Molecularly Imprinted Polymer Film Research Articles

Molecularly Imprinted Polymer for Selective Electrosynthesis of Biphenols

Molecularly imprinted polymers (MIPs) have been widely studied for sensing and separation of compounds selectively. These artificial biomimicking recognition units are highly sensitive and selective to target analytes. Electrochemical preparation of MIPs offers advantages including ease of preparation as well as control over the polymer nucleation and growth, thickness, and film morphology. Moreover, it is possible to follow the formation of cavities electrochemically through the gate effect. Few reports have focussed on selective catalysis by using MIPs. However, the application of these MIPs in the field of electrocatalysis remains unexplored and, therefore, there is a large research scope in this domain.Biphenols are structural motifs of several molecules in nature and for many drugs. They are efficient ligands for catalytic systems and are highly stable under electrochemical condition. In particular, 3,3,5,5-tetramethyl-2,2-biphenol acts as a significant backbone in phosphorus-based ligand systems for calatysis. The oxidation of 2,4-dimethylphenol yields several different products including polycyclic compounds formed by C-H bond activation (Scheme 1). Therefore, designing a scalable process, in which the desired biphenol is selectively produced, is challenging.In the present work, we aim to develop MIPs that can be applied for selective electrosynthesis of the desired C-C coupled biphenol through electro-oxidation of the corresponding phenol. For this purpose, the functional monomer was selected based on the Gibbs free energy of its interaction with the target biphenol template in density functional theory (DFT) simulations. Complexation of the functional monomer with the template was confirmed by spectroscopic titrations. Electroactive monomers can polymerize to form either conducting or nonconducting polymers. In our system, a conductive MIP film was prepared using derivatized thiophene functional monomers. Then, the template extraction process was optimized. Electro-oxidation of 2,4-dimethyl phenol was studied in detail to reach as high yield as possible of the desired biphenol product at a bare platinum electrode. HPLC-MS was used to identify the substrate and products of the electrosynthesis. Then, selectivity of the electrosynthesis study was performed for the MIP film-coated electrode in comparison to a non-imprinted polymer (NIP) film-coated electrode, and a bare electrode. Figure 1

Low-oxidation-potential thiophene-carbazole monomers for electro-oxidative molecular imprinting: Selective chemosensing of aripiprazole

New thiophene-carbazole functional and cross-linking monomers electropolymerizing at potentials sufficiently low for molecular imprinting of an electroactive aripiprazole antipsychotic drug were herein designed and synthesized. Numerous conducting molecularly imprinted polymer (MIP) films are deposited by electropolymerization at relatively low potentials by electro-oxidation of pyrrole, aniline, phenol, or 3,4-ethylenedioxythiophene (EDOT). However, their interactions with templates are not sufficiently strong. Hence, it is necessary to introduce additional recognizing sites in these cavities to increase their affinity to the target molecules. For that, functional monomers derivatized with substituents forming stable complexes with the templates are used. However, oxidation potentials of these derivatives are often, disadvantageously, higher than that of parent monomers. Therefore, we designed and synthesized new functional and cross-linking monomers, which are oxidized at sufficiently low potentials. The deposited MIP and non-imprinted polymer (NIP) films were characterized by PM-IRRAS and UV–vis spectroscopy and imaged with AFM. The structure of the aripiprazole pre-polymerization complex with functional monomers was optimized with density functional theory (DFT), and aripiprazole interactions with imprinted cavities were simulated with molecular mechanics (MM) and molecular dynamics (MD). MIP-aripiprazole film-coated electrodes were used as extended gates for selective determination of aripiprazole with the extended-gate field-effect transistor (EG-FET) chemosensor. The linear dynamic concentration range was 30–300 pM, and the limit of detection was 22 fM. An apparent imprinting factor of the MIP-1 was IF = 4.95. The devised chemosensor was highly selective to glucose, urea, and creatinine interferences. The chemosensor was successfully applied for aripiprazole determination in human plasma. The results obtained were compared to those of the validated HPLC-MS method.

A molecularly imprinted electrochemiluminescence nanoprobe based on complexes consisting of CdTe and multiwall carbon nanotube for sensitive determination of clenbuterol.

An electrochemiluminescence (ECL) nanoprobe was fabricated for the determination of clenbuterol (CLB). A molecularly imprinted polymer (MIP) film was coated on the surface of the glassy carbon electrode modified with CdTe-doped multiwall carbon nanotubes. The MIP film with CLB as the template molecule improves the selectivity ofthe nanoprobe, CdTe is used as ECL signal amplifier, and MWCNT works as the carrier. The ECL intensity is altered by elution and reabsorption of CLB. The possible reaction mechanism and experimental parameters of the nanoprobe are discussed. Under optimized conditions, the quenched ECL intensity and the CLB concentration have a linear relationship in the range 2.3 × 10-9 to 1.5 × 10-5mol·L-1, and the detection limit is 1.0 × 10-9mol·L-1 (S/N = 3). The nanoprobe was successfully applied to the determination of CLB in porksamples. Graphical abstract Schematic representation of the molecularly imprinted electrochemiluminescence nanoprobe based on complexes consisting of CdTe and multiwall carbon nanotube used to determinate clenbuterol.

Directly assembled electrochemical sensor by combining self-supported CoN nanoarray platform grown on carbon cloth with molecularly imprinted polymers for the detection of Tylosin

Molecularly imprinted polymers (MIPs) based on electrochemical sensors (MIP-EC sensors) have obtained ideal achievements in recent years. However, some challenges are still need to be addressed, such as adjustable preparation, unstable sensing interface and great signal-to-noise ratio. Here, based on the ingenious combination of the MIP and the self-supported CoN nanowire arrays grown on carbon cloth (CoN NWs/CC), a robust MIP-EC sensor was developed, in which the MIP film was uniformly coated on the CoN NWs/CC via a bulk polymerization crosslinking process. Especially, CoN NWs/CC were prepared via in-situ transformation of their oxide precursors and then directly as a candidate of EC electrode. Under the optimal conditions, the MIP-EC sensor can detect Tylosin (TS) in the concentration range from 8.6 × 10−11 to 6.7 × 10−5 mol L−1, and the low detection limit (LOD) is 5.5 × 10−12 mol L−1 (S/N = 3). Furthermore, the MIP-EC sensor showed high selectivity, reproducibility and stability. The practicability of the MIP-EC sensor was tested in the actual samples of surface water and soil with the comparison of the traditional ELISA method. The developed MIP-EC sensor with simple and fabrication process can provide a versatile and reliable method, which has great potential application value for the detection of small hazardous molecules.

How Reliable Is the Electrochemical Readout of MIP Sensors?

Electrochemical methods offer the simple characterization of the synthesis of molecularly imprinted polymers (MIPs) and the readouts of target binding. The binding of electroinactive analytes can be detected indirectly by their modulating effect on the diffusional permeability of a redox marker through thin MIP films. However, this process generates an overall signal, which may include nonspecific interactions with the nonimprinted surface and adsorption at the electrode surface in addition to (specific) binding to the cavities. Redox-active low-molecular-weight targets and metalloproteins enable a more specific direct quantification of their binding to MIPs by measuring the faradaic current. The in situ characterization of enzymes, MIP-based mimics of redox enzymes or enzyme-labeled targets, is based on the indication of an electroactive product. This approach allows the determination of both the activity of the bio(mimetic) catalyst and of the substrate concentration.

Carbon Nanotube‐Based Molecularly Imprinted Voltammetric Sensor for Selective Diuretic Analysis of Dialysate and Hemodialysis Wastewater

AbstractA molecularly imprinted polymer (MIP)‐based electrochemical sensor was developed for the monitoring of hydrochlorothiazide (HCT) in dialysate and hemodialysis wastewater. The MIP was constructed by the electropolymerization of ortho‐phenylenediamine on multi‐walled carbon nanotube modified glassy carbon electrode surface. The experimental optimization was carried out by Plackett‐Burman design screening and central composite design. Through square wave voltammetry (SWV) analysis, the sensor presented linear response in the range of 5.0×10−6 to 1.0×10−4 mol L−1 (R=0.9995) and detection limit of 3.2×10−6 mol L−1. The film morphology was investigated by SEM, EDX and AFM, and the electrochemical response was confirmed by EIS. The MIP film exhibited excellent selectivity for HCT, rapid response and good practicability. The sensor was successfully applied for direct and selective determination of HCT in dialysate and hemodialysis wastewater samples with recovery rates ranging from 97 % to 102 % based on the standard addition method.

A novel electrochemical sensor based on molecularly imprinted polymer with binary functional monomers at Fe-doped porous carbon decorated Au electrode for the sensitive detection of lomefloxacin

A novel molecularly imprinted polymer (MIP) electrochemical sensor for the sensitive detection of lomefloxacin (LFX) was developed for the first time. For this, Fe-doped porous carbon (Fe-PC) was firstly synthesized and then used to modify the Au electrode. MIP film with binary functional monomers was fabricated on the Fe-PC modified Au electrode surface by electropolymerization, with LFX as template molecule, o-phenylenediamine (o-PD) and β-cyclodextrin (β-CD) as binary functional monomers. The results showed that the developed sensor exhibited high selectivity and sensitivity in detection of LFX, which was attributed to the large specific surface area, rich porosity and good catalytic property of Fe-PC, as well as high selectivity and affinity of MIP prepared with binary functional monomers. Under the optimal conditions, the current response was linear to the concentration of LFX ranging from 1 to 120 nM, with a detection limit of 0.2 nM (S/N = 3). Moreover, the developed sensor showed good reproducibility and stability toward LFX detection, and it was applied to detect LFX in water and milk samples with good recoveries ranging from 86.6% to 105.0%.

An eco-friendly MIP-solid surface fluorescence immunosensor for detection of CA 19-9 tumor marker using Ni nanocluster as an emitter labels

In the present study, an eco-friendly solid surface fluorescence immunosensor was fabricated for the ultra-selective and sensitive determination of CA 19-9 antigen based on polydopamine (PDA) molecular imprinted polymer (MIP) as an antibody substitution and Ni nanoclusters (Ni NCs) as the fluorescent signal probe. Here, the uniform MIP film for CA 19-9 antigen was established by electropolymerization of DA and target antigen on the surface of ITO electrode. When the imprinted cavities were occupied by CA 19-9 antigen and Ni NCs-Ab, respectively, the fluorescence emission of Ni NCs on the MIP-modified electrode surface was increased. Actually, MIP has been used in immunoassays as antibody substitute. Under optimized experimental conditions, taking advantage of both MIP-FL assays, the proposed immunosensor demonstrated a good analytical performance for the CA 19-9 antigen detection in an excellent linear range from 1 pg mL−1 to 48 ng mL−1 with detection limit of 0.13 pg mL−1 (S/N = 3). The application of the proposed MIP-FL immunosensor for detection of CA 19-9 antigen in human serum samples was evaluated, and the obtained results were found to be in acceptable agreement with those obtained with an ELISA assay as standard method. The developed fluorescence immunosensor demonstrated high specificity and can provide a simple, sensitive and reliable approach for the ultra-trace detection of other tumor markers in clinical monitoring.

SERS-Based Molecularly Imprinted Plasmonic Sensor for Highly Sensitive PAH Detection.

A novel hybrid plasmonic platform based on the synergetic combination of a molecularly imprinted polymer (MIP) thin film with Au nanoparticle (NPs) assemblies, noted as Au@MIP, was developed for surface-enhanced Raman scattering (SERS) spectroscopy recognition of polycyclic aromatic hydrocarbons (PAHs). While the MIP trapped the PAH close to the Au surface, the plasmonic NPs enhanced the molecule's Raman signal. The Au@MIP fabrication comprises a two-step procedure, first, the layer-by-layer deposition of Au NPs on glass and their further coating with a uniform MIP thin film. Profilometry analysis demonstrated that the thickness and homogeneity of the MIP film could be finely tailored by tuning different parameters such as prepolymerization time or spin-coating rate. Two different PAH molecules, pyrene or fluoranthene, were used as templates for the fabrication of pyrene- or fluoranthene-based Au@MIP substrates. The use of pyrene or fluoranthene, as the template molecule to fabricate the Au@MIP thin films, enabled its ultradetection in the nM regime with a 100-fold improvement compared with the nonimprinted plasmonic sensors (Au@NIPs). The SERS data analysis allowed to estimate the binding constant of the template molecule to the MIP. The selectivity of both pyrene- and fluoranthene-based Au@MIPs was analyzed against three PAHs of different sizes. The results displayed the important role of the template molecule used for the Au@MIPs fabrication in the selectivity of the system. Finally, the practical applicability of pyrene-based Au@MIPs was shown by performing the detection of pyrene in two real samples: creek water and seawater. The design and optimization of this type of plasmonic platform will pave the way for the detection of other relevant (bio)molecules in a broad range of fields such as environmental control, food safety, or biomedicine.

Evaluation of Molecularly Imprinted Thin Films for Ephedrine Recognition

Ephedrine is an illicit drug, classified as precursor for methamphetamine, which is also used as stimulant, appetite suppressant, decongestant or asthma. In this study, novel molecularly imprinted polymer (MIP) films were prepared by sol-gel derived techniques, using N-(2-aminoethyl)-3-aminopropyltrimethoxysilane as functional monomer, to recognize ephedrine from aqueous solutions. The films were obtained by air-spraying the precursor solutions, with various concentrations of monomer and template, on glass supports. Infrared, thermogravimetry, ellipsometry, optic and atomic force microscopy analyzes of films provided information regarding the effect of molecular imprinting upon the physical properties of films. Further on, batch rebinding evaluation indicated that thinner films present high affinity for ephedrine, resulting in 6.2 imprinting factor after 15 minutes of contact, which attests the ability of the novel MIP films to recognize and rebind ephedrine.

Hexagonally Packed Macroporous Molecularly Imprinted Polymers for Chemosensing of Follicle-Stimulating Hormone Protein.

Homogenous nanostructuration of molecularly imprinted polymer (MIP) films for follicle-stimulating hormone (FSH)-sensing was achieved by using optimized colloidal crystals as a hard mold. Introduction of a heating step after assembling colloidal crystals of silica beads promoted their adhesion. Thus, precise assembling of beads was not disturbed during further multisteps of surface imprinting, and crack-free hexagonal packing was maintained. Scanning electron microscopy imaging confirmed hexagonal packing of silica colloidal crystals as well as homogenous nanostructuration in MIP films. FSH immobilization over silica beads and later its derivatization with electroactive functional monomers was confirmed by X-ray photoelectron spectroscopy analysis. The nanostructured molecular recognition films prepared in this way were combined with an electrochemical transducer in order to design a capacitive impedimetry-based chemosensing system. It was tested for the determination of FSH in the range from 0.1 fM to 100 pM in 10 mM 2-(N-morpholino) ethane sulfonic acid buffer (pH = 4.2). The detection limit of the chemosensor was 0.1 fM, showing a high selectivity with respect to common protein interferences as well as other protein hormones of the gonadotropin family.

Electrochemiluminescence solid-state imprinted sensor based on graphene/CdTe@ZnS quantum dots as luminescent probes for low-cost ultrasensing of diethylstilbestrol

A novel molecularly imprinted electrochemiluminescence (MIP-ECL) sensor was fabricated for diethylstilbestrol (DES), which exploited the strategy of specific identification by molecularly imprinted polymers (MIPs) instead of expensive biomolecules. Core-shell quantum-dots (QDs) of CdTe@ZnS were utilized to enhance ECL emission. The sensor was assembled as a solid-state electrode by immobilizing CdTe@ZnS/reduced-graphene oxide (r-GO) composite on a glassy carbon electrode (GCE) surface, and then being covered with MIPs film with specific cavities. The fabricated sensor (denoted as MIP/CdTe@ZnS/r-GO/GCE) was based on the obstruction of ECL signals by DES molecules enriched on MIP film. The ECL intensity of the QDs-K2S2O8 system was reduced when the DES molecules were selectively rebound onto the MIP film by molecularly imprinted solid phase extraction (MISPE). Accordingly, the logarithm of the quenched ECL intensity versus the logarithm of the DES concentration was in a good linear relationship over a wide range from 1.8 × 10− 3 to 25.0 nmol/L with the limit of detection (LOD) of 0.25 pmol/L (S/N = 3). The sensor also exhibits excellent selectivity with fast response and good accuracy. Lake water and milk samples were assayed by this sensor, and the recoveries ranging from 92.2%–108.3% were obtained.

Study of horseradish peroxidase and hydrogen peroxide bi-analyte sensor with boronate affinity-based molecularly imprinted film

A novel electrochemical horseradish peroxidase (HRP) sensor was developed based on boronate affinity-based electropolymerized polythionine (PTh) molecularly imprinted polymer (MIP) as specific recognition element for HRP on gold nanoparticles (AuNPs) modified glassy carbon electrode, in which PTh acted as the electrochemical probe for the sensor. The sensor was characterized by scanning electron microscopy and electron dispersive spectroscopy. Electrochemical impedance spectroscopy, cyclic voltammetry, and differential pulse voltammetry were exploited for the study of the properties of the MIP sensor. The MIP sensor exhibited excellent linear response over the range of 2.0 × 10−10 mg/mL ∼ 1.0 × 10−7 mg/mL for HRP. In addition, with MIP film as HRP immobilized matrices, the sensor for the detection of H2O2 was developed with the MIP sensor based on the reduction of H2O2 catalyzed by HRP in the presence of electron mediator PTh. The sensor showed linear relationships between the current response and H2O2 concentration from 6.0 × 10−7 to 2.0 × 10−5 mol/L. HRP and H2O2 bi-analyte sensor based on MIP film was successfully developed in this work. The developed method can also be applicable for enzyme and its enzymatic substrate bi-analyte sensor.

Development of biomimetic enzyme-linked immunosorbent assay based on molecular imprinting technique for semicarbazide detection

ABSTRACT Herein, we present a direct competitive biomimetic enzyme-linked immunosorbent assay (BELISA) method for the determination of semicarbazide (SEM) using a molecularly imprinted polymer (MIP) film as the bionic antibody. The best monomer (methacrylic acid) and molar ratio of monomer to template (4:1) were determined with the aid of computational simulation methods based on density functional theory (DFT). The MIP film was characterised by scanning electron microscopy and adsorption experiments. The results showed that the imprinted film was successfully synthesised with good adsorption performance. Under optimal conditions, the calibration curve was linear in the range of 1.0–1.0×104 ng/mL (R 2 = 0.9863). The detection limit (IC15) and sensitivity (IC50) were 1.0 and 85.7 ng/mL, respectively. This BELISA method was further applied to the analysis of SEM in food samples; recoveries ranged from 86.1% to 90.8%. These observations indicated that the developed method could be adapted for SEM quantification in food.

Autonomous biosensing device merged with photovoltaic technology for cancer biomarker detection

Pursuing self-powered biosensors, this work describes a hybrid device combining a sensing electrochemical system with a photovoltaic cell. The sensing system is a molecularly-imprinted polymer (MIP) and the photovoltaic cell is a dye-sensitized solar cell (DSSC). The biosensing film is tailored on a typical counter electrode (CE) of a conventional DSSC, turning the resulting hybrid system sensitive to a target analyte. The target analyte selected herein was carcinogenic embryonic antigen (CEA), a typical cancer biomarker in colorectal cancer.In detail, the MIP film was tailored on a highly conductive polyaniline CE, by electropolymerizing aniline on top of it, in near basic pH and in the presence of CEA. The protein was later removed by proteinase K action. The resulting vacant sites were able to rebind CEA, as confirmed in a 3-electrodes set-up, by square-wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) studies.The hybrid DSSC/biosensing system was tested by incubating the CEA solution in urine sample on the biosensing film and using the resulting surface to act as counter electrode of the photovoltaic cell. The photovoltaic features of the resulting device confirmed the dependency between power and CEA concentration. In this new set-up, a linear trend was observed between power and log CEA concentration, down to 0.025 ng mL−1 when urine samples were tested.Overall, the hybrid device is inexpensive and self-powered, which holds a great impact in point-of-care applications, especially in low-income countries. This concept may be further extended to other biomarkers implicated in several diseases or other target molecules involved in food safety or environmental monitoring needs.

Surface plasmone resonance sensor for biomimetic detection of progesterone with macroporous molecularly imprinted polymers prepared by visible light

Reversible addition-fragmentation chain transfer (RAFT) polymerization mechanism was used for the preparation of molecularly imprinted polymers (MIPs) film using 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA) as chain transfer reagent and visible light initiator. In addition, the effect of CDTPA concentration on the polymerization rate was monitored, establishing that too high CDTPA concentration would inhibit the polymerization rate. The MIPs film was characterized by contact angle measurement, frontier transfer infrared spectroscopy (FTIR) and scanning electron microscope (SEM) which showed the successful grafting of MIPs films onto surface plasmon resonance (SPR) sensor chip. The response of progesterone sensing ranged from 10−16 to 10−6mol/L with low detection limit of 1× 10−16mol/L in PBS buffer (pH 7.4) and the MIPs film exhibited good selectivity, reproducibility and stability. Moreover, the sensors had been successfully applied to detect progesterone in tap water, lake water and human urine turning out with wide detection range and low detection limit.

Dual biorecognition by combining molecularly-imprinted polymer and antibody in SERS detection. Application to carcinoembryonic antigen

This work reports the innovative combination of a molecularly-imprinted polymer (MIP) and a natural antibody for the accurate surface-enhanced Raman spectroscopy (SERS) detection of carcinoembryonic antigen (CEA). The MIP material acted as a pre-concentration scheme for the target protein, while the natural antibody was responsible to signal the presence of CEA on the MIP platform.Gold-based screen-printed electrodes were used as substrate and gallic acid (GA) was used herein for the first time in the assembly of a MIP film, by electropolymerization, in the presence of CEA. This layer was further covered by a second ultra-thin film of electropolymerized benzoic acid (BA), to avoid non-specific binding. The rebinding features of the MIP film were evaluated by electrochemical impedance spectroscopy (EIS) and a linear response was observed from 1 to 1000 ng/mL.For a sensitive SERS detection, the MIP film was first incubated in sample containing CEA and next incubated in SERS tag. For the SERS tag, gold nanostars (AuNSs) were employed as metal support, coupled to 4-aminothiophenol (4-ATP) as Raman reporter and to a natural antibody for CEA as recognition element. The overall system showed a sensitive response down to 1.0 ng/mL, which was different from the blank signal.Overall, the innovative approach presented herein combines the advantages of using two different targeting elements for CEA. The costs and time of MIP production were substantially low due to selection of electropolymerization approach and the proposal described herein may be extended to other target molecules.

Molecularly imprinted polymer modified glassy carbon electrodes for the electrochemical analysis of isoproturon in water

Isoproturon-imprinted polypyrrole films were electrochemically synthesized onto glassy carbon (GC) electrodes in an ethanol/aqueous solution of pyrrole as a monomer, isoproturon as a template molecule and LiClO4 as supporting electrolyte. Electropolymerization was performed by cyclic voltammetry and chronoamperometry. The isoproturon template molecules were successfully trapped in the polypyrrole film where they created artificial recognition cavities. After the electrochemical extraction of the template, the polypyrrole film acted as a molecularly imprinted polymer (MIP) for the selective recognition of isoproturon whereas the non-imprinted polymer (NIP) film, made in the same conditions except for the presence of isoproturon, did not exhibit any interaction. The MIP and NIP films were characterized by cyclic voltammetry in the presence of redox probes and the thickness of the polymer layers was estimated by EQCM (Electrochemical Quartz Crystal Microbalance) and calculated using Faraday's law. The isoproturon-imprinted polypyrrole films were found to selectively detect isoproturon even in the presence of the interferents carbendazim and carbamazepine. Its limit of detection (LOD) in milli Q water, achieved via square wave voltammetry was as low as 0.5 μg L−1, whereas in real water samples it was found to be 2.2 μg L−1.

Surface plasmon resonance sensor based on Bi-monomer System (BMS) molecularly imprinted polymer for detection of 17β-estradiol in aqueous media

In this work, a hydrophilic and high sensitivity sensor was fabricated based on BMS (MAA : HEMA = 3 : 1, molar ratio) molecularly imprinted polymers (MIPs) film for 17β-estradiol (E2) detection in aqueous media combined with surface plasmon resonance (SPR) technique. In-situ UV polymerization method was used to synthesize the MIPs film on the gold surface which was modified with dodecyl mercaptan. Afterwards, the MIPs film was characterized by infrared spectroscopy (IR), scanning electron microscope (SEM) and contact angle measurements. The results showed that the MIPs film was successfully prepared on the surface of the sensor chip with good hydrophilicity and permeability. The analysis of SPR spectroscopy indicated that the MIPs film displayed greater selectivity to E2 than other competitors and non-imprinted polymers (NIPs) film and showed better adsorption performance than one kind of monomer for the same E2 concentration. The response of E2 sensor ranged from 2.5×10−16 to 2.5×10−8 mol/L with an ultra-low detection limit of 9.14×10−18mol/L in PBS buffer (pH 7.4). In addition, this sensor performed good reusability and stability. Finally, the sensor was successfully applied to detect E2 in tap water and human urine and had wide detection ranges and low detection limits in backgrounds.

Molecularly imprinted graphite spray ionization-ion mobility spectrometry: application to trace analysis of the pesticide propoxur.

A porous graphite sheet modified by a molecularly imprinted polymer (MIP) was directly used as the spray ionization source for ion mobility spectrometry (IMS). Therefore, it was possible to selectively analyze samples extracted by the molecularly imprinted polymer. This obviates the need for the steps of elution, solvent evaporation, dissolution and injection. To prepare the sheet, the graphite surface was first modified by electrodeposition of a molecularly imprinted polypyrrole film. This polypyrrole film was fabricated in a three-electrode electrochemical system using cyclic voltammetry. The electropolymerization of the graphite sheet was carried out with LiClO4 as a supporting electrolyte in the reaction solution. The effects of the amount of monomer, the level of template concentrations, and the time of polymerization on the extraction efficiency of the MIP film were evaluated. The extraction conditions including extraction time, the extraction temperature, the pH values, the salt concentrations, and the stirring rate were also studied. Methanol was selected as the most suitable solvent for both desorption and ionization which occur simultaneously. The pesticide propoxur (acting as a test compound) was extracted from water samples and directly analyzed using IMS. The analytical parameters (working range: 1.0 to 250ng·mL-1; detection limit: 0.3ng·mL-1) indicated that the direct coupling of MIP and IMS has a great potential in terms of reproducibility, and speed of the analysis, while maintaining acceptable sensitivity. Graphical abstract Schematic presentation of molecularly imprinted graphite spray ionization coupled with ion mobility spectrometry (IMS) for rapid/selective extraction and ionization: Application to the pre-concentration of propoxur prior to its quantification by IMS.