Preparation of sulfonic-functionalized graphene oxide as ion-exchange material and its application into electrochemiluminescence analysis

Biosensors and Bioelectronics 26 (2011) 3136–3141

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Preparation of sulfonic-functionalized graphene oxide as ion-exchange material and its application into electrochemiluminescence analysis Guifen Chen a , Shengyong Zhai b , Yanling Zhai a , Ke Zhang a , Qiaoli Yue a , Lei Wang a , Jinsheng Zhao a , Huaisheng Wang a , Jifeng Liu a,∗ , Jianbo Jia c,∗∗ a b c

Department of Chemistry, Liaocheng University, No. 1 Hunan Road, Liaocheng 252059, Shandong, China Chinese Medicine and Biological Engineering Research & Development Center, Changchun University of Chinese Medicine, Changchun 130117, China State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China

a r t i c l e

i n f o

Article history: Received 20 September 2010 Received in revised form 6 December 2010 Accepted 7 December 2010 Available online 16 December 2010 Keywords: Graphene oxide Sulfonic derivatization Ion-exchange capacity Electrochemiluminescence

a b s t r a c t Graphene oxide (GO) obtained from chemical oxidation of flake graphite was derivatized with sulfonic groups to form sulfonic-functionalized GO (GO–SO3 − ) through four sulfonation routes: through amide formation between the carboxylic group of GO and amine of sulfanilic acid (AA–GO–SO3 − ), aryl diazonium reaction of sulfanilic acid (AD–GO–SO3 − ), amide formation between the carboxylic group of GO and amine of cysteamine and oxidation by H2 O2 (CA–GO–SO3 − ), and alkyl diazonium reaction of cysteamine and oxidation by H2 O2 (CD–GO–SO3 − ). Results of Fourier transform infrared spectroscopy and X-ray photoelectrospectrocopy showed that –SO3 − groups were attached onto GO. Thermo gravimetric analysis showed that derivatization with sulfonic groups improved thermo stability of GO. X-ray diffraction results indicated that GO–SO3 − had more ordered ␲–␲ stacking structure than the original GO. GO–SO3 − and cationic polyelectrote, poly (diallyldimethylammoniumchloride) (PDDA) were adsorbed at indium tin oxide (ITO) glass surface through layer-by-layer assembling to form (GO–SO3 − /PDDA)n /ITO multilayers. After tris-(2,2 -bipyridyl) ruthenium (II) dichloride (Ru(bpy)3 2+ ) was incorporated into the multilayers, the obtained Ru(bpy)3 2+ /(GO–SO3 − /PDDA)n /ITO electrodes can be used as electrochemiluminescence sensors for detection of organic amine with high sensitivity (limit of detection of 1 nM) and stability. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Graphene oxide (GO), also called graphite oxide sheet, is a twodimensional nanomaterial prepared from chemical oxidation of natural graphite (Allen et al., 2010; Loh et al., 2010). GO itself can be regarded as graphene sheets derivatized with carboxylic groups at the edges and phenol, hydroxyl and epoxide groups on the basal planes (Lerf et al., 1998). These abundant oxygen-containing functional groups and the large surface area of GO facilitate modification of GO and preparation of GO based composite materials. Recently, GO or GO composite materials have been used to fabricate pH sensor (Bai et al., 2010), photovoltaic device (Wu et al., 2010), supercapacitor (Wang et al., 2010a) and biosensors (Cerveny et al., 2010; Zhang et al., 2010) for electrochemical sensing of uric acid, dopamine, free DNA bases (Zhou et al., 2009) and sulfur-containing compounds (Wang et al., 2009). GO based transistor device has also

∗ Corresponding author. Tel.: +86 635 8239001; fax: +86 635 8239001. ∗∗ Corresponding author. Tel.: +86 431 85262378; fax: +86 431 85262378. E-mail addresses: [email protected] (J. Liu), [email protected] (J. Jia). 0956-5663/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.bios.2010.12.015

been reported for molecular probing in living cells (Wang et al., 2010b). GO or functionalized GO is hydrophilic and readily forms stable aqueous colloids, which can be used as absorbents to absorb NO, NO2 , NH3 (Petit et al., 2009; Seredych and Bandosz, 2007; Seredych et al., 2007, 2009), electrolyte (e.g. NaCl) (Li et al., 2009b) and divalent cations (Park et al., 2008). GO based hybrid materials might can be used to incorporate tris-(2,2 -bipyridyl) ruthenium (II) (Ru(bpy)3 2+ ) at electrode surface to construct electrochemiluminescent (ECL) sensor. Ru(bpy)3 2+ is a widely studied ECL reagent and recycled at the electrode surface upon potential scanning during ECL reaction. Ru(bpy)3 2+ ECL as a sensitive detection method has been used in analysis of oxalate, amine, and biomolecules including NADH, amino acids, DNA (Zhu et al., 2004, 2008) and proteins (Zhu et al., 2010). The immobilization of Ru(bpy)3 2+ on electrode surface will save the reagent and simplify experimental design compared with the solution-phase Ru(bpy)3 2+ ECL (Chen et al., 2007; Li et al., 2009a,c; Zhang et al., 2009). Nafion as a cationexchange polymer is effective for the immobilization of Ru(bpy)3 2+ because of its high ion-exchange selectivity for Ru(bpy)3 2+ and electrochemical stability (Sun et al., 2005). The incorporation and

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ion-exchange of Ru(bpy)3 2+ within Nafion is through the access to –SO3 − sites and electrostatic interaction between Ru(bpy)3 2+ and –SO3 − group. However, leaching of Ru(bpy)3 2+ from the hydrophobic region of Nafion is unavoidable and it results in poor long-term stability of the ECL sensor. Additives such as carbon nanotubes, silica dioxide, titanium dioxide have been introduced to improve the stability of Ru(bpy)3 2+ -Nafion film (Qi et al., 2008; Sun et al., 2005; Zhang et al., 2009). In this work, Ru(bpy)3 2+ was incorporated into GO and sulfonicfunctionalized GO (GO–SO3 − ) via ion-exchange. The absorbing capacity of different GO–SO3 − materials and ECL behavior of immobilized Ru(bpy)3 2+ were studied. Synthesis procedures of GO–SO3 − are illustrated in Scheme S1 in the supplement, where different routes were used to introduce sulfonic groups to GO. Aryl sulfonic acid was attached to GO through amide formation reaction between carboxylic groups of GO and amine of sulfanilic acid (SA) (product was denoted as AA–GO–SO3 − ) and through diazonium reaction of SA (AD–GO–SO3 − ). Alkyl sulfonic acid derivatized GO was obtained through amide formation reaction between carboxylic groups of GO and amine of cysteamine (CA) and through diazonium reaction of CA. And then the attached –SH was oxidized by H2 O2 to form –SO3 − (CA–GO–SO3 − and CD–GO–SO3 − , respectively). The as-prepared GO–SO3 − was characterized using X-ray diffraction (XRD), X-ray photoelectrospectrocopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and thermo gravimetric analysis (TGA), respectively. The ion-exchange capacity of GO–SO3 − and the performance of GO–SO3 − film incorporated with Ru(bpy)3 2+ for ECL detection were studied. It was suggested that GO–SO3 − appeared to be attractive materials for ion-exchange and ECL Ru(bpy)3 2+ sensor construction. 2. Experimental 2.1. Materials All chemicals used in this experiment were analytical reagent grade, Flake graphite (300 mesh) was obtained from Kanglong Co. (Qingdao, China). Tripropylamine (TPA), Ru(bpy)3 Cl2 ·6H2 O were purchased from Alfa Co., poly (diallyldimethylammoniumchloride) (PDDA, 20% aqueous solution) was from Aldrich Co., 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS) and CA were purchased from Aladdin Regents Co. (Shanghai). SA, potassium permanganate (KMnO4 ), phosphorus pentoxide (P2 O5 ), potassium persulfate (K2 S2 O8 ), H2 SO4 (98%), H2 O2 (30 wt.% aqueous solution), sodium hydroxide (NaOH), sodium nitrite (NaNO2 ), hydrochloric acid (HCl) were used as received. Sodium phosphate (Na2 HPO4 and NaH2 PO4 [PO4 3− ] = 50 mM, PBS, pH 7.4) were employed as supporting electrolytes, and water was prepared by Milli-Q water purification system (18 M cm−1 ).

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XRD measurements were carried out on a Bruker D8 X-ray diffractometer using Cu K␣ radiation ( = 0.154 nm). Scans were recorded in the 2 range of 5–60 ◦ at a scan rate of 0.4 ◦ /min. TGA was operated on a Pyris 1 TGA (Perkin Elmer) with a heating rate of 10 K/min and heated to 800 ◦ C under a nitrogen atmosphere. Cyclic voltammetry (CV) was recorded with an CHI 760C electrochemical workstation (Chenhua Co., Shanghai). Ag/AgCl3 M KCl , platinum foil (0.5 mm in diameter) were employed as reference and counter electrodes, respectively. Indium tin oxide (ITO, Shenzhen Lihe Thin Film Co., surface resistance <20 ) glass slides (geometric area of 1.5 × 0.7 cm2 , working area of 0.35 cm2 ) were used as working electrodes. ECL detection was carried out with an MPI-A ECL detector (Xian Remix Electronics Co. Ltd., China), the photomultiplier tube was biased at 800 V. 2.3. Preparation of GO GO was synthesized from flake graphite powder by a modified Hummers method (Xu et al., 2008) and the procedure is illustrated in Supplement. 2.4. Preparation of GO–SO3 − Four different routes were used to prepare GO–SO3 − and the details of preparation are shown in Supplement. 2.5. Ion-exchange capacity study For comparison, the absorption capacity of Nafion, GO, GO–SO3 − , the tested according to the procedure as follow, ITO glass was dip-coated with GO, GO–SO3 − , Nafion with known amount (aqueous dispersion 2.5 wt.%: 20, 40, 60, 80, 100, 120, 140 ␮L, respectively) and dried in air at room temperature (RT). The weight of the Nafion, GO, GO–SO3 − membrane was calculated from the volume and the fraction of the different solution mass. The modified ITO electrodes were immersed in 0.1 mM Ru(bpy)3 2+ solution for 1 h to absorbing Ru(bpy)3 2+ by ion-exchange. The weight of the GO, GO–SO3 − , Nafion membranes was calculated from the volume and the concentration of the different solution. The amount of Ru(bpy)3 2+ adsorbed was calculated from the UV–vis absorption of 2 mL Ru(bpy)3 2+ solution (0.1 mM) after the different modified electrode absorption (Yagi et al., 1994, 1995, 1997; Zhang et al., 1996). The decrease in absorbance at 453 nm of the UV–vis absorption of Ru(bpy)3 2+ solution was observed. An approximately linear relationship was obtained between the absorbance at the absorption maximum (453 nm) of the Ru(bpy)3 2+ and it calculated molar of the Ru(bpy)3 2+ in the different membranes. 2.6. Preparation of GO–SO3 − film incorporated with Ru(bpy)3 2+ and application into ECL detection

2.2. Apparatus and measurements UV–vis absorption spectra were collected on a HP-8453 diodearray UV/vis spectrophotometer. FT-IR spectra were recorded on a FT-IR spectrometer (Nicolet IR2000). A Tacnai G2 TEM was applied to observe the morphology and size of GO, which was operated at an accelerating voltage of 200 kV. Samples for TEM were prepared by placing a drop of the suspension on the carbon-coated copper grid. The surface composition of the GO and GO–SO3 − was evaluated by XPS. XPS measurement was performed on an ESCALABMKII spectrometer (VG Co.) with an Al Ka X-ray radiation as the X-ray source for excitation and a chamber pressure of 3.5 × 10−7 Pa.

(GO/PDDA)n /ITO or (GO–SO3 − /PDDA)n /ITO electrodes was prepared by the layer-by-layer (LBL) self-assembly method. ITO glass was sonicated in ethanol and acetone for 30 min and then sonicated in 1 M NaOH for 10 min, rinsed thoroughly with water between each step. The cleaned electrode was immersed in 0.5% PDDA aqueous solution for 30 min, creating an adsorbed monolayer of PDDA. The weakly adsorbed polymer molecules were removed from the surface by rinsing with water for about 1 min. After drying, the ITO electrode was immersed into GO or GO–SO3 − aqueous suspension (1 mg/mL) for 30 min and then washed with water. Coating was repeated 5 times to gave (GO/PDDA)5 /ITO or (GO–SO3 − /PDDA)5 /ITO. Finally, the multilayer modified ITO electrode was immersed into 0.1 mM Ru(bpy)3 2+

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for 30 min and the obtained Ru(bpy)3 2+ /(GO/PDDA)5 /ITO or Ru(bpy)3 2+ /(GO–SO3 − /PDDA)5 /ITO was used for ECL study.

A c

3.1. TEM analysis The morphology and structure of the GO was observed by TEM and the overall view shown in Fig. 1 clearly illustrates the flake-like shapes of GO. The crumpled structure of the nanosheet exhibited in TEM images maybe due to the multiplicity of oxygen functionalities in thin GO layers (Che et al., 2010; Meyer et al., 2007). GO–SO3 − showed no obvious difference in shape and structure from GO in TEM.

%Transmittance

3. Results and discussion 1626

b

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FT-IR spectra of GO shown in Fig. 2A illustrate the presence of C–O (C–O at 1048 cm−1 ), C–O–C (C–O–C at 1248 cm−1 ), and C O in carboxylic acid and carbonyl moieties (C O at 1720 cm−1 ) in GO. The peak at 1622 cm−1 was due to the skeletal vibrations of unoxidized graphitic domains. The absorption bands below 1000 cm−1 were due to the presence of trace sulfate groups intercalated between GO planes (Wu et al., 2008). After sulfonation (e.g. AA–GO–SO3 − , AD–GO–SO3 − ), the peaks at 1048 cm−1 , 1248 cm−1 , and 1365 cm−1 were severely attenuated in the spectrum of GO–SO3 − . The peaks at 1124 cm−1 , 1034 cm−1 and 835 cm−1 (two S–O and one S-phenyl ) confirmed the presence of –SO3 − group (Shen et al., 2009). For CA–GO–SO3 − , CD–GO–SO3 − before oxidation, the absorption bands in the range of 1200–1000 cm−1 (Fig. 2B, curves a and c) could be due to the grafted –SH group. The new absorption bands appeared at 1300–1100 cm−1 (Fig. 2B, curves b and d) after oxidation with H2 O2 was assigned to the –SO3 − group (Li et al., 2009c). These results showed that –SH groups were attached to GO and can be converted to –SO3 − after oxidation by H2 O2 .

777 836

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3.2. FT-IR analysis

1175 1034 1416 12481124 1349

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Wavenumber / cm 3.3. X-ray photoelectrospectrocopy XPS measurements of elements of S and N for GO, CA–GO–SH, CD–GO–SH and the oxidized forms of CA–GO–SO3 − , CD–GO–SO3 − were listed in Fig. 3A. The peaks at 163.1 eV as shown in Fig. 3A

Fig. 1. TEM image of graphene oxide.

Fig. 2. FT-IR spectra of A, GO (a), AA–GO–SO3 − (b), AD–GO–SO3 − (c). B, CA–GO–SH (a), CA–GO–SO3 − (b), CD–GO–SH (c), CD–GO–SO3 − (d).

(curves d and e) were assigned to grafted –SH group (S2p). After oxidation by H2 O2 , the signal of S2p was diminished with a concomitant growing of a new S2p peak at 167.3 and 167.6 eV for CA–GO–SO3 − , CD–GO–SO3 − (Fig. 3A, curves f and g), and these peaks were attributed to –SO3 − groups on the GO framework. These results were consistent with FT-IR data that –SH groups were attached to GO and can be converted to –SO3 − after oxidation. The binding energy of S2p peaks appeared at 167.1 and 168.1 eV for AA–GO–SO3 − and AD–GO–SO3 − , respectively (Fig. 3A, curves b and c). Comparatively, the peak appeared at 168.5 eV for GO was assigned to intercalated SO4 2− during oxidation of graphite (Fig. 3A, curve a). The binding energy of –SO3 − was shifted slightly to a lower binding energy and this negative shift of binding energy of –SO3 − further demonstrated the formation of attachment of –SO3 − onto GO (Shen et al., 2009). N1s spectra of the sulfonated samples prepared through amide formation reaction (AA–GO–SO3 − , CA–GO–SO3 − ) showed two peaks with their binding energies equal to 399.5 and 401.5 eV (Fig. 3B, curves b and d). The first peak represents N involved in C–N (amide), whereas the second peak can be assigned to C–N+ (from quaternary nitrogen) or NH4 + . N1s spectra for AA–GO–SO3 − , CA–GO–SO3 − indicated the incorporation of amides onto GO through reaction of carboxylic groups of GO with SA or CA, while

G. Chen et al. / Biosensors and Bioelectronics 26 (2011) 3136–3141

S2p

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Intensity (a.u.)

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n = 2d sin 

c b a 160

165

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b a 390

3.5. XRD characterization XRD patterns are shown in Fig. B in the supplement. The (0 0 2) diffraction peak of the flake graphite powder (inset of Fig. B) appeared around 2 = 26.6◦ , and the interlayer space was about 0.335 nm based on the Bragg spacing equation:

f

155

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395

400

405

410

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Bonding Energy / eV Fig. 3. Top: S2p XPS spectra of the GO (a), AA–GO–SO3 − (b), AD–GO–SO3 − (c), CA–GO–SH (d), CD–GO–SH (e), CA–GO–SO3 − (f), and CD–GO–SO3 − (g). Bottom: N1 s XPS spectra of the GO (a), AA–GO–SO3 − (b), AD–GO–SO3 − (c), CA–GO–SO3 − (d), and CD–GO–SO3 − (e).

the AD–GO–SO3 − and CD–GO–SO3 − had no obvious peaks of N1s for C–N (amide). 3.4. TGA analysis TGA results are shown in Fig. A in the supplement. GO showed much lower thermal stability due to the reduced van der Waals interaction and started to lose mass upon heating even below 100 ◦ C and it was attributed to the removal of adsorbed water. The main mass loss (∼51%) took place around 250 ◦ C resulting from the removal of the labile oxygen-containing functional groups such as CO, CO2 and H2 O vapors (Hassan et al., 2009; Yang et al., 2009). The main loss was 64.3% within 500 ◦ C. GO has a layered morphology with oxygen-containing functionality thereby weakening the van der Waals forces between layers. It will disrupt the hexagonal carbon basal planes on the interior of multilayered stacking of GO, thus accelerating the process of weight losing (Shen et al., 2009). After sulfonation, less mass loss took place around 250 ◦ C, the mass loss were 39.2%, 34.1%, 29.3% and 45.4% for AD–GO–SO3 − , AA–GO–SO3 − , CD–GO–SO3 − , CA–GO–SO3 − , respectively. Within 500 ◦ C the mass loss were 51%, 51.9%, 58.8% and 63.5% for the sulfonated GOs, indicating GO–SO3 − samples became more thermostable than GO.

(1)

where n is an integer,  is the angle of incidence of the Xray beam, and  is the X-ray wavelength (in the case of Cu K␣ radiation,  = 0.154 nm). After oxidation, GO showed no distinct diffraction peaks, indicating that GO was in amorphrous state or the d-spacing was much larger than the natural value. For GO synthesized with chemical oxidation method, the oxidation of graphite was known to involve a number of chemical processes such as oxidation of carbon atoms at the periphery of the graphite matrix to form oxygen-containing groups including hydroxyl, carbonyl, epoxy or peroxy groups; oxidation of graphite matrix, followed by the intercalation of anions and acid molecules (López-González et al., 1969; Martín-Rodríguez et al., 1969; Matsuo et al., 2002). So the acid-oxidized graphite shows a variable interplanar distance which depends on the synthesis method, air moisture, and other factors, and the obtained interlayer spacing changes from 3.4 A˚ to higher values (Matsuo et al., 2002). The d-spacing of GO–SO3 − were 9.69 A˚ (9.12 ◦ ), 11.27 A˚ (7.84 ◦ ) for AD–GO–SO3 − and AA–GO–SO3 − , respectively. While the values of d-spacing were 12.9 A˚ (6.84 ◦ ), 11.94 A˚ (7.40 ◦ ) for CD–GO–SO3 − and CA–GO–SO3 − , respectively. And these values were larger than ˚ (Matsuo et al., 2002). XRD results the reported values of GO (6–8 A) demonstrated sulfonation decreased disruption of the GO structure and increased the attractive interactions between the GO layers. In other words, GO–SO3 − samples have more organized ␲–␲ stacking structures than GO and different sulfonated methods resulted in different interplanar distances. The intercalation of SA or CA into the interlayer of GO sheets resulted in an expansion of the (0 0 1) inter-planar spacing. 3.6. Incorporation of Ru(bpy)3 2+ into (GO–SO3 − /PDDA)n /ITO The individual platelets of GO or GO–SO3 − are easily to be stacked to form multilayer assembly through LBL routes and PDDA as a cationic binder. The absorption spectra of the GO–SO3 − film before and after the ion exchange in Ru(bpy)3 2+ aqueous solutions were collected and shown in Fig. 4. The results indicated that the spectra of the GO–SO3 − after absorbing Ru(bpy)3 2+ had characteristic spectra of Ru(bpy)3 2+ in the UV–vis region, exhibited a peak at 453 nm, which was due to electronic p–p* transition and metal to ligand charge transfer (MLCT) adsorption of Ru(bpy)3 2+ (Li et al., 2009c). This suggested that Ru(bpy)3 2+ has been incorporated into GO–SO3 − . The amount of Ru(bpy)3 2+ incorporated into (GO–SO3 − /PDDA)n /ITO was determined by calculating the difference of absorption of Ru(bpy)3 2+ solution before and after Ru(bpy)3 2+ incorporated into (GO–SO3 − /PDDA)n /ITO. The absorption around 453 nm showed that the amount of Ru(bpy)3 2+ incorporated into the (GO–SO3 − /PDDA)n /ITO increased with increasing the number of layers (n) of (GO–SO3 − /PDDA)n /ITO (Fig. 4A), suggesting a growth of the multilayer films (Li et al., 2006). The ion-exchange capacity of GO and GO–SO3 − are listed in Fig. 4B. For comparison, the ion-exchange capacity of Nafion, a widely used cationic ionomer, was also tested for its ion-exchange capacity. The ion-exchange capacity increased in the order: GO < CA–GO–SO3 − < CD–GO–SO3 − < Nafion < AD–GO–SO3 − < AA– GO–SO3 − .

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A 0.35

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mass/mg Fig. 4. (A) UV–vis spectra of Ru(bpy)3 2+ on multilayer films (AA–GO–SO3 − /PDDA)n / ITO electrode with n of 1–6 (from lower to upper curves), the dash line is the UV–vis spectra of AA–GO–SO3 − /PDDA/ITO electrode. (B) The molar of the Ru(bpy)3 2+ complex incorporated in different films coated on the ITO electrode surface. GO (a), AA–GO–SO3 − (b), AD–GO–SO3 − (c), CA–GO–SO3 − (d), CD–GO–SO3 − (e), and Nafion (f).

3.7. Electrochemistry and ECL study The ECL behavior of Ru(bpy)3 2+ incorporated into the film modified electrode is studied using TPA as a coreactant and the ECL mechanism shown in Eqs. (2)–(6) has been widely studied. The ECL emission of Ru(bpy)3 2+ –TPA system results from the reaction between the deprotonated TPA radical (TPA* ) and electrogenerated Ru(bpy)3 3+ to form excited Ru(bpy)3 2+* , which then decays to produce orange emission (Eq. (6)). Ru(bpy)3 2+ → Ru(bpy)3 3+ + e + TPA → Ru(bpy)3

(2) 2+

+ TPA

TPA → TPA∗ + e

[Ru(bpy)3

∗

(3a) (3b)

TPA+∗ → TPA∗ + H+

(4)

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+ TPA → [Ru(bpy)3

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Fig. 5. CVs of Ru(bpy)3 2+ /(AA–GO–SO3 − /PDDA)5 /ITO electrode in 50 mM PBS (pH 7.4) 50 (a), 80 (b), 100 (c), 150 (d), 200 (e), and 250 mV/s (f). Inset: the relationship between the oxidation peak current and the square roots of the scan rate.

c

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9

Ru(bpy)3

f

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] → Ru(bpy)3

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+ h

]

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Fig. 5 shows the CVs of the Ru(bpy)3 2+ incorporated (GO–SO3 − /PDDA)5 /ITO electrodes with the anodic peak of Ru(bpy)3 2+ around 1.14 V. And the peak current of Ru(bpy)3 2+ increased with increasing the GO–SO3 − layer numbers. It was also

found that the oxidation peak currents in CV were proportional to the square roots of different scan rates (1/2 ) in the range of 50−250 mV/s (inset of Fig. 5), indicating Ru(bpy)3 2+ incorporated into GO–SO3 − /PDDA multilayer underwent a diffusion-controlled process, and similar results have been reported on other Ru(bpy)3 2+ immobilized systems. The presence of TPA resulted in increase in the anodic peak current and decrease in the cathodic peak current, indicating that the incorporated Ru(bpy)3 2+ electrochemically catalyze the oxidation of TPA, and the ECL signal increased considerably in the presence of TPA as shown in Fig. C. in the supplement. With increasing the layer numbers the ECL intensity increased (results not shown). However, the ECL intensity of Ru(bpy)3 2+ /(AA–GO–SO3 − /PDDA)5 /ITO showed no obvious differences from other GO–SO3 − samples. The ECL stability of GO, GO–SO3 − multilayer and Nafion film modified electrodes were compared. The electrodes were placed in 0.1 mM Ru(bpy)3 2+ aqueous solution for 30 min for the incorporation of Ru(bpy)3 2+ into multilayers. ECL curves of Ru(bpy)3 2+ /(AA–GO–SO3 − /PDDA)5 /ITO, Ru(bpy)3 2+ /(GO/PDDA)5 /ITO and Ru(bpy)3 2+ /Nafion/ITO in TPA solution under continuous potential scanning were shown in Fig. 6A and inset a and b. It can be observed that ECL signals of Ru(bpy)3 2+ /(AA–SO3 − /PDDA)5 /ITO (relative standard deviation of 0.4%) were more stable than those of Ru(bpy)3 2+ /(GO/PDDA)5 /ITO and Ru(bpy)3 2+ /Nafion/ITO. These results suggested that Ru(bpy)3 2+ can retain stably in (AA–GO–SO3 − /PDDA)5 /ITO than in underivatized GO and Nafion and charge transfer through composite film of GO–SO3 − /PDDA was fast. The long-term stability of Ru(bpy)3 2+ /(AA–GO–SO3 − /PDDA)5 /ITO as ECL sensor was investigated within one week under continuous use. The sensor was stored at RT and used for ECL measurement everyday (each measurement operating of 1.5 h). ECL intensity under continuous use in one weeks was shown in Fig. 6B and decreased less than 10%. This good stability could be attributed to the stable interaction between Ru(bpy)3 2+ and GO–SO3 − , which prevented the incorporated Ru(bpy)3 2+ from leaching into the solution. For sensitivity studies, Ru(bpy)3 2+ /(AA–GO–SO3 − /PDDA)5 /ITO was used to determine TPA and ECL signal varies linearly with the concentration of TPA ranging from 5.0 × 10−7 to 5.0 × 10−4 M with a correlation coefficient of 0.996. The detection limit of TPA was

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G. Chen et al. / Biosensors and Bioelectronics 26 (2011) 3136–3141

6000

sensor for detection of organic amines, and the sensor had high stability and sensitivity toward TPA analysis. So sulfonic derivatized GO can be used as cationic ionomer and was a promising material for reagentless Ru(bpy)3 2+ ECL sensor design.

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J.L. and Q.Y. thank Natural Science Foundation of China for Funding (21075058, 21005036, 20875042), J.J. thanks Natural Science Foundation of China for Funding (20805044). This work was also supported by Higher Educational Science and Technology Program of Shandong (J10LB12), Natural Science Foundation (ZR2010BZ004, 2010GJC20808-15) and Tai-Shan Scholar Research Fund of Shandong Province.

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References

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Intensity (a.u.)

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Time / Day Fig. 6. (A) ECL intensity-time curve under continuous CVs for 46 cycles of Ru(bpy)3 2+ /(AA–GO–SO3 − /PDDA)5 /ITO, Ru(bpy)3 2+ /(GO/PDDA)5 /ITO (inset a) and Ru(bpy)3 2+ /Nafion/ITO (inset b) in 50 mM PBS (pH 7.4) with 5.0 × 10−5 M TPA the scan rate of 50 mV/s. (B) ECL intensity–time curve (day to day) under continuous CVs of Ru(bpy)3 2+ /(AA–GO–SO3 − /PDDA)5 /ITO electrode in 50 mM PBS (pH 7.4) with 5.0 × 10−5 M TPA, the scan rate of 50 mV/s.

1 × 10−9 M, which was obtained from the ECL intensity based on ratio of signal to noise of 3. And this value was lower than the reported results comperable to the reported results (50 mM (Li et al., 2009a), 10 nM (Qi et al., 2008)). 4. Conclusions In conclusion, the sulfonic groups have been grafted onto GO through different routes. GO–SO3 − had ordered stacking structure and can be used as ion-exchange materials and the ion-exchange capacity increased in the order: GO < CA–GO–SO3 − < CD–GO–SO3 − < AD–GO–SO3 − < AA–GO–SO3 − . GO–SO3 − materials (AD–GO–SO3 − , AA–GO–SO3 − ) have higher ion-exchange capacity than the cationic ionomer, Nafion. After LBL assembling of GO–SO3 − and PDDA, the obtained (GO–SO3 − /PDDA)n /ITO was used to incorporate Ru(bpy)3 2+ and Ru(bpy)3 2+ can retain in the multilayer film stably. The resulted Ru(bpy)3 2+ /(GO–SO3 − /PDDA)5 /ITO electrode was used as ECL

Allen, M.J., Tung, V.C., Kaner, R.B., 2010. Chem. Rev. 110, 132–145. Bai, H., Li, C., Wang, X., Shi, G., 2010. Chem. Commun. 46, 2376–2378. Cerveny, S., Barroso-Bujans, F., Alegria, A., Colmenero, J., 2010. J. Phys. Chem. C 114, 2604–2612. Che, J., Shen, L., Xiao, Y., 2010. J. Mater. Chem. 20, 1722–1727. Chen, Y., Chen, J., Sun, J., Zhang, L., Chen, G., 2007. J. Chromatogr. A 1172, 84–91. Hassan, H.M.A., Abdelsayed, V., Khder, A.E.R.S., AbouZeid, K.M., Terner, J., El-Shall, M.S., Al-Resayesb, S.I., El-Azhary, A.A., 2009. J. Mater. Chem. 19, 3832–3837. López-González, J.d.D., Martín-Rodríguez, A., Domínguez-Vega, F., 1969. Carbon 7, 583–588. Lerf, A., He, H., Forster, M., Klinowski, J., 1998. J. Phys. Chem. B 102, 4477–4482. Li, H., Chen, J., Han, S., Niu, W., Liu, X., Xu, G., 2009a. Talanta 79, 165–170. Li, H., Lu, T., Pan, L., Zhang, Y., Sun, Z., 2009b. J. Mater. Chem. 19, 6773–6779. Li, M., Liu, J., Zhao, C., Sun, L., 2006. J. Organomet. Chem. 691, 4189–4195. Li, Y., Yang, F., Yang, X., 2009c. Analyst 134, 2100–2105. Loh, K.P., Bao, Q., Ang, P.K., Yang, J., 2010. J. Mater. Chem. 20, 2277–2289. Martín-Rodríguez, A., López-González, J.d.D., Domínguez-Vega, F., 1969. Carbon 7, 589–594. Matsuo, Y., Higashika, S., Kimura, K., Miyamoto, Y., Fukutsuka, T., Sugie, Y., 2002. J. Mater. Chem. 12, 1592–1596. Meyer, J.C., Geim, A.K., Katsnelson, M.I., Novoselov, K.S., Booth, T.J., Roth, S., 2007. Nature 446, 60–63. Park, S., Lee, K.-S., Bozoklu, G., Cai, W., Nguyen, S.T., Ruoff, R.S., 2008. ACS Nano 2, 572–578. Petit, C., Seredych, M., Bandosz, T.J., 2009. J. Mater. Chem. 19, 9176–9185. Qi, B., Yin, X.-B., Du, Y., Yang, X., 2008. Mater. Lett. 62, 458–461. Seredych, M., Bandosz, T.J., 2007. J. Phys. Chem. C 111, 15596–15604. Seredych, M., Petit, C., Tamashausky, A.V., Bandosz, T.J., 2009. Carbon 47, 445–456. Seredych, M., Pietrzak, R., Bandosz, T.J., 2007. Ind. Eng. Chem. Res. 46, 6925–6935. Shen, J., Hu, Y., Shi, M., Lu, X., Qin, C., Li, C., Ye, M., 2009. Chem. Mater. 21, 3514–3520. Sun, X., Du, Y., Dong, S., Wang, E., 2005. Anal. Chem. 77, 8166–8169. Wang, H., Hao, Q., Yang, X., Lu, L., Wang, X., 2010a. ACS Appl. Mater. Interfaces 2, 821–828. Wang, Y., Li, Z., Hu, D., Lin, C.-T., Li, J., Lin, Y., 2010b. J. Am. Chem. Soc. 132, 9274–9276. Wang, Y., Lu, J., Tang, L., Chang, H., Li, J., 2009. Anal. Chem. 81, 9710–9715. Wu, J., Tang, Q., Sun, H., Lin, J., Ao, H., Huang, M., Huang, Y., 2008. Langmuir 24, 4800–4805. Wu, S., Yin, Z., He, Q., Huang, X., Zhou, X., Zhang, H., 2010. J. Phys. Chem. C 114, 11816–11821. Xu, Y., Bai, H., Lu, G., Li, C., Shi, G., 2008. J. Am. Chem. Soc. 130, 5856–5857. Yagi, M., Nagai, K., Onikubo, T., Kaneko, M., 1994. J. Electroanal. Chem. 383, 61–66. Yagi, M., Nagai, K., Kira, A., Kaneko, M., 1995. J. Electroanal. Chem. 394, 169–175. Yagi, M., Mitsumoto, T., Kaneko, M., 1997. J. Electroanal. Chem. 437, 219–223. Yang, H., Li, F., Shan, C., Han, D., Zhang, Q., Niu, L., Ivaska, A., 2009. J. Mater. Chem. 19, 4632–4638. Zhang, J., Yagi, M., Hou, X., Kaneko, M., 1996. J. Electroanal. Chem. 412, 159–164. Zhang, J., Zhang, F., Yang, H., Huang, X., Liu, H., Zhang, J., Guo, S., 2010. Langmuir 26, 6083–6085. Zhang, L., Li, J., Xu, Y., Zhai, Y., Li, Y., Wang, E., 2009. Talanta 79, 454–459. Zhou, M., Zhai, Y., Dong, S., 2009. Anal. Chem. 81, 5603–5613. Zhu, D., Xing, D., Shen, X., Liu, J., 2004. Biochem. Biophys. Res. Commun. 324, 964–969. Zhu, D., Tang, Y., Xing, D., Chen, W.R., 2008. Anal. Chem. 80, 3566–3571. Zhu, D., Zhou, X., Xing, D., 2010. Biosens. Bioelectron. 26, 285–288.