Molecular imprinting solid phase extraction for selective detection of methidathion in olive oil

A specific adsorbent for extraction of methidathion from olive oil was developed. The design of the molecularly imprinted polymer (MIP) was based on the results of the computational screening of the library of polymerisable functional monomers. MIP was prepared by thermal polymerisation using N,N’-methylene bisacrylamide (MBAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. The polymers based on the itaconic acid (IA), methacrylic acid (MAA) and 2-(trifluoromethyl)acryl acid (TFMAA) functional monomers and one control polymer which was made without functional monomers with cross-linker EGDMA were also synthesised and tested. The performance of each polymer was compared using corresponding imprinting factor. As it was predicted by molecular modelling the best results were obtained for the MIP prepared with MBAA. The obtained MIP was optimised in solid-phase extraction coupled with high performance liquid chromatography (MISPE-HPLC-UV) and tested for the rapid screening of methidathion in olive oil. The proposed method allowed the efficient extraction of methidathion for concentrations ranging from 0.1 to 9 mg L⁻¹ (r² = 0.996). The limits of detection (LOD) and quantification (LOQ) in olive oil were 0.02 mg L⁻¹ and 0.1 mg L⁻¹, respectively. MIPs extraction was much more effective than traditional C18 reverse-phase solid phase extraction.     

Computer aided-molecular design and synthesis of a high selective molecularly imprinted polymer for solid-phase extraction of furosemide from human plasma

Highly selective molecularly imprinted polymers (MIPs) for solid-phase extraction and determination of furosemide in human plasma have been designed and prepared. In order to study the intermolecular interactions in the pre-polymerization mixture and to find a suitable functional monomer in MIP preparation, a computational approach was developed. It was based on the comparison of the binding energy of the complexes between the template and functional monomers. Having confirmed the results of computational method, three MIPs were synthesized with different functional monomers, i.e. acrylamide (AAM), 4-vinylpiridine (4-VP) and acrylonitrile (ACN), and then evaluated using Langmuir-Freundlich (LF) isotherm. Using the MIP prepared by AAM as functional monomer, a molecularly imprinted solid-phase extraction procedure followed by high performance liquid chromatography with ultraviolet detector (MISPE-HPLC-UV) was developed for selective extraction and determination of furosemide in human plasma. For the proposed MISPE-HPLC-UV method, the linearity between responses (peak area) and concentration was found over the range of 75-3500 ng mL⁻¹ with a linear regression coefficient (R²) of 0.997. The limit of detection (LOD) and quantification (LOQ) in plasma were 12.9 and 43.3 ng mL⁻¹, respectively.     

Molecularly imprinted polymers for on-line preconcentration by solid phase extraction of pirimicarb in water samples

The synthesis and performance of a molecularly imprinted polymers (MIPs) as a selective solid phase extraction sorbent for the preconcentration of the carbamate pirimicarb from water samples is described. The MIP was prepared using pirimicarb as the template, methacrylic acid as the functional monomer and ethylene glycol dimethacrylate as the cross-linking monomer, and using chloroform as the solvent. The detection of pirimicarb was carried out by differential pulse voltammetry (DPV) at a hanging mercury drop electrode (HMDE) in 0.1 mol l⁻¹ HCl. Solvents of different polarities were checked for the polymer synthesis, and different experimental variables (sample pH, selection of the eluent used, eluent volume, analyte and eluent flow rates and sample volume) associated with the rebinding/extraction process were optimised. For a 25 ml sample, the process took about 13 min and resulted in a nominal enrichment factor of 50 (eluent MeOH:H₂O:HAc, 7:2:1; 0.5 ml) for pirimicarb. A limit of detection of 4.1 μg l⁻¹ was obtained, and a good reproducibility of the measurements using different MIP microcolumns was found. Furthermore, the MIP selectivity was evaluated by checking several substances with similar and different molecular structures to that of pirimicarb. As an application, pirimicarb was determined in water samples of diverse origin which were spiked at a concentration level of 71.5 μg l⁻¹.     

Surface plasmon resonance-based immunoassay for procalcitonin

A surface plasmon resonance (SPR) biosensor has been developed for rapid immunoassay of procalcitonin (PCT) with high detection sensitivity and reproducibility. The 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC)-activated protein A (PrA), diluted in 1% (v/v) 3-aminopropyltriethoxysilane (APTES) was dispensed on a KOH-treated Au-coated SPR chip, resulting in the covalent binding of PrA in 30 min. This “single-step” PrA immobilization strategy led to the oriented binding of the anti-PCT antibody (Ab) on a PrA-functionalized gold (Au) chip. The leach-proof immobilization procedure is five-fold faster than conventional counterparts, enabling high detection specificity and reproducibility. The IA detects 4–324 ng mL⁻¹ of PCT with a limit of detection (LOD) and a limit of quantification (LOQ) of 4.2 ng mL⁻¹ and 9.2 ng mL⁻¹, respectively. It was capable of detecting PCT in real sample matrices and patient samples with high precision. The Ab-bound SPR chips were stable for more than five weeks.     

Computational design and multivariate optimization of an electrochemical metoprolol sensor based on molecular imprinting in combination with carbon nanotubes

This work describes the development of an electrochemical sensor based on a new molecularly imprinted polymer for detection of metoprolol (MTP) at ultra-trace level. The polypyrrole (PPy) was electrochemically synthesized on the tip of a pencil graphite electrode (PGE) which modified whit functionalized multi-walled carbon nanotubes (MWCNTs). The fabrication process of the sensor was characterized by cyclic voltammetry (CV) and the measurement process was carried out by differential pulse voltammetry (DPV). A computational approach was used to screening functional monomers and polymerization solvent for rational design of molecularly imprinted polymer (MIP). Based on computational results, pyrrole and water were selected as functional monomer and polymerization solvent, respectively. Several significant parameters controlling the performance of the MIP sensor were examined and optimized using multivariate optimization methods such as Plackett–Burman design (PBD) and central composite design (CCD). Under the selected optimal conditions, MIP sensor was showed a linear range from 0.06 to 490 μmol L⁻¹ MTP, a limit of detection of 2.88 nmol L⁻¹, a highly reproducible response (RSD 3.9%) and a good selectivity in the presence of structurally related molecules. Furthermore, the applicability of the method was successfully tested with determination of MTP in real samples (tablet, and serum).     

Development of a molecularly imprinted polymer for pyridoxine using an ion-pair as template

One of the main challenges in the molecularly imprinted polymers (MIP) field is the proper MIP design for water-soluble compounds because of appearance of serious drawbacks in polar solvents and insolubility of those compounds in non-polar solvents which are commonly used for MIP synthesis. In this work a novel and simple method for synthesis of molecularly imprinted polymers for a water-soluble compound was introduced. Pyridoxine was chosen as a target molecule and the ion-pair complex formed between pyridoxine ion (Py⁺) and dodecyl sulfate ion (DS⁻) was transferred into the chloroform via liquid-liquid extraction. Then polymerization was carried out in chloroform. The molecular mechanics and density functional theory were proposed to screen proper monomer. Binding energy, ΔE, of a template and a monomer as a measure of their interaction was considered. Ion-pair [Py⁺-DS⁻] was supposed as a template molecule and acrylic acid, methacrylic acid, allyamine, vinylpridine and 2-hydroxy ethyl methacrylate were as tested monomers. The MIP synthesized using acrylic acid showed the highest selectivity to pyridoxine as predicted from the ΔE calculation. The obtained MIP showed very high affinity against vitamin B6 in comparison to non-imprinted polymers (NIP). It was proved that the obtained MIP with introduced method was much better than that prepared in methanol as porogen. It was showed that the MIP prepared by this new method could be used as an adsorber for extraction and determination of pyridoxine in real and synthetic samples.     

Colorimetric test-systems for creatinine detection based on composite molecularly imprinted polymer membranes

An easy-to-use colorimetric test-system for the efficient detection of creatinine in aqueous samples was developed. The test-system is based on composite molecularly imprinted polymer (MIP) membranes with artificial receptor sites capable of creatinine recognition. A thin MIP layer was created on the surface of microfiltration polyvinylidene fluoride (PVDF) membranes using method of photo-initiated grafting polymerization. The MIP layer was obtained by co-polymerization of a functional monomer (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid, itaconic acid or methacrylic acid) with N, N′-methylenebisacrylamide as a cross-linker. The choice of the functional monomer was based on the results of computational modeling. The creatinine-selective composite MIP membranes were used for measuring creatinine in aqueous samples. Creatinine molecules were selectively adsorbed by the MIP membranes and quantified using color reaction with picrates. The intensity of MIP membranes staining was proportional to creatinine concentration in an analyzed sample. The colorimetric test-system based on the composite MIP membranes was characterized with 0.25 mM detection limit and 0.25–2.5 mM linear dynamic range. Storage stability of the MIP membranes was estimated as at least 1 year at room temperature. As compared to the traditional methods of creatinine detection the developed test-system is characterized by simplicity of operation, small size and low cost.     

Molecular recognition properties of salicylic acid-imprinted polymers

Summary Two molecularly imprinted polymers (MIP) have been prepared using the acidic drug salicylic acid, which can form intramolecular hydrogen bond, as the template and acrylamide or 4-vinylpyridine as the functional monomer. HPLC was used to evaluate the binding performance of the MIP for the template and for several analogues. The results showed that the MIP (P₂) prepared using acrylamide as the functional monomer had no molecular imprinting effect whereas that (P₁) prepared using 4-vinylpyridine as the functional monomer had a significant molecular imprinting effect. The reason the molecular imprinting effect was different for the two MIP was elucidated and the molecular recognition properties of P₁ were studied in detail. It was confirmed that electrostatic interaction played an important role in the molecular recognition of P₁. Scatchard analysis showed that two types of binding site with distinctly different affinity were formed in P₁. Their dissociation constants were estimated to be 7.6×10⁻⁵ mol L⁻¹ and 3.2×10⁻³ mol L⁻¹, respectively. Because P₁ has high affinity and selectivity for salicylic acid not only in organic systems but also in water-containing systems, it gives P₁ the potential for use in the enrichment, separation, and detection of salicylic acid in biological fluids.     

Preparation of temperature sensitive molecularly imprinted polymer for solid-phase microextraction coatings on stainless steel fiber to measure ofloxacin

A kind of new temperature sensitive molecularly imprinted polymer (MIP) with ofloxacin (OFL) as template was prepared for the coating of solid phase microextraction (SPME). Dopamine was self-polymerized on stainless steel fiber (SSF) as the SPME support followed by silanization. Then MIP was synthesized as SPME coating on the modified SSF in a capillary, with N-isopropyl acrylamide as temperature sensitive monomer and methacrylic acid as functional monomer. The synthesis could be well repeated with multiple capillaries putting in the same reaction solution. The obtained MIP fiber was evaluated in detail with different techniques and various adsorption experiments. At last the MIP fiber was used to extract the OFL in milk. Satisfied recoveries between 89.7 and 103.4% were obtained with the limit of quantification (LOQ_LC) of 0.04 μg mL⁻¹ by the method of SPME coupled with high performance of liquid chromatography (HPLC).     

Development of a sensitive and selective kojic acid sensor based on molecularly imprinted polymer modified electrode in the lab-on-valve system

In this work, a kojic acid electrochemical sensor, based on a non-covalent molecularly imprinted polymer (MIP) modified electrode, had been fabricated in the lab-on-valve system. The sensitive layer was synthesized by cyclic voltammetry using o-phenylenediamine as the functional monomer and kojic acid as the template. The template molecules were then removed from the modified electrode surface by washing with NaOH solution. Differential pulse voltammetry method using ferricyanide as probe was applied as the analytical technique, after extraction of kojic acid on the electrode. Chemical and flow parameters associated with the extraction process were investigated. The response recorded with the imprinted sensor exhibited a response in a range of 0.01-0.2 μmol L⁻¹ with a detection limit of 3 nmol L⁻¹. The interference studies showed that the MIP modified electrode had excellent selectivity. Furthermore, the proposed MIP electrode exhibited good sensitivity and low sample/reagent consumption, and the sensor could be applied to the determination kojic acid in cosmetics samples.     

Fast and sensitive detection of ochratoxin A in red wine by nanoparticle-enhanced SPR

Herein, we present a fast and sensitive biosensor for detection of Ochratoxin A (OTA) in a red wine that utilizes gold nanoparticle-enhanced surface plasmon resonance (SPR). By combining an indirect competitive inhibition immunoassay and signal enhancement by secondary antibodies conjugated with gold nanoparticles (AuNPs), highly sensitive detection of low molecular weight compounds (such as OTA) was achieved. The reported biosensor allowed for OTA detection at concentrations as low as 0.75 ng mL⁻¹ and its limit of detection was improved by more than one order of magnitude to 0.068 ng mL⁻¹ by applying AuNPs as a signal enhancer. The study investigates the interplay of size of AuNPs and affinity of recognition elements affecting the efficiency of the signal amplification strategy based on AuNP. Furthermore, we observed that the presence of polyphenolic compounds in wine samples strongly interferes with the affinity binding on the surface. To overcome this limitation, a simple pre-treatment of the wine sample with the binding agent poly(vinylpyrrolidone) (PVP) was successfully applied.     

Development of a model for the rational design of molecular imprinted polymer: Computational approach for combined molecular dynamics/quantum mechanics calculations

A new rational approach for the preparation of molecularly imprinted polymer (MIP) based on the combination of molecular dynamics (MD) simulations and quantum mechanics (QM) calculations is described in this work. Before performing molecular modeling, a virtual library of functional monomers was created containing forty frequently used monomers. The MD simulations were first conducted to screen the top three monomers from virtual library in each porogen-acetonitrile, chloroform and carbon tetrachloride. QM simulations were then performed with an aim to select the optimum monomer and progen solvent in which the QM simulations were carried out; the monomers giving the highest binding energies were chosen as the candidate to prepare MIP in its corresponding solvent. The acetochlor, a widely used herbicide, was chosen as the target analyte. According to the theoretical calculation results, the MIP with acetochlor as template was prepared by emulsion polymerization method using N,N-methylene bisacrylamide (MBAAM) as functional monomer and divinylbenzene (DVB) as cross-linker in chloroform. The synthesized MIP was then tested by equilibrium-adsorption method, and the MIP demonstrated high removal efficiency to the acetochlor. Mulliken charge distribution and ¹H NMR spectroscopy of the synthesized MIP provided insight on the nature of recognition during the imprinting process probing the governing interactions for selective binding site formation at a molecular level. We think the computer simulation method first proposed in this paper is a novel and reliable method for the design and synthesis of MIP.     

Synthesis and study of a molecularly imprinted polymer for the specific extraction of indole alkaloids from Catharanthus roseus extracts

Two molecularly imprinted polymers (MIP) for catharanthine and vindoline have been synthesized in order to specifically extract these natural indole alkaloids from Catharanthus roseus by solid-phase extraction (SPE). Each MIP was prepared by thermal polymerisation using catharanthine (or vindoline) as template, methacrylic acid (or itaconic acid) as functional monomer, ethylene glycol dimethacrylate (EDMA) as cross-linking agent and acetonitrile (or acetone) as porogenic solvent.For catharanthine-MIP, a SPE protocol (ACN–AcOH 99/1 washing and MeOH–AcOH 90/10 elution) allows a good MIP/NIP selectivity (imprinting factor 12.6). The specificity of catharanthine-MIP versus related bisindole alkaloids was assessed by cross-reactivity study. The catharanthine-MIP specifically retained catharanthine and its N-oxide analogue but displayed a weak cross-reactivity for other Vinca alkaloids (vinorelbine, vincristine, vinblastine, vindoline, vinflunine). It appears that the catharanthine-like unit of these molecules are hardly trapped in catharanthine cavities located in the MIP, probably due to the sterical hindrance of the vindoline moiety. Finally, the MIP-SPE applied to C. roseus extract enabled quantitative recovery of catharanthine (101%) and the total removal of vindoline. Its capacity was determined and was equal to 2.43 μmol g⁻¹.Vindoline is a weaker base than catharanthine, so the vindoline-MIP was achieved with a strong acidic monomer (itaconic acid) to increase vindoline–monomer interactions and a modified washing solvent (ACN–HCOOH 99/1) to reduce non-specific interactions. The influence of the amount of HCOOH (protic modifier) percolated during the washing step upon the elution yield and the imprinting factor for vindoline was investigated. This preliminary optimisation of the washing step, and in particular the number of moles of acid percolated, seems useful to emphasize the use of MIP in conditions of high selectivity or high yield. A compromise was obtained with an imprinting factor equal to 7.6 and an elution recovery of 33%. However MIP-vindoline failed to achieve a specific extraction of vindoline since catharanthine was also extracted probably because of strong non-specific interactions occurring between catharanthine and the sorbent.     

Investigating the mechanisms of 17<Emphasis Type="Italic">β</Emphasis>-estradiol imprinting by computational prediction and spectroscopic analysis

Molecular dynamics simulations combined with spectroscopic analysis were applied to understand the nature of recognition in molecularly imprinted polymers (MIPs), and for optimizing the MIP formulation. The best monomers for synthesizing imprinted materials for 17β-estradiol (BE2) were selected by evaluating the strength of the template–monomer interaction derived from molecular dynamics simulations. A number of potential functional monomers for BE2 were screened for hydrogen-bonding strength in order to analyze template–monomer interactions favorable for synthesizing noncovalent MIPs, with the simulations revealing that methacrylic acid, 2-(diethylamino)ethyl methacrylate, and methacrylamide provided the highest binding affinity to BE2. These theoretical predictions agree with previously reported results on batch rebinding studies using the corresponding functional monomers for synthesizing a series of MIPs. Molecular analysis such as ¹H NMR was used for experimentally confirming the prevalent template–monomer interactions derived from the modeling results. Molecular dynamics simulations indicating monomer dimerization in the prepolymerization solution correlated with the nature of the porogenic solvent, which was confirmed by NMR studies on hydrogen-bonding interactions of methacrylic acid in different solvents. Furthermore, batch rebinding studies revealed that the specific functionalities of the monomers essential to rebinding are retained after polymerization, which proves that the application of computational methods for modeling the prepolymerization solution provides useful information for optimizing real MIP systems.     

A computational and experimental investigation of the interaction between the template molecule and the functional monomer used in the molecularly imprinted polymer

A computational approach to screening monomer for preparing molecularly imprinted polymer (MIP) was proposed, using the binding energy, ΔE, of a template molecule and a monomer as a measure of their interaction. For a specified template molecule, a monomer of higher ΔE is suitable for preparing the MIP. To examine the validity of this approach, theophylline (THO) was chosen as the template molecule and methacrylic acid (MAA), acrylamide (AA) and 2-(trifluoromethyl)acrylic acid (TFMAA) were as the functional monomers, respectively. Density functional theory (DFT) at B3LYP/6-31+G**//B3LYP/3-21G level was used to calculate ΔE. It was shown that TFMAA gave the largest ΔE while AA gave the smallest. The details of the interaction between the THO with these monomers were also given by this computing approach. The adsorption of THO on the MIP synthesized using different monomers was studied. The MIP synthesized using TFMAA as monomer showed the highest selectivity to THO while the MIP from AA gave the lowest, as predicted from the ΔE calculation. ¹H NMR spectroscopy showed that, compared to MAA and AA, a stronger H-bond interaction is formed between TFMAA and THO. FT-IR analysis of the MIPs prepared using these three monomers confirmed the existence of CO and OH groups, which forms H-bond with THO. The results described above have given an insight into the interaction between THO and the monomers, and shown the use of ΔE to facilitate the selection of monomers for the synthesis of MIP.     

Sensitive and selective electrochemical determination of quinoxaline-2-carboxylic acid based on bilayer of novel poly(pyrrole) functional composite using one-step electro-polymerization and molecularly imprinted poly(o-phenylenediamine)

A facile and efficient molecularly imprinted polymer (MIP) recognition element of electrochemical sensor was fabricated by directly electro-polymerizing monomer o-phenylenediamine (oPD) in the presence of template quinoxaline-2-carboxylic acid (QCA), based on one-step controllable electrochemical modification of poly(pyrrole)-graphene oxide-binuclear phthalocyanine cobalt (II) sulphonate (PPY-GO-BiCoPc) functional composite on glassy carbon electrode (GCE). The MIP film coated on PPY-GO-BiCoPc functional composite decorated GCE (MIP/PPY-GO-BiCoPc/GCE) was presented for the first time. The synergistic effect and electro-catalytic activity toward QCA redox of PPY-GO-BiCoPc functional composite were discussed using various contrast tests. Also, the effect of experimental variables on the current response such as, electro-polymerization cycles, template/monomer ratio, elution condition for template removal, pH of the supporting electrolyte and accumulation time, were investigated in detail. Under the optimized conditions, the proposed MIP sensor possessed a fast rebinding dynamics and an excellent recognition capacity to QCA, while the anodic current response of square wave voltammetry (SWV) was well-proportional to the concentration of QCA in the range of 1.0 × 10⁻⁸–1.0 × 10⁻⁴ and 1.0 × 10⁻⁴–5.0 × 10⁻⁴ mol L⁻¹ with a low detection limit of 2.1 nmol L⁻¹. The established sensor was applied successfully to determine QCA in commercial pork and chicken muscle samples with acceptable recoveries (91.6–98.2%) and satisfactory precision (1.9–3.5% of SD), demonstrating a promising feature for applying the MIP sensor to the measurement of QCA in real samples.     

Evaluation of molecularly imprinted membranes based on different acrylic copolymers

Polyacrylonitrile and its copolymers with different functional monomers (itaconic acid, acrylic acid and acrylamide) were synthesized via water-phase precipitation polymerization in order to prepare molecularly imprinted polymer (MIP) membranes with recognition properties for the flavonoid naringin (NR). Membranes were prepared by phase inversion technique using dimethylformamide (DMF) as the solvent and adding naringin as template molecule to the casting solution. For comparison, membranes without template (blank) were prepared and tested. All MIP membranes showed high specific binding capacity; among them, the membrane prepared with the copolymer containing acrylamide as functional group, showed the highest binding capacity. Blank membranes only showed non-specific binding. The bound template was totally recovered and regenerated membranes maintained their initial binding capacity after reuse.     

Selective pretreatment and determination of phenazopyridine using an imprinted polymer-electrospray ionization ion mobility spectrometry system

In this research, selective separation and determination of phenazopyridine (PAP) is demonstrated using molecular imprinted polymer (MIP) coupled with electrospray ionization ion mobility spectrometry (ESI-IMS). In the non-covalent approach, selective MIP produced using PAP and methacrylic acid (MAA) as a template molecule and monomer, respectively. The created polymer is utilized as a media for solid-phase extraction (SPE), revealing selective binding properties for the analyte from pharmaceutical and serum samples. A coupled MIP-IMS makes it possible to quantitize PAP in the range of 1-100 ng mL⁻¹ and with a 0.2 ng mL⁻¹ detection limit. Furthermore, the MIP selectivity is evaluated by application of some substances with analogous and different molecular structures to that of PAP. This method is successfully applied for the determination of PAP in pharmaceutical and serum samples.     

Novel surface molecularly imprinted sol-gel polymer applied to the online solid phase extraction of methyl-3-quinoxaline-2-carboxylic acid and quinoxaline-2-carboxylic acid from pork muscle

A new molecularly imprinted polymer (MIP), selective for major metabolites of quinoxaline-1,4-dioxides was firstly prepared by combining surface molecular imprinting technique with the sol–gel process. Methyl-3-quinoxaline-2-carboxylic acid (MQCA) was used as template, 3-aminopropyltriethoxysilane as functional monomer, and tetraethoxysilicane as cross-linker. The MIP was characterized by Fourier transform infrared and evaluated through static adsorption experiments. The results indicated that MIP had high adsorption capacity, fast binding kinetics for MQCA, and the polymer showed a high degree of cross-reactivity for quinoxaline-2-carboxylic acid (QCA). The MIP was then applied as a selective sorbent in an online solid phase extraction (SPE) coupled with high-performance liquid chromatography (HPLC). For a 50-mL sample solution, enrichment factors of 1,349 and 1,046 for QCA and MQCA, respectively, and limits of detection (S/N = 3) of 0.8 and 2 ng L⁻¹ for QCA and MQCA, respectively, were obtained (corresponding to 0.02 and 0.04 ng g⁻¹ in solid samples for final 100 mL of sample solutions of 5 g of pork). The sample preparation protocol was simplified and only included one step extraction with acetonitrile (MeCN) after the release of target analytes through acidic hydrolysis without further sample cleanup. The new MIP-SPE-HPLC method was successfully applied to the quantification of trace QCA and MQCA in pork muscle with good recoveries ranging from 67% to 80% and RSD below 8%.