECL response, the effects of pH value of electrolyte solution and scan rate on ECL intensity were investigated by detecting H2O2 at the concentration of 300 μM. Fig. 4A showed the effect of pH value from 5.7 to 13 on ECL signal. As shown in curve a, with the increase of pH from 5.7 to 8.4, the CdSe QDs ECL intensity increased dramatically, and then tended to be stable up to pH 10.8. When pH value continued to increase, ECL intensity would be reduced. It can be seen in curve b that the luminol ECL intensity increased gradually with the increase of pH value from 5.7 to 9.9, and then decreased at higher pH up to pH 13. The luminol ECL intensity reached to maximum at pH 9.9. Therefore, pH 9.9 was chosen as the optimal condition in the experiment. The scan rate could influence the ECL intensity due to the ECL efficiency notably depended on the rate of yield and quench of the excited state. With the increase of scan rate, the CdSe QDs ECL intensity gradually increased and reached to a stable value at the scan rate of 0.10 V/s (Fig. 4B, curve a), suggesting the emitted photons of CdSe QDs reached to the maximum state. The catalytic reaction of H2O2 and CdSe QDs played an important role in the process of electrochemical luminescence of luminol, so the effect of scan rate on the luminol ECL signal mainly came from the rate of H2O2 and luminol diffusing to the surface of the electrode. It can be observed that the ECL intensity of luminol came to the maximum value at the scan rate of 0.1 V/s (Fig. 4B, curve b). From the above result, 0.1 V/s was selected the optimal scan rate value.
When CdSe QDs, luminol and H2O2 existed simultaneously, the light signals of CdSe QDs and luminol were both enhanced. This can be attributed to the catalytic effect of CdSe QDs and the resonance energy transfer between luminol and QDs. The response mechanism can be described as follows: According to the above reaction equations, it can be found that Eq. (8) can promote Eq. (3) to produce more O2%−. So the combination of Eqs. (3) and (8) obtain Eq. (10): (10)
(11)
CdSE∗ → CdSe QDs + hv
(12)
The Eq. (10) showed that CdSe QDs have electrocatalytic effect on luminol-H2O2 system. Moreover, Eq. (11) revealed the excited state of luminol could transfer energy to CdSe QDs. Therefore, CdSe QDs can play a role of catalyst to improve luminol luminescence signal, but also act as an electrochemiluminescence acceptor to produce a strong signal,
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Fig. 4. Effect of (A) pH of ECL detection solution and (B) scan rate value.
method has much lower limit of detection and wider liner response range, which can be attributed to following reasons: (1) The GO has large surface and greatly improved the loading capacity of CdSe QDs, meanwhile, GO-Au can enhanced the ECL intensity due to their good conductivity; (2) a dual- signals ECL ratiometric strategy was developed based on the synergic effect of the catalysis effect and ECL resonance energy transfer. Therefore, the proposed method has a good sensitivity to detecting H2O2. To evaluate the selectivity of the prepared method towards H2O2, the effect of coexisting substances like K+, Na+, Ca2+, Mg2+, Pb2+, ethanol, methanol, acetone and glucose were performed on the determination 300 μM H2O2. As shown in Fig. S2, it can be seen that the coexisting substances almost didn't affect the detection of H2O2.
3.6. H2O2 determination Under the optimal experiment conditions, as shown in Fig. 5A, the anodic ECL intensity from luminol and the cathodic ECL intensity of CdSe QDs both increased with the increase of H2O2 concentration. It can be seen from Fig. 5B, a good linear relationship between the H2O2 concentration and the ratio of cathodic to anodic ECL intensity (ICdSe QDs/ILuminol) can be obtained in the concentration range from 0.5 to 500 μM. The regression equation was y = 0.00133x + 0.89177, with a correlation coefficient R of 0.9972, the limit of detection (LOD) of this method was 0.5 μM. In addition, Fig. 5C and Fig. 5D shows the relationship between H2O2 concentration and ECL intensity of CdSe QDs and luminol. The regression equations were y1 = 23.52676x1 + 1847.02721 with the R1 of 0.9720 and y2 = 14.13575x2 + 2201.43747 with the R2 of 0.9421. It is obvious that the correlation coefficient of ratiometry was increased (R > R1 > R2), indicating the accuracy was enhanced based on the ratiometric method. This work of liner response range and limit of detection were compared with previous reference. As presented in Table S1, this
3.7. Analysis of hydrogen peroxide in spiked water samples The application of the proposed method for real water samples was investigated by the spike recovery experiment. The real river samples spiked with different concentrations of H2O2 standard solution were
Fig. 5. (A) ECL signals from CdSe QDs and luminol for the direct detection of H2O2 at the different concentration (0.5, 50, 100, 300, 400, 500 μM); (B) The calibration curve between H2O2 concentration and the ratio of CdSe QDs to luminol ECL peak intensity; (C) Relationship between the CdSe QDs ECL intensity to the concentration of H2O2; (D) Relationship between the luminol ECL intensity to the concentration of H2O2.
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Y. Hu et al.
Table 1 Analysis of hydrogen peroxide in spiked water samples. [7] Samples
Spiked (μM)
Detected (μM)
RSD (%)
Recovery (%)
Tap water
0 100 300 500 0 100 300 500
0 93 ± 3.3 307 ± 13.5 438 ± 14.7 0 98 ± 5.7 313 ± 19.3 425 ± 15.7
– 3.5 4.5 3.4 – 5.8 6.4 3.5
– 93.0 102.3 87.6 – 98.0 104.3 90.4
Spring water
[8]
[9]
[10]
[11]
detected and the experimental results were listed in Table 1. As performed in Table 1, H2O2 was not detected in tap water and spring water. The quantitative spike recoveries of H2O2 were 87.6%–104.3% and the relative standard deviation (RSD) was 3.4%–6.4% for the real water samples, indicating that this approach was acceptable and applicable for H2O2 detection in real sample.
[12]
[13]
4. Conclusions
[14]
In a word, a dual signals electrochemiluminescence ratiometric strategy was designed for hydrogen peroxide direct detection. Luminol ECL signal could be enhanced due to the catalytic impact of CdSe QDs on the oxidation of luminol, meanwhile a stronger cathodic ECL signal from CdSe QDs was generated because of the excited state of luminol can transfer its energy to CdSe QDs. Therefore, an enzyme-free ECL sensor was constructed based on both signals at two different potentials increased with the increase of H2O2 concentration. And a linear relationship between the H2O2 concentration from 0.5 to 500 μM and the ratio of cathodic to anodic ECL intensity (ICdSe QDs/ILuminol) was achieved. This method exhibited good sensitivity and reproducibility, and it will be promising for the detection of active oxygen in environmental samples.
[15]
[16] [17]
[18] [19]
[20] [21]
Acknowledgements
[22]
Financial support from the National Natural Science Foundation of China (41576098, 81773483), the Science and Technology Department of Zhejiang Province of China (2016C33176, LGF18B070002) and Natural Science Foundation of Ningbo (2012C50043, 2017A610231, 2017A610228) are gratefully acknowledged. This research was also sponsored by K.C. Wong Magna Fund in Ningbo University.
[23]
[24]
[25]
Appendix A. Supplementary data
[26]
Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jelechem.2018.03.008.
[27]
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