Biosensors and Bioelectronics 57 (2014) 232–238

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Overoxidized polyimidazole/graphene oxide copolymer modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid, guanine and adenine Xiaofang Liu, Ling Zhang, Shaping Wei n, Shihong Chen n, Xin Ou, Qiyi Lu Key Laboratory of Luminescent and Real-Time Analytical Chemistry, Ministry of Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, PR China

art ic l e i nf o

a b s t r a c t

Article history: Received 12 January 2014 Received in revised form 6 February 2014 Accepted 9 February 2014 Available online 20 February 2014

In the present work, a novel strategy based on overoxidized polyimidazole (PImox) and graphene oxide (GO) copolymer modified electrode was proposed for the simultaneous determination of ascorbic acid (AA), dopamine (DA), uric acid (UA), guanine (G) and adenine (A). The copolymer was characterized by the scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). Due to the synergistic effects between PImox and GO, the proposed electrode exhibited excellent electrochemical catalytic activities and high selectivity and sensitivity toward the oxidation of AA, DA, UA, G and A. The peak separations between AA and DA, AA and UA, UA and G, and G and A were 140 mV, 200 mV, 380 mV and 300 mV, respectively. The linear response ranges for AA, DA, UA, G and A were 75–2275 μM, 12–278 μM, 3.6–249.6 μM, 3.3–103.3 μM and 9.6–215 μM, respectively, and corresponding detection limits were 18 μM, 0.63 μM, 0.59 μM, 0.48 μM and 1.28 μM. & 2014 Elsevier B.V. All rights reserved.

Keywords: Polyimidazole Graphene oxide Simultaneous determination Small biomolecules

1. Introduction Ascorbic acid (AA) is popularly known for its antioxidant properties and presents in the human diet as a vital vitamin. It has been used for the prevention and treatment of scurvy, common cold, mental illness, cancer and AIDS (Noroozifar and Motlagh, 2003). Dopamine (DA) is an important neurotransmitter in the mammalian central nervous system (Huang et al., 2008). Abnormal levels of DA will lead to neurological disorders such as Parkinsonism and schizophrenia (Wightman et al., 1988; Martin, 1998). Uric acid (UA) is the primary end product of purine metabolism. The extreme abnormalities of UA levels will lead to some diseases, such as gout and hyperuricaemia (Dutt and Mottola, 1974). Adenine (A) and guanine (G) are the main nucleotides in deoxyribonucleic acid (DNA). The abnormal changes of A and G in organism suggest the deficiency and mutation of the immunity system and may indicate the presence of various diseases (Shahrokhian et al., 2012). AA, DA, UA, A and G usually coexist in physiological fluids such as serum and aurine (Niu et al., 2013; Balamurugan et al., 2013). Therefore, a sensitive and selective method for simultaneous determination of them is highly

n

Corresponding authors. Tel./fax: þ86 23 68253172. E-mail addresses: [email protected] (S. Wei), [email protected] (S. Chen). http://dx.doi.org/10.1016/j.bios.2014.02.017 0956-5663 & 2014 Elsevier B.V. All rights reserved.

desirable for biomedical chemistry and diagnostic research. Unfortunately, previous reports only focus on individual or simultaneous determination of two to four compounds. For example, Huang et al. (2014) utilized Au@carbon dots–chitosan composite as an electrode modifier to detect dopamine. Kul et al. (2013) used poly(Nile blue A) and functionalized multi-walled carbon nanotube modified electrodes to detect ascorbic acid. Sheng et al. (2012) reported the nitrogen doped graphene modified electrode for simultaneous determination of ascorbic acid, dopamine, and uric acid. Yin et al. (2010) utilized the graphene–Nafion composite film modified electrode to simultaneously determine guanine and adenine. Recently, Niu et al. (2013) used the nano-Au/DNA/nano-Au/poly(SFR) composite modified electrode for simultaneous determination of dopamine, uric acid, guanine, and adenine. To the best of our knowledge, no report is available in the literature for simultaneous determination of AA, DA, UA, G, and A. In the past few decades, electrochemical techniques have received considerable interest for the detection of small biomolecules owing to their high sensitivity, rapid response, and low expense (Zhou et al., 2013; Huang et al., 2011). However, it is very difficult to simultaneously determine five species directly at bare electrodes because the overlapping of their oxidation potentials and the pronounced electrode fouling often result in poor selectivity and reproducibility at bare electrodes (Premkumar and Khoo, 2005; Kumar et al., 2005). To overcome this problem, various materials

X. Liu et al. / Biosensors and Bioelectronics 57 (2014) 232–238

have been utilized to construct and modify the electrodes, such as polymers (Balamurugan and Chen, 2007; Zheng et al., 2008), selfassembled monolayers (Kalimuthu and John, 2006; Shervedani et al., 2006), and nanomaterials including carbon nanotubes (Cui et al., 2012; Abbaspour and Noori, 2011), nanoparticles (Thiagarajan and Chen, 2007; Zhang and Jiang, 2005), and metal oxide (Shakkthivel and Chen, 2007; Li et al., 2000). Specifically, graphene oxide (GO) has attracted considerable attention because it not only owns some properties of graphene with large surface area, thermal, mechanical properties, and capability of chemical modification, but also possesses some other properties such as hydrophilicity, multiple oxygen moieties, and controllable electronic properties (Zeng et al., 2013). Meanwhile, some investigations have been conducted for the application of conducting polymers in the area of sensors (Nie et al., 2013; Kamyabi et al., 2013; Zhuang et al., 2011; Qian et al., 2013). Among variety of conducting polymers, polyimidazole (PIm) is a technologically important material owing to its unique electrical, electrochemical, and optical properties. Imidazole (Im) can be polymerized on the surface of electrode to form chemically stable homogeneous PIm film with controlled thickness (Wang et al., 2012). Furthermore, this PIm film can be overoxidized at high anodic potentials to produce overoxidized polyimidazole (PImox) film. During the overoxidation process, oxygen containing groups such as carbonyl and carboxyl were introduced to the imidazole unit, thus resulting in the improvement of the permselective and antifouling properties of the sensor. In this paper, the composites of GO and PImox were prepared to construct a sensor for simultaneous determination of AA, DA, UA, G, and A. The obtained PImox–GO copolymer exhibited excellent catalytic activity to AA, DA, UA, G, and A. The electrochemical behaviors of the sensor were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV).

2. Experimental 2.1. Reagents and materials Graphene oxide (GO) was obtained from Nanjing Xianfeng Nano Co. (Nanjing, China). Imidazole (Im) was purchased from Sigma Chemical Co. (St. Louis, Mo, USA). Sodium dodecylsulfate (SDS), uric acid, ascorbic acid, dopamine, adenine, and guanine were purchased from Aladdin in Chemical Reagents Co. Ltd. (Chengdu, China). Phosphate-buffered saline (PBS) solutions (0.10 M) at various pH values were prepared using 0.10 M Na2HPO4 and 0.10 M KH2PO4. The supporting electrolyte was 0.10 M KCl. 2.2. Apparatus Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) measurements were performed using a CHI 660A electrochemical workstation (Shanghai Chenhua Instrument, Co., China). Scanning electron microscopy (SEM) was carried out using a Hitachi scanning electron microscope (SEM, S-4800, Hitachi, Japan). Transmission electron microscopy (TEM) was conducted using a TECNAI 10 (PHILIPS FEI Co., Holland). Atomic force microscopy (AFM) images were taken using a scanning probe microscope (Vecco, USA). X-ray photoelectron spectroscopy (XPS) measurements were carried out with a VG Scientific ESCALAB250 spectrometer, using Al KR X-ray (1486.6 eV) as the light source. Fourier transform infrared spectroscopy (FT-IR) measurement was carried out using a Jasco FT/IR300E instrument (Jasco Ltd., Tokyo, Japan). The conventional three-electrode system included a platinum wire auxiliary electrode, a saturated calomel reference electrode (SCE) and the

233

modified electrode as the working electrode. All measurements were carried out at room temperature. 2.3. Preparation of the sensor A glassy carbon electrode (GCE, diameter 4.0 mm) was carefully polished with 0.3 and 0.05 μm alumina slurry, and then washed thoroughly with ethanol and ultrapure water. 0.30 mol imidazole monomer was dispersed into 3.0 mL GO solution (5.0 mg mL  1) containing 0.30 mol SDS under ultrasonication for 60 min at room temperature. The PIm–GO composite film was fabricated on the electrode surface by cyclic voltammetry (CV) scanning of GCE in the above mixture solution from  0.20 to 0.80 V with a scan rate of 0.10 V s  1 for 8 cycles. Subsequently, the PIm–GO modified electrode was washed with double distilled water and then transferred into 0.10 M PBS (pH 3.0) for electrochemical oxidation at þ1.8 V for 250 s. The electrode was carefully rinsed with double-distilled water and dried in air as PImox–GO/GCE. For comparison, PImox/GCE and GO/GCE were prepared using the similar procedure.

3. Results and discussion 3.1. Characterization of the PImox–GO TEM and SEM were employed to investigate the morphologies of modified films. The TEM and SEM images of GO are shown in Fig. 1A and B, respectively. As presented in Fig. 1A and B, the typically crumpled and wrinkled structure of GO was observed. Furthermore, the monolayer structure also could be clearly seen. Fig. 1C shows the SEM image of PImox film without GO, which presented a porous structure. Fig. 1D shows the SEM image of nanocomposite film of PImox–GO. As expected, the GO nanosheets were covered with a porous PImox film, indicating that the PImox–GO nanocomposite film was successfully fabricated on the electrode surface by CV scanning and electrochemical oxidation process. AFM was conducted to observe the surface topography of PImox–GO nanocomposite and a typical topographic AFM image is shown in Fig. 1E. From Fig. 1E, a porous layer of composite film was clearly observed, which was due to the electrodeposition of imidazole monomer on the indium tin oxide (ITO) surface. Herein, GO could not be clearly observed in the AFM image of PImox–GO. It was probable that the GO nanosheets were covered with a uniform nanoparticle layer of PImox. FT-IR spectra were employed to characterize the formation of the PIm–GO copolymer. As seen from Fig. 2A (curve a), the FT-IR spectrum of PIm exhibited CQC band of aromatic ring at 1642 cm  1 (Tian et al., 2013) and CQN– stretching band at 1468 cm  1 (Raj et al., 2012). In addition, two peaks at 2850 and 2918 cm  1 were due to C–H stretching vibrations. Fig. 2A (curve b) shows the FT-IR spectrum of PIm–GO nanocomposite. Compared with the FT-IR spectrum of PIm (curve a), the peak of CQC obviously became stronger in the FT-IR spectrum of PIm–GO (curve b). Furthermore, two new peaks appeared at 1204 cm  1 and 3435 cm  1 (curve b), which were ascribed to C–O band and O–H band of GO, respectively (Yang et al., 2014). This fact demonstrated that PIm–GO nanocomposite was successfully fabricated. To gain the information concerning the chemical composition in PImox–GO nanocomposite, XPS measurements were performed on the PIm–GO and PImox–GO modified films and the results are shown in Fig. 2B. As seen from Fig. 2B, a N 1s peak was observed at the XPS spectra of both PIm–GO (curve a) and PImox–GO (curve b), which was attributed to imidazole. In addition, both PIm–GO

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Fig. 1. (A) TEM image of GO. SEM images of (B) GO, (C) PImox and (D) PImox–GO films. (E) AFM image of PImox–GO films.

and PImox–GO illustrated the C 1s and O 1s peaks at 285.0 and 531.6 eV, respectively. The O/C intensity ratio increased from 1.28 of PIm–GO to 1.67 of PImox–GO after electrochemical overoxidation, indicating that the overoxidation process can introduce oxygen containing groups during the formation of PImox–GO. The C 1s spectra of PIm–GO (Fig. 2C) and PImox–GO (Fig. 2D) showed four peaks located at binding energies of 285.0, 286.4, 287.84, and 289.14 eV, corresponding to sp2 carbon, C–O bond, CQO bond, and HO–CQO bond, respectively. Compared with the C 1s spectrum of PIm–GO, the C 1s spectrum of PImox–GO showed an increased intensity of oxygen groups, indicating that oxygen containing groups can be introduced during the overoxidation process. EIS was employed to probe the interface properties of surfacemodified electrodes and the results are presented in Fig. 3. The semicircle diameter in the impedance spectrum equals to the electron transfer resistance (Ret), which controls the electron

transfer kinetics of the redox probe at the electrode interface. As seen from Fig. 3, when PImox–GO was modified on the GCE (curve b), the semicircle domain increased obviously compared with the bare GCE (curve a). The reasonable explanation may be that Pimox–GO modified film would hinder the electron transfer of the electrochemical probe ferricyanide anions, which led to an increase in Ret value. 3.2. Optimization of detection conditions The effect of pH value on the simultaneous determination of AA, DA, UA, G, and A at PImox–GO/GCE was investigated by differential pulse voltammetry (DPV). Fig. 4 presents the effect of pH value on the peak current and peak potential for 868 μM AA, 60 μM UA, 55 μM DA, 40 μM G, and 32 μM A coexisting in various pH values of PBS. As seen from Fig. 4A, the peak currents of AA, G, and A reached the maximum at pH 3.0, and UA and DA produced

X. Liu et al. / Biosensors and Bioelectronics 57 (2014) 232–238

235

Intensity (a.u)

9600

Intensity (a.u)

Intensity (a.u)

a b C=N C=C O-H

C-H

8800 8000 7200

O 1s

396

402

408

Binding energy (eV)

ITO

C-O

C 1s N 1s

b a

4000

3000

2000

1000

600

Wavenumber / cm-1

b C-O c C=O d HO-C=O

b C-O c C=O b

b c 284

d HO-C=O

a

a

280

200

a sp2C

Intensity (a.u)

a sp2C

Intensity (a.u)

400

Binding energy (eV)

c

d

288

292

Binding energy (eV)

280

284

288

d 292

Binding energy (eV)

Fig. 2. (A) FTIR spectra of (a) PIm and (b) PIm–GO. (B) The XPS spectra of (a) PIm–GO and (b) PImox–GO. The C 1s XPS spectra of (C) PIm–GO and (D) PImox–GO.

-Z'' im / ohm

400

200 b a

0 0

500

1000

1500

Z' re / ohm Fig. 3. EIS of (a) bare GCE and (b) PImox–GO/GCE in 5.0 mM K3[Fe(CN)6]/K4[Fe (CN)6] (1:1) solution.

the highest response at pH 2.0. Furthermore, the peak currents of DA in pH 3.0 and 5.0 were higher than 4.0, which were consistent with those reported in the literature (Noroozifar et al., 2013). The reasonable explanation may be as follows. AA (pKa ¼4.10), DA (pKa ¼8.87), UA (pKa ¼5.4), G (pKa ¼9.2), and A (pKa ¼9.8) exist as cationic form at lower pH due to protonation. The difference in pKa of above five species would result in a mutual influence between them in the existing form when they coexist in the solution. The PImox film can be regarded as polymer films with negative charge (Wang et al., 2012), which would effectively collect the cations and reject the diffusion of anions to the films due to the electrostatic

interaction. When they coexist in the solution, pH 3.0 may be more beneficial to the adsorption and electrochemical oxidation of AA, G, and A on the PImox–GO composite modified electrode, and pH 2.0 is more beneficial to the adsorption and electrochemical oxidation of UA and DA. Fig. 4B shows the effect of pH on the oxidation potentials of AA, DA, UA, G, and A at PImox–GO/GCE. As observed, the oxidation potentials shifted negatively with increasing pH, indicating that protons participated in the electrode reaction process. Although there was no significant difference on the separation of peak potentials for five species from pH 2.0 to pH 5.0, the maximum separation of peak potentials for AA–DA was observed at pH 3.0. Furthermore, UA, G, and A can be completely separated at this pH. Considering the effect of pH on both peak currents and the separations of peak potentials, pH 3.0 PBS was chosen as the supporting buffer solution for further experiments. The ratio of imidazole monomer with GO in the electropolymerization process was optimized to obtain an efficient sensor toward small biomolecules detection. The changes of DPV responses with the concentration of imidazole monomer in the range of 0.05–0.20 M under constant GO concentration (5.0 mg mL  1) were investigated and the results are shown in Fig. S1 (see Supplementary material). As seen from Fig. S1, the maximum DPV response was obtained at the modified electrode with 5.0 mg mL  1 GO and 0.10 M imidazole monomer for the electropolymerization. Thus, this optimal ratio of imidazole monomer with GO for electropolymerization was employed to prepare the sensor in our experiment. Generally, the thickness of the electropolymerized film would impact on the current response of the electrode. A thicker film would reject the interferences, but the sensitivity to analyte would be lowered and response time would be increased. For a too thin

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40 1.2 A A DA 24

E/V

I / μA

32 0.8

G

G AA

16

UA 2

3

4

5

6

pH

0.4

UA DA AA

0.0 2

3

4

5

6

pH

Fig. 4. Effect of pH on (A) DPV peak current and (B) DPV peak potential for the oxidation of 868 μM AA, 60 μM UA, 55 μM DA, 40 μM G, and 32 μM A in 0.10 M PBS.

film, the permselective behavior would not be satisfactory. Therefore the electropolymerization circles of PIm–GO were investigated. Fig. S2 displays the effect of electropolymerization circles of PIm–GO on the DPV responses towards five species under the same electrochemical oxidation time of 250 s at PImox–GO/GCE. As observed, the DPV response currents of five substances reached the maximum at 8 circles. Thus, the electropolymerized cycles of 8 was employed to prepare the sensor in following experiments. Since oxygen containing groups can be introduced on the PImox– GO film during the overoxidization process, different electrochemical oxidation times would affect the electrochemically catalytic activities of the sensor towards the five substances. Fig. S3 depicts the DPV response of PImox–GO/GCE for five species with different electrochemical oxidation times of PImox–GO composite under the same electropolymerization circles of PIm–GO (8 circles). Obviously, the maximum DPV response currents for five substances were obtained at electrochemical oxidation time of 250 s. Thus, electrochemical oxidation time of 250 s was chosen in the following experiments. 3.3. Cyclic voltammetric behaviors of the modified electrode In order to obtain the effective surface areas of the bare GCE and PImox–GO GCE, CV experiments were performed at bare GCE (Fig. S4A) and PImox–GO GCE (Fig. S4B) with various scan rates in 5.0 mM [Fe(CN)6]3  /[Fe(CN)6]4  , according to Randles–Sevcik equation: I P ¼ 2:69  105  D0 1=2  A  v1=2  n3=2  C 0 For [Fe(CN)6]3 /[Fe(CN)6]4 (5.0 mM), n¼ 1, C0 ¼5  10  6 mol cm  3, and D0 ¼1  10  5 cm2 s  1, the effective surface areas of the bare GCE and PImox–GO GCE were estimated to be 0.108 cm2 and 0.131 cm2, respectively, indicating that the PImox–GO modified film can increase the effective surface area of modified GCE. Cyclic voltammetric behavior of PImox–GO/GCE was investigated in 0.10 M pH 3.0 PBS in the presence of alone AA, DA, UA, G, or A. As seen from Fig. S5, the oxidation peak of AA, DA, UA, G, and A appeared at about 180, 320, 520, 900 and 1200 mV, respectively. In order to demonstrate the performance of PImox–GO/GCE, the CV behaviors of different modified electrodes were compared in 0.10 M PBS (pH 3.0) containing the mixture of 1096 μM AA,123 μM DA, 119 μM UA, 43 μM G, and 80 μM A. Fig. S6 (curve a) depicts the DPV response at the bare GCE. As shown in curve a, an inconspicuous anodic peak at 0.9 V can be attributed to the oxidation of G. However, the oxidation peaks of AA, DA, and UA completely overlapped and came into a broad peak. Furthermore, the anodic peak of A could not be observed. Obviously, it is impossible to simultaneously detect these compounds at the bare GCE. For the GO/GCE (curve b) and PImox/GCE (curve c), though

the oxidation peaks of DA, UA, G, and A were obviously observed at 0.35 V, 0.53 V, 0.88 V and 1.2 V, respectively, the oxidation peak of AA was indistinguishable and small at 0.23 V, indicating the infeasibility of the simultaneous determination of AA, DA, UA, G, and A at GO/GCE and PImox/GCE. As expected, PImox–GO/GCE (curve d) resolved the merged voltammetric peak into five welldefined peaks at approximate potentials of 0.18 V, 0.32 V, 0.52 V, 0.90 V, and 1.2 V. Furthermore, a remarkable increase in each peak current was observed with comparison to GO/GCE and PImox/GCE. This fact showed that the simultaneous determination of AA, DA, UA, G, and A could be achieved at PImox–GO/GCE. The reasons may be as follows. First, GO with high density of oxygen containing groups would provide a selective interface via hydrogen bonds with the proton-donating group of AA, DA, UA, G, and A, which would be beneficial to catalyze the oxidation of five substances at the surface of the electrode. Second, during the overoxidization process, the oxygen containing groups such as C–O, CQO and OH–CQO can be generated on the PImox–GO film, which also could provide a selective interface via hydrogen bonds with the proton-donating group of AA, DA, UA, G, and A, thus endowing the PImox–GO film with excellent cation exchange and molecular sieve properties. Third, porous PImox covered onto the GO resulted in an increase in the effective surface area of modified GCE. Based on the synergic effect of GO and PImox film to facilitate the discrimination of AA, DA, UA, G, and A, the modified electrode displayed excellent catalytic activity and selectivity toward the oxidation of AA, DA, UA, G, and A. 3.4. Simultaneous detection of AA, DA, UA, G, and A The primary intention of the present investigation is to simultaneously detect AA, DA, UA, G, and A. Fig. 5A displays the DPV curves of different concentrations AA, DA, UA, G, and A in the mixture at PImox–GO/GCE. As expected, five well-separated peaks were observed, and all of peak currents increased linearly with increasing the concentration of AA, DA, UA, G and A. This experiment result indicated that the simultaneous discrimination of above five species was feasible in mixture solution using DPV. For further demonstrating the feasibility of the modified electrode for the simultaneous determination of AA, DA, UA, G, and A, the electrooxidation of each species in the mixture was investigated when the concentration of one species changed, while the concentration of other four species remained constant. Fig. 5B shows the DPV curves with varied concentration of AA and constant concentration of DA (55 μM), UA (60 μM), G (16 μM), and A (50 μM). The peak currents of AA increased linearly with an increase in AA concentration from 75 to 2275 μM, with the linear function Ip,AA (μA)¼10.32þ 0.030CAA (μM) (R¼ 0.9980), and a detection limit of 18 μM. Fig. 5C depicts

X. Liu et al. / Biosensors and Bioelectronics 57 (2014) 232–238

237

80

75

60 I / μΑ

40

40 20

50

I / μΑ

I / μΑ

30

20

0

1

2

C / mM

25 10 0 0.0

0.4

0.8

1.2

0.0

0.4

0.8

E/V

1.2

E/V

80

75

UA

50 I / μΑ

I / μΑ

60

60

40

50

20 0

150

I / μΑ

I / μΑ

75

DA

80

300

C / μΜ

40

25 0

0

100

200 μΜ

25 20 0 0.0

0.4

0.8

0.0

1.2

0.4

60

60

60 30

I / μA

I / μA

40

50 0

60 C / μM

I / μΑ

I / μΑ

A

75

15

20

1.2

80

G 45

40

0.8

E/V

E/V

120

20

0

100 c / μΜ

200

25

0

0 0.0

0.4

0.8

1.2

E/V

0.0

0.4

0.8

1.2

E/V

Fig. 5. DPV curves at PImox–GO/GCE in 0.10 M PBS (pH 3.0) for (A) simultaneous response to AA (75, 150, 225, 300, 375, 630, 810, and 1215 μM), DA (7, 14, 28, 42, 56, 98, 126, and 196 μM), UA (10, 20, 30, 46, 62, 98, 128, and 208 μM), G (4.2, 8.4, 12.6, 16.8, 21.0, 32.2, 42, and 70.0 μM), and A (11, 22, 33, 44, 55, 84, 106, and 150 μM); (B) containing 55 μM DA, 60 μM UA, 16 μM G, 50 μM A and different concentrations of AA (from inner to outer): 75, 240, 425, 795, 1165, 1535, 1905, and 2275 μM; (C) containing 278 μM AA, 18 μM UA, 23 μM G, 66 μM A and different concentrations of DA (from inner to outer): 12, 26, 54, 106, 148, 180, 222, and 278 μM; (D) containing 555 μM AA, 42 μM DA, 31 μM G, 53 μM A and different concentrations of UA (from inner to outer): 3.6, 9.6, 21.6, 45.6, 81.6, 129.6, 189.6, and 249.6 μM; (E) containing 344 μM AA, 24 μM DA, 28 μM UA, 31 μM A and different concentrations of G (from inner to outer): 3.3, 14.3, 25.3, 36.3, 50.3, 69.3, 86.3, and 103.3 μM; (F) containing 555 μM AA, 28 μM DA, 42 μM UA, 23 μM G and different concentrations of A (from inner to outer): 9.6, 20.2, 46.9, 73.5, 105.2, 126.8, 166.8, and 215.0 μM.

the DPV curves of DA under a constant concentration of AA (278 μM), UA (18 μM), G (23 μM), and A (66 μM). The linear relationship between the peak current and the concentration of DA was obtained in the concentration range of 12–278 μM, with the linear function Ip,DA(μA)¼16.80þ 0.211CDA (μM) (R¼0.9935) and a detection limit of 0.63 μM. Fig. 5D illustrates the DPV curves of UA in the presence of AA (555 μM), DA (41.8 μM), G (30.7 μM), and A (53.3 μM). The linear response range was from 3.6 to 249.6 μM with the linear function Ip,UA(μA)¼8.32þ0.258CUA(μM) (R¼0.9935) and

a detection limit of 0.59 μM. Fig. 5E illustrates the DPV curves of G in the presence of AA (344 μM), DA (24 μM), UA (28 μM), and A (31 μM). The linear response range was from 3.3 to 103.3 μM, with the linear function Ip,G (μA)¼ 12.97þ0.421CG (μM) (R¼0.9911) and a detection limit of 0.48 μM. Fig. 5F illustrates the DPV curves of A in the mixture of AA (555 μM), UA (28 μM), DA (42 μM), and G (23 μM). The linear response range was from 9.6 to 215.0 μM, with the linear function Ip,A (μA)¼29.09þ0.232CA (μM) (R¼0.9922) and a detection limit of 1.28 μM. Compared with other nanomaterials

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Table 1 Comparison of the response characteristics of different modified electrodes. Electrode

OMC–Nafion/ GCE Poly(eriochrome black T)/GCE ZnO-RMs Graphene–Nafion/GCE GMC/GCE PImox–GO/GCE

Method

DPV DPV CV DPV DPV DPV

Linear response range (μM)

Limit of detection (μM)

Reference

AA

DA

UA

G

A

AA

DA

UA

G

A

100–1000 150–1000 15–240 – – 75–2275

5.0–50 0.1–200 6–960 – – 12–278

10–80 10–130 50–800 – – 3.6–249.6

– – – 2–120 25–200 3.3–103.3

– – – 5–170 25–150 9.6–215

20 10 1.4 – – 18

0.5 0.02 0.7 – – 0.63

4 1.0 4.5 – – 0.59

– – – 0.58 0.76 0.48

– – – 0.75 0.63 1.28

modified sensors, the PImox–GO/GCE exhibited a low detection limit and wide linear range. The results are shown in Table 1. In addition, in order to address the measurement crosstalks and limitations (cut-off values), the DPV response for each single species with various concentrations was investigated in the case of exactly similar setup system only the absence of other four species. The response performances such as linear response ranges and detection limits were obtained (data not shown), as expected, which were nearly similar to those obtained in the mixture of five species. This fact further confirmed that it was feasible to simultaneously discriminate above five species in mixture solution using the proposed sensor. 3.5. Interference, stability and reproducibility In order to evaluate the ability of anti-interference, several coexisting compounds were selected. No significant interference was found for the detection of AA (400 μM), DA (50 μM), UA (60 μM), G (30 μM), and A (55 μM) from the following compounds: NaCl, KCl, KNO3, NaSO4, ZnCl2, CaCl2, citric acid, glucose, bovine serum albumin, immunoglobulin, and hemoglobin. The stability of the PImox–GO/GCE was also investigated. When not in use, the PImox–GO/GCE was stored at 4 1C in a refrigerator. The response of PImox–GO/GCE to AA, DA, UA, G, and A lost 5.3%, 4.8%, 6.5%, 4.5%, and 5.4% of its original response after storage for 7 days, respectively. The reproducibility of the proposed sensor was tested using eight different electrodes. The relative standard deviations (RSD) of the DPV response currents for these species were less than 6.8%. Thus, the modified electrode showed a high stability and good reproducibility and anti-interference ability.

4. Conclusions In this study, a novel sensor based on the overoxidized polyimidazole (PImox) and graphene oxide (GO) copolymer was proposed to simultaneously determine AA, DA, UA, G, and A. Due to the synergic effect between GO and PImox, the PImox–GO modified electrode not only exhibited excellent electrocatalytic activities towards the oxidation of AA, DA, UA, G and A, but also resolved their overlapped oxidation peaks into five well-defined peaks. The proposed sensor exhibited a rapid, simple, and sensitive protocol for simultaneous detection of the five species with low detection limit. Thus, the proposed method provides a promising strategy for simultaneous detection of DA, AA, UA, G, and A in biological samples.

Acknowledgments This work was supported by the National Natural Science Foundation of China (21075100, 21275119), Ministry of Education

Zheng et al., 2009 Yao et al., 2007 Tang et al., 2008 Yin et al., 2010 Thangaraj and Kumar (2013) This work

of China (708073), Specialized Research Fund for the Doctoral Program of Higher Education (20100182110015). Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.bios.2014.02.017. References Abbaspour, A., Noori, A., 2011. Biosens. Bioelectron. 26, 4674–4680. Balamurugan, A., Chen, S.M., 2007. Anal. Chim. Acta 596, 92–98. Balamurugan, J., Senthil Kumar, S.M., Thangamuthu, R., Pandurangan, A., 2013. J. Mol. Catal. A 372, 13–22. Cui, R.J., Wang, X.Y., Zhang, G.H., Wang, C., 2012. Sens. Actuators B 161, 1139–1143. Dutt, V.V.S.E., Mottola, H.A., 1974. Anal. Chem. 46, 1777–1781. Huang, J.S., Liu, Y., Hou, H.Q., You, T.Y., 2008. Biosens. Bioelectron. 24, 632–637. Huang, K.J., Jing, Q.S., Wu, Z.W., Wang, L., Wei, C.Y., 2011. Colloids Surf. B 88, 310–314. Huang, Q.T., Zhang, H.Q., Hu, S.R., Li, F.M., Weng, W., Chen, J.H., Wang, Q.X., He, Y.S., Zhang, W.X., Bao, X.X., 2014. Biosens. Bioelectron. 52, 277–280. Kalimuthu, P., John, S.A., 2006. Anal. Biochem. 357, 188–193. Kamyabi, M.A., Hajari, N., Turner, A.P.F., Tiwari, A., 2013. Talanta 116, 801–808. Kul, D., Ghica, M.E., Pauliukaite, R., Brett, C.M.A., 2013. Talanta 111, 76–84. Kumar, S.S., Mathiyarasu, J., Phani, K.L., 2005. J. Electroanal. Chem. 578, 95–103. Li, Q.W., Wang, Y.M., Luo, G.A., 2000. Mater. Sci. Eng. C 11, 71–74. Martin, C., 1998. Chem. Br. 34, 40–42. Nie, T., Xu, J.K., Lu, L.M., Zhang, K.X., Bai, L., Wen, Y.P., 2013. Biosens. Bioelectron. 50, 244–250. Niu, L.M., Lian, K.Q., Shi, H.M., Wu, Y.B., Kang, W.J., Bi, S.Y., 2013. Sens. Actuators B 178, 10–18. Noroozifar, M., Motlagh, K., 2003. Talanta 61, 173–179. Noroozifar, M.S., Khorasani-Motlagh, M., Parizi, M.B., Akbari, R., 2013. Ionics 19, 1317–1327. Premkumar, J., Khoo, S.B., 2005. J. Electroanal. Chem. 576, 105–112. Qian, T., Yu, C.F., Wu, S.S., Shen, J., 2013. Biosens. Bioelectron. 50, 157–160. Raj, V., Madheswari, D., Mubarak Ali, M., 2012. J. Appl. Polym. Sci. 124, 1649–1658. Shahrokhian, S., Rastgar, S., Amini, M.K., Adeli, M., 2012. Bioelectrochemistry 86, 78–86. Shakkthivel, P., Chen, S.M., 2007. Biosens. Bioelectron. 22, 1680–1687. Shervedani, R.K., BagherzAeh, M., Mozaffari, S.A., 2006. Sens. Actuators B 115, 614–621. Sheng, Z.H., Zheng, X.Q., Xu, J.Y., Bao, W.J., Wang, F.B., Xia, X.H., 2012. Biosens. Bioelectron. 34, 125–131. Tang, C.F., Kumar, S.A., Chen, S.M., 2008. Anal. Biochem. 380, 174–183. Thangaraj, R., Kumar, A.S., 2013. J. Solid State Electrochem. 17, 583–590. Thiagarajan, S., Chen, S.M., 2007. Talanta 74, 212–222. Tian, J., Deng, S.Y., Li, L.D., Shan, D., He, W., Zhang, J.X., Shi, Y., 2013. Biosens. Bioelectron. 49, 466–471. Wang, C., Yuan, R., Chai, Y.Q., Chen, S.H., Hu, F.X., Zhang, M.H., 2012. Anal. Chim. Acta 741, 15–20. Wightman, R.M., May, L.J., Michael, A.C., 1988. Anal. Chem. 60, 769A–779A. Yao, H., Sun, Y.Y., Lin, X.H., Tang, Y.H., Huang, L.Y., 2007. Electrochim. Acta 52, 6165–6171. Yang, J.H., Ramaraj, B., Yoon, K.R., 2014. J. Alloys Compd. 583, 128–133. Yin, H.S., Zhou, Y.L., Ma, Q., Ai, S.Y., Ju, P., Zhu, L.S., Lu, L.N., 2010. Process Biochem. 45, 1707–1712. Zeng, Y.B., Zhou, Y., Kong, L., Zhou, T.S., Shi, G.Y., 2013. Biosens. Bioelectron. 45, 25–33. Zhang, L., Jiang, X., 2005. J. Electroanal. Chem. 583, 292–299. Zheng, D., Ye, J.S., Zhou, L., Zhang, Y., Yu, C.Z., 2009. J. Electroanal. Chem. 625, 82–87. Zheng, W., Li, J., Zheng, Y.F., 2008. Biosens. Bioelectron. 23, 1562–1566. Zhou, S.H., Shi, H.Y., Feng, X., Xue, K.W., Song, W.B., 2013. Biosens. Bioelectron. 42, 163–169. Zhuang, Z.J., Li, J.Y., Xu, R., Xiao, D., 2011. Int. J. Electrochem. Sci. 6, 2149–2161.

graphene oxide copolymer modified electrode for the simultaneous determination of ascorbic acid, dopamine, uric acid, guanine and adenine.

In the present work, a novel strategy based on overoxidized polyimidazole (PImox) and graphene oxide (GO) copolymer modified electrode was proposed fo...
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