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Enhanced electrochemiluminescence sensor for detecting dopamine based on gold nanoflower@graphitic carbon nitride polymer nanosheet–polyaniline hybrids Qiyi Lu,a Juanjuan Zhang,a Xiaofang Liu,a Yuanya Wu,b Ruo Yuan*a and Shihong Chen*a In this work, an enhanced electrochemiluminescence (ECL) sensor based on gold nanoflower@graphitic carbon nitride polymer nanosheet–polyaniline hybrids (AuNF@g-C3N4–PANI) was prepared for the detection of dapamine (DA). First, the bulk g-C3N4 was prepared through polymerizing melamine under 600  C. And then the g-C3N4 nanosheet was obtained by ultrasonication-assisted liquid exfoliation of bulk g-C3N4. Finally, polyaniline (PANI) and gold nanoflowers (AuNFs) were successively formed on the g-C3N4 nanosheet through an in situ synthesis method. The resulting AuNF@g-C3N4–PANI hybrids were modified onto the surface of glassy carbon electrode to achieve a sensor (AuNF@g-C3N4–PANI/GCE) for detecting dopamine. Under the optimal conditions, the ECL signal increased linearly with the

Received 29th August 2014 Accepted 13th October 2014

concentration of dopamine. The linear range of 5.0  109 to 1.6  106 M was obtained, while the detection limit was 1.7  109 M. The prepared sensor exhibited a low detection limit and high sensitivity

DOI: 10.1039/c4an01595a

for the determination of dopamine. The combination of g-C3N4 nanosheet, PANI and AuNF would

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provide a new opportunity for the ECL sensor.

1. Introduction Dopamine (DA), an important neurotransmitter, plays a signicant role in the mammalian central nervous system.1 Abnormal release of dopamine will contribute to some incurable diseases such as schizophrenia and Parkinson's disease.2 Hence, the sensitive determination of DA becomes increasingly signicant in the eld of clinical disease diagnosis and the research of physiological functions.3 Among various analysis methods for dopamine, such as the uorescence methods,4 electrochemical methods,5 ion chromatography with conductivity detection,6 and high performance liquid chromatography (HPLC),7 electrochemiluminescence (ECL) is a better alternative due to its outstanding features such as low background signal, good temporal, high sensitivity, and good selectivity.3,8,9 To the best of our knowledge, quenched ECL methods for the determination of DA have been widely reported.9 Signal-on detection is better than signal-off detection because of the serious false positives caused by interference in the signal-off detection.10

a

Key Laboratory of Luminescent and Real-Time Analytical Chemistry, Southwest University, Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, PR China

b

Chongqing Key Laboratory for Advanced Materials and Technologies of Clean Electrical Power Sources, Institute for Clean Energy & Advanced Materials, Southwest University, Chongqing 400715, P.R. China. E-mail: [email protected]; [email protected]; Fax: +86-023-68254000; Tel: +86-023-68252277

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Thus, it is most desirable for us to develop a signal-on ECL method to sensitively detect DA. Recently, various carbon materials have been used to modify electrodes to detect dopamine, such as graphene oxide,3 carbon nanotubes,11 carbon microspheres,12 and carbon dots.13 However, these carbon materials have limitations, either expensive or difficult to synthesize. Thus, it is impending for us to use a simple, economical, sustainable, and environmentally friendly carbon material to develop an ECL sensor for detecting DA. The graphitic carbon nitride polymer (g-C3N4), an analogue of graphite, has attracted a lot of attention in the last few years due to its unique structure and properties.14,15 As the most stable allotrope of carbon nitride and a thermally and chemically stable semiconductor, it has been widely used in the elds such as catalysis,16–18 photoelectronic materials,19,20 and degradation.21–23 However, the application of g-C3N4 in the eld of sensor is in the initial stage, and only a few studies were reported. Recently, Tian and co-workers demonstrated for the rst time that ultrathin graphitic carbon nitride (g-C3N4) nanosheets can serve as a low-cost, green, and highly efficient electrocatalyst toward the reduction of hydrogen peroxide, and further demonstrated their application for electrochemical glucose biosensing.24 Cheng et al. reported for the rst time the electrogenerated chemiluminescence (ECL) behavior of g-C3N4, which was used as a luminophore to detect trace Cu2+ with

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peroxydisulfate as the coreactant and detect rutin with triethanolamine (TEA) as a coreactant.25,26 Owing to the outstanding ECL performance of g-C3N4, the sensors exhibited high selectivity for the determination of trace Cu2+ in nanomolar concentration and low detection limit for the detection of rutin. Furthermore, owing to the sp2 hybridization of nitrogen and carbon, g-C3N4 has a stacked two-dimensional structure and the smallest direct band gap (2.7 eV),14 and thus can be easily manipulated post-functionalization or elementally doped.27 For instance, carbon nanotubes28 and fullerenes29 have been used to combine with g-C3N4 to improve the activity of g-C3N4. Conductive polymers such as polyaniline (PANI) also have been used to functionalize g-C3N4 to improve the electroconductivity and light photocatalytic activities of g-C3N4.30 Additionally, it was reported that g-C3N4 can be modied by metal nanomaterials including Pt,14 Au,21 Pd,31 and Ru32 to make hybrids suitable for applications. Although the functionalized g-C3N4 hybrids have been widely studied, their applications in the sensing eld were still at a very early stage. Li and co-workers used the carboxylated g-C3N4 and graphene hybrids to construct an ECL immunosensor for the determination of squamous cell carcinoma antigens.33 Owing to the combination of the outstanding features of g-C3N4 and graphene, the ECL immunosensor exhibited good reproducibility, high sensitivity, and long-term stability. Additionally, the Fe–g-C3N4 hybrids were used to construct a sensor for detecting glucose with high selectivity and sensitivity.34 All the above facts indicated that g-C3N4, specially functionalized g-C3N4 hybrids, would provide promising applications in the sensing system. Au nanoclusters (AuNCs),35 Ru(bpy)32+,36 1(O2)*2,3 and CdSe quantum dots37 have been used as luminophores in ECL systems. Comparing with aforementioned luminophores, gC3N4 exhibits some attractive advantages including nontoxicity, inexpensiveness, and environmentally friendliness. Furthermore, it also can be prepared on a large scale by a simple thermal pyrolysis method.21,24,34 Yet, the poor solubility of bulk g-C3N4 in water limited its applications in many elds. Some studies have reported that the g-C3N4 nanosheet which is synthesized by ultrasonication-assisted liquid exfoliation of bulk g-C3N4, has a shorter photoinduced charge carrier transferring distance, higher solubility and larger surface area,38 so as to broaden the application of g-C3N4. Inspired by above observations, it is our goal to construct a g-C3N4 hybrid based sensor for the determination of DA to expand the potential applications of g-C3N4 in the ECL eld. In the present work, bulk g-C3N4 was prepared through polymerizing melamine under 600  C. Then, the g-C3N4 nanosheet was synthesized by ultrasonication-assisted liquid exfoliation of bulk g-C3N4. Subsequently, the g-C3N4–PANI composite was obtained through an in situ deposition oxidative polymerization of the aniline monomer on the g-C3N4 nanosheet. Finally, gold nanoower (AuNF) was in situ formed on the g-C3N4–PANI composite to achieve the AuNF@g-C3N4–PANI hybrids, which were used to construct an ECL sensor for the determination of DA based on the fact that DA could increase the ECL signal at the AuNF@g-C3N4–PANI/GCE. Due to the combination of the remarkable features of the g-C3N4 nanosheet, PANI and AuNF,

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our proposed strategy would open a new avenue to develop the sensors, especially the ECL sensors since both g-C3N4 and gold nanomaterials exhibited an excellent ECL behavior.

2.

Experimental

2.1

Reagents and chemical

Melamine (2,4,6-triamino-1,3,5-trazine, 99%) was obtained from Aladdin Ltd. (Shanghai, China). Phosphate-buffered saline (PBS) solutions with various pH were prepared by using the stock solution of 0.10 M KH2PO4 and Na2HPO4. 0.10 M KCl was used as a supporting electrolyte. Aniline and gold chloride tetrahydrate (HAuCl4$4H2O) were obtained from Sigma Chemical Co. (St. Louis, MO, USA). Potassium persulfate (K2S2O8) was obtained from Shanghai Chemical Reagent Co. (Shanghai, China). Doubly distilled water was used throughout the experiments. All other chemicals reagents were of analytical grade without further purication. 2.2

Apparatus

The ECL signal was detected using a model MPI-A electrochemiluminescence analyzer (Xi'an Remax Electronic Science &Technology Co. Ltd., Xi'an, China), equipped with a photomultiplier tube (PMT) with the voltage set at 600 V and the potential scan from 0 to 1.3 V for the determination. Electrochemical signals were detected using a CHI660D electrochemical workstation (CH Instruments Co., China). Scanning electron micrographs were obtained using a scanning electron microscope (SEM, Hitachi, Japan). The FT-IR spectra were recorded using a Nexus 670 FT-IR spectrophotometer (Nicolet Instruments). The chemical composition of the surface was studied using Powder X-ray diffraction (XRD) (XRD, Purkinje General InstrumentXD-3) with Cu Ka radiation (l ¼ 0.15406 nm). 2.3

Synthesis of g-C3N4 nanosheet

The g-C3N4 nanosheet was synthesized according to the literature with minor modications.24 First, 15 g melamine was added into an alumina crucible and heated at 600  C for 2 h in a muffle furnace with a heating rate of 5  C min1. Aer cooling to room temperature, the yellow bulk g-C3N4 powder was obtained. Then, 0.25 g g-C3N4 powder was dispersed in 250 mL water with vigorous ultrasound for 10 h. Aer that, the mixture was centrifuged at 5000 rpm for 5 min to remove the remaining unexfoliated bulk g-C3N4 powder. Finally, the liquid supernatant was dried in air to obtain the g-C3N4 nanosheet. 2.4

Synthesis of g-C3N4–PANI composite

The g-C3N4 nanosheet (0.050 g) was dispersed in 15 mL water. Then, 0.017 g ammonium persulfate (NH4)2S2O8 and 0.75 mL 1.0 M HCl solution were added into the above dispersion of the g-C3N4 nanosheet. Aer the mixed solution was stirred for 40 min in an ice water bath, the aniline monomer (50 mL) was added under mechanical stirring for 8 h in an ice water bath. The prepared green g-C3N4–PANI composite was centrifuged and washed in ethanol and distilled water, respectively, and then redispersed in water for further use.

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3.

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3.1

Scheme 1 Schematic diagram of the preparation process of AuNF@gC3N4–PANI hybrids.

2.5

Synthesis of AuNF@g-C3N4–PANI hybrids

The AuNF@g-C3N4–PANI hybrids were synthesized as follows. 1.0 mL 1.0% HAuCl4 aqueous solution was added into the 15 mL of 2.0 mg mL1 g-C3N4–PANI suspension. Subsequently, the mixture was le overnight to allow the adsorption of AuCl4 on g-C3N4–PANI to form a seed solution. Then, 2.0 mL 1.0% HAuCl4 aqueous solution was added into the seed solution under stirring. Aer that, ascorbic acid (AA) was added into the mixture in situ to form AuNF on the g-C3N4–PANI composite. The mechanisms of the formation of AuNFs were described as follows. First, the seed of gold nanoparticles (AuNPs) was obtained through reducing the AuCl4 adsorbed on the g-C3N4– PANI by AA. Then, more AuNPs were formed in the surrounding of the AuNP seed to achieve AuNFs. The Scheme 1 exhibits the preparation process of the AuNF@g-C3N4–PANI hybrids.

2.6

Preparation of the sensor

The glassy carbon electrode (GCE, 4.0 mm in diameter) was polished with 0.3 mm and 0.05 mm alumina particles on silk, and then sonicated in double distilled water and ethanol, respectively. Aer that, 15 mL AuNF@g-C3N4–PANI hybrid suspensions were dripped onto the pretreated GCE surface and dried in air to obtain the sensor (AuNF@g-C3N4–PANI/GCE). For a comparison, g-C3N4/GCE and g-C3N4–PANI/GCE were prepared using the similar procedure of AuNF@g-C3N4–PANI/GCE by replacing AuNF@g-C3N4–PANI with the g-C3N4 nanosheet or g-C3N4– PANI.

2.7

Results and discussion Characterization of the AuNF@g-C3N4–PANI

The morphologies of the g-C3N4 nanosheet, g-C3N4–PANI, and AuNF@g-C3N4–PANI hybrids were characterized by SEM. As shown in Fig. 1A, the nanosheet structure of the g-C3N4 nanosheet was clearly observed. Aer being coated with PANI, the SEM image of g-C3N4–PANI composites obviously became brighter because PANI has good conductivity (Fig. 1B). For the SEM image of AuNF@g-C3N4–PANI hybrids (Fig. 1C), the bright gold nanoparticles were observed on the g-C3N4–PANI composite. Fig. 1D was the enlarged picture of Fig. 1C, as can be seen, well-dened gold nanoowers were observed, and their sizes were about 150–250 nm. The X-ray diffraction (XRD) patterns of a series of materials are presented in Fig. 2A. As seen from curve a, two diffraction peaks of bulk g-C3N4 at 27.67 and 13.30 were observed, which were indexed for graphitic materials to the (002) and (100) peaks, respectively.14 Compared with bulk g-C3N4, the g-C3N4 nanosheet presented only one diffraction peaks at 27.67 (curve b), indicating that the nanosheet lm was obtained via a liquid exfoliating method.38 Curve c is the diffraction peak of PANI, as seen, the crystallinity of PANI is weak. Aer being coated with PANI (curve d), the diffraction peaks of PANI can not be observed owing to the weak crystallinity of PANI, which was consistent with the fact reported by Ge et al.30 As seen from curve e, the AuNF@g-C3N4–PANI showed four additional peaks of Au at 38.53 , 43.57 , 63.69 , and 76.60 , which corresponds to (111), (200), (220), and (311) faces of Au, respectively. These facts further indicated that gold nanoowers (AuNFs) were in situ formed on the g-C3N4–PANI. Fig. 2B shows the FT-IR spectra of a series of materials. As seen from the FT-IR spectrum of bulk g-C3N4 (curve a), the peak at 807 cm1 was assigned to the vibration of the triazine ring. The absorption bands located in the range of 1239–1641 cm1 for stretching vibrations of C–N of bulk g-C3N4 were clearly observed. The broad peaks between 3000 and 3600 cm1

Experimental measurements

The ECL detection was performed at room temperature in 3.0 mL PBS solution containing K2S2O8. A three-electrode system was used through detection. A modied glassy carbon electrode was used as the working electrode, while a platinum wire as the auxiliary electrode, and an Ag/AgCl (sat.) electrode as the reference electrode. In this work, dopamine could enhance the ECL signal of AuNF@g-C3N4–PANI/GCE in K2S2O8 solution. The determination was based on the change in the ECL intensity (DI ¼ I0  It), here, It and I0 are the ECL signals with and without DA, respectively.

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Fig. 1 SEM photos of the g-C3N4 nanosheet (A), g-C3N4–PANI (B) and AuNF@g-C3N4–PANI hybrids (C), the enlarged picture of AuNF@g-C3N4–PANI hybrids (D).

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(A) the X-ray diffraction patterns (XRD) and (B) FT-IR spectra of (a) bulk g-C3N4, (b) g-C3N4 nanosheet, (c) PANI, (d) g-C3N4–PANI and (e) AuNF@g-C3N4–PANI.

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Fig. 2

correspond to N–H stretching and the interactions of hydrogenbonding. Curve b was the FT-IR spectrum of the g-C3N4 nanosheet. As seen, the absorption bands of the g-C3N4 nanosheet were nearly identical with bulk g-C3N4, indicating that no more functional groups formed during the preparation of the g-C3N4 nanosheet. Curve c was the FT-IR spectrum of PANI, the C]C stretching of the quinonoid and benzenoid rings at 1585 and 1507 cm1 for PANI were observed. Aer the nanosheet was combined with PANI (curve d), the FT-IR spectra of g-C3N4 and PANI are observed in curve d. Aer being coated with AuNF, the FT-IR spectrum of AuNF@g-C3N4–PANI (curve e) was nearly identical to that of g-C3N4–PANI (curve d), which was due to the fact that AuNF did not present the characteristic absorption bands in the FT-IR spectrum.

3.2

ECL and CV behavior of the modied electrode

In order to investigate the ECL property of g-C3N4, the g-C3N4 modied electrode (g-C3N4/GCE) was rst tested in 0.10 M PBS without (curve a) and with 80 mM K2S2O8 (curve b), respectively. The results are shown in Fig. 3A. As seen from curve a, an ECL peak with a weak intensity was observed at the potential of approximately 1.29 V at g-C3N4/GCE without K2S2O8, indicating that the g-C3N4 was a luminophore. In this case, the ECL mechanism was described as follows:15 First, the g-C3N4 was reduced to g-C3N4c (1) and the dissolved O2 was reduced to

Fig. 3 (A) ECL behaviors of g-C3N4/GCE in 0.10 M PBS (pH 7.0) without (a) and with 80 mM K2S2O8 (b); ECL behaviors of g-C3N4– PANI/GCE (c) and AuNF@g-C3N4–PANI/GCE (d) in 0.10 M PBS (pH 7.0) with 80 mM K2S2O8. (B) CV curves recorded on AuNF@g-C3N4–PANI/ GCE in 0.10 M PBS (pH 7.0) in the absence (a) and presence of 1.0 mM (b) DA.

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OHc (2) and (3). Then, the OHc reacted with g-C3N4c to produce the g-C3N*4 (4). When the excited state g-C3N*4 fell to the ground state, light was emitted (9). Compared with curve a, the ECL intensity obviously enhanced in the presence of K2S2O8 (curve b), indicating that K2S2O8 as the coreactant played a signicant role in the process of ECL of g-C3N4. The possible ECL mechanism was described as follows. First, the g-C3N4 was reduced to g-C3N4c (1). Meanwhile, S2O82 was reduced to SO4c, a strong oxidant (5). Then, the SO4c reacted with g-C3N4c to produce the g-C3N*4 (6). Another possible mechanism to generate g-C3N*4 can be described as follows. The SO4c reacted with g-C3N4 to generate the g-C3N4+ (7). Subsequently, the g-C3N4+ reacted with g-C3N4c to produce g-C3N*4 (8). When g-C3N*4 was decayed back to g-C3N4, the emission was obtained (9). Corresponding mechanisms are presented as follows:15,25 g-C3N4 + e / g-C3N4c

(1)

O2 + 2H2O + 2e / 2H2O2

(2)

H2O2 + e / OH + OHc

(3)

OHc + g-C3N4c / g-C3N*4 + OH

(4)

S2O82 + e / SO4c + SO42

(5)

g-C3N4c + SO4c / g-C3N*4 + SO42

(6)

g-C3N4 + SO4c / g-C3N4+ + SO42

(7)

g-C3N4+ + g-C3N4c / g-C3N*4 + g-C3N4

(8)

g-C3N*4 / g-C3N4 + hv

(9)

and/or

Obviously, the ECL signal with S2O82 as coreactants is much higher than that with only dissolved O2 as coreactants. This fact was consistent with the literature reported by Chen et al.15 In our present work, K2S2O8 was chosen as the coreactant to improve the sensitivity of the prepared sensor. The ECL behaviors of g-C3N4–PANI/GCE and AuNF@g-C3N4– PANI/GCE have been investigated in 0.10 M PBS containing 80 mM K2S2O8, and the results are presented in curve c and d of Fig. 3A, respectively. As seen from curve c, although the enhancement in ECL intensity was unobvious aer PANI was induced onto g-C3N4, PANI was important for the coating of AuNF. When AuNF was induced on g-C3N4–PANI (curve d), the ECL intensity enhanced greatly and the AuNF@g-C3N4–PANI/ GCE exhibited the strongest ECL signal as compared to g-C3N4/ GCE and g-C3N4–PANI/GCE, indicating that AuNF could enormously enhance the ECL intensity. The combination of the gC3N4 nanosheet and AuNF would be benecial to the improvement of the sensitivity for the determination of DA. The CV behavior of the AuNF@g-C3N4–PANI/GCE was investigated in the absence and presence of DA. As shown in Fig. 3B, no redox peaks were observed at the AuNF@g-C3N4–

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PANI/GCE without DA (curve a). However, a pair of well-dened redox peaks appeared in the presence of DA. The oxidation peak appeared at 0.20 V, while the reduction peak appeared at 0.11 V. The facts indicating that the AuNF@g-C3N4–PANI hybrids exhibited excellent electrocatalytic activity for DA.

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3.3

Optimization of experimental conditions

The dependence of the ECL intensity on the pH of tested solutions and the concentration of K2S2O8 was studied in the the AuNF@g-C3N4–PANI/GCE in 0.10 M PBS containing 0.50 mM dopamine. The change in ECL intensity (DI) against the pH of PBS ranged from 5.0 to 9.0 is shown in Fig. 4A. It was found that the DI achieved the maximum value at pH 7.0. Thus, the optimal pH of 7.0 was chosen in the further study to obtain a high analytical sensitivity for ECL detection of DA. Fig. 4B exhibited the effect of the concentration of K2S2O8 on the DI in pH 7.0 PBS with 0.50 mM dopamine. As seen, the DI increased with the concentration of K2S2O8 and leveled off aer 80 mM of K2S2O8. Thus, 80 mM was chosen as the optimal concentration of K2S2O8. 3.4

ECL detection of dopamine

The AuNF@g-C3N4–PANI/GCE was used to detect DA under the optimal conditions. As shown in Fig. 5A, with the increase in the concentration of DA from 5.0  109 to 1.6  106 M, the ECL signal linearly increased. As seen in Fig. 5B, curve a is the calibration curve between DI and the concentration of DA. The corresponding calibration equation was DI (a.u) ¼ 5.52C + 595.35 (R ¼ 0.9967), with a detection limit (signal to noise ¼ 3) of 1.7  109 M. Li et al. reported an enhanced ECL sensor for the determination of DA based on bovine serum albuminstabilized AuNCs. In their work, the mechanism was explained as follows. When DA was absorbed on the ITO, the electrons can transfer from the DA to the conduction band of ITO, then transfer to the LUMO of AuNCs, which is propitious to generate Au25c.39 In our work, the ECL enhancement mechanism of DA may be similar to the above case. A charge transfer complex was formed between DA and AuNF@g-C3N4–PANI, and the electron could transfer more feasible to the LUMO of g-C3N4, resulting in the generation of g-C3N4c. The more DA was adsorbed on the surface of AuNF@g-C3N4–PANI, the more g-C3N4c can be generated, resulting in an enhancement in the ECL intensity.

Effect of pH on DI in 0.10 M PBS containing 80 mM K2S2O8 (A); effect of K2S2O8 concentration on DI of the AuNF@g-C3N4–PANI/GCE in 0.10 M PBS (pH 7.0) (B). Fig. 4

6560 | Analyst, 2014, 139, 6556–6562

Fig. 5 (A) The ECL response of AuNF@g-C3N4–PANI/GCE for DA in 0.10 M PBS (pH 7.0) containing 80 mM K2S2O8, curve a / i: 0.00, 5.00, 155, 405, 555, 755, 1005, 1255, and 1555 nM DA. (B). Calibration curves of AuNF@g-C3N4–PANI/GCE (a), g-C3N4/GCE (b) and g-C3N4–PANI/ GCE (c).

As control experiments, the ECL response of g-C3N4/GCE and g-C3N4–PANI/GCE towards DA was also investigated under the optimal conditions (Fig. 5B). As seen, the linear range of the aforementioned sensors were 8.0  109 to 6.6  107 and 1.0  108 to 1.2  107, respectively. Compared to the g-C3N4/ GCE and g-C3N4–PANI/GCE, the AuNF@g-C3N4–PANI/GCE exhibited a wider linear range and a lower detection limit. A comparison between this work and other reports are exhibited in Table 1. As seen, in this work, the detection limit achieved 109 M, which is comparable or better than that of previous reports. Furthermore, comparing with our previous work,3,49 this work not only exhibited a wider linear range and lower detection limit, but also opened a new avenue to develop ECL sensors based on g-C3N4–S2O82 ECL systems. The above fact indicated that the AuNF@g-C3N4–PANI/GCE exhibited outstanding performance for the detection of DA owing to the combination of the remarkable features of the g-C3N4 nanosheet and AuNF. 3.5

Stability and interference determination of the sensor

Fig. 6 shows the ECL intensity of the AuNF@g-C3N4–PANI/GCE for the successive measurements (n ¼ 10) with 0.60 mM DA under the optimum conditions. The relative standard deviation (R.S.D.) was 1.3%. The storage stability of the AuNF@g-C3N4– PANI/GCE was also measured in the peroxydisulfate solution with 0.60 mM DA. It was observed that the ECL intensity lost 11.6% of the original ECL intensity aer two weeks, showing an acceptable stability. The selectivity is one of the major concerns for biosensors. To examine the selectivity of the AuNF@g-C3N4–PANI modied GCE, the interfering substances including 0.10 mM Na+, K+, Cl, Mg2+, NO3, uric acid and ascorbic acid were tested. It was found that the above interfering substances do not cause a noticeable interference to the detection of 0.60 mM DA. Thus, the AuNF@g-C3N4–PANI/GCE has high selectivity for the determination of DA. 3.6

Analytical application of the sensor in real samples

The AuNF@g-C3N4–PANI modied electrode was used to detect the recoveries of DA in the diluted dopamine hydrochloride

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Analyst Comparison of this work with other ECL biosensors for the detection of DA

Electrodes

Method

Reduced graphene oxide/multiwall carbon nanotubes/ gold nanoparticles/GCE Electrochemically reduced graphene oxide electrode

ECL DPVa

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CdS–polyamidoamine incorporating electrodeposited gold nanoparticle/GCE Polypyrrole–reduced graphite oxide core–shell microspheres/GCE

ECL DPV

Nickel oxide nanoparticles and carbon nanotubes within a dihexadecylphosphate lm/GCE Porous carbon/GCE

CVb

Ag2Se quantum Dots/GCE

ECL

Au@carbon dots–chitosan/GCE

DPV

Organic electrochemical transistors with graphene-modied gate electrodes Mono-dispersed Mn3O4 nanoparticles/GCE

Amperometric measurement DPV

Polyethyleneimine-wrapped carbon nanotubes/GCE

DPV

AuNF@g-C3N4–PANI/GCE

ECL

a

DPV, differential pulse voltammetry.

b

DPV

Linear range (M) 2.0  107 7.0  106 1.0  107 1.0  105 5.0  108 1.0  105 1.0  108 1.0  105 7.0  108 4.8  106 9.0  109 3.0  107 5.0  107 1.9  105 1.0  108 1.0  104 5.0  109 1.0  106 1.0  106 7.0  106 5.0  108 4.0  106 5.0  109 1.6  106

Detection limit (M)

References

to

6.7  108

3

to

1.0  107

40

to

1.2  108

41

to

1.0  109

42

to

5.0  108

43

to

2.9  109

44

to

1.0  107

45

to

1.0  109

13

to

5.0  109

46

to

1.0  107

47

to

5.7  109

48

to

1.7  109

This work

CV, cyclic voltammetric proles.

injection sample by the standard addition method and the results are summarized in Table 2. The average recoveries ranged between 93.4% and 102% in the dopamine hydrochloride injection sample, indicating that the AuNF@g-C3N4–PANI/ GCE has potential applications for the determination of DA in the eld of clinical disease diagnosis.

4. Conclusions

Fig. 6

The ECL stability of the AuNF@g-C3N4–PANI/GCE.

Table 2 Recoveries of DA in the hydrochloride injection sample at AuNF@g-C3N4–PANI/GCE

Sample Diluted injection

Added (nM)

Found (nM)

Recovery (%)

25.0 45.0 75.0 105 135

24.7 45.8 73.9 101 127

98.8 102 98.5 95.9 93.4

This journal is © The Royal Society of Chemistry 2014

In this paper, a novel ECL biosensor based on AuNF@g-C3N4– PANI hybrids for the determination of DA was developed. As a luminophore, the g-C3N4 nanosheet was used to construct the ECL biosensor, which may expand the application of ECL in the eld of analytical chemistry. Due to the combination of the excellent ECL behaviors of g-C3N4 and AuNF, the AuNF@gC3N4–PANI nanocomposites provide a promising material to develop ECL dopamine sensors. Comparing with previous work, the resulting sensor shows outstanding performances including high sensitivity and low limit of detection for the determination of DA.

Acknowledgements This work was supported by the National Natural Science Foundation of China (21075100, 21275119), Ministry of Education of China (Project 708073), Research Fund for the Doctoral Program of Higher Education (RFDP) (20110182120010), Natural Science Foundation of Chongqing

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City (CSTC-2011BA7003, CSTC-2010BB4121, CSTC2014JCYJA20005), and the Fundamental Research Funds for the Central Universities (XDJK2012A004).

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Enhanced electrochemiluminescence sensor for detecting dopamine based on gold nanoflower@graphitic carbon nitride polymer nanosheet-polyaniline hybrids.

In this work, an enhanced electrochemiluminescence (ECL) sensor based on gold nanoflower@graphitic carbon nitride polymer nanosheet-polyaniline hybrid...
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