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Accepted Manuscript
Title: Electrochemical determination of tartrazine using amolecularly imprinted polymer multiwalled carbonnanotubes - ionic liquid supported Pt nanoparticles compositefilm coated electrode
Author: Lijuan Zhao Baizhao Zeng Faqiong Zhao
PII: S0013-4686(14)01802-7DOI: http://dx.doi.org/doi:10.1016/j.electacta.2014.08.108Reference: EA 23336
To appear in: Electrochimica Acta
Received date: 17-7-2014Revised date: 25-8-2014Accepted date: 25-8-2014
Please cite this article as: L. Zhao, B. Zeng, F. Zhao, Electrochemical determination oftartrazine using a molecularly imprinted polymer ndash multiwalled carbon nanotubes -ionic liquid supported Pt nanoparticles composite film coated electrode, ElectrochimicaActa (2014), http://dx.doi.org/10.1016/j.electacta.2014.08.108This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.
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Graphical Abstract
The novel tartrazine imprinted polymer multiwalled carbon nanotubes - ionic liquid
supported Pt nanoparticles composite film coated glassy carbon electrode shows high
sensitivity and selectivity to tartrazine.
Graphical Abstract (for review)
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Highlights
A novel tartrazine imprinted polymer based senor was fabricated.
MWNTs-IL supported Pt nanoparticles composition was used to enhance sensitivity.
The IL functionalized MWNTs was prepared using Click chemistry.
The sensor showed high selective and sensitive response in sensing tartrazine.
Research Highlights
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Electrochemical determination of tartrazine using a molecularly 1
imprinted polymer multiwalled carbon nanotubes - ionic liquid 2
supported Pt nanoparticles composite film coated electrode 3
Lijuan Zhao, Baizhao Zeng, Faqiong Zhao 4
Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of 5
Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 6
430072, Hubei Province, P. R. China 7
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Corresponding author. Tel: 86-27-68752701, Fax: 86-27-68754067.
E-mail address: [email protected] (FQ Zhao)
*Revised Manuscript (including Abstract)
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Abstract 22
A novel tartrazine imprinted polymer multiwalled carbon nanotubes - ionic 23
liquid supported Pt nanoparticles composite film coated glassy carbon electrode 24
(MIPMWNTs-IL@PtNPs/GCE) was presented. It was fabricated by coating a GCE 25
with MWNTs-IL@PtNPs mixture, followed by MIP suspension. The IL 26
functionalized MWNTs was prepared by Click chemistry, and Pt nanoparticles were 27
then loaded on it using ethylene glycol as reducing agent. The MIP was prepared by 28
typical free radical polymerization using 4-vinylpyridine as functional monomer. The 29
resulting MIPMWNTs-IL@PtNPs/GCE showed good analytical performance when 30
it was used for the electrochemical determination of tartrazine. Under the optimized 31
conditions, the peak current was linear to tartrazine concentration in the ranges of 32
0.03 5.0 M and 5.0 20 M with sensitivities of 0.72 A/M mm2 and 0.24 33
A/M mm2, respectively; the detection limit was 8 nM (S/N=3). The sensor was 34
successfully applied to the determination of tartrazine in practical samples and the 35
recovery for the standards added was 96 108 %. 36
Keywords: Tartrazine; Molecularly imprinted polymer; Click chemistry; Pt 37
nanoparticles; Electrochemical sensor 38
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1. Introduction 44
Tartrazine (TT, Fig. S1) is a synthetic organic food dye that can be found in 45
common food products such as beverages, candies, dairy products and bakery 46
products [1, 2]. However, the content of TT must be controlled due to its potential 47
harmfulness to human beings [3, 4]. In China, the permitted maximum limit of TT 48
additive in foods is 0.1 g/kg (individually or in combination) (GB2760-1996) [5]. The 49
assay of TT in foods can be carried out using many techniques, such as 50
spectrophotometry [6], high performance liquid chromatographymass spectrometry 51
(HPLCMS) [7] and capillary electrophoresis [8]. In recent years, sensitive 52
electrochemical methods for the determination of TT were proposed [1-5, 9]. 53
Especially, Jiang et al. [10] prepared a molecularly imprinted polypyrrole sensor for 54
the detection of TT, using K3Fe(CN)6 as probe, which not only showed high 55
sensitivity but also had high selectivity due to the superior properties of molecularly 56
imprinted polymer (MIP) [11, 12]. However, there is no report on the direct 57
electrochemical determination of TT with a MIP based sensor. 58
To improve the performance of electrochemical MIP sensors, support material 59
is generally carefully selected. Multiwalled carbon nanotubes (MWNTs) and MWNTs 60
based composite materials are favorable candidates due to their high specific surface 61
area, electrical conductivity and chemical stability [13, 14]. For example, metal 62
nanoparticles-MWNTs compositions have received increasing interest. They have 63
potential application in sensor [15], electrochemical determination [16] and catalysis 64
[17], and several routes have been developed to prepare metal nanoparticles-MWNTs 65
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compositions, including chemical deposition [18], electrochemical deposition [19] 66
and the direct assembly of metal nanoparticles [20]. However, MWNTs without 67
surface modification are short of sufficient binding sites for anchoring metal 68
nanoparticles, which usually leads to poor dispersion of metal nanoparticles [21]. To 69
improve the situation, surface functionalization of MWNTs is generally necessary. 70
Ionic liquid (IL) shows great potential for overcoming the above mentioned 71
issue due to its high chemical stability, good solubility, high ionic conductivity and 72
wide electrochemical window [22, 23]. Functionalization of MWNTs with IL is 73
expected to improve conductivity, compatibility and stability, and to make full use of 74
MWNTs in sensors [24]. In addition, IL was also used as solvent and stabilizer to 75
produce metal nanoparticles [25, 26], and it was found that the low interfacial tension 76
of IL resulted in high nucleation rates, allowing generation of very small particles [27]. 77
For example, Niu et al. [28] used MWNTs-IL to support Au nanoparticles, the 78
gold-nanoparticle/MWNTs-IL nanohybrid showed good electrocatalysis toward 79
oxygen reduction. In that case, the MWNTs-IL was prepared through chemical 80
bonding, which allowed chemical tailoring of surface properties and provided higher 81
degree of tenability compared with noncovalent functionalization [29]. Up to now, 82
common esterification [30] and amidation [28] reactions have been developed to 83
enable the covalent attachment of IL onto MWNTs. 84
So far, the Cu(I)-catalyzed azide/alkyne Click (CuAAC) reaction has received a 85
great deal of attention from researchers in fields ranging from organic synthesis to 86
material chemistry, and it is one of the most versatile methods for the conjugation of 87
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complex organic moieties with nanoscopic objects such as quantum dots, biomaterials, 88
and carbon nanotubes [31-33]. The main advantages of Click chemistry are 89
suppleness, toleration of other functional groups, stereospecificity and quantitative 90
transformation in high yield and purity [34, 35]. Moreover, the nanoconjugate of IL 91
and MWNTs using such method can show remarkable solubility and stability in 92
aqueous solvents because the triazole ring can participate in the hydrogen bonding 93
[29]. However, to the best of our knowledge, there is no report on the preparation of 94
IL functionalized MWNTs using Click chemistry, let alone the preparation of such 95
composition supported Pt nanoparticles. 96
Herein, we firstly reported a facile and highly efficient approach to obtain IL 97
functionalized MWNTs supported Pt nanoparticles. The approach involved the 98
synthesis of azide functionalized MWNTs with IL using Click chemistry, then Pt 99
nanoparticles were supported using ethylene glycol as reducing agent. As a result, 100
when MIP was dropped on the MWNTs-IL@PtNPs modified GCE for detecting TT, 101
the resulting sensor (MIPMWNTs-IL@PtNPs/GCE) showed high sensitivity and 102
selectivity and it was successfully applied to the detection of TT in practical samples. 103
2. Experimental 104
2.1. Reagents 105
Tratarzine, sunset yellow, Amaranth, Brilliant blue G and Allura red were 106
purchased from Aladdin Chemistry Co., Ltd. (Shanghai, China) and their stock 107
solutions (0.010 M) were prepared with water and stored in a refrigerator at 4 C. 108
2,2`-Azobis-(isobutyronitrile) (AIBN) was obtained from Shanghai Shisihewei 109
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Chemical Industry Limited Company (China). 4-Vinylpyridine (4-VP) and ethylene 110
glycol dimethacrylate (EGDMA) were purchased from Sigma-Aldrich (Madrid, Spain) 111
and purified by distillation under vacuum. 1-Butylimidazole (purity: 99%) and 112
propargyl bromide came from J&K Chemical Ltd. (Shanghai, China). Ionic liquid 113
1-propargyl-3-butyl imidazolium bromide was synthesized according to the literature 114
[36] (see Supplementary Materials). The short multiwalled carbon nanotubes (OD: 10 115
- 20 nm, length: 0.5 - 2 m) came from Xianfeng Reagent Co. Ltd. (Nanjing, China). 116
All other chemicals used were of analytical reagent grade. The water used was 117
redistilled. 118
2.2. Apparatus 119
Cyclic voltammetric and differential pulse voltammetric experiments were 120
performed with a CHI 620D electrochemical workstation (CH Instrument Company, 121
Shanghai, China). A conventional three-electrode system was adopted. The working 122
electrode was a modied GCE (diameter: 2 mm), and the auxiliary and reference 123
electrodes were a platinum wire and a saturated calomel electrode (SCE), respectively. 124
The scanning electron microscope (SEM) images were obtained using field emission 125
SEM (ZEISS, Germany). Transmission electron microscopy (TEM) images were 126
obtained using JEOL Ltd. Ultraviolet visible (UV-vis) absorption spectra were 127
recorded by a U-3900 spectrometer (Hitachi Co., Japan). The Fourie transform 128
infrared (FT-IR) absorption spectra were recorded with a model Nexus-670 129
spectrometer (Nicolet, USA). The pH values of solutions were measured with a 130
pHS-2 meter (Leici Instrumental Factory, Shanghai, China). All experiments were 131
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carried out at room temperature. 132
2.3. Click coupling between propargyl IL and N3-MWNTs 133
Azide functionalized MWNTs (N3-MWNTs) was synthesized according to the 134
literature [29]. The nanoconjugate of propargyl IL grafted MWNTs was synthesized 135
via Click reaction. Briefly, 50 mg N3-MWNTs was dispersed in 10 mL 136
tert-butanol/water (1:1, V/V) solution and 0.5 mmol propargyl IL (95.5 mg) was 137
added. Then, 0.05 mmol CuSO45H2O (12.5 mg) and 0.25 mmol sodium ascorbate 138
(49.5 mg) were added as catalysts at room temperature. After stirred for 24 h at room 139
temperature, the solid was separated from the mixture by centrifugation. The products 140
were washed with water and ethanol for three times. Then, the collected solid (i.e. 141
MWNTs-IL) was dried at 40 C under vacuum. 142
2.4. Synthesis of MWNTs-IL supported Pt nanoparticles 143
The simple sketch for synthesis is shown in Scheme 1. At first, 25 mg 144
MWNTs-IL was dispersed in 10 mL ethylene glycol (EG) and sonicated for 1 h. 145
Subsequently, 2.65 mL of H2PtCl6-EG solution (5.0 mg/mL) was added to the 146
MWNTs-IL solution and sonicated for 0.5 h. The pH of the solution was adjusted to 147
10 using NaOH-EG solution (0.5 M), and then the solution was stirred under flowing 148
argon at 130 C for 3 h. Afterwards, the solid material produced was centrifuged, 149
washed three times with deionized water and finally dried at 40 C under vacuum for 150
24 h. Thus MWNTs-IL supported Pt nanoparticles (MWNTs-IL@PtNPs) were 151
obtained. 152
2.5. Preparation of molecularly imprinted polymer 153
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The MIP was prepared through a typical precipitation polymerization. TT (1 154
mmol), 4-VP (4 mmol) and methanol/water (100 mL, 4:1, V/V) were added into a 155
one-neck roundbottom flask (250 mL) successively, and a clear homogeneous 156
solution was obtained, to which EGDMA (20 mmol) and AIBN (0.16 mmol) were 157
added successively. After being purged with argon for 15 min, the flask was then 158
sealed and immersed into a thermostatted oil bath at 60 C for 24 h. When the 159
polymerization was completed, the resulting polymer was collected by centrifugation 160
and it was purified through Soxhlet extraction with methanol-acetic acid (9:1, V/V, 161
for 48 h) and then methanol (for 24 h) until no template could be detected in the 162
extraction solution, and the polymer was dried at 40 C under vacuum to the constant 163
weight. Similarly, the non-imprinted polymer (NIP) was prepared and purified under 164
the identical conditions except that the template was omitted. 165
2.6. Preparation of sensors 166
The bare GCE was polished with slurry alumina (0.05 m), and then washed 167
thoroughly with water, with the aid of ultrasonication. Then 4.0 L 168
MWNTs-IL@PtNPs suspension (1 mg/mL in water) was drop cast on the cleaned 169
GCE. After the solvent was evaporated under an infrared lamp, 6.0 L MIP 170
suspension (2 mg/mL in DMF) was dropped onto the resulting 171
MWNTs-IL@PtNPs/GCE and let to dry in air. Thus a MIPMWNTs-IL@PtNPs film 172
coated GCE (MIPMWNTs-IL@PtNPs/GCE) was obtained. Similarly, a 173
NIPMWNTs-IL@PtNPs/GCE sensor was prepared. 174
2.6. Determination of adsorption amount 175
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The equilibrium adsorption amounts were determined to evaluate the selective 176
rebinding property of the obtained MIP and NIP materials. A 5 mg MIP (or NIP) 177
material was added to 5 mL TT solutions (containing 20 M 0.23 mM TT); after 178
stirring for 12 h at room temperature, the mixture was centrifuged and the supernatant 179
was collected and determined by UV-vis absorption spectrometry. The adsorption 180
amount was calculated according to the formula: Q = V (C0 - CS)/m, where V, C0, CS 181
and m represented the volume of solution (L), initial solution concentration (M), the 182
solution concentration after rebinding (M) and the mass of MIP (or NIP) material (g), 183
respectively. 184
2.7. Electrochemical measurements 185
Electrochemical investigation of TT was carried out in an electrochemical cell 186
containing 10 mL of 0.2 M PBS (pH = 7.0) and proper TT. After accumulation for 8 187
min under open-circuit, cyclic voltammograms (CVs) or differential pulse 188
voltammograms (DPVs) were recorded in another blank PBS (pH = 7.0). The 189
potential scan range was 0.4 V 1.1 V. After every measurement, the electrode was 190
rinsed with methanol-acetic acid solution (9:1, V/V) to remove TT for reuse. 191
3. Results and discussion 192
3.1. Preparation of MWNTs-IL supported Pt nanoparticles 193
In this work, the surface of MWNTs was functionalized with IL via two-step. 194
Firstly, azide functionalized MWNTs was prepared using iodine azide reagent, in 195
which the azide groups were introduced to the edges of MWNTs, presumably via a 196
Hassner-type addition of IN3 to the double bonds and subsequent elimination of HI 197
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[37]. In the following step, IL was chemically anchored to the N3-MWNTs surface via 198
Click reaction to form an IL overlayer, which facilitated the load of PtNPs. Afterwards, 199
MWNTs-IL@PtNPs was prepared by using EG as solvent and reducing agent. It 200
should be pointed out that in this case the imidazole groups of MWNTs-IL served as 201
functional group for the immobilization of Pt precursor through electrostatic 202
interaction and coordination [38]. Therefore, PtNPs revealed well distribution on the 203
surface of MWNTs-IL. 204
3.2. Morphological and structural characterization 205
Fig. 1 shows the TEMs of MWNTs-IL supported PtNPs with different 206
magnifications, and they confirmed that the MWNTs-IL was decorated successfully 207
with many well-dispersed PtNPs. The average size of PtNPs was 1.7 nm. Furthermore, 208
the CVs of PtNPs supported was recorded in a 0.5 M H2SO4 solution (Fig. S2). 209
Compared with MWNTs-IL/GCE, typical hydrogen adsorption/desorption peaks were 210
observed for the MWNTs-IL@PtNPs/GCE in the potential range of -0.2 V 0 V, and 211
the cathodic peak around 0.31 V was due to the reduction of Pt oxide. 212
Fig. 2 shows the FT-IR spectra of azide functionalized MWNTs, propargyl IL 213
and MWNTs-IL. The absorption at 2053 cm-1
(Fig. 2a) should be ascribed to N3 214
stretching, and the peak at 1723 cm-1
was due to C=O stretching of carboxyl of 215
MWNTs, which suggested that azide functionalized MWNTs was obtained. The 216
propargyl IL exhibited a peak at 2131 cm-1
(Fig. 2b), which was assigned to CH 217
stretching vibration. Furthermore, the characteristic vibration bands (1563, 1459 and 218
1158 cm1
) were corresponding to the imidazolium cation. As shown in Fig. 2c, after 219
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the Click reaction, these bands of imidazolium cation appeared, and the peaks of N3 220
and CH completely disappeared. This indicated that MWNTs-IL was synthesized 221
successfully. 222
SEM was also employed to observe the morphology of MIP and NIP materials. 223
As shown in Fig. 3, the MIP showed reticular structure and the size of particles was 224
small. However, the NIP was spherical, with an average size of 1 m. This indicated 225
that the template had profound influence on particle nucleation and growth during the 226
precipitation polymerization. The influence of template was in agreement with 227
previously reported results. In the non-imprinted system, the functional monomer 228
4-VP could form dimmers by hydrogen-bond and the solution contains both free 4-VP 229
and 4-VP dimmers. But in the imprinted system, there was an additional molecular 230
interaction between 4-VP and the template, which might somehow affect the growth 231
of the cross-linked polymer nuclei and resulted in the formation of smaller polymer 232
particles [39]. 233
3.3. Adsorption curves 234
The equilibrium template binding results of MIP and NIP materials were shown 235
in Fig. S3. The MIP material bond more template than NIP and changed with its 236
concentration more rapidly, suggesting the presence of specific binding sites in the 237
MIP material. When TT concentration exceeded 1.8 104
M, the adsorption amount 238
stayed almost unchanged. The maximum adsorption amount of MIP was about 77.3 239
mol/g. For the NIP, the adsorption amount of TT changed more slowly with increase 240
of TT concentration. Similarly, when TT concentration exceeded 1.3 104
M, the 241
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adsorption curve exhibited a platform. This means that a saturated adsorption was 242
achieved and the adsorption capacity of NIP was about 22.8 mol/g, which was much 243
smaller than that of MIP. These results also partially accounted the higher surface area 244
of the MIP material compared to NIP (as confirmed by SEM). As the surface area of 245
MIP material was higher, its adsorption amount was higher too, besides its enhanced 246
adsorption. Obviously, through molecular imprinting, the adsorption amount of TT 247
was greatly enhanced. 248
3.4. Voltammetric behavior of TT 249
Fig. 4 shows the electrochemical behavior of 50 M TT at different modified 250
electrodes. TT exhibited only an anodic peak at about +0.92 V, revealing that TT 251
underwent a totally irreversible process (Fig. S4). At the MIP/GCE, TT produced a 252
small peak, this can be ascribed to the poor conductivity and small effective surface 253
area of MIP (curve a). At the MIPMWNTs/GCE (curve b), the peak current of TT 254
increased inconspicuously and the background was larger than that of MIP/GCE, 255
meaning that MWNTs can significantly enhance the current response. But the CV of 256
MIPMWNTs-IL/GCE exhibited one well-defined peak and bigger background, due 257
to the better conductivity of MWNTs-IL and the preconcentration effect of IL. 258
Compared with other modified GCEs, the MIPMWNTs-IL@PtNPs/GCE produced a 259
remarkable high peak for TT (curve d). This could be ascribed to the electrocatalysis 260
of PtNPs because they could accelerate the electron transfer and provide the necessary 261
conduction pathway [40]. It should be pointed out that the 262
MIPMWNTs-IL@PtNPs/GCE showed greater peak current than 263
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NIPMWNTs-IL@PtNPs/GCE (inset), indicating that the MIP also played an 264
important role in sensing TT. Therefore, the MIP-MWNTs-IL@PtNPs/GCE virtually 265
combined the effect of MIP, PtNPs, MWNTs and IL, and thus showed excellent 266
electrochemical response and selectivity to TT. 267
3.5. Optimization of conditions 268
3.5.1. The amount of MWNTs-IL@PtNPs and MIP 269
The influence of MWNTs-IL@PtNPs and MIP on the voltammetric response of 270
TT was explored. Results showed that the peak current increased quickly by 271
increasing the volume of MWNTs-IL@PtNPs suspension and it reached the 272
maximum value at 4.0 L (Fig. 5A), then a further increase caused a gradual decrease. 273
This was caused by the increase of film thickness of MWNTs-IL@PtNPs, generating 274
an obvious increase of the interface electron transfer resistance. Therefore, 4.0 L of 275
MWNTs-IL@PtNPs suspension was adopted for further study. 276
As for the amount of MIP, when it was lower (e.g. 2.0 or 4.0 L, 2 mg/mL), the 277
peak current was higher, but the selectivity was poor; when it was too much (e.g. 8.0 278
L), the MIP easily peeled off the electrode surface. Here, the optimum amount of 279
MIP suspension was 6.0 L. 280
3.5.2. Solution pH 281
Solution pH was one of the most important parameters for the practical 282
application, which was studied over the range of 5.0 - 9.0 (consisting of Na2HPO4 and 283
NaH2PO4). It was observed that the peak current got the maximum at pH 7.0 (Fig. 5B). 284
Thus, pH 7.0 PBS was selected as the supporting electrolyte in this study. Besides, the 285
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effect of pH value on the peak potential was examined. With increasing pH, the 286
oxidation peak potential gradually shifted negatively, suggesting that proton was 287
involved in the electrochemical reaction of TT. 288
3.5.3. Accumulation time 289
The effect of preconcentration time on peak current was tested (Fig. 5C). It was 290
clear that the peak current of TT increased gradually and then reached a plateau after 291
8 min, meaning that 8 min was sufficient for TT to reach the saturated rebinding onto 292
the MIPMWNTs-IL@PtNPs/GCE. Consequently, 8 min was selected as the optimal 293
accumulation time. 294
3.6. Calibration curve 295
Fig. 6 shows the DPVs of TT under the optimized experimental conditions. It can 296
be seen that the peak current increases with increasing TT concentration, and good 297
linear relationships are obtained in the ranges of 0.03 - 5.0 M and 5.0 - 20 M. The 298
regression equations are IP (A) = 2.251c (M) + 0.146 (R2 = 0.9932) and IP (A) = 299
0.758c (M) + 7.717 (R2 = 0.9962), with sensitivities of 0.72 A/M mm2 and 0.24 300
A/M mm2 respectively. We think this is related to the specific adsorption and mixed 301
adsorption (i.e. specific and nonspecific adsorption) of TT. At lower concentration, 302
specific adsorption dominates, while at higher concentration, mixed adsorption 303
dominates. As the specific adsorption is stronger, the sensitivity is higher. In this case, 304
the limit of detection is ca. 8 nM (S/N=3). The comparison of the 305
MIPMWNTs-IL@PtNPs/GCE with other methods for TT determination is listed in 306
Table 1 [1-4, 10, 41-43]. It can be seen that the MIPMWNTs-IL@PtNPs/GCE offers 307
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a relatively wide linear range and a lower detection limit. The 308
NIPMWNTs-IL@PtNPs/GCE shows a smaller linear range and lower sensitivity 309
than the MIPMWNTs-IL@PtNPs/GCE, which can be explained by the lack of 310
specific binding sites on the NIP film. 311
3.7. Selectivity, repeatability and stability 312
The selectivity of the MIPMWNTs-IL@PtNPs/GCE was evaluated by testing 313
the electrochemical response of 1.0 M TT in the presence of 10-fold excess of 314
interfering substances, such as sunset yellow, Allura red and Brilliant blue G, 315
Amaranth and sodium salicylate. As shown in Fig. 7, when the interfering substances 316
were present, the peak current showed small change (from 95 % to 102 %) for TT, 317
which indicated that the MIPMWNTs-IL@PtNPs/GCE had good selectivity. 318
To evaluate the reproducibility, five MIPMWNTs-IL@PtNPs/GCEs were 319
prepared by the same way and a 1.0 M TT solution was determined. As a result, the 320
relative standard deviation (RSD) of the peak current was 5.7 % (n = 5). The 321
repeatability was investigated by monitoring a 1.0 M TT solution using one modified 322
electrode, and the RSD of peak current was 3.9 % (n = 5). After stored for two week 323
in a refrigerator, the MIPMWNTs-IL@PtNPs/GCE retained 93% of its initial current 324
response for 1.0 M TT; after one month-storage, it still retained 86% of its initial 325
current response. These reflected the good reproducibility and stability of 326
MIPMWNTs-IL@PtNPs/GCE. 327
3.8. Application 328
Finally, in order to test the practical application of the proposed electrochemical 329
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sensor, the MIPMWNTs-IL@PtNPs/GCE was applied to the determination of TT in 330
practical samples, including Fanta drink, Mirinda drink and orange powder. The drink 331
samples were purchased from a local market. For the determination, 2.0 mL Fanta 332
drink, Mirinda drink or 100 mg orange powder was taken, and dissolved in 10 mL 333
PBS (pH 7.0). The results are shown in Table 2, in the three samples, the TT 334
concentrations are ca. 1.31 M, 1.34 M and 1.82 M, respectively. In addition, the 335
accuracy of the proposed method was testified by performing a recovery test after 336
spiking the samples. The value of recovery was between 96% and 108% and the RSD 337
was below 5%. This suggested that the method had good accuracy and reliability, and 338
the sensor showed good applicability in the detection of TT in real samples. 339
4. Conclusions 340
In conclusion, a novel molecularly imprinted polymer ionic liquid 341
functionalized multiwalled carbon nanotubes supported PtNPs composite film coated 342
glassy carbon electrode was fabricated for TT sensing, in which IL functionalized 343
MWNTs was prepared by Click chemistry, and PtNPs were prepared using ethylene 344
glycol as reducing agent. In the composite film, MWNTs provided large surface, IL 345
acted as anchors to immobilize PtNPs, PtNPs showed electrocatalysis and MIP was 346
recognization element. The modified electrode exhibited high selectivity, 347
reproducibility and sensitivity. The novel strategy reported herein can be further used 348
in constructing sensors for other objects. 349
5. Acknowledgements 350
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The authors appreciate the financial support of the National Natural Science 351
Foundation of China (Grant No.: 21277105). 352
353
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492
Captions 493
Scheme 1 Schematic diagram of the modification of MWNTs with IL and the 494
preparation of MWNTs-IL@PtNPs composition. 495
Table 1 Comparison of different electrochemical sensors for TT. 496
Table 2 Determination results of TT in practical samples using a 497
MIPMWNTs-IL@PtNPs/GCE (n=3). 498
Fig. 1. TEM images of MWNTs-IL@PtNPs at different magnifications. 499
Fig. 2. FT-IR spectra of azide functionalized MWNTs (a); propargyl IL (b) and 500
MWNTs-Click-IL (c). 501
Fig. 3. SEM images of the MIP (A) and NIP (B) materials. 502
Fig. 4. Cyclic voltammograms of MIP/GCE (a), MIPMWNTs/GCE (b), 503
MIPMWNTs-IL/GCE (c) and MIPMWNTs-IL@PtNPs/GCE (d) in pH 7.0 PBS 504
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24
containing 50 M TT. Inset: the CVs of MIPMWNTs-IL@PtNPs/GCE and 505
NIPMWNTs-IL@PtNPs/GCE; scan rate: 50 mV s-1. 506
Fig. 5. Optimization of different conditions affecting the determination of 1.0 M TT 507
solution. (A) Influence of the amount of MWNTs-IL@PtNPs used; (B) influence of 508
solution pH; inset: the plot of peak potential versus pH; (C) influence of accumulation 509
time. Other conditions as in Fig. 4. 510
Fig. 6. (A) Differential pulse voltammograms of TT at 511
MIPMWNTs-IL@PtNPs/GCE. TT concentration: 0.05, 0.1, 0.5, 0.8, 1, 3, 5, 8, 10, 512
13, 15, 18, 20 M (from a to m). (B) The calibration curves for TT at 513
MIPMWNTs-IL@PtNPs/GCE and NIPMWNTs-IL@PtNPs/GCE. Other conditions 514
as in Fig. 4. 515
Fig. 7. Influence of coexistent substances on the electrochemical response of 516
MIPMWNTs-IL@PtNPs/GCE to TT. Solution composition: 1.0 M TT, or 1.0 M 517
TT in the presence of 10-fold excess of sunset yellow, Allura red and Brilliant blue G, 518
Amaranth and sodium salicylate. Other conditions as in Fig. 4. 519
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Scheme 1
Figure(s)
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Fig. 2
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Fig. 4
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Fig. 5
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Fig. 6
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Fig. 7
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Table 1 Comparison of different electrochemical sensors for TT
Electrodes Sensitivity
(A/M/mm2)
Linear range
(M)
Detection
limit (M)
References
Graphene layer-wrapped
phosphotungstic acid
hybrid modified glassy
carbon electrode
- 0.11 - 5.6 0.056 [1]
-Cyclodextrin-coated
poly(diallyldimethylammo
nium chloride)
-functionalized graphene
composite film modified
glassy carbon-rotating disk
electrode
-
0.05 - 20
277 - 586
0.0143 [2]
Acetylene black
nanoparticle-modified
glassy carbon electrode
- 0.28 - 33.7 0.19 [3]
Multi-walled carbon
nanotubes modified glassy
carbon electrode
- 0.37 - 75.0 0.19 [4]
Molecularly imprinted
polymer modified glassy
carbon electrode
0.03 0.001 - 0.01 0.001 [10]
Gold nanoparticles carbon
paste electrode
2.53 0.05 - 1.6 0.002 [41]
Carbon nanotubeionic
liquid nanocamposite
modified sol-gel derived
carbon-ceramic electrode
0.032 3 - 70 1.1 [42]
Cathodically pretreated
boron-doped diamond
electrode
- 0.02 - 4.76 0.062 [43]
MIP-MWNTs-IL@PtNPs
film coated glassy carbon
electrode
0.72
0.24
0.03 - 5.0
5.0 - 20
0.008 This work
Table(s)
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Table 2 Determination results of TT in samples by using a
MIPMWNTs-IL@PtNPs/GCE (n = 3).
Samples Added
(M)
Expected
(M)
Found
(M)
Recovery
(%)
Fanta
drink
0
0.50
3.0
6.0
-
1.81
4.31
6.31
1.31
1.73
4.56
6.46
-
96
106
102
Mirinda
drink
0
0.50
3.0
6.0
-
1.84
4.34
7.34
1.34
1.98
4.20
7.11
-
108
97
97
Orange
powder
0
0.50
3.0
6.0
-
2.32
4.82
7.82
1.82
2.43
4.96
7.70
-
105
103
98
