Biosensors and Bioelectronics 70 (2015) 289–298
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Poly(ionic liquids) functionalized polypyrrole/graphene oxide nanosheets for electrochemical sensor to detect dopamine in the presence of ascorbic acid Hui Mao a,b, Jiachen Liang a,b, Haifeng Zhang a,b, Qi Pei a,b, Daliang Liu a,b, Shuyao Wu a,b, Yu Zhang a,b, Xi-Ming Song a,b,n a b
Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, Liaoning University, Shenyang 110036, China College of Chemistry, Liaoning University, Shenyang 110036, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 February 2015 Received in revised form 17 March 2015 Accepted 23 March 2015
Novel poly(ionic liquids) functionalized polypyrrole/graphene oxide nanosheets (PILs/PPy/GO) were prepared by the polymerization of 1-vinyl-3-ethylimidazole bromide (VEIB) on the surface of N-vinyl imidazolium modified PPy/GO nanosheets. Due to the synergistic effects of GO with well-defined lamellar structures, conductive PPy and biocompatible PILs, PILs/PPy/GO modified glassy carbon electrode (GCE) presented the excellent electrochemical catalytic activity towards dopamine (DA) with good stability, high sensitivity and wide linear range in the present of ascorbic acid (AA) with high concentration. PILs played an essential role for the simultaneous determination of DA and AA in a mixture, whose existence effectively improved the transmission mode of electrons and resulted in the different electrocatalytic performance towards the oxidation of DA and AA. It is indicated that PILs/PPy/GO nanosheets can act as a good steady and sensitive electrode material for the development of improved DA sensors. & 2015 Elsevier B.V. All rights reserved.
Keywords: Poly(ionic liquids) (PILs) Polypyrrole (PPy) Graphene oxide (GO) Dopamine (DA) Ascorbic acid (AA) Electrochemical sensor
1. Introduction Thin film with two-dimensional (2D) nanostructures has been considered as a kind of promising modified electrode material with good stability and excellent sensitivity for the application to build electrochemical sensors and biosensors, due to its good environmental stability, thinner thickness and large surface area (Janáky and Visy, 2013; Jiang et al., 2004; Pang et al., 2000; Zhang et al., 2014). Graphene is a monolayer nanosheet composed of sp2-hybridized carbon atoms arranged in hexagonal honeycomb lattice, which is well known as the thinnest nanomaterial in the world and has attracted tremendous attentions due to its exceptional thermal mechanical, and electrical properties with promising applications (such as developing an ultra-high-resolution electrochemical biosensor with single-DNA resolutions (Akhavan et al., 2012) and the electrochemical detection of leukemia (Akhavan et al., 2014a; Akhavan et al., 2014b)), since it was separated from graphite (Geim, 2009; Geim and Novoselov, 2007; Novoselov et al., 2004). Recently, novel composite film materials n Corresponding author at: Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, Liaoning University, Shenyang 110036, China. Fax: þ 86 2462202380. E-mail address: [email protected] (X.-M. Song).
http://dx.doi.org/10.1016/j.bios.2015.03.059 0956-5663/& 2015 Elsevier B.V. All rights reserved.
composed of conducting polymers (CPs) and graphene (G) or graphene oxide (GO) have attracted a tremendous amount of attentions and become a research focus, because they possess both excellent properties of conducting polymers and graphene or graphene oxide, such as high electric conductivity at room temperature, long term environmental stability, good electrochemical activity and biocompatibility (Guiseppi-Elie, 2010; Lee et al., 2006) of CPs, as well as unique electrical and chemical properties of G or GO (Kuila et al., 2011; Liu et al., 2012b). Therefore, CPs/G or CPs/GO nanocomposite materials can be applied in many fields such as energy storage, supercapacitors or electrochemical sensors and biosensors for the detection of certain special substances, for instance, polyaniline/grapheme (PANI/G) (Gómez et al., 2011) and polypyrrole/graphene oxide (PPy/GO) (Zhu et al., 2012) exhibited good electrochemical properties and cycling performance, which should be promisingly used for the fabrication of inexpensive, high-performance electrochemical supercapacitors; poly(3,4ethylenedioxythiophene)/graphene oxide (PEDOT/GO) nanocomposite modified electrode exhibited lowered impedance and increased charge storage capacity as well as improved sensitivity to the oxidation of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA) (Weaver et al., 2014). However, most CPs/G or CPs/GO nanocomposites were prepared by electrochemical deposition (Chang et al., 2012; Si et al., 2011; Zhu et al., 2012)
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which limited their high-volume production. CPs/G or CPs/GO nanocomposites synthesized by chemical precipitation technique or liquid/liquid interfacial polymerization were often used for supercapacitors (Bora and Dolui, 2012; Gómez et al., 2011), but rarely for electrochemical sensors and biosensors due to the hydrophobicity and poor dispersibility of the pristine CPs on the surface of electrode. Poly(ionic liquids) (PILs) have attracted great interest during the past few years, because that they combined the unique properties of ionic liquids (ILs) (such as low flammability and toxicity, enhanced ionic conductivity, high polarity, good chemical stability, etc.) (Holbrey and Seddon, 1999) with the intrinsic polymer properties and presented the advantages of both ionic liquids and polymers (Marcilla et al., 2006), which can be applied in various fields. For instance, glucose oxidase adsorbed on PILs-Au nanoparticle composites exhibited direct electron transfer and bioelectrocatalytic properties towards the oxidation of glucose (Lee et al., 2012); Ag nanoparticles-PIL-graphene sheets were utilized to fabricate a nonenzymatic hydrogen peroxide sensor (Wang and Yun, 2013), PILs functionalized graphene (PILs-G) with the immobilized glucose oxidase (GOD) modified electrode exhibited excellent direct electrochemical response for glucose with good sensitivity and wide linear range (Zhang et al., 2011), and so on. Therefore, PILs as a modifier may contribute more excellent performance to electrode materials for electrochemical sensors and biosensors. Herein, novel ternary composites, PILs/PPy/GO nanosheets, which combined the advantages of GO, PPy and PILs, were firstly prepared by the polymerization of 1-vinyl-3-ethylimidazolium bromide (VEIB) on the surface of N-vinyl imidazolium modified
PPy/GO nanosheets (Scheme 1). Due to the synergistic effects of GO with well-defined lamellar structures, conductive PPy and biocompatible PILs, PILs/PPy/GO modified glassy carbon electrode (GCE) presented the excellent electrochemical catalytic activities towards dopamine (DA) with good stability, high sensitivity and wide linear range in the presence of ascorbic acid (AA) of high concentration. The PILs played an essential role for the simultaneous determination of DA and AA in the mixture, whose existence obviously changed their surface charge property to electropositivity, resulting in the significant improvement of PILs/PPy/ GO dispersibility in aqueous solution, transmission mode of electrons and different electrocatalytic performance towards the oxidation of DA and AA. These research results indicated that PILs/ PPy/GO can act as a steady and sensitive electrode material, especially for detecting of dopamine in the presence of ascorbic acid.
2. Material and methods 2.1. Material Pyrrole (Py) (Sinopharm Chemical Reagent Co. Ltd., Z98.0%) and Bromoethane (Sinopharm Chemical Reagent Co. Ltd., Z98.0%) are chemical grade. N-vinyl imidazole was purchased from Yancheng Medical Chemical Factory (China), which were distilled under vacuum before use. High-purity graphite powder was purchased from Sinopharm Chemical Reagent Co. Ltd.. All the other reagents were analytical grade, and used without further purification, including KMnO4 (Tianjin Baishi Chemical Co. Ltd,
Scheme 1. The reaction procedure for the preparation of PILs/PPy/GO nanosheets.
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Z99.5%), FeCl3 6H2O (Z99.0%), H2SO4 (Z 98.3%), KOH ( Z85.0%), chloroform (Z 98.0%), uric acid (UA) (Z99.0%), citric acid monohydrate (CA) (Z99.5%) and NaCl (Z99.5%) (Sinopharm Chemical Reagent Co. Ltd.), 1,4-dibromobutane ( Z98.0%), L-tryptophan (Trp) (Z99.0%) and 2,2-azobisisobutyronitrile (AIBN) (Z98.0%) (Aladdin reagent (Shanghai) Co., Ltd.), L-ascorbic acid (AA) (Z 99.7%), H3PO4 ( Z98.0%), Na2HPO4 ( Z99.0%) and NaH2PO4 (Z 99.0%) (Tianjin Yongda Chemical Reagent Co., Ltd.), H2O2 (Shenyang Xinhua Reagent Factory, Z30.0%), NaNO3 (Tianjin Bodi Chemicals Co., Ltd., Z 99.0%), dimethyl formamide (DMF) (Tianjin Beilian Fine Chemicals Development Co., Ltd., Z 99.5%), ethanol (Tianjin Damao Chemical Factory, Z99.7%) and dopamine hydrochloride (DA) (Alfa Aesar, Z 99.0%). 2.2. Preparation of GO nanosheets GO was prepared by a modified Hummers method (Hummers and Offeman, 1958). In a typical procedure, H2SO4 (67.5 mL, 98.3 wt%) was added to a mixture of high-purity graphite powder (2.0 g) and NaNO3 (1.6 g), and the mixture was cooled to 0 °C in an ice bath under stirring. KMnO4 (9.0 g) was slowly added in portion into the above mixture during 1 h to prevent the temperature over 5 °C. The ice bath was removed, and then the reaction was warmed to 3573 °C. After 30 min, the black suspension was changed to beige dope and the mixture was kept for 5 days at room temperature. Then, the mixture was diluted by warm deionized water (560 mL) and further treated with a H2O2 (30 wt%, about 5 mL) solution until the bright-yellow suspension was obtained. The brown precipitate was collected by centrifugation, washed several times with water to the solution was neutral, then, washed several times with ethanol and finally dried under vacuum at 45 °C for 24 h.
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dispersed in DMF (25 mL) by ultrasonication for 5 min then held at 60 °C for 24 h under stirring. The products were collected by centrifugation, washed several times with water and ethanol, finally dried under vacuum at 45 °C for 24 h. 2.6. Preparation of PILs/PPy/GO nanosheets PILs/PPy/GO nanosheets were prepared by the polymerization of 1-vinyl-3-ethylimidazole bromide (VEIB) synthesized according the literature (Marcilla et al., 2004) on the surface of ILs/PPy/GO which owned the polymerizable vinyl groups. In a typical procedure, 30 mg of VEIB and 5 mg AIBN were dissolved in 20 ml of chloroform. 6 mg of ILs/PPy/GO were added into the above solution and dispersed in it after ultrasound for 5 min. Then, the mixture was removed to the oil bath and the reaction was carried out under refluxing for 4 h with balloon protection filled with N2 at 70 °C. The products were collected by centrifugation, and then washed and redispersed with chloroform and water for several times to remove unreacted chemicals and outgrowths. Finally, the obtained black powders were dried in vacuum at 45 °C for 24 h. The reaction procedure for preparation of PILs/PPy/GO nanosheets is shown in Scheme 1. 2.7. Preparation of PILs/PPy/GO nanosheets modified GCE The obtained PILs/PPy/GO nanosheets were dispersed in ethanol to give 1 mg/mL black suspension. The film was prepared by dropping 2.5 μL of suspension onto the clean GCE surface and then evaporating the solvent in the environment. The modified GCE was used as the working electrode. Otherwise, GO modified GCE and PPy/GO modified GCE were also prepared for the comparison. 2.8. Characterizations and apparatus
2.3. Preparation of PPy/GO nanosheets PPy/GO nanosheets were prepared through in situ chemical polymerization of Py on GO under ultrasonic irradiation as reported in the literature (Wang et al., 2013). In a typical procedure, GO (0.05 g) was dispersed in deionized water (20 mL) after ultrasound for 30 min with a bath sonicator. 1 mmol Py was added into the above mixture by ultrasonication for another 30 min. Then, 3 mmol FeCl3 6H2O dissolved in 13.5 mL of de-ionized water was added into the above mixture system. The reaction was further carried out by ultrasonication for 30 min. The black precipitates were collected by centrifugation, and then washed with water and ethanol for several times to remove unreacted chemicals and outgrowths. Finally, they were dried in vacuum at 45 °C for 24 h. 2.4. Preparation of PPy/GO-(CH2)4Br nanosheets PPy/GO-(CH2)4Br nanosheets were prepared by the substitution reaction of 1,4-dibromobutane and PPy/GO in DMF with KOH as reported in the literature (Qiu et al., 2011). In a typical procedure, PPy/GO (30 mg), 1,4-dibromobutane (0.67 mmol) and KOH (0.9 mmol) were dispersed in DMF (25 mL) by ultrasonication for 5 min then held at 60 °C for 24 h under stirring. The products were collected by centrifugation, washed several times with water and ethanol, finally dried under vacuum at 45 °C for 24 h. 2.5. Preparation of ILs/PPy/GO nanosheets N-vinyl imidazolium-type ILs modified PPy/GO nanosheets (ILs/ PPy/GO) were synthesized by the ionization reaction of N-vinyl imidazole and PPy/GO-(CH2)4Br in DMF. In a typical procedure, PPy/GO-(CH2)4Br (12 mg) and N-vinyl imidazole (1.15 mmol) were
The images of GO, PPy/GO and PILs/PPy/GO were obtained by Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements, respectively. SEM measurements were performed on a Hitachi SU-8010 electron microscope with primary electron energy of 10 kV. TEM experiments were performed on a JEM-2100 electron microscope (JEOL, Japan) with an acceleration voltage of 200 kV. The zeta-potential data of the products were obtained by using a Zeta-Plus4 instrument (Brookhaven Corp., USA). Fourier transform infrared spectroscopy (FTIR) Spectra of KBr powder-pressed pellets were recorded on a Perkin Elmer Spectrum one FTIR spectrometer (Perkin-Elmer Corp., USA). Analysis of the X-ray photoelectron spectra (XPS) was performed on an ESCLAB 250 using Al as the exciting source. Transmission spectra of GO, PPy/GO and PILs/PPy/GO dispersed in aqueous solution were recorded on TU-1900 UV/visible spectrophotometer (Beijing Purkinje General Instrument Co., Ltd., China). An SDT Q600 Simultaneous DSC-TGA Instrument (TA Corp., USA) was used to investigate the thermal stability of GO, PPy/GO and PILs/PPy/GO in the temperature range from room temperature to 700 °C under condensed N2 at a rate of 10.0 °C/min. Raman spectra of GO, PPy/ GO and PIL/PPy/GO were performed on a LabRAM XploRA Raman microscope (HORIBA Jobin Yvon, France) with excitation laser wavelength at 638 nm. The electrochemical performance of PILs/ PPy/GO was investigated by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with a CHI600D Electrochemical Station (Shanghai CHENHUA instrument Co., Ltd.). In a three-electrode system, a modified GCE, a platinum wire and an Ag/AgCl electrode were used as the working electrode, the counter electrode and the reference electrode, respectively. The measurements were performed in 0.05 M phosphate buffer solution (PBS) (pH¼4.0, 20 °C) with 0.05 M NaCl. The pH value was adjusted with H3PO4 by PP-20 acidity-conductivity meter (Sartorious Instrument
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Co., Ltd., GER).
3. Results and discussion 3.1. Morphology and characterizations of PILs/PPy/GO nanosheets Figs. S1 and 1 give SEM and TEM images of GO, PPy/GO and PILs/PPy/GO, respectively, which were synthesized by the procedure as in Scheme 1. GO reveals a typical lamellar structure with wrinkled forms as shown in Figs. S1(a) and 1(a). Figs. S1(b) and 1 (b) presents SEM and TEM images PPy/GO, respectively, which only exhibits a kind of flaky texture together with a number of layers stacking as the previous report (Wang et al., 2013). It is indicates that the surface of GO sheets are uniformly coated with PPy. After the polymerization of VEIB, PILs/PPy/GO were obtained, which are clearly observed as flaky textures with wrinkled forms in Figs. S1(c) and 1(c). Furthermore, some nanoscrolls are obviously found in PILs/PPy/GO, which may be due to the curliness of PILs/PPy/GO nanosheets. The zeta-potential data of GO and PPy/GO present a strongly negative charge of nearly 23 mV and 9.4 mV in aqueous solution, respectively (Fig. S2(a) and (b)). Compared to GO, a shift towards the positive direction may be due to the positive charges of PPy gained from doped protons (Zhang et al., 2013). However, the zeta-potential data of PILs/PPy/GO present a strongly positive charge of nearly 31 mV in aqueous solution (Fig. S2(c)), which indicates that the surface charge property of PPy/GO has been obviously changed after modified by PILs. Otherwise, the dispersibility of PILs/PPy/GO has been also improved comparing to GO and PPy/GO. After ultrasound for 30 min, GO, PPy/GO and PILs/ PPy/GO were well dispersed in aqueous solution when they were kept for 1 min (Fig. 2(i)). It is clearly observed that PPy/GO and GO obviously precipitated out from aqueous solution after kept for 3 h and 1 day (Fig. 2(ii) and (iii)), respectively, while a part of PILs/PPy/ GO nanosheets were still well dispersed in aqueous solution (Fig. 2 (iii)-c), which is well demonstrated that the dispersibility of PILs/ PPy/GO has been improved much better than that of GO and PPy/ GO in aqueous solution after modifying PILs on the surface of PPy/ GO.
Scheme 1 gives the reaction procedure of PILs/PPy/GO nanosheets and the chemical structures of the five nanosheets are correspondingly characterized by FTIR spectra in Fig. S3, which is consistent with previous reports (Liu and Wan, 2001a, b; Qiu et al., 2011; Shi and Deng, 2005; Wang et al., 2009; Zhang et al., 2010). Fig. S3(a) presents the typical FTIR spectra of GO. A broad absorption band at 3430 cm 1 is corresponding to –OH groups stretching vibration and the peak at 1636 cm 1 is due to the typical C ¼ O stretching vibration of COOH groups. The peaks in the range 1455–1090 cm 1 are assigned to C–O stretching vibrations in C–OH/C–O–C (epoxy). Presence of the pyrrole ring is confirmed by the peak at 1467 cm 1. The peaks at 1193 and 1040 cm 1 as well as the peaks at 852 and 780 cm 1 are assigned to the ¼C–H in-plane vibrations and the ¼C–H out-of-plane vibrations, respectively (Fig. S3(b)). After the substitution reaction of 1,4-dibromobutane and PPy/GO, the peaks at 2920 and 2843 cm 1 are associated to the moiety of –(CH2)4Br (Fig. 3(c)), which proves that the bromobutyl groups have been successfully grafted on the surface of PPy/GO. Otherwise, the peak at 1685 cm 1 confirmed the existence of imidazolium cation (Qiu et al., 2011) and the peak at 1571 cm 1 is associated to C–C and C–N stretching vibrations of the imidazolium ring (Shi and Deng, 2005) in Fig. S3(e). It indicates that PILs (polyVEIB) has been successfully modified on the surface of PPy/GO, which has formed as PILs/PPy/GO. XPS data have also been used to characterize the chemical structure of PILs/PPyNTs, which is shown in Fig. 3. The elements of C, N, O are obviously observed in survey spectra (Fig. 3(i)). In the C 1s core-line spectra of PILs/PPyNTs, the main peak is fitted with four peaks at 284.8 (C–C/C–H) (Carrillo et al., 2013), 285.4 (C–N in Py rings (De la Fuente Salas et al., 2014)), 286.5 (Chetero of imidazolium groups in PILs (Kolbeck et al., 2014)) and 288.8 eV (O–C ¼O due to the overoxidation of PPy occurred at the β-carbons of Py rings (Carquigny et al., 2009; Chebil et al., 2014)), respectively (Fig. 3(ii)). For the N 1s core-line spectra as shown in Fig. 3(iii), the two types of nitrogen atoms have been found at the peaks of 399.5 and 401.3 eV, respectively, which are attributed to –NH– in Py rings (Wei et al., 2010) and π-cation in PILs (Jia et al., 2010). The main peaks of O 1s at 533.2 and 531.6 eV in Fig. 3(iv) are associated with C–O and carbonyl group (C ¼ O) (Chebil et al., 2014), respectively, which also suggests that the overoxidation of PPy occured at
Fig. 1. TEM images of (a) GO, (b) PPy/GO and (c) PILs/PPy/GO.
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Fig. 2. Photographs of (a) GO, (b) PPy/GO and (c) PILs/PPy/GO dispersed in aqueous solution after (i) 1 min, (ii) 3 h and (iii) 1 day.
Fig. 3. XPS spectra of PILs/PPyNTs: (i) survey spectra; (ii) C 1s; (iii) N 1s; (iv) O 1s.
the β-carbons of Py rings (Carquigny et al., 2009). UV–vis spectra and TGA thermograms of GO, PPy/GO and PILs/ PPy/GO are shown in Fig. 4, which also prove the chemical structure of them. GO presents a main absorption band at 227 nm in Fig. 4(i)-a, which is consistent with the previous report (Konwer et al., 2011). As shown in Fig. 4(i)-b, the bands at 410 nm and 217 nm shown in Fig. 4(i)-b may be related to the synergistic effect of π–πn absorption peak of long conjugated chain in PPy main chain (Wang et al., 2010) and the conjugation of PPy with GO (Konwer et al., 2011), respectively. However, the UV–vis spectra of PILs/PPy/GO shows a main absorption band at 464 nm (Fig. 4(i)-c).
This red shift of the peak from 410 nm to 464 nm is most presumably due to the cationic–π and π–πn interactions between imidazolium in PILs and pyrrole aromatic rings (Qiu et al., 2012). Thermogravimetric analysis (TGA) data can further prove that PILs/PPy/GO are composed of GO, PPy and PILs. Fig. 4(ii) exhibits TGA thermograms of GO, PPy/GO and PILs/PPy/GO in the temperature range from room temperature to 700 °C under condensed N2 at a rate of 10 °C/min, respectively. The typical characteristic curve of GO consist with the previous report (Wang et al., 2013) can be clearly observed in Fig. 4(ii)-a. The initial weight loss (about 13.5%) occurred below 150 °C, because that water molecules were
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Fig. 4. (i) UV–vis spectra, (ii) TGA thermograms and (iii) Raman spectra of (a) GO, (b) PPy/GO composites and (c) PILs/PPy/GO.
removed from the gallery space of the GO. The major weight loss (about 28.4%) in the range of 150–250 °C and a slower weight loss (about 16.8%) above 250 °C are ascribed to the decomposition of – OH, –COOH and epoxy groups from GO and the destruction of the carbon skeleton of GO framework, respectively. Compared to GO, more delayed decomposition and more mass remained at 700 °C can be found for PPy/GO in Fig. 4(ii)-b. It is indicated that the thermal stability of PPy/GO was significantly improved in the existence of PPy, which is consisted with the previous report (Wang et al., 2013). However, compared to PPy/GO, PILs/PPy/GO exhibited a little rapid weight loss in the range of 150–360 °C (Fig. 4(ii)-c), which is due to the decomposition of the surface-bound PILs molecules (Tung et al., 2011). It can be further evidenced the present of PILs on the surface of PILs/PPy/GO. Raman spectroscopy was often employed to investigate the carbon-containing structures. Fig. 4(iii) displays Raman spectra of GO, PPy/GO and PILs/PPy/GO. As shown in Fig. 4(iii)-a, GO exhibits a typical D band and G band at 1347 and 1564 cm 1, which is related to the presence of sp3 defects and tangential vibration of sp2 carbon atoms in hexagonal plane (Tung et al., 2011), respectively. According to the previous reports (Akhavan, 2015; Calizo et al., 2007; Kim et al., 2009; Kudin et al., 2008), the 2D band is much sensitively related to stacking of the sheets of graphene materials. Herein, the 2D band of GO appears at 2718 cm 1 and shows a widened peak shifted into larger wavenumbers, meanwhile, the I2D/IG intensity ratio is calculated to 0.096, which indicates the multi-layer structures of GO (Akhavan, 2015). For PPy/ GO, both these D and G band shift to 1341 and 1562 cm 1 in Fig. 4
(iii)-b, respectively, indicating π–π interaction between PPy and GO, which is similar to the previous report (Bora and Dolui, 2012). In addition, both these D and G band of PILs/PPy/GO shift to 1352 and 1557 cm 1 in Fig. 4(iii)-c, respectively, which may be due to the enhanced π–π interaction of PILs, PPy and GO. 3.2. Electrochemical behavior and CV response of PILs/PPy/GO nanosheets modified GCE towards dopamine and ascorbic acid The electrochemical behaviour of PILs/PPy/GO modified GCE is shown in Fig. 5, compared with the bare GCE, GO modified GCE and PPy/GO modified GCE which acted as the blank under exactly the same conditions. Fig. 5(i) gives the CV curves of the bare GCE, GO modified GCE, PPy/GO modified GCE and PILs/PPy/GO modified GCE in 0.05 M phosphate buffer solution (PBS) (with 0.05 M NaCl, pH ¼4.0, 20 °C) at the scanning rate of 50 mV/s. As it is seen, there are no peaks in the CV curves by the bare GCE, GO modified GCE and PPy/GO modified GCE and their response current are much weaker than that of PILs/PPy/GO modified GCE. Due to the existence of PILs and its excellent dispersibility in ethanol, PILs/PPy/ GO can be uniformly coated on the surface of GCE, and thus a pair of sensitive and reversible current peaks caused by the redox reactions of PPy (Mi et al., 2008) at 0.4 V and 0.35 V appeared in the CV curve by PILs/PPy/GO modified GCE, which could not be seen in the CV curve by PPy/GO modified GCE, showing a pivotal role of PILs for the electron transfer on the surface of the electrode. Fig. 5 (ii) presents the CV curves of the above four electrodes in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C) with 2 μM DA and 3 mM
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Fig. 5. Cyclic voltammograms of (a) the bare GCE, (b) GO modified GCE, (c) PPy/GO modified GCE and (d) PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH¼ 4.0, 20 °C), with scanning rate at 50 mV/s: (i) with 0 mM DA and 0 mM AA; (ii) with 2 μM DA and 3 mM AA; (iii) with 2 μM DA; (iv) with 3 mM AA.
AA at the scanning rate of 50 mV/s. As shown in Fig. 5(ii)-a, b and c, the CV response of the bare GCE, GO or PPy/GO modified GCE are only observed as one peak at 0.38, 0.42 or 0.36 V for the oxidation of AA and DA in PBS with 2 μM DA and 3 mM AA, respectively, indicating that the peak potential for AA and DA is indistinguishable. However, two well-defined oxidation peaks at 0.18 and 0.4 V, corresponding to the oxidation of AA and DA, respectively, are clearly observed in the CV response of PILs/PPy/GO modified GCE (Fig. 5(ii)-d). It is worth noting that the concentration of AA (3 mM) is 1500 times higher than that of DA (2 μM) in the mixture, which provides the possibility of the detection DA in the practical application, because AA coexists with DA in the extracellular fluid of the central nervous system, where the concentration of AA is about 100–1000 times higher than that of DA (Liu et al., 2012a). The potential difference between the two peaks is 0.22 V, which is enough to well distinguish DA from AA. It should be noted that the peak potential for DA and AA can not be differentiated by PPy/GO modified GCE, but after modifying PILs on their surface, the peak potential for DA with very low concentration can be well differentiated from AA with millimole level concentration. Otherwise, the CV responses of the bare GCE, GO, PPy/GO and PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C) only with 2 μM DA or 3 mM AA at the scanning rate of 50 mV/s are also displayed in Fig. 5(iii) and (iv), respectively. When the CV measurements were only carried out in PBS with 2 μM DA, as shown in Fig. 5(iii)-a, b and c, no peaks could be found in the CV responses of the bare GCE, GO and PPy/GO modified GCE,
indicating that no response of DA can be detected at such a low concentration using the three kinds of electrodes. However, a pair of sensitive and reversible current peaks at 0.34 and 0.4 V appears obviously in Fig. 5(iii)-d, which was caused by the redox reactions of DA occurring at the surface of PILs/PPy/GO modified GCE. When the CV measurements were only carried out in PBS with 3 mM AA, as shown in Fig. 5(iv)-a, b and c, one peak at 0.42, 0.43 and 0.47 V could be observed in the CV response of the bare GCE, GO and PPy/ GO modified GCE, respectively, due to the oxidation of AA. However, a peak at 0.18 V can be found in the CV response of PILs/PPy/ GO modified GCE in Fig. 5(iv)-d), where the oxidation potential of AA sharply shifts negatively because of the introduction of PILs. Therefore, it is obvious that PILs played an essential role for the simultaneous determination of DA and AA in a mixture. The kinetics of electrode reactions at PILs/PPy/GO modified GCE was investigated using CV by evaluating the effect of scanning rate on the oxidation peak current of DA and AA in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C) with 2 μM DA and.3 mM AA. As shown in Fig. 6(i), the oxidation peak current of DA and AA increased simultaneously along with the increasing of scanning rate. The plot of the oxidation peak current at 0.4 V against the square root of scanning rates in the range of 10–100 mV/s presented an excellent linear relationship (R2 ¼0.9942) in Fig. 6(ii), which indicated that the oxidation reaction of DA was a typical diffusioncontrolled process. However, the plot of the oxidation peak current at 0.18 V against scanning rates in the range of 10–100 mV/s presented an excellent linear relationship (R2 ¼0.9979) in Fig. 6(iii),
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Fig. 6. (i) Cyclic voltammogram of PILs/PPy/GO modified GCE at a scanning rate of (a) 10; (b) 20; (c) 30; (d) 40; (e) 50; (f) 60; (g) 70; (h) 80; (i) 90; (j) 100 mV/s in 0.05 M PBS (with 0.05 M NaCl, pH¼ 4.0, 20 °C) with 2 μM DA and.3 mM AA; (ii) plot of peak current at 0.4 V vs. the square root of scanning rates; (iii) plot of peak current at 0.18 V vs. scanning rates.
which indicated that the oxidation reaction of AA was a typical surface-controlled process. These results are well indirectly indicated that PILs/PPy/GO exhibited a positive charge in aqueous solution due to PILs existed on the surface of PPy/GO, which was consistent with their results of zeta-potential data. Besides the surface charge property and dispersibility of PILs/PPy/GO were changed by modifying PILs on the surface of PPy/GO, the transmission mode of electrons was also effectively improved, which resulted in the different electrocatalytic performance towards the oxidation of DA and AA. 3.3. DPV response of PILs/PPy/GO nanosheets modified GCE for the application to the detection of dopamine in the presence of ascorbic acid Differential pulse voltammetry (DPV) was carried out using PPy/GO and PILs/PPy/GO modified GCE in PBS with 2 μM DA in the absence or presence of AA, respectively. As shown in Fig. 7(i)-a, the DPV response of PPy/GO modified GCE is barely observed in PBS with 2 μM DA in the absence of AA. When the DPV measurement was carried out in PBS with 2 μM DA and 3 mM AA, a weak peak can be found at 0.38 V due to the oxidation of AA in Fig. 7(i)-b. Significantly, a strong peak of near 0.4 V due to the oxidation of DA can be clearly observed in the DPV response of PILs/PPy/GO modified GCE performing in PBS with 2 μM DA in the absence of AA in Fig. 7(ii)-a. In addition, two well-defined strong peaks at
0.18 V and 0.4 V are obviously found in the DPV response of PILs/ PPy/GO modified GCE performing in PBS with 2 μM DA and 3 mM AA in Fig. 7(ii)-b, which is attributed to the oxidation of DA and AA, respectively. Therefore, it is again demonstrated that PILs played an essential role for the simultaneous determination of DA and AA in a mixture. Fig. 8(i) presents DPV response of PILs/PPy/GO modified GCE in PBS with 3 mM AA and different concentrations of DA. Two welldefined oxidation peaks appeared obvious at 0.18 and 0.4 V, which is corresponding to the oxidation potential of AA and DA, respectively. Along with the increasing of the concentrations of DA ([DA]), the oxidation peak current of DA gradually increased, but the oxidation peak current of AA mostly kept constant. Fig. 8(ii) displays the plot depicting the oxidation peak current of DA versus [DA] of PILs/PPy/GO modified GCE which indicates that the oxidation peak current of DA at 0.4 V presented an excellent linear relationship to [DA] from 4 to 18 μM (R2 ¼0.9991) and the slope is 2.499 μA/μM. According to the criterion of a signal-to-noise ratio ¼ 3 (S/N ¼3), the detection limit and sensitivity of PILs/PPy/ GO modified GCE for DA are estimated to 73.3 nM (n ¼10) and 2.499 μA/μM, respectively, which are much better than that of previous graphene-based DA sensors, such as overoxidized polyimidazole/graphene oxide copolymer modified electrode (Liu et al., 2014) and Nitrogen doped graphene (NG) modified electrode (Sheng et al., 2012), etc., summarized in Table 1. Otherwise, the standard deviation is calculated to 1.06 10 7 (A), which is
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Fig. 7. Differential pulse voltammograms of (i) PPy/GO modified GCE and (ii) PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C), with scanning rate at 50 mV/s: (a) with 2 μM DA and 0 mM AA; (b) with 2 μM DA and 3 mM AA.
Fig. 8. (i) Differential pulse voltammograms of PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH ¼ 4.0, 20 °C) with 3 mM AA and different [DA]: (a) 4, (b) 5, (c) 6, (d) 7, (e) 8, (f) 9, (g) 10, (h) 14, (i) 18 μM; (ii) plot of the peak current vs. [DA].
obtained at lower concentrations (in PBS with 5 μM DA and 3 mM AA). Amperometry test was preformed with successive addition of 8 μL 36 mM DA, 8 μL 0.2 M AA, 8 μL 0.2 M UA, 8 μL 0.2 M Trp and 8 μL 0.2 M CA into 8 mL PBS under stirring constantly in a time interval of 200 s, where the concentrations of DA, AA, UA, Trp and CA in the testing solution were 36 μM, 200 μM, 200 μM, 200 μM and 200 μM, respectively. As shown in Fig. S4, when 8 μL 36 mM DA was injected into 8 mL PBS, the response current increased
rapidly and the response time of PILs/PPy/GO modified GCE for DA was less than 8 s. However, when 8 μL certain concentration of different interfering substance, such as AA, UA, Trp and CA, was injected into the above system in order, no changes could be observed in the response current. In addition, the stability of PILs/ PPy/GO modified GCE was measured by monitoring its peak current at 0.4 V in the CV response to DA in PBS with 2 μM DA and 3 mM AA, and found the peak current was reduced by 9.32% after
Table 1 Comparison of the response characteristics of PILs/PPy/GO modified GCE with graphene-based other materials modified GCE as electrochemical sensors to detect DA. Materials
Detection limit (nM)
Linear ranges (μM)
Sensitivity (μA/μM)
References
Graphene NGa Trp-GRb AuNPs–β-CD–Grac PPyox/graphened PImox-GOe PILs/PPy/GO
2460 250 290 150 100 630 73.3
4–100 0.5–170 0.5–110 0.5–150 0.5–10 3.6–249.6 4–18
0.0659 0.03195 0.5202 2.198 0.015 0.211 2.499
Kim et al. (2010) Sheng et al. (2012) Lian et al. (2014) Tian et al. (2012) Zhuang et al. (2011) Liu et al. (2014) This work
a
Nitrogen doped graphene. Tryptophan-functionalized graphene. c Gold nanoparticles-decorated graphene. d Overoxidized polypyrrole/graphene. e Overoxidized polyimidazole/graphene oxide copolymer. b
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100 cycles. These results demonstrate that PILs/PPy/GO modified GCE can be applied to simultaneous determination of DA and AA in their mixture, especially as a good steady electrochemical sensor for DA with high sensitivity and selectivity.
4. Conclusions In summary, novel PILs functionalized PPy/GO nanosheets, lamellar PILs/PPy/GO, were successfully synthesized and used as a modifier for electrode to effectively detect DA with good stability, high sensitivity and wide linear range in the existence of AA with high concentration. The existence of PILs on the surface of PILs/ PPy/GO nanosheets not only changed the surface charge property and dispersibility of PPy/GO, but also effectively improved the transmission mode of electrons and resulted in the different electrocatalytic performance towards the oxidation of DA and AA. It is indicated that PILs/PPy/GO can act as a good steady and sensitive electrode material for the development of improved DA sensors.
Acknowledgements The financial supports from the National Natural Science Foundation of China (nos. 51203072, 51273087 and 21203082), the Research Fund for the Doctoral Program of Liaoning Province (nos. 20131042, 20121031), the Foundation for Innovative Research Groups of Liaoning Provincial Universities (no. LT2011001) and the Foundation of “211 Project” for Innovative Talents Training in Liaoning University are greatly appreciated.
Appendix A. Supplementary Information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.bios.2015.03.059.
References Akhavan, O., 2015. Carbon 81, 158–166. Akhavan, O., Ghaderi, E., Rahighi, R., 2012. ACS Nano 6, 2904–2916. Akhavan, O., Ghaderi, E., Hashemi, E., Rahighi, R., 2014a. Nanoscale 6, 14810–14819. Akhavan, O., Ghaderi, E., Rahighi, R., Abdolahad, M., 2014b. Carbon 79, 654–663. Bora, C., Dolui, S., 2012. Polymer 53, 923–932. Calizo, I., Balandin, A., Bao, W., Miao, F., Lau, C., 2007. Nano Lett. 7, 2645–2649. Carquigny, S., Sanchez, J.-B., Berger, F., Lakard, B., Lallemand, F., 2009. Talanta 78, 199–206. Carrillo, I., Sanchez de la Blanca, E., Fierro, J., Raso, M., Acción, F., Enciso, E., Redondo, M., 2013. Thin Solid Films 539, 154–160. Chang, H.-H., Chang, C.-K., Tsai, Y.-C., Liao, C.-S., 2012. Carbon 50, 2331–2336. Chebil, S., Monod, M., Fisicaro, P., 2014. Electrochim. Acta 123, 527–534. De la Fuente Salas, I.M., Sudhakar, Y., Selvakumar, M., 2014. Appl. Surf. Sci. 296, 195–203. Gómez, H., Ram, M.K., Alvi, F., Villalba, P., Stefanakos, E.L., Kumar, A., 2011. J. Power Sources 196, 4102–4108.
Geim, A.K., 2009. Science 324, 1530–1534. Geim, A.K., Novoselov, K.S., 2007. Nat. Mater. 6, 183–191. Guiseppi-Elie, A., 2010. Biomaterials 31, 2701–2716. Holbrey, J., Seddon, K., 1999. Clean Prod. Process. 1, 223–236. Hummers Jr, W.S., Offeman, R.E., 1958. J. Am. Chem. Soc. 80 1339-1339. Janáky, C., Visy, C., 2013. Anal. Bioanal. Chem. 405, 3489–3511. Jia, W., Wu, Y., Huang, J., An, Q., Xu, D., Wu, Y., Li, F., Li, G., 2010. J. Mater. Chem. 20, 8617–8623. Jiang, C., Markutsya, S., Pikus, Y., Tsukruk, V.V., 2004. Nat. Mater. 3, 721–728. Kim, K.S., Zhao, Y., Jang, H., Lee, S.Y., Kim, J.M., Kim, K.S., Ahn, J.-H., Kim, P., Choi, J.-Y., Hong, B.H., 2009. Nature 457, 706–710. Kim, Y.-R., Bong, S., Kang, Y.-J., Yang, Y., Mahajan, R.K., Kim, J.S., Kim, H., 2010. Biosens. Bioelectron. 25, 2366–2369. Kolbeck, C., Taccardi, N., Paape, N., Schulz, P.S., Wasserscheid, P., Steinrück, H.-P., Maier, F., 2014. J. Mol. Liq. 192, 103–113. Konwer, S., Boruah, R., Dolui, S.K., 2011. J. Electron. Mater. 40, 2248–2255. Kudin, K.N., Ozbas, B., Schniepp, H.C., Prud'Homme, R.K., Aksay, I.A., Car, R., 2008. Nano Lett. 8, 36–41. Kuila, T., Bose, S., Khanra, P., Mishra, A.K., Kim, N.H., Lee, J.H., 2011. Biosens. Bioelectron. 26, 4637–4648. Lee, H.T., Liu, Y.C., Lin, L.H., 2006. J. Polym. Sci., Part A: Polym. Chem. 44, 2724–2731. Lee, S., Ringstrand, B.S., Stone, D.A., Firestone, M.A., 2012. ACS Appl. Mater. Interfaces 4, 2311–2317. Lian, Q., He, Z., He, Q., Luo, A., Yan, K., Zhang, D., Lu, X., Zhou, X., 2014. Anal. Chim. Acta 823, 32–39. Liu, J., Wan, M., 2001a. J. Mater. Chem. 11, 404–407. Liu, J., Wan, M., 2001b. Synth. Met. 124, 317–321. Liu, S.-Q., Sun, W.-H., Hu, F.-T., 2012a. Sens. Actuators, B 173, 497–504. Liu, X., Zhang, L., Wei, S., Chen, S., Ou, X., Lu, Q., 2014. Biosens. Bioelectron. 57, 232–238. Liu, Y., Dong, X., Chen, P., 2012b. Chem. Soc. Rev. 41, 2283–2307. Marcilla, R., Alberto Blazquez, J., Rodriguez, J., Pomposo, J.A., Mecerreyes, D., 2004. J. Polym. Sci. Part A: Polym. Chem. 42, 208–212. Marcilla, R., Alcaide, F., Sardon, H., Pomposo, J.A., Pozo-Gonzalo, C., Mecerreyes, D., 2006. Electrochem. Commun. 8, 482–488. Mi, H., Zhang, X., Ye, X., Yang, S., 2008. J. Power Sources 176, 403–409. Novoselov, K.S., Geim, A.K., Morozov, S., Jiang, D., Zhang, Y., Dubonos, S., Grigorieva, I., Firsov, A., 2004. Science 306, 666–669. Pang, S.C., Anderson, M.A., Chapman, T.W., 2000. J. Electrochem. Soc. 147, 444–450. Qiu, L., Liu, B., Peng, Y., Yan, F., 2011. Chem. Commun. 47, 2934–2936. Qiu, L., Peng, Y., Liu, B., Lin, B., Peng, Y., Malik, M.J., Yan, F., 2012. Appl. Catal. A – Gen. 413, 230–237. Sheng, Z.-H., Zheng, X.-Q., Xu, J.-Y., Bao, W.-J., Wang, F.-B., Xia, X.-H., 2012. Biosens. Bioelectron. 34, 125–131. Shi, F., Deng, Y., 2005. Spectrochim. Acta. A Mol. Biomol. Spectrosc. 62, 239–244. Si, P., Chen, H., Kannan, P., Kim, D.-H., 2011. Analyst 136, 5134–5138. Tian, X., Cheng, C., Yuan, H., Du, J., Xiao, D., Xie, S., Choi, M.M., 2012. Talanta 93, 79–85. Tung, T.T., Kim, T.Y., Shim, J.P., Yang, W.S., Kim, H., Suh, K.S., 2011. Org. Electron. 12, 2215–2224. Wang, H., Hao, Q., Yang, X., Lu, L., Wang, X., 2009. Electrochem. Commun. 11, 1158–1161. Wang, P., Zheng, Y., Li, B., 2013. Synth. Met. 166, 33–39. Wang, Q., Yun, Y., 2013. Microchim. Acta 180, 261–268. Wang, X.Y., Heng, L.P., Yang, N.L., Xie, Q., Zhai, J., 2010. Chin. Chem. Lett. 21, 884–887. Weaver, C.L., Li, H., Luo, X., Cui, X.T., 2014. J. Mater. Chem. B 2, 5209–5219. Wei, Y., Li, L., Yang, X., Pan, G., Yan, G., Yu, X., 2010. Nanoscale Res. Lett. 5, 433–437. Zhang, J., Chen, P., Oh, B.H., Chan-Park, M.B., 2013. Nanoscale 5, 9860–9866. Zhang, J., Yang, H., Shen, G., Cheng, P., Zhang, J., Guo, S., 2010. Chem. Commun. 46, 1112–1114. Zhang, L., Wen, Y., Yao, Y., Xu, J., Duan, X., Zhang, G., 2014. Electrochim. Acta 116, 343–354. Zhang, Q., Wu, S., Zhang, L., Lu, J., Verproot, F., Liu, Y., Xing, Z., Li, J., Song, X.-M., 2011. Biosens. Bioelectron. 26, 2632–2637. Zhu, C., Zhai, J., Wen, D., Dong, S., 2012. J. Mater. Chem. 22, 6300–6306. Zhuang, Z., Li, J., Xu, R., Xiao, D., 2011. Int. J. Electrochem. Sci. 6, 2149–2161.
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Biosensors and Bioelectronics journal homepage: www.elsevier.com/locate/bios
Poly(ionic liquids) functionalized polypyrrole/graphene oxide nanosheets for electrochemical sensor to detect dopamine in the presence of ascorbic acid Hui Mao a,b, Jiachen Liang a,b, Haifeng Zhang a,b, Qi Pei a,b, Daliang Liu a,b, Shuyao Wu a,b, Yu Zhang a,b, Xi-Ming Song a,b,n a b
Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, Liaoning University, Shenyang 110036, China College of Chemistry, Liaoning University, Shenyang 110036, China
art ic l e i nf o
a b s t r a c t
Article history: Received 1 February 2015 Received in revised form 17 March 2015 Accepted 23 March 2015
Novel poly(ionic liquids) functionalized polypyrrole/graphene oxide nanosheets (PILs/PPy/GO) were prepared by the polymerization of 1-vinyl-3-ethylimidazole bromide (VEIB) on the surface of N-vinyl imidazolium modified PPy/GO nanosheets. Due to the synergistic effects of GO with well-defined lamellar structures, conductive PPy and biocompatible PILs, PILs/PPy/GO modified glassy carbon electrode (GCE) presented the excellent electrochemical catalytic activity towards dopamine (DA) with good stability, high sensitivity and wide linear range in the present of ascorbic acid (AA) with high concentration. PILs played an essential role for the simultaneous determination of DA and AA in a mixture, whose existence effectively improved the transmission mode of electrons and resulted in the different electrocatalytic performance towards the oxidation of DA and AA. It is indicated that PILs/PPy/GO nanosheets can act as a good steady and sensitive electrode material for the development of improved DA sensors. & 2015 Elsevier B.V. All rights reserved.
Keywords: Poly(ionic liquids) (PILs) Polypyrrole (PPy) Graphene oxide (GO) Dopamine (DA) Ascorbic acid (AA) Electrochemical sensor
1. Introduction Thin film with two-dimensional (2D) nanostructures has been considered as a kind of promising modified electrode material with good stability and excellent sensitivity for the application to build electrochemical sensors and biosensors, due to its good environmental stability, thinner thickness and large surface area (Janáky and Visy, 2013; Jiang et al., 2004; Pang et al., 2000; Zhang et al., 2014). Graphene is a monolayer nanosheet composed of sp2-hybridized carbon atoms arranged in hexagonal honeycomb lattice, which is well known as the thinnest nanomaterial in the world and has attracted tremendous attentions due to its exceptional thermal mechanical, and electrical properties with promising applications (such as developing an ultra-high-resolution electrochemical biosensor with single-DNA resolutions (Akhavan et al., 2012) and the electrochemical detection of leukemia (Akhavan et al., 2014a; Akhavan et al., 2014b)), since it was separated from graphite (Geim, 2009; Geim and Novoselov, 2007; Novoselov et al., 2004). Recently, novel composite film materials n Corresponding author at: Liaoning Key Laboratory for Green Synthesis and Preparative Chemistry of Advanced Materials, Liaoning University, Shenyang 110036, China. Fax: þ 86 2462202380. E-mail address: [email protected] (X.-M. Song).
http://dx.doi.org/10.1016/j.bios.2015.03.059 0956-5663/& 2015 Elsevier B.V. All rights reserved.
composed of conducting polymers (CPs) and graphene (G) or graphene oxide (GO) have attracted a tremendous amount of attentions and become a research focus, because they possess both excellent properties of conducting polymers and graphene or graphene oxide, such as high electric conductivity at room temperature, long term environmental stability, good electrochemical activity and biocompatibility (Guiseppi-Elie, 2010; Lee et al., 2006) of CPs, as well as unique electrical and chemical properties of G or GO (Kuila et al., 2011; Liu et al., 2012b). Therefore, CPs/G or CPs/GO nanocomposite materials can be applied in many fields such as energy storage, supercapacitors or electrochemical sensors and biosensors for the detection of certain special substances, for instance, polyaniline/grapheme (PANI/G) (Gómez et al., 2011) and polypyrrole/graphene oxide (PPy/GO) (Zhu et al., 2012) exhibited good electrochemical properties and cycling performance, which should be promisingly used for the fabrication of inexpensive, high-performance electrochemical supercapacitors; poly(3,4ethylenedioxythiophene)/graphene oxide (PEDOT/GO) nanocomposite modified electrode exhibited lowered impedance and increased charge storage capacity as well as improved sensitivity to the oxidation of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA) (Weaver et al., 2014). However, most CPs/G or CPs/GO nanocomposites were prepared by electrochemical deposition (Chang et al., 2012; Si et al., 2011; Zhu et al., 2012)
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which limited their high-volume production. CPs/G or CPs/GO nanocomposites synthesized by chemical precipitation technique or liquid/liquid interfacial polymerization were often used for supercapacitors (Bora and Dolui, 2012; Gómez et al., 2011), but rarely for electrochemical sensors and biosensors due to the hydrophobicity and poor dispersibility of the pristine CPs on the surface of electrode. Poly(ionic liquids) (PILs) have attracted great interest during the past few years, because that they combined the unique properties of ionic liquids (ILs) (such as low flammability and toxicity, enhanced ionic conductivity, high polarity, good chemical stability, etc.) (Holbrey and Seddon, 1999) with the intrinsic polymer properties and presented the advantages of both ionic liquids and polymers (Marcilla et al., 2006), which can be applied in various fields. For instance, glucose oxidase adsorbed on PILs-Au nanoparticle composites exhibited direct electron transfer and bioelectrocatalytic properties towards the oxidation of glucose (Lee et al., 2012); Ag nanoparticles-PIL-graphene sheets were utilized to fabricate a nonenzymatic hydrogen peroxide sensor (Wang and Yun, 2013), PILs functionalized graphene (PILs-G) with the immobilized glucose oxidase (GOD) modified electrode exhibited excellent direct electrochemical response for glucose with good sensitivity and wide linear range (Zhang et al., 2011), and so on. Therefore, PILs as a modifier may contribute more excellent performance to electrode materials for electrochemical sensors and biosensors. Herein, novel ternary composites, PILs/PPy/GO nanosheets, which combined the advantages of GO, PPy and PILs, were firstly prepared by the polymerization of 1-vinyl-3-ethylimidazolium bromide (VEIB) on the surface of N-vinyl imidazolium modified
PPy/GO nanosheets (Scheme 1). Due to the synergistic effects of GO with well-defined lamellar structures, conductive PPy and biocompatible PILs, PILs/PPy/GO modified glassy carbon electrode (GCE) presented the excellent electrochemical catalytic activities towards dopamine (DA) with good stability, high sensitivity and wide linear range in the presence of ascorbic acid (AA) of high concentration. The PILs played an essential role for the simultaneous determination of DA and AA in the mixture, whose existence obviously changed their surface charge property to electropositivity, resulting in the significant improvement of PILs/PPy/ GO dispersibility in aqueous solution, transmission mode of electrons and different electrocatalytic performance towards the oxidation of DA and AA. These research results indicated that PILs/ PPy/GO can act as a steady and sensitive electrode material, especially for detecting of dopamine in the presence of ascorbic acid.
2. Material and methods 2.1. Material Pyrrole (Py) (Sinopharm Chemical Reagent Co. Ltd., Z98.0%) and Bromoethane (Sinopharm Chemical Reagent Co. Ltd., Z98.0%) are chemical grade. N-vinyl imidazole was purchased from Yancheng Medical Chemical Factory (China), which were distilled under vacuum before use. High-purity graphite powder was purchased from Sinopharm Chemical Reagent Co. Ltd.. All the other reagents were analytical grade, and used without further purification, including KMnO4 (Tianjin Baishi Chemical Co. Ltd,
Scheme 1. The reaction procedure for the preparation of PILs/PPy/GO nanosheets.
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Z99.5%), FeCl3 6H2O (Z99.0%), H2SO4 (Z 98.3%), KOH ( Z85.0%), chloroform (Z 98.0%), uric acid (UA) (Z99.0%), citric acid monohydrate (CA) (Z99.5%) and NaCl (Z99.5%) (Sinopharm Chemical Reagent Co. Ltd.), 1,4-dibromobutane ( Z98.0%), L-tryptophan (Trp) (Z99.0%) and 2,2-azobisisobutyronitrile (AIBN) (Z98.0%) (Aladdin reagent (Shanghai) Co., Ltd.), L-ascorbic acid (AA) (Z 99.7%), H3PO4 ( Z98.0%), Na2HPO4 ( Z99.0%) and NaH2PO4 (Z 99.0%) (Tianjin Yongda Chemical Reagent Co., Ltd.), H2O2 (Shenyang Xinhua Reagent Factory, Z30.0%), NaNO3 (Tianjin Bodi Chemicals Co., Ltd., Z 99.0%), dimethyl formamide (DMF) (Tianjin Beilian Fine Chemicals Development Co., Ltd., Z 99.5%), ethanol (Tianjin Damao Chemical Factory, Z99.7%) and dopamine hydrochloride (DA) (Alfa Aesar, Z 99.0%). 2.2. Preparation of GO nanosheets GO was prepared by a modified Hummers method (Hummers and Offeman, 1958). In a typical procedure, H2SO4 (67.5 mL, 98.3 wt%) was added to a mixture of high-purity graphite powder (2.0 g) and NaNO3 (1.6 g), and the mixture was cooled to 0 °C in an ice bath under stirring. KMnO4 (9.0 g) was slowly added in portion into the above mixture during 1 h to prevent the temperature over 5 °C. The ice bath was removed, and then the reaction was warmed to 3573 °C. After 30 min, the black suspension was changed to beige dope and the mixture was kept for 5 days at room temperature. Then, the mixture was diluted by warm deionized water (560 mL) and further treated with a H2O2 (30 wt%, about 5 mL) solution until the bright-yellow suspension was obtained. The brown precipitate was collected by centrifugation, washed several times with water to the solution was neutral, then, washed several times with ethanol and finally dried under vacuum at 45 °C for 24 h.
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dispersed in DMF (25 mL) by ultrasonication for 5 min then held at 60 °C for 24 h under stirring. The products were collected by centrifugation, washed several times with water and ethanol, finally dried under vacuum at 45 °C for 24 h. 2.6. Preparation of PILs/PPy/GO nanosheets PILs/PPy/GO nanosheets were prepared by the polymerization of 1-vinyl-3-ethylimidazole bromide (VEIB) synthesized according the literature (Marcilla et al., 2004) on the surface of ILs/PPy/GO which owned the polymerizable vinyl groups. In a typical procedure, 30 mg of VEIB and 5 mg AIBN were dissolved in 20 ml of chloroform. 6 mg of ILs/PPy/GO were added into the above solution and dispersed in it after ultrasound for 5 min. Then, the mixture was removed to the oil bath and the reaction was carried out under refluxing for 4 h with balloon protection filled with N2 at 70 °C. The products were collected by centrifugation, and then washed and redispersed with chloroform and water for several times to remove unreacted chemicals and outgrowths. Finally, the obtained black powders were dried in vacuum at 45 °C for 24 h. The reaction procedure for preparation of PILs/PPy/GO nanosheets is shown in Scheme 1. 2.7. Preparation of PILs/PPy/GO nanosheets modified GCE The obtained PILs/PPy/GO nanosheets were dispersed in ethanol to give 1 mg/mL black suspension. The film was prepared by dropping 2.5 μL of suspension onto the clean GCE surface and then evaporating the solvent in the environment. The modified GCE was used as the working electrode. Otherwise, GO modified GCE and PPy/GO modified GCE were also prepared for the comparison. 2.8. Characterizations and apparatus
2.3. Preparation of PPy/GO nanosheets PPy/GO nanosheets were prepared through in situ chemical polymerization of Py on GO under ultrasonic irradiation as reported in the literature (Wang et al., 2013). In a typical procedure, GO (0.05 g) was dispersed in deionized water (20 mL) after ultrasound for 30 min with a bath sonicator. 1 mmol Py was added into the above mixture by ultrasonication for another 30 min. Then, 3 mmol FeCl3 6H2O dissolved in 13.5 mL of de-ionized water was added into the above mixture system. The reaction was further carried out by ultrasonication for 30 min. The black precipitates were collected by centrifugation, and then washed with water and ethanol for several times to remove unreacted chemicals and outgrowths. Finally, they were dried in vacuum at 45 °C for 24 h. 2.4. Preparation of PPy/GO-(CH2)4Br nanosheets PPy/GO-(CH2)4Br nanosheets were prepared by the substitution reaction of 1,4-dibromobutane and PPy/GO in DMF with KOH as reported in the literature (Qiu et al., 2011). In a typical procedure, PPy/GO (30 mg), 1,4-dibromobutane (0.67 mmol) and KOH (0.9 mmol) were dispersed in DMF (25 mL) by ultrasonication for 5 min then held at 60 °C for 24 h under stirring. The products were collected by centrifugation, washed several times with water and ethanol, finally dried under vacuum at 45 °C for 24 h. 2.5. Preparation of ILs/PPy/GO nanosheets N-vinyl imidazolium-type ILs modified PPy/GO nanosheets (ILs/ PPy/GO) were synthesized by the ionization reaction of N-vinyl imidazole and PPy/GO-(CH2)4Br in DMF. In a typical procedure, PPy/GO-(CH2)4Br (12 mg) and N-vinyl imidazole (1.15 mmol) were
The images of GO, PPy/GO and PILs/PPy/GO were obtained by Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements, respectively. SEM measurements were performed on a Hitachi SU-8010 electron microscope with primary electron energy of 10 kV. TEM experiments were performed on a JEM-2100 electron microscope (JEOL, Japan) with an acceleration voltage of 200 kV. The zeta-potential data of the products were obtained by using a Zeta-Plus4 instrument (Brookhaven Corp., USA). Fourier transform infrared spectroscopy (FTIR) Spectra of KBr powder-pressed pellets were recorded on a Perkin Elmer Spectrum one FTIR spectrometer (Perkin-Elmer Corp., USA). Analysis of the X-ray photoelectron spectra (XPS) was performed on an ESCLAB 250 using Al as the exciting source. Transmission spectra of GO, PPy/GO and PILs/PPy/GO dispersed in aqueous solution were recorded on TU-1900 UV/visible spectrophotometer (Beijing Purkinje General Instrument Co., Ltd., China). An SDT Q600 Simultaneous DSC-TGA Instrument (TA Corp., USA) was used to investigate the thermal stability of GO, PPy/GO and PILs/PPy/GO in the temperature range from room temperature to 700 °C under condensed N2 at a rate of 10.0 °C/min. Raman spectra of GO, PPy/ GO and PIL/PPy/GO were performed on a LabRAM XploRA Raman microscope (HORIBA Jobin Yvon, France) with excitation laser wavelength at 638 nm. The electrochemical performance of PILs/ PPy/GO was investigated by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) with a CHI600D Electrochemical Station (Shanghai CHENHUA instrument Co., Ltd.). In a three-electrode system, a modified GCE, a platinum wire and an Ag/AgCl electrode were used as the working electrode, the counter electrode and the reference electrode, respectively. The measurements were performed in 0.05 M phosphate buffer solution (PBS) (pH¼4.0, 20 °C) with 0.05 M NaCl. The pH value was adjusted with H3PO4 by PP-20 acidity-conductivity meter (Sartorious Instrument
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Co., Ltd., GER).
3. Results and discussion 3.1. Morphology and characterizations of PILs/PPy/GO nanosheets Figs. S1 and 1 give SEM and TEM images of GO, PPy/GO and PILs/PPy/GO, respectively, which were synthesized by the procedure as in Scheme 1. GO reveals a typical lamellar structure with wrinkled forms as shown in Figs. S1(a) and 1(a). Figs. S1(b) and 1 (b) presents SEM and TEM images PPy/GO, respectively, which only exhibits a kind of flaky texture together with a number of layers stacking as the previous report (Wang et al., 2013). It is indicates that the surface of GO sheets are uniformly coated with PPy. After the polymerization of VEIB, PILs/PPy/GO were obtained, which are clearly observed as flaky textures with wrinkled forms in Figs. S1(c) and 1(c). Furthermore, some nanoscrolls are obviously found in PILs/PPy/GO, which may be due to the curliness of PILs/PPy/GO nanosheets. The zeta-potential data of GO and PPy/GO present a strongly negative charge of nearly 23 mV and 9.4 mV in aqueous solution, respectively (Fig. S2(a) and (b)). Compared to GO, a shift towards the positive direction may be due to the positive charges of PPy gained from doped protons (Zhang et al., 2013). However, the zeta-potential data of PILs/PPy/GO present a strongly positive charge of nearly 31 mV in aqueous solution (Fig. S2(c)), which indicates that the surface charge property of PPy/GO has been obviously changed after modified by PILs. Otherwise, the dispersibility of PILs/PPy/GO has been also improved comparing to GO and PPy/GO. After ultrasound for 30 min, GO, PPy/GO and PILs/ PPy/GO were well dispersed in aqueous solution when they were kept for 1 min (Fig. 2(i)). It is clearly observed that PPy/GO and GO obviously precipitated out from aqueous solution after kept for 3 h and 1 day (Fig. 2(ii) and (iii)), respectively, while a part of PILs/PPy/ GO nanosheets were still well dispersed in aqueous solution (Fig. 2 (iii)-c), which is well demonstrated that the dispersibility of PILs/ PPy/GO has been improved much better than that of GO and PPy/ GO in aqueous solution after modifying PILs on the surface of PPy/ GO.
Scheme 1 gives the reaction procedure of PILs/PPy/GO nanosheets and the chemical structures of the five nanosheets are correspondingly characterized by FTIR spectra in Fig. S3, which is consistent with previous reports (Liu and Wan, 2001a, b; Qiu et al., 2011; Shi and Deng, 2005; Wang et al., 2009; Zhang et al., 2010). Fig. S3(a) presents the typical FTIR spectra of GO. A broad absorption band at 3430 cm 1 is corresponding to –OH groups stretching vibration and the peak at 1636 cm 1 is due to the typical C ¼ O stretching vibration of COOH groups. The peaks in the range 1455–1090 cm 1 are assigned to C–O stretching vibrations in C–OH/C–O–C (epoxy). Presence of the pyrrole ring is confirmed by the peak at 1467 cm 1. The peaks at 1193 and 1040 cm 1 as well as the peaks at 852 and 780 cm 1 are assigned to the ¼C–H in-plane vibrations and the ¼C–H out-of-plane vibrations, respectively (Fig. S3(b)). After the substitution reaction of 1,4-dibromobutane and PPy/GO, the peaks at 2920 and 2843 cm 1 are associated to the moiety of –(CH2)4Br (Fig. 3(c)), which proves that the bromobutyl groups have been successfully grafted on the surface of PPy/GO. Otherwise, the peak at 1685 cm 1 confirmed the existence of imidazolium cation (Qiu et al., 2011) and the peak at 1571 cm 1 is associated to C–C and C–N stretching vibrations of the imidazolium ring (Shi and Deng, 2005) in Fig. S3(e). It indicates that PILs (polyVEIB) has been successfully modified on the surface of PPy/GO, which has formed as PILs/PPy/GO. XPS data have also been used to characterize the chemical structure of PILs/PPyNTs, which is shown in Fig. 3. The elements of C, N, O are obviously observed in survey spectra (Fig. 3(i)). In the C 1s core-line spectra of PILs/PPyNTs, the main peak is fitted with four peaks at 284.8 (C–C/C–H) (Carrillo et al., 2013), 285.4 (C–N in Py rings (De la Fuente Salas et al., 2014)), 286.5 (Chetero of imidazolium groups in PILs (Kolbeck et al., 2014)) and 288.8 eV (O–C ¼O due to the overoxidation of PPy occurred at the β-carbons of Py rings (Carquigny et al., 2009; Chebil et al., 2014)), respectively (Fig. 3(ii)). For the N 1s core-line spectra as shown in Fig. 3(iii), the two types of nitrogen atoms have been found at the peaks of 399.5 and 401.3 eV, respectively, which are attributed to –NH– in Py rings (Wei et al., 2010) and π-cation in PILs (Jia et al., 2010). The main peaks of O 1s at 533.2 and 531.6 eV in Fig. 3(iv) are associated with C–O and carbonyl group (C ¼ O) (Chebil et al., 2014), respectively, which also suggests that the overoxidation of PPy occured at
Fig. 1. TEM images of (a) GO, (b) PPy/GO and (c) PILs/PPy/GO.
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Fig. 2. Photographs of (a) GO, (b) PPy/GO and (c) PILs/PPy/GO dispersed in aqueous solution after (i) 1 min, (ii) 3 h and (iii) 1 day.
Fig. 3. XPS spectra of PILs/PPyNTs: (i) survey spectra; (ii) C 1s; (iii) N 1s; (iv) O 1s.
the β-carbons of Py rings (Carquigny et al., 2009). UV–vis spectra and TGA thermograms of GO, PPy/GO and PILs/ PPy/GO are shown in Fig. 4, which also prove the chemical structure of them. GO presents a main absorption band at 227 nm in Fig. 4(i)-a, which is consistent with the previous report (Konwer et al., 2011). As shown in Fig. 4(i)-b, the bands at 410 nm and 217 nm shown in Fig. 4(i)-b may be related to the synergistic effect of π–πn absorption peak of long conjugated chain in PPy main chain (Wang et al., 2010) and the conjugation of PPy with GO (Konwer et al., 2011), respectively. However, the UV–vis spectra of PILs/PPy/GO shows a main absorption band at 464 nm (Fig. 4(i)-c).
This red shift of the peak from 410 nm to 464 nm is most presumably due to the cationic–π and π–πn interactions between imidazolium in PILs and pyrrole aromatic rings (Qiu et al., 2012). Thermogravimetric analysis (TGA) data can further prove that PILs/PPy/GO are composed of GO, PPy and PILs. Fig. 4(ii) exhibits TGA thermograms of GO, PPy/GO and PILs/PPy/GO in the temperature range from room temperature to 700 °C under condensed N2 at a rate of 10 °C/min, respectively. The typical characteristic curve of GO consist with the previous report (Wang et al., 2013) can be clearly observed in Fig. 4(ii)-a. The initial weight loss (about 13.5%) occurred below 150 °C, because that water molecules were
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Fig. 4. (i) UV–vis spectra, (ii) TGA thermograms and (iii) Raman spectra of (a) GO, (b) PPy/GO composites and (c) PILs/PPy/GO.
removed from the gallery space of the GO. The major weight loss (about 28.4%) in the range of 150–250 °C and a slower weight loss (about 16.8%) above 250 °C are ascribed to the decomposition of – OH, –COOH and epoxy groups from GO and the destruction of the carbon skeleton of GO framework, respectively. Compared to GO, more delayed decomposition and more mass remained at 700 °C can be found for PPy/GO in Fig. 4(ii)-b. It is indicated that the thermal stability of PPy/GO was significantly improved in the existence of PPy, which is consisted with the previous report (Wang et al., 2013). However, compared to PPy/GO, PILs/PPy/GO exhibited a little rapid weight loss in the range of 150–360 °C (Fig. 4(ii)-c), which is due to the decomposition of the surface-bound PILs molecules (Tung et al., 2011). It can be further evidenced the present of PILs on the surface of PILs/PPy/GO. Raman spectroscopy was often employed to investigate the carbon-containing structures. Fig. 4(iii) displays Raman spectra of GO, PPy/GO and PILs/PPy/GO. As shown in Fig. 4(iii)-a, GO exhibits a typical D band and G band at 1347 and 1564 cm 1, which is related to the presence of sp3 defects and tangential vibration of sp2 carbon atoms in hexagonal plane (Tung et al., 2011), respectively. According to the previous reports (Akhavan, 2015; Calizo et al., 2007; Kim et al., 2009; Kudin et al., 2008), the 2D band is much sensitively related to stacking of the sheets of graphene materials. Herein, the 2D band of GO appears at 2718 cm 1 and shows a widened peak shifted into larger wavenumbers, meanwhile, the I2D/IG intensity ratio is calculated to 0.096, which indicates the multi-layer structures of GO (Akhavan, 2015). For PPy/ GO, both these D and G band shift to 1341 and 1562 cm 1 in Fig. 4
(iii)-b, respectively, indicating π–π interaction between PPy and GO, which is similar to the previous report (Bora and Dolui, 2012). In addition, both these D and G band of PILs/PPy/GO shift to 1352 and 1557 cm 1 in Fig. 4(iii)-c, respectively, which may be due to the enhanced π–π interaction of PILs, PPy and GO. 3.2. Electrochemical behavior and CV response of PILs/PPy/GO nanosheets modified GCE towards dopamine and ascorbic acid The electrochemical behaviour of PILs/PPy/GO modified GCE is shown in Fig. 5, compared with the bare GCE, GO modified GCE and PPy/GO modified GCE which acted as the blank under exactly the same conditions. Fig. 5(i) gives the CV curves of the bare GCE, GO modified GCE, PPy/GO modified GCE and PILs/PPy/GO modified GCE in 0.05 M phosphate buffer solution (PBS) (with 0.05 M NaCl, pH ¼4.0, 20 °C) at the scanning rate of 50 mV/s. As it is seen, there are no peaks in the CV curves by the bare GCE, GO modified GCE and PPy/GO modified GCE and their response current are much weaker than that of PILs/PPy/GO modified GCE. Due to the existence of PILs and its excellent dispersibility in ethanol, PILs/PPy/ GO can be uniformly coated on the surface of GCE, and thus a pair of sensitive and reversible current peaks caused by the redox reactions of PPy (Mi et al., 2008) at 0.4 V and 0.35 V appeared in the CV curve by PILs/PPy/GO modified GCE, which could not be seen in the CV curve by PPy/GO modified GCE, showing a pivotal role of PILs for the electron transfer on the surface of the electrode. Fig. 5 (ii) presents the CV curves of the above four electrodes in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C) with 2 μM DA and 3 mM
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Fig. 5. Cyclic voltammograms of (a) the bare GCE, (b) GO modified GCE, (c) PPy/GO modified GCE and (d) PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH¼ 4.0, 20 °C), with scanning rate at 50 mV/s: (i) with 0 mM DA and 0 mM AA; (ii) with 2 μM DA and 3 mM AA; (iii) with 2 μM DA; (iv) with 3 mM AA.
AA at the scanning rate of 50 mV/s. As shown in Fig. 5(ii)-a, b and c, the CV response of the bare GCE, GO or PPy/GO modified GCE are only observed as one peak at 0.38, 0.42 or 0.36 V for the oxidation of AA and DA in PBS with 2 μM DA and 3 mM AA, respectively, indicating that the peak potential for AA and DA is indistinguishable. However, two well-defined oxidation peaks at 0.18 and 0.4 V, corresponding to the oxidation of AA and DA, respectively, are clearly observed in the CV response of PILs/PPy/GO modified GCE (Fig. 5(ii)-d). It is worth noting that the concentration of AA (3 mM) is 1500 times higher than that of DA (2 μM) in the mixture, which provides the possibility of the detection DA in the practical application, because AA coexists with DA in the extracellular fluid of the central nervous system, where the concentration of AA is about 100–1000 times higher than that of DA (Liu et al., 2012a). The potential difference between the two peaks is 0.22 V, which is enough to well distinguish DA from AA. It should be noted that the peak potential for DA and AA can not be differentiated by PPy/GO modified GCE, but after modifying PILs on their surface, the peak potential for DA with very low concentration can be well differentiated from AA with millimole level concentration. Otherwise, the CV responses of the bare GCE, GO, PPy/GO and PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C) only with 2 μM DA or 3 mM AA at the scanning rate of 50 mV/s are also displayed in Fig. 5(iii) and (iv), respectively. When the CV measurements were only carried out in PBS with 2 μM DA, as shown in Fig. 5(iii)-a, b and c, no peaks could be found in the CV responses of the bare GCE, GO and PPy/GO modified GCE,
indicating that no response of DA can be detected at such a low concentration using the three kinds of electrodes. However, a pair of sensitive and reversible current peaks at 0.34 and 0.4 V appears obviously in Fig. 5(iii)-d, which was caused by the redox reactions of DA occurring at the surface of PILs/PPy/GO modified GCE. When the CV measurements were only carried out in PBS with 3 mM AA, as shown in Fig. 5(iv)-a, b and c, one peak at 0.42, 0.43 and 0.47 V could be observed in the CV response of the bare GCE, GO and PPy/ GO modified GCE, respectively, due to the oxidation of AA. However, a peak at 0.18 V can be found in the CV response of PILs/PPy/ GO modified GCE in Fig. 5(iv)-d), where the oxidation potential of AA sharply shifts negatively because of the introduction of PILs. Therefore, it is obvious that PILs played an essential role for the simultaneous determination of DA and AA in a mixture. The kinetics of electrode reactions at PILs/PPy/GO modified GCE was investigated using CV by evaluating the effect of scanning rate on the oxidation peak current of DA and AA in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C) with 2 μM DA and.3 mM AA. As shown in Fig. 6(i), the oxidation peak current of DA and AA increased simultaneously along with the increasing of scanning rate. The plot of the oxidation peak current at 0.4 V against the square root of scanning rates in the range of 10–100 mV/s presented an excellent linear relationship (R2 ¼0.9942) in Fig. 6(ii), which indicated that the oxidation reaction of DA was a typical diffusioncontrolled process. However, the plot of the oxidation peak current at 0.18 V against scanning rates in the range of 10–100 mV/s presented an excellent linear relationship (R2 ¼0.9979) in Fig. 6(iii),
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Fig. 6. (i) Cyclic voltammogram of PILs/PPy/GO modified GCE at a scanning rate of (a) 10; (b) 20; (c) 30; (d) 40; (e) 50; (f) 60; (g) 70; (h) 80; (i) 90; (j) 100 mV/s in 0.05 M PBS (with 0.05 M NaCl, pH¼ 4.0, 20 °C) with 2 μM DA and.3 mM AA; (ii) plot of peak current at 0.4 V vs. the square root of scanning rates; (iii) plot of peak current at 0.18 V vs. scanning rates.
which indicated that the oxidation reaction of AA was a typical surface-controlled process. These results are well indirectly indicated that PILs/PPy/GO exhibited a positive charge in aqueous solution due to PILs existed on the surface of PPy/GO, which was consistent with their results of zeta-potential data. Besides the surface charge property and dispersibility of PILs/PPy/GO were changed by modifying PILs on the surface of PPy/GO, the transmission mode of electrons was also effectively improved, which resulted in the different electrocatalytic performance towards the oxidation of DA and AA. 3.3. DPV response of PILs/PPy/GO nanosheets modified GCE for the application to the detection of dopamine in the presence of ascorbic acid Differential pulse voltammetry (DPV) was carried out using PPy/GO and PILs/PPy/GO modified GCE in PBS with 2 μM DA in the absence or presence of AA, respectively. As shown in Fig. 7(i)-a, the DPV response of PPy/GO modified GCE is barely observed in PBS with 2 μM DA in the absence of AA. When the DPV measurement was carried out in PBS with 2 μM DA and 3 mM AA, a weak peak can be found at 0.38 V due to the oxidation of AA in Fig. 7(i)-b. Significantly, a strong peak of near 0.4 V due to the oxidation of DA can be clearly observed in the DPV response of PILs/PPy/GO modified GCE performing in PBS with 2 μM DA in the absence of AA in Fig. 7(ii)-a. In addition, two well-defined strong peaks at
0.18 V and 0.4 V are obviously found in the DPV response of PILs/ PPy/GO modified GCE performing in PBS with 2 μM DA and 3 mM AA in Fig. 7(ii)-b, which is attributed to the oxidation of DA and AA, respectively. Therefore, it is again demonstrated that PILs played an essential role for the simultaneous determination of DA and AA in a mixture. Fig. 8(i) presents DPV response of PILs/PPy/GO modified GCE in PBS with 3 mM AA and different concentrations of DA. Two welldefined oxidation peaks appeared obvious at 0.18 and 0.4 V, which is corresponding to the oxidation potential of AA and DA, respectively. Along with the increasing of the concentrations of DA ([DA]), the oxidation peak current of DA gradually increased, but the oxidation peak current of AA mostly kept constant. Fig. 8(ii) displays the plot depicting the oxidation peak current of DA versus [DA] of PILs/PPy/GO modified GCE which indicates that the oxidation peak current of DA at 0.4 V presented an excellent linear relationship to [DA] from 4 to 18 μM (R2 ¼0.9991) and the slope is 2.499 μA/μM. According to the criterion of a signal-to-noise ratio ¼ 3 (S/N ¼3), the detection limit and sensitivity of PILs/PPy/ GO modified GCE for DA are estimated to 73.3 nM (n ¼10) and 2.499 μA/μM, respectively, which are much better than that of previous graphene-based DA sensors, such as overoxidized polyimidazole/graphene oxide copolymer modified electrode (Liu et al., 2014) and Nitrogen doped graphene (NG) modified electrode (Sheng et al., 2012), etc., summarized in Table 1. Otherwise, the standard deviation is calculated to 1.06 10 7 (A), which is
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Fig. 7. Differential pulse voltammograms of (i) PPy/GO modified GCE and (ii) PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH ¼4.0, 20 °C), with scanning rate at 50 mV/s: (a) with 2 μM DA and 0 mM AA; (b) with 2 μM DA and 3 mM AA.
Fig. 8. (i) Differential pulse voltammograms of PILs/PPy/GO modified GCE in 0.05 M PBS (with 0.05 M NaCl, pH ¼ 4.0, 20 °C) with 3 mM AA and different [DA]: (a) 4, (b) 5, (c) 6, (d) 7, (e) 8, (f) 9, (g) 10, (h) 14, (i) 18 μM; (ii) plot of the peak current vs. [DA].
obtained at lower concentrations (in PBS with 5 μM DA and 3 mM AA). Amperometry test was preformed with successive addition of 8 μL 36 mM DA, 8 μL 0.2 M AA, 8 μL 0.2 M UA, 8 μL 0.2 M Trp and 8 μL 0.2 M CA into 8 mL PBS under stirring constantly in a time interval of 200 s, where the concentrations of DA, AA, UA, Trp and CA in the testing solution were 36 μM, 200 μM, 200 μM, 200 μM and 200 μM, respectively. As shown in Fig. S4, when 8 μL 36 mM DA was injected into 8 mL PBS, the response current increased
rapidly and the response time of PILs/PPy/GO modified GCE for DA was less than 8 s. However, when 8 μL certain concentration of different interfering substance, such as AA, UA, Trp and CA, was injected into the above system in order, no changes could be observed in the response current. In addition, the stability of PILs/ PPy/GO modified GCE was measured by monitoring its peak current at 0.4 V in the CV response to DA in PBS with 2 μM DA and 3 mM AA, and found the peak current was reduced by 9.32% after
Table 1 Comparison of the response characteristics of PILs/PPy/GO modified GCE with graphene-based other materials modified GCE as electrochemical sensors to detect DA. Materials
Detection limit (nM)
Linear ranges (μM)
Sensitivity (μA/μM)
References
Graphene NGa Trp-GRb AuNPs–β-CD–Grac PPyox/graphened PImox-GOe PILs/PPy/GO
2460 250 290 150 100 630 73.3
4–100 0.5–170 0.5–110 0.5–150 0.5–10 3.6–249.6 4–18
0.0659 0.03195 0.5202 2.198 0.015 0.211 2.499
Kim et al. (2010) Sheng et al. (2012) Lian et al. (2014) Tian et al. (2012) Zhuang et al. (2011) Liu et al. (2014) This work
a
Nitrogen doped graphene. Tryptophan-functionalized graphene. c Gold nanoparticles-decorated graphene. d Overoxidized polypyrrole/graphene. e Overoxidized polyimidazole/graphene oxide copolymer. b
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100 cycles. These results demonstrate that PILs/PPy/GO modified GCE can be applied to simultaneous determination of DA and AA in their mixture, especially as a good steady electrochemical sensor for DA with high sensitivity and selectivity.
4. Conclusions In summary, novel PILs functionalized PPy/GO nanosheets, lamellar PILs/PPy/GO, were successfully synthesized and used as a modifier for electrode to effectively detect DA with good stability, high sensitivity and wide linear range in the existence of AA with high concentration. The existence of PILs on the surface of PILs/ PPy/GO nanosheets not only changed the surface charge property and dispersibility of PPy/GO, but also effectively improved the transmission mode of electrons and resulted in the different electrocatalytic performance towards the oxidation of DA and AA. It is indicated that PILs/PPy/GO can act as a good steady and sensitive electrode material for the development of improved DA sensors.
Acknowledgements The financial supports from the National Natural Science Foundation of China (nos. 51203072, 51273087 and 21203082), the Research Fund for the Doctoral Program of Liaoning Province (nos. 20131042, 20121031), the Foundation for Innovative Research Groups of Liaoning Provincial Universities (no. LT2011001) and the Foundation of “211 Project” for Innovative Talents Training in Liaoning University are greatly appreciated.
Appendix A. Supplementary Information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.bios.2015.03.059.
References Akhavan, O., 2015. Carbon 81, 158–166. Akhavan, O., Ghaderi, E., Rahighi, R., 2012. ACS Nano 6, 2904–2916. Akhavan, O., Ghaderi, E., Hashemi, E., Rahighi, R., 2014a. Nanoscale 6, 14810–14819. Akhavan, O., Ghaderi, E., Rahighi, R., Abdolahad, M., 2014b. Carbon 79, 654–663. Bora, C., Dolui, S., 2012. Polymer 53, 923–932. Calizo, I., Balandin, A., Bao, W., Miao, F., Lau, C., 2007. Nano Lett. 7, 2645–2649. Carquigny, S., Sanchez, J.-B., Berger, F., Lakard, B., Lallemand, F., 2009. Talanta 78, 199–206. Carrillo, I., Sanchez de la Blanca, E., Fierro, J., Raso, M., Acción, F., Enciso, E., Redondo, M., 2013. Thin Solid Films 539, 154–160. Chang, H.-H., Chang, C.-K., Tsai, Y.-C., Liao, C.-S., 2012. Carbon 50, 2331–2336. Chebil, S., Monod, M., Fisicaro, P., 2014. Electrochim. Acta 123, 527–534. De la Fuente Salas, I.M., Sudhakar, Y., Selvakumar, M., 2014. Appl. Surf. Sci. 296, 195–203. Gómez, H., Ram, M.K., Alvi, F., Villalba, P., Stefanakos, E.L., Kumar, A., 2011. J. Power Sources 196, 4102–4108.
Geim, A.K., 2009. Science 324, 1530–1534. Geim, A.K., Novoselov, K.S., 2007. Nat. Mater. 6, 183–191. Guiseppi-Elie, A., 2010. Biomaterials 31, 2701–2716. Holbrey, J., Seddon, K., 1999. Clean Prod. Process. 1, 223–236. Hummers Jr, W.S., Offeman, R.E., 1958. J. Am. Chem. Soc. 80 1339-1339. Janáky, C., Visy, C., 2013. Anal. Bioanal. Chem. 405, 3489–3511. Jia, W., Wu, Y., Huang, J., An, Q., Xu, D., Wu, Y., Li, F., Li, G., 2010. J. Mater. Chem. 20, 8617–8623. Jiang, C., Markutsya, S., Pikus, Y., Tsukruk, V.V., 2004. Nat. Mater. 3, 721–728. Kim, K.S., Zhao, Y., Jang, H., Lee, S.Y., Kim, J.M., Kim, K.S., Ahn, J.-H., Kim, P., Choi, J.-Y., Hong, B.H., 2009. Nature 457, 706–710. Kim, Y.-R., Bong, S., Kang, Y.-J., Yang, Y., Mahajan, R.K., Kim, J.S., Kim, H., 2010. Biosens. Bioelectron. 25, 2366–2369. Kolbeck, C., Taccardi, N., Paape, N., Schulz, P.S., Wasserscheid, P., Steinrück, H.-P., Maier, F., 2014. J. Mol. Liq. 192, 103–113. Konwer, S., Boruah, R., Dolui, S.K., 2011. J. Electron. Mater. 40, 2248–2255. Kudin, K.N., Ozbas, B., Schniepp, H.C., Prud'Homme, R.K., Aksay, I.A., Car, R., 2008. Nano Lett. 8, 36–41. Kuila, T., Bose, S., Khanra, P., Mishra, A.K., Kim, N.H., Lee, J.H., 2011. Biosens. Bioelectron. 26, 4637–4648. Lee, H.T., Liu, Y.C., Lin, L.H., 2006. J. Polym. Sci., Part A: Polym. Chem. 44, 2724–2731. Lee, S., Ringstrand, B.S., Stone, D.A., Firestone, M.A., 2012. ACS Appl. Mater. Interfaces 4, 2311–2317. Lian, Q., He, Z., He, Q., Luo, A., Yan, K., Zhang, D., Lu, X., Zhou, X., 2014. Anal. Chim. Acta 823, 32–39. Liu, J., Wan, M., 2001a. J. Mater. Chem. 11, 404–407. Liu, J., Wan, M., 2001b. Synth. Met. 124, 317–321. Liu, S.-Q., Sun, W.-H., Hu, F.-T., 2012a. Sens. Actuators, B 173, 497–504. Liu, X., Zhang, L., Wei, S., Chen, S., Ou, X., Lu, Q., 2014. Biosens. Bioelectron. 57, 232–238. Liu, Y., Dong, X., Chen, P., 2012b. Chem. Soc. Rev. 41, 2283–2307. Marcilla, R., Alberto Blazquez, J., Rodriguez, J., Pomposo, J.A., Mecerreyes, D., 2004. J. Polym. Sci. Part A: Polym. Chem. 42, 208–212. Marcilla, R., Alcaide, F., Sardon, H., Pomposo, J.A., Pozo-Gonzalo, C., Mecerreyes, D., 2006. Electrochem. Commun. 8, 482–488. Mi, H., Zhang, X., Ye, X., Yang, S., 2008. J. Power Sources 176, 403–409. Novoselov, K.S., Geim, A.K., Morozov, S., Jiang, D., Zhang, Y., Dubonos, S., Grigorieva, I., Firsov, A., 2004. Science 306, 666–669. Pang, S.C., Anderson, M.A., Chapman, T.W., 2000. J. Electrochem. Soc. 147, 444–450. Qiu, L., Liu, B., Peng, Y., Yan, F., 2011. Chem. Commun. 47, 2934–2936. Qiu, L., Peng, Y., Liu, B., Lin, B., Peng, Y., Malik, M.J., Yan, F., 2012. Appl. Catal. A – Gen. 413, 230–237. Sheng, Z.-H., Zheng, X.-Q., Xu, J.-Y., Bao, W.-J., Wang, F.-B., Xia, X.-H., 2012. Biosens. Bioelectron. 34, 125–131. Shi, F., Deng, Y., 2005. Spectrochim. Acta. A Mol. Biomol. Spectrosc. 62, 239–244. Si, P., Chen, H., Kannan, P., Kim, D.-H., 2011. Analyst 136, 5134–5138. Tian, X., Cheng, C., Yuan, H., Du, J., Xiao, D., Xie, S., Choi, M.M., 2012. Talanta 93, 79–85. Tung, T.T., Kim, T.Y., Shim, J.P., Yang, W.S., Kim, H., Suh, K.S., 2011. Org. Electron. 12, 2215–2224. Wang, H., Hao, Q., Yang, X., Lu, L., Wang, X., 2009. Electrochem. Commun. 11, 1158–1161. Wang, P., Zheng, Y., Li, B., 2013. Synth. Met. 166, 33–39. Wang, Q., Yun, Y., 2013. Microchim. Acta 180, 261–268. Wang, X.Y., Heng, L.P., Yang, N.L., Xie, Q., Zhai, J., 2010. Chin. Chem. Lett. 21, 884–887. Weaver, C.L., Li, H., Luo, X., Cui, X.T., 2014. J. Mater. Chem. B 2, 5209–5219. Wei, Y., Li, L., Yang, X., Pan, G., Yan, G., Yu, X., 2010. Nanoscale Res. Lett. 5, 433–437. Zhang, J., Chen, P., Oh, B.H., Chan-Park, M.B., 2013. Nanoscale 5, 9860–9866. Zhang, J., Yang, H., Shen, G., Cheng, P., Zhang, J., Guo, S., 2010. Chem. Commun. 46, 1112–1114. Zhang, L., Wen, Y., Yao, Y., Xu, J., Duan, X., Zhang, G., 2014. Electrochim. Acta 116, 343–354. Zhang, Q., Wu, S., Zhang, L., Lu, J., Verproot, F., Liu, Y., Xing, Z., Li, J., Song, X.-M., 2011. Biosens. Bioelectron. 26, 2632–2637. Zhu, C., Zhai, J., Wen, D., Dong, S., 2012. J. Mater. Chem. 22, 6300–6306. Zhuang, Z., Li, J., Xu, R., Xiao, D., 2011. Int. J. Electrochem. Sci. 6, 2149–2161.
