Biosensors and Bioelectronics 68 (2015) 563–569

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Molecularly imprinted electrochemical sensor for propyl gallate based on PtAu bimetallic nanoparticles modified graphene–carbon nanotube composites Min Cui a, Jiadong Huang b, Yu Wang b, Yumin Wu a,n, Xiliang Luo c,nn a

College of Chemical Engineering, Qingdao University of Science & Technology, Qingdao 266042, PR China School of Biological Science and Technology, University of Jinan, Jinan 250022, PR China c Key Laboratory of Sensor Analysis of Tumor Marker, Ministry of Education, College of Chemistry and Molecular Engineering, Qingdao University of Science & Technology, Qingdao 266042, PR China b

art ic l e i nf o

a b s t r a c t

Article history: Received 28 November 2014 Received in revised form 8 January 2015 Accepted 13 January 2015 Available online 14 January 2015

A novel molecularly imprinted electrochemical sensor for propyl gallate (PG) determination was developed via electropolymerization of an o-phenylenediamine membrane in the presence of template molecules on glassy carbon electrode surface modified by PtAu bimetallic nanoparticles-capped graphene-carbon nanotubes composites (PtAu-GrCNTs). The modified electrodes were characterized by cyclic voltammetry, scanning electron microscope, x-ray diffraction and chronoamperometry. Moreover, experimental parameters such as scan cycles, incubation time, molar ratios of template molecules to functional monomers and extraction time were optimized. It was found that the PtAu-GrCNTs composite could effectively enhance the electron transfer efficiency and remarkably improve the sensitivity of the sensor. The results revealed the sensor displayed superb resistance to no-specific binding, very attractive detection limit as low as 2.51  10  8 mol/L, and a wide linear range from 7  10  8 mol/L to 1  10  5 mol/L towards PG. Furthermore, the MIPs sensor was also successfully used for the detection of PG in food samples. Therefore, the MIPs-based electrochemical sensing strategy might provide a sensitive, rapid, and cost-effective method for PG determination and related food safety analysis. & 2015 Elsevier B.V. All rights reserved.

Keywords: Molecularly imprinted polymers Electrochemical sensor PtAu bimetallic nanoparticles Graphene–carbon nanotubes composites Propyl gallate

1. Introduction Synthetic phenolic antioxidants such as propyl gallate (PG), tertiary butyl hydroquinone (TBHQ), butylated hydroxyanisole (BHA), which have been used in food industry extensively, are playing important roles in retarding oxidation reactions in foodstuffs (Andreu-Navarro et al., 2011; Wang et al., 2012; Richard Prabakar and Sriman Narayanan, 2010). Because of its highly effective preservative ability, PG has been added into various food products including edible oils to avoid food quality decay. However, the addition of PG may cause loss of nourishment and even produce of toxic substances to people health. Therefore, it is important to develop effective methods for sensitive and specific detection of PG in foodstuffs. Nowadays, commonly used approaches for detecting PG mainly include high performance liquid chromatography (HPLC) (Saada et al., 2007), gas chromatography (GC) (Gonzalez et al., 1999) and n

Corresponding author. Fax: þ 86 532 84863434. Corresponding author. Fax: þ 86 532 84022681. E-mail addresses: [email protected] (Y. Wu), [email protected] (X. Luo). nn 0956-5663/& 2015 Elsevier B.V. All rights reserved.

capillary electrophoresis (CE) (Zhao and Hao, 2013). Although these techniques have the advantages of high sensitivity, they may suffer from some drawbacks such as complex pretreatment steps, long assay time, expensive experimental equipment, and consumption of large amounts of reagents. Thus, the development of simple, rapid and cost-effective methods for quantitative assay of PG with high sensitivity still remains a grand challenge. During the last two decades, the molecularly imprinted technique (MIT) has become a valuable tool for molecular recognition owing to its unique advantages such as simplicity, rapidness, and low cost (Lofgreen Jennifer and Ozin Geoffrey, 2014; Emmanuel and Naomi, 2013). Molecularly imprinted polymers (MIPs) are prepared by polymerizing with cross-linkers, functional monomers and template molecules through covalent or non-covalent interactions (Lian et al., 2012; Sindhu et al., 2013). After the removal of template molecules, complementary cavities with the template molecules in shape, size and functional groups are formed, which can rebind template molecules with high specificity (Zheng et al., 2013; Wang et al., 2013; Abbas and Ho, 2014). Due to the high affinity between MIPs (after the extraction of template molecules) and template molecules, MIPs have already been recognized as an effective technique for molecular diagnosis


M. Cui et al. / Biosensors and Bioelectronics 68 (2015) 563–569

(Romana, 2014; Song et al., 2014; Xing et al., 2012). Graphene (Gr), a two-dimensional sheet of carbon atoms bonded by sp2 hybrid (Victor et al., 2014), has attracted considerable attentions in many fields owing to its special properties, such as excellent electrical conductivity, large specific surface area, good biocompatibility, and exceptional mechanical strength (Zhang et al., 2012; Li et al., 2014; Yan et al., 2014). However, Gr tends to aggregate or restack through strong π–π stacking (Niu et al., 2013). One of the effective methods to solve the problem is to decorate Gr sheets with metal nanoparticles and other carbon materials, such as gold nanoparticles (Li et al., 2013), platinum nanoparticles (Jiang et al., 2013), and carbon nanotubes (CNTs) (Akbar et al., 2014; Sun et al., 2013; Mani et al., 2014; Grosse et al., 2013) relying on their high surface area, high chemical stability, outstanding chargetransfer characteristics and low electrical resistance (Elyasi et al., 2013; Doostania et al., 2013; Karimi-Maleh et al., 2013). Moreover, platinum and gold bimetallic nanoparticles (PtAuNPs) have attracted increasing attention as electrode materials to offer an enhanced sensitivity (Deng et al., 2010; Xiao et al., 2013; Basu and Basu, 2011; Wang et al., 2014). Herein, we develop a novel MIPs-based electrochemical sensor for sensitive and specific detection of PG. This sensor is constructed via electropolymerization of an o-phenylenediamine membrane in the presence of template molecules on the surface of a glassy carbon electrode (GCE) modified by PtAu bimetallic nanoparticles-capped graphene–carbon nanotubes (PtAu-GrCNTs) composites. The PtAu-GrCNTs composites as electrode materials can significantly increase the active surface area and enhance the electron transfer efficiency, so as to improve the sensitivity of the electrochemical sensor. Moreover, the sensor has the advantages of rapid, convenient, and low cost detection with simple operation, and it can be successfully applied to detect PG in food samples.

2. Experimental 2.1. Reagents and apparatus Graphite, ethylene glycol, o-phenylenediamine, N,N-dimethyl formamide (DMF) and multiwalled carbon nanotubes (CNTs) were purchased from Aladdin Chemistry Co., Ltd. (Shanghai, China). Propyl gallate (PG), butylated hydroxyanisole (BHA), 2, 6-Di-tertbutyl-4-methylphenol (BHT) and tert-butylhydroquinone (TBHQ) were purchased from Sheng Yu chemical reagent Co., Ltd. (Jinan, China). Chloroauric acid (HAuCl4) and chloroplatinic acid (H2PtCl6) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Several vegetable sample oils were bought from local supermarket. All the solutions were prepared by deionized water. X-ray diffraction (XRD) was collected by x-ray diffractometer (Bruker D8 Focus, Germany) with Cu Kα radiation at 40 kV and 40 mA. Cyclic voltammetry (CV) and chronoamperometry experiments were conducted with a model VersaSTAT 3 electrochemical workstation (Princeton Applied Research, USA). Scanning electron microscopy (SEM) images were performed with field emission SEM (ZEISS, Germany). Electrochemical measurements were carried out with a three-electrode system consisting of a platinum wire auxiliary electrode, a Ag/AgCl reference electrode and a modified GCE as working electrode. 2.2. Synthesis of PtAu-GrCNTs nanoparticles The PtAu-GrCNTs nanoparticles were synthesized via a onestep chemical co-reduction method according to the previous report (Lu et al., 2013) with modification, as shown in Scheme 1A. In brief, firstly, 60 mg of GO and 20 mg of MWCNTs-COOH were added into deionized water and ultrasonically treated for 2 h to form a homogeneous dispersion. Sequentially, 2.08 mL of 1 wt% H2PtCl6 solution, 1.64 mL of 1 wt% HAuCl4 solution and 80 mL of ethylene glycol (EG) were added into the above mixture, and ultrasonically treated for another 1 h. The mixture was heated to 120 °C for 24 h

Scheme 1. (A) Schematic illustration of the preparation process of the PtAu-GrCNTs composite. (B) Schematic illustration of the MIPs sensor for PG determination.

M. Cui et al. / Biosensors and Bioelectronics 68 (2015) 563–569


with stirring. The resulting dispersion solution was filtered and washed by deionized water for several times. After dried, the PtAu-GrCNTs nanoparticles were collected. Before use, 1 mg of PtAu-GrCNTs nanoparticles should be dispersed into 1 mL of N, N-dimethyl formamide and ultrasonically treated for 2 h. Gr-CNTs, Au-GrCNTs, Pt-GrCNTs, PtAu-Gr and PtAu-CNTs nanoparticles were prepared with similar procedures.

functional monomer, respectively, because PG has –OH groups and o-phenylenediamine has –NH2 groups, they could interact with each other through hydrogen bonds. Besides, MIPs film was coated on the PtAu-GrCNTs/GCE surface by electropolymerization, which can form very close contact between the MIPs material and the PtAu-GrCNTs/GCE, and therefore the electric sensing signal can be effectively transferred to the electrode.

2.3. The fabrication processes of the MIPs and non-molecularly imprinted polymers (NIPs) sensors

3.2. Surface morphology of various composites

Bare GCE was polished with 0.05 μm alumina slurry, rinsed thoroughly with deionized water repeatedly and dried at room temperature (RT). Before use, the bare GCE was activated by polarization at þ 1.6 V and  1.6 V for 60 s, respectively. The step by step fabrication process of the MIPs/PtAu-GrCNTs/ GCE was shown in Scheme 1B: (i) 10 μL of PtAu-GrCNTs homogeneous solution was drop-coated on the GCE surface and dried overnight at RT. (ii) o-phenylenediamine polymer film with the PG templates was electrochemically deposited onto the PtAu-GrCNTs/ GCE surface through CV electropolymerization in 0.05 mol/L of phosphate buffer solution (PBS, pH 6.5) containing 0.1 mol/L PG and 0.15 mol/L o-phenylenediamine. CV was conducted between 0.35 V and þ0.85 V with a scanning rate of 0.05 V/s for several cycles to obtain an excellent imprinted film. After the electropolymerization, the MIPs/PtAu-GrCNTs/GCE was dried overnight at RT. (iii) The template molecules were extracted by 0.1 mol/L of hydrochloric acid solution repeatedly, so as to obtain the MIPs sensor. (iv) The NIPs sensor was fabricated with the same procedure but without the addition of the template molecules (PG). 2.4. Treatment of oil samples In this study, three kinds of vegetable oils (Samples I–III) which are common in our daily life were selected as detection samples. The samples were treated as follow: 5.0 g of every oil sample was mixed with 5.0 mL pure methanol thoroughly for 12 h, and then 1.0 mL supernatant was diluted with methanol solution, respectively. 2.5. Electrochemical measurements All electrochemical measurements were performed in 0.05 mol/L PBS (pH 6.5) containing 5.0 mmol/L K3[Fe(CN)6] and 0.2 mol/L KCl. Chronoamperometry was performed at the potential of 0.5 V and the equilibrium time was set at 800 s. CVs were conducted over a potential range from 0.2 V to þ0.6 V at a scan rate of 50 mV/s. All measurements were performed at RT.

3. Results and discussion 3.1. Design principle of the MIPs sensor In this work, for the preparation of the MIPs sensor, PtAuGrCNTs nanocomposites were firstly modified on the GCE surface. PtAu-GrCNTs nanoparticles have many advantages such as large surface area, good dispersibility, excellent conductivity and so forth, which can remarkably increase the electroactive surface area for the deposition of the MIPs material and enhance the electron transfer efficiency, and thus dramatically improve the performance for target-responsive signal transduction and sensitivity of the sensor. Moreover, the combination functions between the template molecules and functional monomers are very important for the identification property of the prepared MIPs sensor. Here, PG and o-phenylenediamine was selected as template molecule and

The morphologies and microstructure of the Gr-CNTs, PtAuCNTs, PtAu-Gr, and PtAu-GrCNTs composites were investigated by SEM, as shown in Fig. 1. Clearly, CNTs were absorbed on the surfaces of Gr sheets or filled into the Gr sheets (Fig. 1A), indicating successful preparation of the Gr-CNTs hybrid nanomaterial. Through attaching to the surfaces of Gr sheets, CNTs could prevent the reduced Gr sheets from restacking. Fig. 1B and C are the SEM images of the PtAu-CNTs and PtAu-Gr composites, respectively. It can be observed that the dispersion of PtAu nanoparticles on the surfaces of Gr sheets was more uniform than that of CNTs, but in both cases, aggregation of PtAu nanoparticles were happened. While for the PtAu-GrCNTs composite (Fig. 1D), PtAu nanoparticles were uniformly distributed on the Gr-CNTs support, and no aggregation was observed. Therefore, the PtAu-GrCNTs composite exhibited the largest surface area. Based on the excellent conductivity of the Gr, CNTs and the PtAu nanoparticles, respectively, it is reasonable to conclude that the PtAu-GrCNTs composite will have good conductivity. The morphologies of electrodes coated with MIPs and NIPs were also investigated by SEM, respectively, as shown in Fig. S3 (Supporting information). As both electrodes were coated with polymers, and the only difference is the presence or absence of a small molecule of PG during polymerization, it was hard to compare their SEM features clearly. However, these surface morphologies were totally different from that of Fig. 1, which could verify successful polymerization of the polymers. 3.3. XRD characterization XRD measurements were performed to characterize the structure of various composites (Fig. S1, Supporting information). Curve a was the XRD pattern of the Gr-CNTs composite, and an intense peak appeared at about 26°, which was assigned to the C (002) plane, a very common characteristic peak for both Gr and CNTs. Another peak at around 43° was associated with the (100) plane of the hexagonal structure of carbon. Curve b and c were the XRD patterns of the Au-GrCNTs and Pt-GrCNTs composites, respectively. The 2θ value of (111) peak for the Au-GrCNTs composites was at about 38.1° and that for the Pt-GrCNTs composites was at 39.86°. Curve d was the XRD pattern of the PtAu-GrCNTs composites, and the reflections for both Au (38.28°) and Pt (39.84°) were observed, which were very close to that for the monometallic AuGrCNTs composites (38.1°) and Pt-GrCNTs composites (39.86°). These results, together with the above SEM characterization, indicated the Pt-Au bimetallic nanoparticles and PtAu-GrCNTs composites were synthesized successfully. 3.4. Electrochemical characteristics of modified electrodes CV measurements were employed to investigate the modification process of the electrode. As shown in Fig. 2, it was found that a pair of well-defined current peaks appeared at 0.17 mV and 0.26 mV for the bare GCE, a typical redox peak range of K3[Fe(CN)6] (curve a). With the electrode modified by the PtAuGrCNTs composite, a remarkably increased peak current was obtained, which should be ascribed to the fact that the incorporation


M. Cui et al. / Biosensors and Bioelectronics 68 (2015) 563–569

Fig. 1. SEM images of the Gr-CNTs composite (A), PtAu-CNTs composite (B), PtAu-Gr composite (C), and the PtAu-GrCNTs composite (D).


Current / µA






c e a

0 -250 -500 -750 -200





Potential / mV Fig. 2. CVs obtained for the bare GCE (a), PtAu-GrCNTs/GCE (b), MIPs/PtAu-GrCNTs/ GCE (c), MIPs/PtAu-GrCNTs/GCE after removing of the template (d), PtAu-CNTs/GCE (e), and PtAu-Gr/GCE (f). Measurements were performed in PBS containing 5 mM of K3[Fe(CN)6] and 0.2 M KCl.

of PtAu bimetallic nanoparticles with Gr-CNTs hybrid nanomaterials could significantly increase the electroactive surface area of the modified electrode and effectively facilitate the electron transfer between the electrode and the redox probe (curve b). After electropolymerization of MIPs on the surface of the electrode, the redox peak currents apparently declined, indicating that the MIPs film prevented the penetration and arrival of redox probe to the electrode surface (curve c). In contrast, the redox peak currents increased significantly after the template molecules (PG) were removed (curve d). This result implied that the vacant

recognition sites enhanced the penetration and arrival of redox probe to the surface of electrode after extracting the template molecules. To demonstrate the advantages of the PtAu-GrCNTs composites modified electrodes, a further control experiment was performed using electrodes modified with the PtAu-CNTs or PtAu-Gr composites, respectively. Compared with the redox peak currents obtained with the PtAu-GrCNTs composite modified electrode (curve b), dramatically smaller currents were observed for the PtAu-CNTs (curve e) or PtAu-Gr composites (curve f) modified electrodes. These results show clear evidence that the PtAu-GrCNTs composites can effectively enhance the electron transfer of the redox probe, and have the potential to improve the electrochemical performance of the sensor. 3.5. Optimization of experiment conditions For the detection of PG with the MIPs sensor, chronoamperometry measurements were performed in a solution containing K3[Fe(CN)6]. According to the above investigation, it is clear that in the presence of PG, it will selectively bind to the MIPs sensor and cause a decrease of the measured current (the higher concentration of PG, the larger decrease of the current). In order to achieve a sensitive MIPs sensor, it is necessary to optimize the experimental conditions (to ensure the MIPs sensor can bind more PG and generate more significant response). 3.5.1. Optimization of scan cycles The thickness of the molecularly imprinted membrane is an

M. Cui et al. / Biosensors and Bioelectronics 68 (2015) 563–569


Fig. 3. (A) Effect of different electropolymerization scan cycles on the current response. (B) Effect of different molar ratios of template molecule to functional monomer on the current response. (C) Effect of different extraction time on the current response. (D) Effect of different incubation time on the current response. The PG concentration is 5  10  6 mol/L. Error bars are standard deviations across three repetitive experiments.

important parameter that affects the sensitivity and stability of the constructed sensor. In this work, the membrane thickness was controlled by adjusting the number of scanning cycles during the electropolymerization process. As shown in Fig. 3A, the current response increased with the increasing of the number of scan cycles and reached maximum at 30 cycles. When the scan cycles were more than 30 cycles, the current response decreased, suggesting that the membrane was too thick to remove the template molecules completely. Therefore, 30 cycles were used to produce an imprinted membrane with a suitable thickness. 3.5.2. Optimization of the molar ratios of template molecules to functional monomers The amounts of template molecules embedded in the polymer matrix after electrodeposition are directly affected by the molar ratios of template molecules to functional monomers. To investigate the imprinting effect of different molar ratios, different membranes were prepared and investigated using a series of molar ratios of 2:1, 2:2, 2:3, 2:4 and 2:5. As shown in Fig. 3B, the MIPs sensor fabricated at a molar ratio of 2:3 exhibited the strongest current signal. When the molar ratios were lower, the current response decreased obviously, possibly because excess functional monomers prevented the targets from approaching the electrodes surface. When the molar ratios were higher, the current signals were also decreased. The reason might be that the functional monomers were inadequate and excess template molecules could not combine with the functional monomers, resulting in reduced amounts of available binding sites. Therefore, the optimal molar ratio of template molecules to functional monomers was 2:3.

3.5.3. Influence of extraction time To examine the influence of extraction time on the current response and improve the recognition ability of the prepared sensor, the MIPs/PtAu-GrCNTs/GCE electrodes were washed by 0.1 mol/L of hydrochloric acid solution for 5 min, 10 min, 15 min, 20 min, and 25 min to remove template molecules, respectively. It was found that the maximized current response was obtained when the extraction time was 10 min (Fig. 3C). That is, 10 min's extraction is enough to remove the template molecules, and further extraction in the strong acid may slightly damage the formed MIPs film and lead to signal decrease. Therefore, 10 min was chosen as the optimal extraction time. 3.5.4. Effect of incubation time It is important to optimize the incubation time to achieve the maximum current response of the sensor. The MIPs sensors were incubated in PG solution for 5 min, 10 min, 15 min, 20 min, and 25 min at RT, respectively. As shown in Fig. 3D, the current signal increased with the increase of the incubation time and reached equilibrium when the incubation time was 10 min. Thus, to achieve high sensitivity and save assaying time, the incubation time of 10 min was chosen. 3.6. Analytical performance of the sensor 3.6.1. Calibration curve of the sensor In this work, chronoamperometry measurements were performed to investigate the performances of the MIPs-based sensors and the NIPs-based sensors towards different concentrations of PG


M. Cui et al. / Biosensors and Bioelectronics 68 (2015) 563–569

Here, the first step is reversible (binding/dissociation) as (polymer)rev, which can undergo surface rearrangement to adopt a more stable surface configuration as step 2: Kf

Step 2: (polymer)rev → (polymer)irrev


In step 2, once (polymer)rev adopts a stable surface configuration of (polymer)irrev, the surface does not rearrange back to its unstable configuration of (polymer)rev. Therefore, step 2 may be considered irreversible as (polymer)irrev. Using the model presented by steps 1 and 2, the following constants were determined: Kb is the binding constant (mol/L), Kd is the dissociation constant (mol/L), Kf is the surface stable constant (mol/L). According to the previous report (Hennessey et al., 2009), the surface stable constant Kf of 3.5  10  6 mol/L was obtained, indicating quite stable binding of PG to the MIPs.

Fig. 4. Calibration curves of the PG-imprinted sensor (line a) and the non-imprinted sensor (line b). Error bars are standard deviations across three repetitive experiments.

(from 0 to 1.0  10  5 mol/L). As shown in Fig. 4, under optimum condition, the current response (net current change) of the MIPsbased sensor (line a), which was much larger than that of the NIPssensor (line b), increased with the increase of the PG concentration. The linear range of the sensor was from 7  10  8 mol/L to 1  10  5 mol/L, with a limit of detection (LOD) of 2.51  10  8 mol/L. The result indicated that the MIPs sensor based on the PtAu-GrCNTs nanocomposite showed promising potential for quantitative assay of PG with desirable sensitivity. 3.6.2. Comparison of PG-imprinted sensor with other analysis methods The analytical performances of the MIPs sensor for PG were compared with those of other PG assays, as summarized in Table S1 (see Supporting information). Clearly, this MIPs sensor is more sensitive than other assays. According to the report by AOAC official method 938.15 about phenolic antioxidants in oils, fats, and butter oil, usually, up to 100–200 μg/g of synthetic phenolic antioxidants is allowed (Wang et al., 2012). Therefore, the LOD of this PG sensor (0.0053 μg/mL) is more than enough to detect PG in oil samples even after many times of dilution.

3.6.4. The selectivity of the sensor The binding selectivity of the prepared MIPs sensor for PG and other structural analogs, such as butylated hydroxyanisole (BHA), 2, 6-Di-tert-butyl-4-methylphenol (BHT) and tert-butylhydroquinone (TBHQ) was also evaluated. The obtained results of PG-imprinted sensor and non-imprinted sensor were shown as Fig. 5. Clearly, the current response of MIPs sensor to PG was much larger than that of other three interfering species, indicating the MIPs sensor had high selectivity towards PG. The results also suggested that the binding sites in imprinted sensor were only complementary with PG in size and shape, and there was no significant response to other structural analogs of PG, implying excellent selectivity of the MIPs PG sensor. 3.6.5. The reproducibility and stability of the sensor The reproducibility of the imprinted sensor was estimated by detecting a 5.0  10  6 mol/L PG solution with 5 different electrodes, which were prepared under the same fabrication condition, respectively. The current response showed a RSD of 4.1% for five independent measurements, indicating very good reproducibility. Stability is another important parameter for a sensor, and the stability of the MIPs sensor was evaluated by storing 5 independently fabricated electrodes at 4 °C for 2 weeks. During this period, these electrodes remained 93% of their initial responses in average (for the determination of 5.0  10  6 mol/L PG), exhibiting a very desirable stability.

3.6.3. Investigation of the MIPs polymer and PG interactions Based on the data of Fig. 4, the binding-rebinding interactions between the MIPs polymer and the template molecules PG were investigated. Fig. 4 (line a) shows the data obtained with CV measurements, and the response curve in Fig. 4 (line a) resemble the binding interaction between the polymer I (after extraction of PG) and the template of PG (fitting the data to a Langmuir expression, Luo et al., 2013). Similar to the specific interaction between the antibody and antigen, the interaction between polymer I (after extraction of template) and templates might be characterized by a two-step process as below (Hennessey et al., 2009). Firstly, the templates (PG) bind to the polymer I (after extraction of PG): Kb

Step 1: polymer I+ PG ⇄ (polymer)rev Kd


(“Polymer I” represents the polymer after the extraction of templates. “Polymer” represents the polymer associated with the templates).

Fig. 5. The current responses for PG (5  10  6 mol/L) and other structural analogs (5  10  4 mol/L) on PG-imprinted sensors and non-imprinted sensors. Error bars are standard deviations across three repetitive experiments.

M. Cui et al. / Biosensors and Bioelectronics 68 (2015) 563–569

3.6.6. Analysis of PG in real samples In order to investigate the practical application of the fabricated sensor, PG in three kinds of vegetable oils (Samples I–III) was analyzed by the standard addition method. The sample solutions were prepared according to Section 2.4, and the assay results of these samples are summarized in Table S2 (see Supporting information). It was found that the recovery was from 98.3% to 103.0%, which manifested that this sensor had the ability of determining PG in complicated real samples.

4. Conclusions A novel molecularly imprinted electrochemical sensor for highly sensitive and selective detection of PG in foodstuffs based on the PtAu-GrCNTs composite was constructed. The PtAu-GrCNTs composite provided a highly conductive and large surface area substrate for the electrodeposition of the MIPs material, and after careful optimization of the conditions for the formation of the MIPs material, the MIPs sensor exhibited excellent selectivity towards its target PG. The prepared sensor displayed a wide dynamic linear range from 7  10  8 mol/L to 1  10  5 mol/L with a detection limit as low as 2.51  10  8 mol/L. This MIPs sensor possesses advantages such as outstanding selectivity, high sensitivity and long-term stability, and it can be used for PG determination in food samples.

Acknowledgments This research was supported by the Natural Science Foundation of Shandong Province of China (ZR2012BM008), the Taishan Scholar Program of Shandong Province, China, and the Qingdao Basic Research-Cooperative Fund Project (12-1-4-3-(33)-jch), China.

Appendix A. Supplementary information Supplementary data associated with this article can be found in the online version at

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Molecularly imprinted electrochemical sensor for propyl gallate based on PtAu bimetallic nanoparticles modified graphene-carbon nanotube composites.

A novel molecularly imprinted electrochemical sensor for propyl gallate (PG) determination was developed via electropolymerization of an o-phenylenedi...
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