gold nanoparticles

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Sensors and Actuators B 191 (2014) 415–420 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevie...

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Sensors and Actuators B 191 (2014) 415–420

Contents lists available at ScienceDirect

Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb

An ECL sensor for dopamine using reduced graphene oxide/multiwall carbon nanotubes/gold nanoparticles Dehua Yuan, Shihong Chen ∗ , Ruo Yuan ∗ , Juanjuan Zhang, Xiaofang Liu Education Ministry Key Laboratory on Luminescence and Real-Time Analysis, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, China

a r t i c l e

i n f o

Article history: Received 16 August 2013 Received in revised form 28 September 2013 Accepted 3 October 2013 Available online 16 October 2013 Keywords: Electrochemiluminescence Sensor Multiwall carbon nanotubes Graphene Gold nanoparticles Dopamine

a b s t r a c t An eletrochemiluminescence (ECL) sensor based on ECL of peroxydisulfate solution for detecting the dopamine (DA) was proposed using reduced graphene oxide/multiwall carbon nanotubes/gold nanoparticles (rGO/MWCNTs/AuNPs) hybrid modified glassy carbon electrode (GCE). The rGO/MWCNTs/AuNPs was synthesized by an effective and facile in situ chemical reaction using polyethyleneimine (PEI) as a reducing agent for both GO/MWCNTs and AuCl4 − . The ECL behaviors of peroxydisulfate solution have been investigated at the rGO/MWCNTs/AuNPs/GCE, and DA was found to be able to enhance the ECL of peroxydisulfate solution. Under the optimized conditions, the enhanced ECL signal intensity of peroxydisulfate solution was linear with the concentration of DA in the range between 0.20 and 70 ␮M (R = 0.9902) with a detection limit (S/N = 3) of 0.067 ␮M. Furthermore, the developed sensor exhibited a high sensitivity, good reproducibility, stability for the detection of DA. The applicability of the proposed sensor was also evaluated by detecting DA in dopamine hydrochloride injection, human urine and serum.

1. Introduction Dopamine (DA) is one of the most important catecholamine neurotransmitters and plays a significant role in the function of the central nervous, renal, cardiovascular and hormonal systems as well as in drug addiction [1,2]. Abnormal levels of DA will lead to several diseases such as Parkinson’s disease and schizophrenia [3], hypertension as well as heart failure [4]. Obviously, rapid and sensitive determination of DA has an important value in the field of physiological function research and clinical disease diagnosis. Various methods have been studied for the determination of DA including high performance liquid chromatography (HPLC) [5], fluorescence method [6], and ion chromatography with conductivity detection [7]. However, these analysis methods have a number of disadvantages, including time-consuming, sample pretreatments, complex manipulations and low sensitivity, so it is attractive to develop novel materials for sensitive determination of DA in the electrochemical field. Electrochemiluminescence (ECL) has remarkable features such as simplicity, rapidity, high sensitivity and easy controllability. ECL sensor as powerful device has been used extensively for the sensitive detection of a wide variety of analytes [8–11]. The detection of

∗ Corresponding authors. Tel.: +86 23 68253172; fax: +86 23 68253172. E-mail addresses: [email protected] (D. Yuan), [email protected] (S. Chen), [email protected] (R. Yuan). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.10.013

© 2013 Elsevier B.V. All rights reserved.

DA has been reported based on its quenching effect on the ECL. For example, Liu et al. developed an ECL method for the determination of DA based on quenching effect on the anodic ECL of CdSe quantum dots [12]. However, so far to our knowledge, only few enhanced ECL methods have been applied to determine DA. Li et al. reported the enhancement ECL of bovine serum albumin stabilized Au nanoclusters for detecting DA and got linear behavior over 2.5–47.5 ␮M [2]. However, the concentration of DA in human body is less than 1 ␮M [13,14], which is so low that ECL sensors with higher sensitivity are desirable. Graphene has attracted immense attention due to its unique properties, such as excellent electronic transport properties, good fracture strength and high aspect ratio properties and has been applied in the areas of sensors [15–18]. Recently, reduced graphene-based metal nanocomposites have been applied in sensing devices [19,20]. Chen et al. developed an ECL sensor based on graphene/gold nanoclusters to determine H2 O2 [19]. Chen et al. developed a glucose biosensor based on graphene-gold nanoparticles (AuNPs) [20]. In those reports, hydrazine was used as reducing agent to reduce graphene oxide (GO). However, hydrazine is highly toxic and its use should be minimized [21]. In order to overcome this limitation, polyethyleneimine (PEI), an amino-rich cationic polyelectrolyte, has been used as reducing agent for GO [22]. Due to the high density of imino-groups on PEI, it also has been used as reductant for the formation of AuNPs [14,23]. Additionally, multiwalled carbon nanotubes (MWCNTs) [11,24,25] and Au nanoparticles (AuNPs) [26,27] are extremely attractive materials

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Fig. 1. SEM images of (A) rGO/MWCNTs and (B) rGO/MWCNTs/AuNPs films.

for fabricating ECL sensors because of their unique physical, electrical and catalytic properties and both of them have been also used to enhance ECL signal of luminol-H2 O2 system. In this work, reduced graphene oxide/multiwall carbon nanotubes/gold nanoparticles (rGO/MWCNTs/AuNPs) hybrid was prepared through in situ chemical reaction between the metal ion and the rGO/MWCNTs with PEI. Based on the fact that dopamine can enhance the ECL signal at rGO/MWCNTs/AuNPs modified electrode in the presence of peroxydisulfate, an ECL sensor was proposed for the determination of DA. The novel method exhibited sensitive ECL responses to DA even in the presence of a high concentration of uric acid and ascorbic acid.

and washed several times by double-distilled water. The synthetic process of rGO/MWCNTs/AuNPs is shown in Scheme 1. 2.4. Construction of rGO/MWCNTs/AuNPs modified electrode The glassy carbon electrode (GCE, ˚ = 4 mm) was polished with 0.3 and 0.05 ␮m alumina powder successively, followed by washing with distilled water and sonicating in ethanol, distilled water, respectively. Subsequently, rGO/MWCNTs/AuNPs suspension prepared by dispersing in 0.1 wt% chitosan solution was dropped on the surface of GCE to achieve the rGO/MWCNTs/AuNPs/GCE. 2.5. ECL detection and data processing

2. Experimental 2.1. Reagents and materials Graphene oxide (GO) was obtained from Nanjing Xianfeng nano Co. (Nanjing, China). Multi-wall carbon nanotubes (MWCNTs, 95% purity) were obtained from Chengdu Organic Chemicals Co. Ltd. of the Chinese Academy of Science and purified by fluxing in concentrated nitric acid for 7 h prior to use. Gold chloride (HAuCl4 ), polyethyleneimine (PEI) and uric acid were obtained from Sigma Chemical (St. Louis, MO, USA). Ascorbic acid and DA were obtained from Chemical Reagent Co. (Chongqing, China). Potassium persulfate (K2 S2 O8 ) was purchased from Shanghai Chemical Reagent Company (Shanghai, China). Phosphate buffer (0.1 M) was prepared using 0.1 M Na2 HPO4 and 0.1 M KH2 PO4 . The supporting electrolyte was 0.1 M KCl. Double-distilled water was used throughout the experiments.

The ECL detection was performed at room temperature in a 10 mL homemade quartz cell. A three-electrode system consisted of a modified GCE (˚ = 4 mm) as the working electrode, a platinum wire as the auxiliary electrode and an Ag/AgCl (sat.) electrode as the reference electrode. Cyclic voltammetry mode with continuous potential scanning from −2.0 to 0 V and the scan rate of 0.1 V s−1 was applied to obtain ECL signal in 0.1 M K2 S2 O8 (pH 7.0). A high voltage of 800 V was supplied to the photomultiplier for luminescence intensity determination. In this work, the ECL intensity increased with the concentration of DA. The determination was based on the ECL intensity changes (I = Is − Io ), where Is was the ECL intensity with adding DA, Io was the ECL intensity without adding DA. The limit of detection (LOD) for DA was calculated by using the formulae LOD = 3SB /m [28,29], here, m is the slope of the corresponding calibration curve and SB is the standard deviation for the blank responses.

2.2. Apparatus 3. Results and discussion The ECL emission was monitored with a model MPI-A electrochemiluminescence analyzer (Xi’an Remax Electronic Science &Technology Co. Ltd., Xi’an, China). Scanning electron micrographs were studied with a scanning electron microscope (SEM, Hitachi, Japan). The UV–vis absorption spectra were recorded in the range of 200–800 nm, using a UV–vis spectrometer (UV–vis 8500). All experiments were carried out at room temperature. 2.3. Preparation of rGO/MWCNTs/AuNPs hybrid 2.5 mg GO sheets and 2.5 mg MWCNTs were mixed completely in 5 mL double-distilled water by a combination of vigorous stirring and sonication. Afterwards, PEI (3%, 0.1 mL) was added into the mixture (pH 1.0) and heated under reflux at 135 ◦ C for 3 h. Then, 2.5 mL 1.0 wt% HAuCl4 was added into the obtained solution and heated at 70 ◦ C for 2 h. The final product was collected through centrifugation

3.1. SEM and UV–vis characterization of the rGO/MWCNTs/AuNPs The morphology and microstructure of as-prepared hybrids were characterized using SEM. As showed in Fig. 1A, the image of rGO/MWCNTs presents sheet structure belonging to the rGO, which was fully covered by MWCNTs. Compared to Fig. 1A, many bright nanoparticles were observed at the SEM image of rGO/MWCNTs/AuNPs hybrid (Fig. 1B), and the sizes of particles were in a range from 100 to 200 nm, indicating the successful assembly of AuNPs on rGO/MWCNTs composite. This fact confirmed the feasibility of proposed strategy for producing the rGO/MWCNTs/AuNPs hybrid. The UV–vis absorption spectra were further investigated for confirming the formation of rGO/MWCNTs/AuNPs hybrid and the results were shown in Fig. 2. For the absorption spectra of

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Scheme 1. The preparation procedure of rGO/MWCNTs/AuNPs and the ECL sensor.

rGO/MWCNTs (curve a) and rGO/MWCNTs/AuNPs (curve b), the absorption peak at 267 nm could be ascribed to the characteristic peak of rGO/MWCNTs [20]. The absorption peak at about 550 nm in curve b is attributed to the characteristic absorption of AuNPs [20,22]. The results strongly suggested the feasibility of proposed strategy for producing the rGO/MWCNTs/AuNPs hybrid in situ.

3.2. ECL behavior of the sensor Fig. 3 showed the ECL intensity of the rGO/MWCNTs/AuNPs/GCE in 0.1 M phosphate buffer (pH 7.0) without K2 S2 O8 (curve a) and with 0.1 M K2 S2 O8 (curve c). As seen, rGO/MWCNTs/AuNPs/GCE almost had no ECL signal in the absence of S2 O8 2− (curve a). However, a strong ECL signal was observed at rGO/MWCNTs/AuNPs/GCE in the presence of S2 O8 2− (curve b) and ECL peak appeared at the potential of approximate −1.95 V. For comparison, the ECL intensity of the bare GCE in 0.1 M phosphate buffer (pH 7.0) with 0.1 M K2 S2 O8 has been studied. As shown in Fig. 3 curve b, the ECL signal observed at bare GCE was much lower than that observed at rGO/MWCNTs/AuNPs/GCE (curve c). This fact indicated that the integration of rGO, MWCNTs and AuNPs would markedly enhance the ECL signal of the modified electrode and improve the sensitivity of the sensor for the determination of DA.

3.3. Optimization of analytical conditions The pH of the working solution would affect the ECL intensity of the modified electrode. The effect of pH from 4.0 to 9.0 on the performance of ECL sensor was investigated. The enhanced ECL intensity (I) values were calculated after the 30 ␮M DA being added and the results were showed in Fig. 4A. As can be seen, the maximum ECL intensity (I) could be obtained at pH 7.0. So phosphate buffer (pH 7.0) was chosen in the subsequent experiments. The effect of K2 S2 O8 concentration on the ECL intensity has been investigated in the range of 0.05 to 0.15 M in the presence of 30 ␮M DA. As shown in Fig. 4B, the enhanced ECL intensity (I) was most strong in the presence of 0.1 M K2 S2 O8 . Therefore, 0.1 M of K2 S2 O8 was used for subsequent experiments. 3.4. ECL detection of DA In this work, with the addition of DA into the phosphate buffer solution containing 0.1 M K2 S2 O8 , an enhanced catholic ECL signal was observed at the rGO/MWCNTs/AuNPs/GCE. A calibration curve was plotted for the ECL intensity and the DA concentration using the rGO/MWCNTs/AuNPs modified GCE (Fig. 5). Under the optimum conditions, the enhanced ECL intensity presented a good linearity with the concentration of DA in the range of 0.20–70 ␮M

ECL Intensity / a.u.

3000

Absorbance

267

267 b 550

a

c

2000

1000

0

b a

-2.0 300

400

500

600

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Wavelength/nm Fig. 2. UV–vis absorption spectra of (a) rGO/MWCNTs and (b) rGO/MWCNTs/AuNPs.

-1.5 -1.0 -0.5 0.0 Potential / V(vs. Ag/AgCl)

Fig. 3. ECL profiles of rGO/MWCNTs/AuNPs/GCE in 0.1 M phosphate buffer solution (pH 7.0) (a) without K2 S2 O8 and (c) with 0.1 M K2 S2 O8 , (b) bare GCE in 0.1 M phosphate buffer solution (pH 7.0) containing 0.1 M K2 S2 O8 . Scan rate: 100 mV s−1 .

Enhanced ECL Intensity / a.u

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3200 2800 2400 2000 4

5

6

pH

7

8

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3200 2800 2400 2000 0.04

0.06 0.08 0.10 0.12 Concentration of K2S2O8

0.14

Fig. 4. Effect of (A) pH and (B) the concentration of K2 S2 O8 on the enhanced ECL intensity of rGO/MWCNTs/AuNPs/GCE under the 30 ␮M DA. Table 1 Comparison of the proposed method for the determination of DA with the other reported methods. Electrodes

Method

Linear range (␮M)

Detection limit (␮M)

Ref.

PEI-MWNTs-AuNPs/GCE Mn3 O4 /GCE SWCNT/Fe2 O3 /graphite electrode Ag2 Se Ds/PEI/MWCNTs/GCE BSAc -stabilized Au nanoclusters/ITOd electrode CdSe quantum dots/ITO rGO/MWCNTs/AuNPs/GCE

DPVa DPVa SWVb ECL ECL ECL ECL

0.05–4.0 10–70 3.2–31.8 0.5–19.5 2.5–47.5 0.5–70 0.20–70

0.00656 0.1 0.36 – – 0.5 0.067

[14] [30] [31] [32] [2] [12] This work

a

DPV, differential pulse voltammetry. SWV, square wave voltammetry. c BSA, bovine serum albumin. d ITO, indium tin oxide. b

with a LOD of 0.067 ␮M. The linear equation was I = 112.4C + 11.10 (here, C was the concentration of DA), and the correlation coefficient was 0.9902. Table 1 compares the linear range and detection limit of the proposed method with the other reported methods [2,12,14,30–32]. As can be observed, our proposed sensor displayed wider linear range and lower detection limit compared to references [2,12,30–32]. However, Jin et al. [14] reported a significantly lower limit of electrochemical detection than the ECL sensor described in our work, but not as wide a linear range. The possible ECL enhancement mechanism may be as follows: SO4 •− radical, which is produced by the electroreduction of S2 O8 2− , is a strong oxidant. The dissolved oxygen is reduced to OOH•. The OOH• could react with SO4 •− to product light-emitting species 1 (O2 )2 * [27], then light emitted. It has been reported that the adsorption of DA on the TiO2 surface via coordinating dopamine with undercoordinated titanium atoms can form a charge transfer complex [33]. Therefore, in this work, the ␲–␲ interaction between phenyl

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8000 6000

ΔI=112.4C+11.10 R=0.9902

4000 2000

structure of DA and rGO/MWCNTs would form a charge transfer complex and makes the electron transfer more feasible [34]. 3.5. Selectivity, reproducibility, repeatability and stability of the sensor In order to monitor the selectivity of the sensor, the interferences of uric acid, ascorbic acid, epinephrine, norepinephrine, tyrosine, thyroxine and a series of ions such as Na+ , K+ , Mg2+ , Ca2+ , Cl− and SO4 2− were investigated for the determination of DA. It was found that uric acid, ascorbic acid, tyrosine, Na+ , K+ , Mg2+ , Ca2+ , Cl− or SO4 2− at a concentration of 10 times higher than DA did not cause an obvious interference with the determination of DA (30 ␮M). However, epinephrine, norepinephrine and thyroxine could cause an obvious interference for the determination of DA (30 ␮M) when the concentration of epinephrine, norepinephrine, and thyroxine were more than 6.0 ␮M, 9.0 ␮M and 3.0 ␮M, respectively. The reproducibility of the sensor for DA was estimated by determining DA (30 ␮M) with five sensors. Five sensors exhibited similar ECL responses and the relative standard deviation (R.S.D.) was 3.2%, indicating that the reproducibility of the proposed sensor for DA detection was acceptable. The relative standard deviation (R.S.D.) was 1.6% for successive measurements (n = 11) at 30.0 ␮M DA (Fig. 6), suggesting a good repeatability of the proposed sensor for DA detection. The storage stability of the proposed sensor was also examined by monitoring the ECL signal of the sensor at 30.0 ␮M DA. When not in use, the sensor was stored at 4 ◦ C. It was found that no remarkable change was observed after discontinuity using for one month in our work, demonstrating that the sensor possessed good stability.

0 3.6. Analytical application of the sensor in the real samples

0

20

40 C / μM

60

80

Fig. 5. Calibration curve of DA concentration and enhanced ECL intensity.

The applicability of the proposed ECL sensor was evaluated by detecting the DA in dopamine hydrochloride injection sample, human urine and serum samples from adult healthy volunteers

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Acknowledgments

ECL Intensity / a.u

4500

This work is supported by National Natural Science Foundation of China (21075100, 21275119), Municipal Key Laboratory on Luminescence and Real-Time Analysis, Southwest University, and the Fundamental Research Funds for the Central Universities (XDJK2012A004).

3000

1500

References

0 100

200 300 Time/s

400

Fig. 6. The ECL stability of proposed sensor to 30 ␮M DA.

Table 2 The recovery of the proposed sensor in hydrochloride injection, human urine and serum samples. Sample

Detecteda (␮M)

Added (␮M)

Founda (␮M)

Recovery (%)

Diluted injection

15.4 ± 0.3 15.4 ± 0.3 15.4 ± 0.3

5.0 10.0 20.0

4.7 ± 0.2 10.3 ± 0.2 20.8 ± 0.3

94 103 104

Urine 1

5.0 20.0 30.0

4.9 ± 0.2 19.7 ± 0.2 30.8 ± 0.1

98 98.5 103

Urine 2

5.0 20.0 30.0

5.3 ± 0.4 20.8 ± 0.3 29.7 ± 0.4

106 104 99.0

Serum 1

5.0 20.0 30.0

4.8 ± 0.4 20.9 ± 0.3 30.6 ± 0.3

96.0 105 102

Serum 2

5.0 20.0 30.0

5.3 ± 0.3 19.8 ± 0.3 29.6 ± 0.4

106 99.0 98.7

Recovery calculated as a mean of three measurements. a Mean value ± standard deviation of three measurements.

using the standard addition method. Dopamine hydrochloride injection was diluted with 0.1 M phosphate buffer (pH 7.0) as real sample for analysis. The human urine and serum samples were diluted 10 times with 0.1 M phosphate buffer (pH 7.0). The results were shown in Table 2 and the recoveries ranged from 94.0% to 106%, showing a preliminary application of the sensor for the determination of DA in commercial samples.

4. Conclusion rGO/MWCNTs/AuNPs composite was fabricated and applied to construct a modified electrode (rGO/MWCNTs/AuNPs/GCE). This synthetic route involves a mild heat treatment process and in situ reduction of HAuCl4 on rGO/MWCNTs. Based on the fact dopamine can enhance the ECL signal at rGO/MWCNTs/AuNPs/GCE in the presence of peroxydisulfate, an ECL method was developed for the determination of DA. Proposed ECL sensor exhibited a wider linear response range than those of other enhancement ECL methods. In addition, the proposed method exhibited high sensitivity and stability, good reproducibility and repeatability. The rGO/MWCNTs/AuNPs could become a promising material for ECL investigations to some biomolecules.

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Biographies Dehua Yuan is an MS candidate in the College of Chemistry and Chemical Engineering of Southwest University, China. Her main research interests are the development of biosensors. Shihong Chen is a professor of Chemistry and Chemical Engineering in Southwest University, China. She received her PhD degree in analytical chemistry from this university in 2008. Her main research interests are the development of biosensors. Ruo Yuan is a professor at College of Chemistry and Chemical Engineering, South west University, China. He received a PhD degree in analytical chemistry from Hunan University. The main research interests of Prof. Yuan are connected with the development of electrochemical devices for bio- and immunosensors. Juanjuan Zhang is an MS candidate in the College of Chemistry and Chemical Engineering of Southwest University, China. Her main research interests are the development of biosensors. Xiaofang Liu is an MS candidate in the College of Chemistry and Chemical Engineering of Southwest University, China. Her main research interests are the development of biosensors.