Molecularly Imprinted Polymer-Hybrid Electrochemical Sensor for the

Article pubs.acs.org/IECR

Molecularly Imprinted Polymer-Hybrid Electrochemical Sensor for the Detection of β‑Estradiol Sonia Des Azevedo, Dhana Lakshmi, Iva Chianella,* Michael J. Whitcombe, Kal Karim, Petya K. Ivanova-Mitseva, Sreenath Subrahmanyam, and Sergey A. Piletsky Cranfield Health, Vincent Building, Cranfield University, Cranfield, Bedfordshire, MK43 0AL, U.K. S Supporting Information *

ABSTRACT: This paper discusses the construction of a novel electrochemical sensor for 17β-estradiol (E2) based on a molecularly imprinted polymer (MIP)-conducting polymer modified hybrid electrode. A bifunctional monomer, Nphenylethylene diamine methacrylamide (NPEDMA), was used for the construction of the electrochemical sensor. Conducting films were prepared on the surface of a gold electrode by electropolymerization of the aniline moiety of NPEDMA. A layer of MIP was photochemically grafted over the polyaniline, via N,N-diethyldithiocarbamic acid benzyl ester (iniferter) activation of the methacrylamide groups. Computational modeling was used to select the most suitable monomer for preparation of MIPs for E2. Experimental parameters such as deposition time, cyclic voltammetric (CV) scan cycles, and conditions for polymer accumulation were optimized. The detection limit of the resulting sensor, determined by CV, was 6.86 × 10−7 M. Furthermore, the hybrid electrode was successfully used to analyze E2 in water without complex sample pretreatment. These results reveal that the MIP hybrid sensor has potential to be an effective technique for the electrochemical determination of E2 in real-time in complicated matrices.

1. INTRODUCTION Naturally occurring conjugates of estrogens, such as the endocrine disruptor 17β-estradiol (E2) and its prime metabolites estriol (E3) and estrone (E1) are largely excreted from the human body as sulfates and glucuronide conjugates, via urine. The fact that the free parent compounds are frequently found in either sewage effluents or in environmental waters is a significant issue, causing concern in relation to their effect on both aquatic life and public health, such as alterations in reproductive function and development, and implications in breast tumors and other endocrinal disorders.1−3 Therefore, development of an inexpensive biosensor for the real time detection of estrogen is of significant importance. Electrochemical detection of E2 offers great advantages because it is rapid, inexpensive, and easy to perform. Major drawbacks of this method however are the undesirably high detection limit and lack of selectivity of unmodified electrodes. Combining molecularly imprinted polymers (MIPs), which can selectively capture and concentrate analytes, with electrochemical detection can enhance selectivity of the sensor and enable it to operate at detection limits low enough for practical use. MIPs are synthetic polymers possessing binding sites specific for a target compound, used as template during synthesis of the material. A functional monomer, which interacts chemically with the template, is copolymerized with cross-linking monomers to create a rigid polymer network. After polymerization the template is removed and binding sites, complementary in size, shape, and chemical functionality, are created. The sites are capable of specifically and selectively rebinding the compound used as template.4−7 MIPs have successfully been applied in solid phase extraction,8,9 as drug delivery vehicles,10 in bioassays,11 to induce crystallization,12 and as the recognition element in biosensors.13−16 One of the most attractive features © XXXX American Chemical Society

of MIPs as the capture agent of biosensors is the increased lifetime of the sensor. This not only helps in the regeneration and reuse of the sensor, but also makes it more useful for field use due to its robust nature. Polymers imprinted with E2 have been successfully synthesized and showed high absorption capacities in solid phase extraction, rapid binding kinetics, and good selectivity to trace levels of E2 in water and in biological samples.17−21 Molecularly imprinted solid-phase extraction was applied to the detection of 17β-estradiol from fish and prawn samples by high performance liquid chromatography.22 The detection and quantification limits were 0.023 and 0.076 mg L−1. More recently a MIP-based “immunosensor” for estradiol was fabricated on a quartz crystal microbalance and incorporated into a microfluidic chip by pressing a “stamp” coated with MIP nanoparticles, imprinted with specific antibodies, into a layer of another polymer, creating secondary imprints capable of binding the original antigen.23 These few examples show the benefits of sensing technology, when combined with MIPs. The limitations of these applications are the inability of sensing in the field and the complex preparation procedures. The lack of a direct path for conduction from the polymer active sites to the electrode seriously limits their use as receptors in electrochemical sensors. As we have previously demonstrated, a way to mitigate this Special Issue: Recent Advances in Nanotechnology-based Water Purification Methods Received: October 31, 2012 Revised: February 1, 2013 Accepted: February 1, 2013

A

dx.doi.org/10.1021/ie302999j | Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Industrial & Engineering Chemistry Research

Article

Figure 1. Schematic diagram of steps followed during the development of MIP hybrid sensor for E2. N-phenylethylene diamine methacrylamide (NPEDMA) was used as a functional monomer for the synthesis of a conducting graftable polymer on the surface of the electrode.

problem is to incorporate polymers based on N-phenylethylene diamine methacrylamide (NPEDMA) as part of the sensor.24 NPEDMA combines two orthogonal polymerizable functionalities, an aniline group (for the conductive polyaniline layer) and a methacrylamide (for further attachment of polymers), which are able to form an electrical contact between the MIP component and the sensor element (Figure 1).24,25 Using this approach we integrated an estradiol MIP with the sensor via grafting to poly(NPEDMA) for the construction of a hybrid sensor for E2. In this work we report a convenient method for the construction of a novel electrochemical sensor for βestradiol based on a computationally designed MIP.

an energy of 75 W. The gold sensors were immersed in ethanol/methanol solution, then dried and prepared for polymerization by placing a small line (horizontal) of Araldite glue leaving about 1 cm × 1 cm of electrode working area. 2.5. Electrochemical Setup. Three electrodes were used for the electrochemical procedure: a working (gold electrode), an Ag/AgCl reference, and a platinum counter electrode. These were set up using a mountable stand. The working, reference, and counter electrodes were then connected to the electrochemical instrument, a potentiostat, Autolab 4.9, using crocodile clips AGS20. The three electrodes were accommodated and submerged in a 10 mL beaker containing the electrolyte solution, such that most of the surface area of the working electrode was covered with the electrochemical solution. 2.6. Baseline Measurement. Prior to adding the E2 analyte, a baseline was acquired for each electrode (and later for MIP and NIP sensors, respectively). Baseline measurements were obtained from a solution of ethanol/PBS (2.5/7.5 mL) or acetonitrile/water (9.68/320 mL) for the polymerization of NPEDMA. Cyclic voltammetry (CV) was then performed between different ranges of potentials according to the type of experiment using the Autolab 4.9 interface connected to a PC. 2.7. Electrochemical Testing of 17β-Estradiol. For the testing of E2, after recording the baseline, a range of increasing volumes (5−15 μL) of a stock solution of 17β-estradiol (3.67 × 10−3 M) were added in the testing solution. After each addition, CV was performed using the same range and conditions as the baseline signal. 2.8. Electrochemical Polymerization of NPEDMA on Gold Electrodes. The polymerization of NPEDMA was carried out in accordance with a previously published report.24 A 2.44 mM stock solution of the monomer was prepared by dissolving 30 mg of NPEDMA in 2 mL of acetonitrile. A 320 μL aliquot of this solution was taken and diluted to 10 mL by the addition of 9.18 mL of water and 500 μL of 1 M perchloric acid. Polymerization was then performed by CV between −0.2 V and +1 V with a scan rate of 50 mV/s. Before NPDEMA

2. MATERIALS AND METHODS 2.1. Chemicals. 17β-Estradiol (E2), progesterone, estriol, and α-estradiol, methacrylic acid (MAA), and ethylene glycol dimethacrylate (EGDMA) were purchased from Sigma Ltd., UK. N,N′-Diethyldithiocarbamic acid benzyl ester, the iniferter or living initiator was from TCI Europe, Belgium. Gold-coated glass electrodes were acquired from NanoSPR Devices, USA, and screen-printed carbon/platinized electrodes were from DropSens, Spain. All other chemicals were of analytical or HPLC grade and utilized as received (e.g., acetonitrile, acetone, hydrochloric acid (HCl), ethanol (EtOH), dimethylformide (DMF)). 2.2. Contact Angle Measurements. Sessile water contact angle (CA) measurements were made using Cam 100 optical Angle Meter (KSV Instruments Ltd., Finland) with the software provided. 2.3. Computational Molecular Modeling. The rational design of MIPs was carried out on a PC running Linux executing the software package SYBYL 7.3 (Tripos Inc.) used to simulate monomer−template interactions. 2.4. Gold Electrodes Preparation. Gold-coated glass slides were cut with a gold-cutter into 1 cm × 2 cm rectangles. These were then cleaned by immersion in DMF for about 30 min, rinsed with deionized water and then placed into a plasma chamber, and nitrogen plasma was applied for 5 to 15 min with B



Article

2.13. Cross-Reactivity Study. Cross-reactivity studies were performed using the same protocol utilized for E2 rebinding to MIP, with 17α-estradiol (α-E2), estriol (E3), and progesterone (P4) stock solutions being prepared instead of E2. Briefly, MIP sensors, specific for E2 were tested using increasing concentrations (from 3.67 × 10−4 M stock solution, 1.84 × 10−7, 3.67 × 10−7, 5.41 × 10−7, 7.33 × 10−7, 9.15 × 10−7, 1.10 × 10−6, 1.46 × 10−6 M) of each of the hormones (α-E2, E3, P4), and CV was recorded as for the testing of E2.

polymerization, a baseline was recorded in 2.5/7.5 mL EtOH/ PBS. This was repeated also before E2 testing. 2.9. Immobilization of Iniferter to Pendant Double Bonds of NPEDMA Layer over Gold Electrode. A solution of N,N′-Diethyldithiocarbamic acid benzyl ester, the iniferter or living initiator, was prepared in hexane (10 mL, 0.63 mM). The gold electrodes containing the NPEDMA thin film were immersed in the iniferter solution with the help of crocodile clips AGS20 mounted on a clamp. After the removal of oxygen by purging nitrogen for 10 min, the system was irradiated under dark for 60 min using a fiber optic UV lamp delivering a 50 W cm−2, mounted at a distance of 4 cm from the beaker. The electrode was then washed with water and dried in a stream of nitrogen gas. Contact angle measurements were performed to confirm the grafting of iniferter as described in section 2.2. 2.10. Grafting of MIP and NIP Thin Films onto the Iniferter-Activated NPEDMA. The protocol for the preparation of the gold electrodes and the production of the 17βestradiol MIP was similar to the procedure reported before.24 EGDMA was used as cross-linking monomer, acetonitrile as porogen, and MAA was used as the best suited functional monomer. For the grafting of MIP and NIP, a solution of E2 (17 mg, 62.5 μmol), MAA (27 mg, 319 μmol), and EGDMA (1.2 g, 6.06 mmol) was prepared in acetonitrile (2.5 g) in a 30 mL capacity vial. The reaction mixture was sonicated for 10 min. The ratio of template to monomer was 1:4. The iniferteractivated polymer-coated electrode was immersed in the reaction mixture and clamped using a crocodile clip. After the removal of oxygen by purging nitrogen for 10 min, the system was irradiated under dark for 1 h using a fiber optic UV lamp delivering 50 W cm−2, mounted at a distance of 4 cm from the beaker. The electrode was then washed with water and dried in a stream of nitrogen gas. A similar procedure was also followed to prepare the (nonimprinted) control-grafted electrodes. In this case the same steps were carried out with the exclusion of the template E2 from the polymerization mixture. 2.11. Extraction of Template. After polymer grafting, template removal was carried out by flashing the electrode with 5 mL of water, followed by 5 mL of 5% acetic acid in methanol and finally 5 mL of 0.1 M NaOH prepared in methanol until the electrochemical signal for E2, as monitored by CV, disappeared (5−6 washing cycles). Electrodes were then rinsed three times with ethanol and water. These were then dried with nitrogen gas and stored in the dark to prevent light decomposition. NIP sensors were subjected to the same washing conditions used for the MIP material. 2.12. Rebinding and Measurement of 17β-Estradiol with MIP and NIP. Electrochemical experiments were performed using an Autolab 4.9 connected to a PC with the polymer-modified working electrode, a platinum auxiliary electrode, and an Ag/AgCl reference electrode. CV was performed from −0.2 V to +1 V at 50 mV s−1 scan rate. Briefly, a blank solution made of EtOH/PBS (2.5/7.5 mL) was prepared and polymer-modified electrodes were immersed in this solution, to which aliquots (5 μL at the time) of different stock solution of E2 prepared in 50% DMF/50% water were added in an ascending order (from 3.67 × 10−4 M stock solution, 1.84 × 10−7, 3.67 × 10−7, 5.49 × 10−7, 7.33 × 10−7 M), (from 7.34 × 10−3 M stock solution, 3.67 × 10−6, 7.33 × 10−6, 1.11 × 10−5, 1.47 × 10−5 M), and (from 3.67 × 10−2 M stock solution, 1.82 × 10−5, 3.67 × 10−5, 5.5 × 10−5, 7.33 × 10−5 M).

3. RESULTS AND DISCUSSION Screen printed carbon/platinized electrode (Pt) as well as gold electrodes were initially considered as working electrodes for the study. Preliminary investigations revealed that a much more pronounced signal for E2 was seen on the Pt electrode as compared with the gold electrodes (data not shown). This was probably because E2 was capable of accumulating more on the porous carbon layer than on the smooth gold metal surface However, because of difficulty in polymerizing NPDEMA on Pt electrodes, gold electrodes were preferred and finally selected as working electrodes. Before the polymer grafting, the electrochemical behavior of 17β-estradiol (E2) at the poly-NPEDMA gold-modified electrode was investigated and no peak for E2 was observed. This was not surprising, as the conductivity of the polyNPEDMA gold modified electrodes is not as high as the bare gold electrode, indicating that the use of a MIP layer on the conductive polymer should be able to increase the amount of E2 immobilized (adsorbed) producing a detectable signal. 3.1. Polymerization Procedure. Surface confined grafting of all polymers was readily initiated upon UV irradiation of the electro-polymerized poly-NPEDMA layer, containing the iniferter in the presence of deoxygenated solutions of crosslinkers and monomers such as EGDMA and MAA, respectively. This permitted precise control of the macromolecular architectures of the grafted surfaces. Figure 1 presents the schematic representation of the polymerization process. It was previously shown that NPEDMA can be polymerized using either the free radical initiator (via the double bond) or by oxidative polymerization/electro-polymerization mechanism (via the aniline part).24 However, for this work, we employed electro-polymerization to create a conductive layer followed by UV-activation of double bonds for attachment of the living initiator, diethyl dithiocarbamic acid benzyl ester, followed by MIP and NIP grafting using the initiator attached to the conductive polymer. 3.2. Electrochemical Polymerization of NPEDMA on Gold Electrodes. As it is shown in Figure S1 reported in Supporting Information, anodic and cathodic peaks around +0.6 V and +0.5 V, respectively, were seen growing up to 15 CV scans confirming successful polymerization of NPDEMA. Furthermore, successful electrochemical polymerization of NPEDMA onto the gold electrodes was confirmed by the formation of a green layer of poly-NPEDMA (formed on the working part of the electrodes). Nevertheless further confirmation of successful polymerization was also done using contact angle measurements (Table 1). 3.3. Computational Molecular Modeling. Computational molecular modeling (in silico method for rational design of polymers) was used to screen the most promising monomers for synthesis of MIPs for E2. The rational design protocol, which has been already extensively explained elsewhere,26 involved four steps. Briefly the first step was the design of a C



Article

Table 1. Water Contact Angle Measurement Data, Prior and Post Each Modification Step of the Electrode Surface: Electropolymerization of NPEDMA; grafting of Iniferter, MIP, and NIP Layersa surfaces bare electrodes poly-NPEDMA iniferter layer MIP layer NIP layer

average ± STDEV (degrees ± STDEV) 64.31 66.79 70.56 60.76 61.28

± ± ± ± ±

1.69 1.70 1.46 5.72 3.38

a

Standard deviations (STDEV) were calculated using three replicates for each measurement.

functional monomer database or virtual library. The second step was the design of a molecular model of template E2. The third step was the screening of the library of functional monomers for their possible interactions with the template E2 using the LEAPFROG algorithm. Monomers giving the highest binding scores (see Table S1 in Supporting Information) are those forming the strongest complexes with the template and therefore they represented the best candidates for polymer preparation. For E2, the best binding monomers were identified as bisacrylamide, itaconic acid, 2-hydroxyethyl methacrylate, acrylamide, EGMP, and methacrylic acid. Finally methacrylic acid, which has been extensively investigated in the literature, was the preferred monomer for the preparation of MIPs for E2 (Figure 2B). The last and fourth step of the modeling involved refinement using Molecular Mechanics (MM) and Molecular Dynamics simulations for optimization of the polymer composition. These were performed as described elsewhere,27 and the best monomer/template ratio (Figure 2C) was identified. 3.4. Sensor Responses of MIP and NIP. Figure 3A presents CVs of the MIP sensor straight after polymerization (solid line) and after removal of the template E2 (dashed line). The solid curve confirms that E2 is still trapped inside the polymer matrix, as indicated by the oxidation peak at +0.4 V, while the dashed lined curve shows that the template was successfully removed following extensive washing (no peak at +0.4 V). The rebinding studies were performed at several concentrations (Figure 3B). The anodic peak of E2 (solid line) suggested that oxidation of E2 takes place at around +0.40 V.

Figure 3. CVs of MIP sensor: (A) after polymer synthesis, containing the template (solid line) and post template removal (dashed line); (B) rebound template (solid line, 3.67 × 10−7 M E2) and post-template removal (dashed line).

After rigorous washing with a combination of solvents (as explained in section 2.11), the second curve (dashed line) was obtained. The absence of an oxidation peak for E2 at +0.40 V indicates that E2 has been removed completely. The CVs confirm both a successful grafting of the specific MIP sensor and successful E2 rebinding after the template extraction. At higher concentrations of template (from 1.82 × 10−5 to 7.33 × 10−5 M), the electrochemical oxidation of E2 could not be observed indicating the influence of sample saturation on the E2 oxidation peak (data not shown). Therefore, rebinding studies were carried out at lower concentrations, ranging from 1.84 × 10−7 to 7.33 × 10−7 M (Figure S2 in Supporting

Figure 2. Minimum-energy conformations of (A) E2; (B) complex of E2 with methacrylic acid; (C) 2:1 complex of methacrylic acid monomer with the E2 template, as determined by computer modeling. Oxygen atoms are shown in red, carbon atoms are white, and the light blue atoms are hydrogen. D



Article

Information). The anodic peak current of E2 was enhanced linearly as the concentration of E2 increased. When the NIP electrode was tested at the same conditions, no template peak was observed (Figure S3 in Supporting Information), which confirms the specificity of the synthesized MIP. Preliminary calibration curves for MIP and NIP sensors are shown in Figure S4 in Supporting Information. From the calibration curve a detection limit of 6.89 × 10−7 M was calculated for the MIP sensor. A detection limit could not be calculated for the NIP sensor as a real response to E2 was not recorded. The selectivity of the MIP sensors was assessed using 17αestradiol (α-E2), progesterone (P4), and estriol (E3), which are structurally related to E2 (Figure 4). When the MIP sensor was

Figure 4. Molecular structure of 17β-estradiol (E2), 17α-estradiol (αE2), estriol (E3), and progesterone.

exposed to solutions of different concentrations of both, α-E2 and progesterone, no binding was observed (Figure 5A,B). This fact demonstrates excellent selectivity and specificity for E2 over both α-E2 and progesterone. When E3 was tested in a similar manner, it did not show any response for the lower concentrations (1.84 × 10−7 M and 3.67 × 10−7 M), but started to show a response with the two highest concentrations tested (5.49 × 10−7 M and 7.33 × 10−7 M) (Figure 5C). This shows that the MIP sensor lacks selectivity for E3 at high concentrations, which is not surprising due to the similarity of the two molecular structures, with the only difference between the two being an extra hydroxyl group in E3 which seem to interfere only slightly with the binding.

Figure 5. CVs of MIP sensor in the presence of different concentrations of (A) α-E2; (B) progesterone and (C) E3. In panel A the CVs at concentrations of 3.67 × 10−7, 5.49 × 10−7, 7.33 × 10−7, and 9.15 × 10−7 M are the same as that with 1.10 × 10−6 M, and are not shown for clarity of the figure. In panel B the CVs at concentrations of 3.67 × 10−7 M and 5.49 × 10−7 M are overlapping with that at concentration of 1.84 × 10−7 M and are not shown for clarity of the figure. In panel C the CVs for concentrations at 1.84 × 10−7 and 3.67 × 10−7 M are very similar to that at 0 M, and are not shown for clarity of the figure.

4. CONCLUSIONS Traditional methods of β-estradiol detection in food and environmental samples suffer from a number of disadvantages such as a need for long detection time and are expensive and require trained personnel. Furthermore, some methods have limitations that arise from a lack of stability, sensitivity, or specificity of the assay components. Although the development of electrochemical sensing devices based on MIPs can have drawbacks due to nonconductive nature of the polymers, their integration with electrochemical transducers would produce robust devices capable of working in complicated matrices, overcoming many of the problems found in clinical, food, and environmental analysis. The development of an electrochemical sensor for 17β-estradiol (E2) based on a MIP-conducting polymer modified hybrid electrode, constructed using the bifunctional monomer NPEDMA, has been described here. Conducting films were prepared on the surface of Au electrodes

by electropolymerization of the aniline moiety of NPEDMA. The detection limit of the resulting MIP sensor assessed by cyclic voltammetry was found to be 6.86 × 10−7 M with a linearity range between 1 × 10−7 M and 8 × 10−7 M. An improvement of the detection limit could easily be achieved by replacing cyclic voltammetry with a more sensitive electrochemical technique such as for example chronoamperometry. Further improvements of the detection limit and a wider linearity range could be obtained by increasing the sensor surface area using gold or platinum nanoparticles28 before NPEDMA deposition. The MIP sensor developed here also demonstrated high selectivity, showing a lack of cross-reactivity E



Article

with α-E2 and progesterone and only a limited cross-reactivity with the highest concentrations of E3. This highlights that the β-hydroxyl group present both in E2 and E3 is the main functionality responsible for the binding to the MIP, as was also shown by the results of the computer modeling study, as reported in Figure 3. In conclusion these findings confirm that the MIP-electrochemical sensor developed here has potential to successfully determine E2 in real-time in complicated matrices.

■

(10) Hoshino, Y.; Koide, H.; Urakami, T.; Kanazawa, H.; Kodama, T.; Oku, N.; Shea, K. J. Recognition, neutralization, and clearance of target peptides in the bloodstream of living mice by molecularly imprinted polymer nanoparticles: A plastic antibody. J. Am. Chem. Soc. 2010, 132, 6644. (11) Ge, Y.; Turner, A. P. F. Molecularly imprinted sorbent assays: Recent developments and applications. Chem. A. Eur. J 2009, 15, 8100. (12) Whitcombe, M. J. Molecularly imprinted polymers: Smart hydrogel crystal gardens. Nat. Chem. 2011, 3, 657. (13) Whitcombe, M. J.; Chianella, I.; Larcombe, L.; Piletsky, S. A.; Noble, J.; Porter, R.; Horgan, A. The rational development of molecularly imprinted polymer-based sensors for protein detection. Chem. Soc. Rev. 2011, 40, 1547. (14) Suryanarayanan, V.; Wu, C. T.; Ho, K. C. Molecularly imprinted electrochemical sensors. Electroanalysis 2010, 22, 1795. (15) Malitesta, C.; Mazzotta, E.; Picca, R. A.; Poma, A.; Chianella, I.; Piletsky, S. A. MIP sensors−The electrochemical approach. Anal. Bioanal. Chem. 2012, 402, 1827. (16) Lépinay, S.; Kham, K.; Millot, M. C.; Carbonnier, B. In-situ polymerized molecularly imprinted polymeric thin films used as sensing layers in surface plasmon resonance sensors: Mini-review focused on 2010−2011. Chem. Pap. 2012, 66, 340. (17) Wang, S.; Wang, R. Y.; Wua, X. O.; Wang, Y.; Xue, C.; Wu, J. H.; Hong, J. L.; Liu, J.; Zhou, X. M. Magnetic molecularly imprinted nanoparticles based on dendritic-grafting modification for determination of estrogens in plasma samples. J. Chromatogr. B 2012, 905, 105. (18) Qi, X. O.; Yang, X. O.; Wang, B.; Yang, H.; Deng, A. Development of a broad selective molecularly imprinted polymersbased solid phase extraction of contraceptive drug levonorgestrel from water samples. Intern. J. Environ. Anal. Chem. 2012, 92, 268. (19) Lucci, P.; Nunez, O.; Galceran, M. T. Solid-phase extraction using molecularly imprinted polymer for selective extraction of natural and synthetic estrogens from aqueous samples. J. Chromatogr. A 2011, 1218, 4828. (20) Shi, Y.; Peng, D. D.; Shi, C. H.; Zhang, X.; Xie, Y. T.; Lu, B. Selective determination of trace 17β-estradiol in diary and meat samples by molecularly imprinted solid-phase extraction and HPLC. Food Chem. 2011, 126, 1916. (21) Buszewski, B.; Ričanyová, J.; Gadzała-Kopciuch, R.; Szumski, M. Supamolecular recognition of estrogens via molecularly imprinted polymers. Anal. Bioanal. Chem. 2010, 397, 2977. (22) Jiang, T.; Zhao, L.; Chu, B.; Feng, Q. Z.; Yan, W.; Lin, J. M. Molecularly imprinted solid-phase extraction for the selective determination of 17β-estradiol in fishery samples with high performance liquid chromatography. Talanta 2009, 78, 442. (23) Schirhagl, R.; Qian, J.; Dickert, F. L. Immunosensing with artificial antibodies in organic solvents or complex matrices. Sens. Actuators B: Chem. 2012, 173, 585. (24) Lakshmi, D.; Bossi, A.; Whitcombe, M. J.; Chianella, I.; Fowler, S. A.; Subrahmanyam, S.; Piletska, E. V.; Piletsky, S. A. Electrochemical sensor for catechol and dopamine based on a catalytic molecularly imprinted polymer-conducting polymer hybrid recognition element. Anal. Chem. 2009, 81, 3576. (25) Berti, F.; Todros, S.; Lakshmi, D.; Whitcombe, M. J.; Chianella, I.; Ferroni, M.; Piletsky, S. A.; Turner, A. P. F.; Marrazza, G. Quasimonodimensional polyaniline nanostructures for enhanced molecularly imprinted polymer based sensing. Biosens. Bioelectron 2010, 26, 497. (26) Chianella, I.; Lotierzo, M.; Piletsky, S. A.; Tothill, I. E.; Chen, B.; Karim, K.; Tuner, A. P. F. Rational design of a polymer specific for microcystin-LR using a computational approach. Anal. Chem. 2002, 74, 1288. (27) Piletska, E. V.; Turner, N. W.; Turner, A. P. F.; Piletsky, S. A. Controlled release of the herbicide simazine from computationally designed molecularly imprinted polymers. J. Controlled Release 2005, 108, 132−139. (28) Yuan, L.; Zhang, J.; Zhou, P.; Chen, J.; Wang, R.; Wen, T.; Li, Y.; Jiang, H. Electrochemical sensor based on molecularly imprinted

ASSOCIATED CONTENT

S Supporting Information *

The electropolymerization of NPEDMA on the gold sensor; the binding energies of various template-functional monomers complexes; the sensorgrams for the rebinding of several concentrations of E2 both to MIP and NIP sensors; and the resulting calibration curves. This material is available free of charge via the Internet at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: i.chianella.1998@cranfield.ac.uk. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors thank the European Union for funding this work under the Framework 7 programme, CP-FP 226524, Water treatment by molecularly imprinted materials (WATERMIM), and http://mipdatabase.com/ for the useful article analysis in the MIP field.

■

REFERENCES

(1) Racz, L.; Goel, R. K. Fate and removal of estrogens in municipal wastewater. J. Environ. Monit. 2010, 12, 58. (2) Burkhardt-Holm, P.; Segner, H.; Burki, R.; Peter, A.; Schubert, S.; Suter, M. J. F.; Borsuk, M. E. Estrogenic endocrine disruption in Switzerland: Assessment of fish exposure and effects. Chimia 2008, 62, 376. (3) Cummings, S. R.; Duong, T.; Kenyon, E.; Cauley, J. A.; Whitehead, M.; Krueger, K. A. Serum estradiol level and risk of breast cancer during treatment with raloxifene. J. Am. Med. Assoc. 2002, 287, 216. (4) Vasapollo, G.; Sole, R. D.; Mergola, L.; Lazzoi, M. R.; Scardino, A.; Scorrano, S.; Mele, G. Molecularly imprinted polymers: Present and future prospective. Int. J. Mol. Sci. 2011, 12, 5908. (5) Nicholls, I. A.; Andersson, H. S.; Golker, K.; Henschel, H.; Karlsson, B. C. G.; Olsson, G. D.; Rosengren, A. M.; Shoravi, S.; Suriyanarayanan, S.; Wiklander, J. G.; Wikman, S. Rational design of biomimetic molecularly imprinted materials: Theoretical and computational strategies for guiding nanoscale structured polymer development. Anal. Bioanal. Chem. 2011, 400, 1771. (6) Chen, L. G.; Xu, S. F.; Li, J. H. Recent advances in molecular imprinting technology: Current status, challenges and highlighted applications. Chem. Soc. Rev. 2011, 40, 2922. (7) Alexander, C.; Andersson, H. S.; Andersson, L. I.; Ansell, R. J.; Kirsch, N.; Nicholls, I. A.; O’Mahony, J.; Whitcombe, M. J. Molecular imprinting science and technology: A survey of the literature for the years up to and including 2003. J. Mol. Recognit. 2006, 19, 106. (8) Beltran, A.; Borrull, F.; Marcé, R. M. Molecularly-imprinted polymers: Useful sorbents for selective extractions. Trans. Anal. Chem. 2010, 29, 1363. (9) Bui, B. T. S.; Haupt, K. Molecularly imprinted polymers: Synthetic receptors in bioanalysis. Anal. Bioanal. Chem. 2010, 398, 2481. F



Article

membranes at platinum nanoparticles-modified electrode for determination of 17β-estradiol. Biosens. Bioelectron. 2011, 29, 29.

G


Molecularly Imprinted Polymer-Hybrid Electrochemical Sensor for the

Recommend Documents