The replacement of antibodies by molecularly imprinted polymers (MIPs) has been investigated for many decades. However, indirect protocols (including natural primary and secondary antibodies) are still utilized to evaluate the ability of MIP thin films to recognize target molecules. MIPs can be prepared as either a thin film or as particles, and cavities that are complementary to the template can be generated on their surfaces. We have prepared thin film MIPs and particle MIPs prepared by solvent evaporation and phase inversion, respectively, from solutions of poly(ethylene-co-vinyl alcohol) (pEVAL) in the presence of the target analytes amylase, lysozyme, and lipase. These were first adsorbed on MIP thin films and by MIP particles that contain fluorescent quantum dots. Sandwich fluoroimmunoassays were then conducted to quantify them in MIP-coated 96-well microplates. The method was applied to determine amylase in saliva, and results were compared with a commercial analytical system.
A molecularly imprinted polymer (MIP) for the specific retention of neopterin has been developed. A set of 6 polymers was prepared by radical polymerization under different experimental condition using methacrylic acid as functional monomer and ethylene glycol dimethacrylate as crosslinker, with the aim to understand their influence on the efficiency of the MIP. The performance of each MIP was tested in batch experiments via their binding capacity. The MIP prepared in the presence of nickel ions in dimethylsulfoxide-acetonitrile mixture (P4) exhibited the highest binding capacity for neopterin (260 μmol per gram of polymer). A selectivity study with two other pteridines demonstrated the polymer P4 also to possess the best selectivity.
A molecularly imprinted polymer for the specific retention of neopterin was developed. A set of 6 polymers was prepared under different experimental condition. The performance of each MIP was tested through their binding capacity. The MIP P4 prepared in the presence of nickel ions exhibited the highest binding capacity
A novel kind of transferrin imprinted polymer particles was synthesized by a hierarchical strategy. First, transferrin was immobilized on silica beads by non-covalent absorption. Then, a pre-polymerization mixture, composed of 1,4-bis(acryloyl)piperazine, methacrylamide, methacrylic acid, ammonium sulfate and polyoxyethylene sorbitan monolaurate, was irrigated into the pores of silica particles, and polymerized at 25 °C. Finally, the silica matrix was etched with ammonium hydrogen fluoride, not only to remove the template protein, but also to expose protein recognition sites on the surface of the imprinted polymer. The binding capacity of the transferrin-imprinted particles is 6.3 mg of protein per gram of material, and the time required to reach adsorption equilibrium was less than 10 min. The imprinting factor of transferrin is ca. 3.3 in the presence of ribonuclease B, cytochrome c and β-lactoglobulin. The results indicate that these imprinted polymer particles can recognize transferrin with good selectivity, high binding capacity and fast mass transfer. They may be applied as an artificial antibody to remove the high abundance proteins in plasma.
A novel kind of transferrin imprinted polymer particles was synthesized by a hierarchical strategy. Transferrin was immobilized on silica beads by non-covalent absorption. The pre-polymerization mixture was irrigated into the pores of silica particles and polymerized at 25°C. After the removal of the silica matrix and template protein, protein recognition sites were exposed on the surface of the prepared polymer and applied for the transferrin recognition
We report on an ultrasensitive fluorescence immunoassay for human chorionic gonadotrophin antigen (hCG). It is based on the use of silica nanoparticles coated with a copolymer (prepared from a fluorene, a phenylenediamine, and divinylbenzene; PF@SiO2) that acts as a fluorescent label for the secondary monoclonal antibody to β-hCG antigen. In parallel, Fe3O4 nanoparticles were coated with polyaniline, and these magnetic particles (Fe3O4@PANI) served as a solid support for the primary monoclonal antibody to β-hCG antigen. The PF@SiO2 exhibited strong fluorescence and good dispersibility in water. A fluorescence sandwich immunoassay was developed that enables hCG concentrations to be determined in the 0.01–100 ng·mL−1 concentration range, with a detection limit of 3 pg·mL−1.
Fluorescence detection of prepared immune reagent nano-composites using the fluorescence cell
We describe a molecularly imprinted polymer (MIP) for the solid-phase extraction of the skin protectant allantoin. The MIP was deposited on the surface of monodisperse silica microspheres possessing acroyl groups on the surface (MH-SiO2). The resulting MIP microspheres (MH-SiO2@MIP) showed a 3.4-fold higher adsorption capacity and a 1.9-fold better selectivity for allantoin than the respective non-imprinted polymer (MH-SiO2@NIP). The monolayer adsorption capacities of the MH-SiO2@MIP and the MH-SiO2@NIP were calculated with the help of the Langmuir model and found to be 6.8 and 1.9 mg•g−1, respectively. Adsorption kinetics fit a pseudo-second order rate mechanism, with an initial adsorption rate of 1.44 for the MH-SiO2@MIP, and of 0.07 mg•g−1•min−1 for the MH-SiO2@NIP. The material can be regenerated, and its adsorption capacity for allantoin remains stable for at least five regeneration cycles. It was successfully used as a sorbent for the selective solid-phase extraction of allantoin from Rhizoma dioscoreae.
A molecularly imprinted polymer for the selective separation of allantoin was developed. It was successfully used as a sorbent for the selective solid-phase extraction of allantoin from Rhizoma dioscoreae.
We report on the preparation of fluorescent silica nanoparticles (SiNPs) modified with chitosan and lucigenin by using a reverse microemulsion method. The introduction of chitosan to the lucigenin doped SiNPs is shown to improve the fluorescence quantum yield. The modified SiNPs were used as fluorescent markers in an aptamer-based method for selective determination of thrombin. In this protocol, thrombin was sandwiched between streptavidin-coated magnetic beads and the fluorescent SiNPs modified with a thrombin-binding aptamer. The method was successfully applied to the determination of thrombin in human serum and showed a detection limit as low as 0.02 nM. In our perception, the protocol presented here is promising in that such SiNPs may be applied to the sensitive fluorescent detection of other analytes by changing the corresponding aptamer.
The introduction of chitosan to the lucigenin doped SiNPs is shown to improve the fluorescence quantum yield. The modified SiNPs were used as fluorescent markers in an aptamer-based method for selective determination of thrombin. The effect of chitosan concentration on fluorescence intensity of lucigenin/SiO2 nanoparticles (the volume of chitosan solution is 100 μL)
Magnetic Fe3O4@SiO2 core shell nanoparticles containing diphenylcarbazide in the shell were utilized for solid phase extraction of Hg(II) from aqueous solutions. The Hg(II) loaded nanoparticles were then separated by applying an external magnetic field. Adsorbed Hg(II) was desorbed and its concentration determined with a rhodamine-based fluorescent probe. The calibration graph for Hg(II) is linear in the 60 nM to 7.0 μM concentration range, and the detection limit is at 23 nM. The method was applied, with satisfying results, to the determination of Hg(II) in industrial waste water.
We have prepared a hydrophilic molecularly imprinted polymer (MIP) for the hydrophobic compound bisphenol A (BPA) in aqueous solution using 3-acrylamido-N,N,N-trimethylpropan-1-aminium chloride (AMTC) as the functional monomer. Under redox-polymerization conditions, BPA forms an ion-pair with AMTC, which was confirmed by 1H-NMR titration. The imprinting effect in aqueous solution was evaluated by comparison of this material with the corresponding non-imprinted polymer (NIP) and with a control polymer (CP) bearing no AMTC. The MIP showed the highest activity among the three polymers, and the imprinting factors as calculated from the amount of BPA bound to the MIP divided by the amounts bound to NIP and CP, respectively, are 1.8 and 6.0. The MIP was selective for BPA in aqueous solution, while structurally related compounds are not recognized. Such a selectivity for a hydrophobic compound is rarely observed in aqueous medium because non-specific binding of BPA inevitably leads to hydrophobic interaction.
A molecularly imprinted polymer (MIP) was prepared by self-polymerization of dopamine in the presence of bovine hemoglobin (BHb) and then deposited on the surface of an electrode modified with gold nanoparticles (AuNPs). Scanning electron microscopy, cyclic voltammetry, and differential pulse voltammetry were employed to characterize the modified electrode using the hexacyanoferrate redox system as an electroactive probe. The effects of BHb concentration, dopamine concentration, and polymerization time were optimized. Under optimized conditions, the modified electrode selectively recognizes BHb even in the presence of other proteins. The peak current for hexacyanoferrate, typically measured at + 0.17 V (vs. SCE), depends on the concentration of BHb in the 1.0 × 10−11 to 1.0 × 10−2 mg mL−1 range. Due to the ease of preparation and tight adherence of polydopamine to various support materials, the present strategy conceivably also provides a platform for the recognition and detection of other proteins.
Gold nanoparticles and molecularly imprinted self-polymerization dopamine were modified on gold electrode surface to recognize and determine bovine hemoglobin. Under the optimized conditions, the modified electrode showed specific adsorption, selective recognition, and sensitive detection of bovine hemoglobin.
A label-free and single-step method is reported for rapid and highly sensitive detection of bisphenol A (BPA) in aqueous samples. It utilizes an aptamer acting as a probe molecule immobilized on a commercially available array of interdigitated aluminum microelectrodes. BPA was quantified by measuring the interfacial capacitance change rate caused by the specific binding between bisphenol A and the immobilized aptamer. The AC signal also induces an AC electrokinetic effect to generate microfluidic motion for enhanced binding. The capacitive aptasensor achieves a limit of detection as low as 10 fM(2.8 fg ⋅ mL − 1) with a 20 s response time. The method is inexpensive, highly sensitive, rapid and therefore provides a promising technology for on-site detection of BPA in food and water samples.
A. AC electrokinetics effect plays a vital role in BPA detection by introducing microfluidic movement to accelerate the molecular transport to the electrode surface.
B. The ACEK capacitive aptasensor has a limit of detection as low as 10 fM (2.8 fg ⋅ mL − 1) with a 20-s response time.
An ion imprinted polymer coated onto magnetite (Fe3O4) nanoparticles is shown to be a useful magnetic sorbent for the fairly selective preconcentration of vanadium. The sorbent was prepared by radical copolymerization of 3-(triethoxysilyl)propyl methacrylate (the monomer), ethylene glycol dimethacrylate (the cross-linker), and the vanadium(IV) complex of 1-(2-pyridylazo-2-naphthol) in the presence of magnetite nanoparticles. The material was characterized by IR spectroscopy, scanning electron microscopy, and thermal analysis. The vanadium(IV) ions were removed from the imprint by a solution containing thiourea and HCl, and the eluent was submitted to AAS. The analytical efficiency and relative standard deviation are 99.4 and ±2.3 %, respectively, under optimum conditions, and the limit of detection is 20 ng mL−1. The method was successfully applied to the preconcentration and determination of vanadium(IV) ions in crude oil.
An ion imprinted polymer is coated on to magnetite nanoparticles as a useful magnetic sorbent for the fairly selective preconcentration of vanadium which can be used for vanadium determination in crude oil.
We have prepared a surface imprinted polymer (SIP) film for label-free recognition of immunoglobulin G (IgG). The IgG-SIPs were obtained by covalent immobilization of IgG via a cleavable covalent bond and a suitable spacer unit to a gold electrode, followed by electrodepostion of a nm-thin film of polydopamine (PDA). The IgG was then removed by destruction of the cleavable bond so that complementary binding sites were created on the surface of the film. IgG-SIPs with various thicknesses of the PDA films were compared with respect to their affinity to IgG using a quartz crystal microbalance combined with flow injection analysis. The films were also characterized by cyclic voltammetry and scanning electron microscopy. The IgG-SIPs with a film thickness of around 17 nm showed the most pronounced imprinting effect (IF 1.66) and a binding constant of 296 nM.
A strategy for preparation of the IgG-Surface Imprinted Polymeric (IgG-SIP) thin films was developed. IgG was covalently immobilized via a cleavable cross-linker to a gold electrode surface followed by electrochemical deposition of a nanometer thin PDA film. After cleaving S-S bond in the linker the IgG was removed leaving behind the complementary binding sites confined in the surface of the polymer film. The prepared IgG-SIPs were applied for IgG recognition.
Acetylcholinesterase (AChE) from Electrophorus electricus was immobilized on the surface of amino-modified magnetic beads (AChE-MB), and its activity evaluated by the quantification of acetylcholine hydrolysis. A reference mixture composed of AChE binders (galanthamine and a probe coumarin, K i = 0.031 ± 0.010 μM) and non-binders (ketamine and propranolol) was used to probe the fishing assay. The performance of the bioconjugation assay was demonstrated with a library of 12 reference coumarins from which two ligands were directly identified by LC-MS/MS in a single assay, demonstrating the usefulness of this approach.
A bioconjugate-screening assay with AChE-modified magnetic beads was developed to direct identification of AChE binders, in mixtures, by LC-MS/MS. A reference mixture of twelve coumarins was used and, the two ligands were identified.
The food antioxidant quercetin was used as a template in an ultrathin molecularly imprinted polymer (MIP) film prepared by photopolymerization. Indium tin oxide (ITO) plates were electrografted with aryl layers via a diazonium salt precursor bearing two terminal hydroxyethyl groups. The latter act as hydrogen donors for the photosensitizer isopropylthioxanthone and enabled the preparation of MIP grafts through radical photopolymerization of methacrylic acid (the functional monomer) and ethylene glycol dimethacrylate (the crosslinker) in the presence of quercetin (the template) on the ITO. The template was extracted, and the remaining ITO electrode used for the amperometric determination of quercetin at a working potential of 0.26 V (vs. SCE). The analytical range is from 5.10−8 to 10−4 mol L−1, and the detection limit is 5.10−8 mol L−1.
This work describes the grafting of a molecularly imprinted polymer (MIP) film by combining diazonium surface chemistry and surface-initiated photopolymerization. The MIP grafts specifically and selectively recognize quercetin in pure solution in THF and in real green tea infusion.
We report on a method for the determination of the herbicide atrazine in tap water samples using melamine-modified gold nanoparticles (Mel-AuNPs). If a solution containing atrazine is added to a solution of such NPs, a color change occurs from wine-red to blue. This is due to a transition from monodisperse to aggregated Mel-AuNPs and caused by strong hydrogen bonding between atrazine and melamine. The color change can be monitored by a UV–vis spectrophotometer or with bare eyes. The ratio of the absorbances at 640 and 523 nm is linearly related to the logarithm of the atrazine concentration in the 0.165 to 16.5 μM range, and (with different slope) in the 16.5 μM to 330 μM range. The detection limit of atrazine is as low as 16.5 nM (S/N = 3). The method was successfully applied to the determination of atrazine in spiked tap water and gave recoveries that ranged from 72.5 % to 102.3 %.
ᅟ
We have investigated the gas sensing properties of ZnO thin films (100 to 200 nm thickness) deposited by room-temperature radio frequency magnetron sputtering. The sensitivity of the films to ethanol vapor was measured in the 10 to 50 ppm concentration range at operating temperatures between 200 and 400 °C. A synergetic effect of decreasing grain size and increasing operating temperature was observed towards the improvement of the sensitivity, reaching a value of 54 and a limit of detection as low as 0.61 ppm. The decrease in the grain size resulted in prolonged response time but faster recovery. In any case, both response time and recovery time are < 400 s. The results demonstrate that room-temperature magnetron sputtering is a viable approach to enhance the performances of ZnO films in sensors for ethanol vapor.
Sensor response for ZnO films in presence of 50 ppm ethanol as a function grain size and temperature
Platinum nanoparticles (Pt-NPs) with sizes in the range from 10 to 30 nm were synthesized using protein-directed one-pot reduction. The model globular protein bovine serum albumin (BSA) was exploited as the template, and the resulting BSA/Pt-NPs were studied by transmission electron microscopy, energy dispersive X-ray spectroscopy, and resonance Rayleigh scattering spectroscopy. The modified nanoparticles display a peroxidase-like activity that was exploited in a rapid method for the colorimetric determination of hydrogen peroxide which can be detected in the 50 μM to 3 mM concentration range. The limit of detection is 7.9 μM, and the lowest concentration that can be visually detected is 200 μM.
Pt-NPs were synthesized using BSA-directed one-pot reduction and BSA/Pt-NPs composite can effectively catalyze the oxidation of TMB producing blue solution in the presence of H2O2.
Hetero-dimeric magnetic nanoparticles of the type Au-Fe3O4 have been synthesised from separately prepared, differently shaped (spheres and cubes), monodisperse nanoparticles. This synthesis was achieved by the following steps: (a) Mono-functionalising each type of nanoparticles with aldehyde functional groups through a solid support approach, where nanoparticle decorated silica nanoparticles were fabricated as an intermediate step; (b) Derivatising the functional faces with complementary functionalities (e.g. amines and carboxylic acids); (c) Dimerising the two types of particles via amide bond formation. The resulting hetero-dimers were characterised by high-resolution TEM, Fourier transform IR spectroscopy and other appropriate methods.
Nano-LEGO: Assembling two types of separately prepared nanoparticles into a hetero-dimer is the first step towards complex nano-architectures. This study shows a solid support approach to combine a gold and a magnetite nanocrystal.
We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO2) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO2 and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO2. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films.
Illustration of the fabricated polystyrene/titania hybrids imprinted with 1-pyrenebutyric acid providing the interaction between the organic and inorganic components through the pyrene and carboxylic moieties
We have investigated the possibility of sampling ammonium ion using the diffusive-gradients-in-thin-films technique (DGT) by introducing a novel binding agent that is based on micro-sized zeolite. The performance of zeolite-DGT was characterized by measurement of the following parameters: (1) the diffusion coefficient of ammonium ion in hydrogel; (2) the adsorption rate of ammonium ion by the zeolite binding gel; (3) the elution efficiency, and (4) the effects of pH, ionic strength and interfering ions on DGT. The method was validated by studying the uptake of ammonium ion from in freshwaters by zeolite gels which was found to be fast enough to meet the requirements of DGT. The concentrations determined via DGT agreed well with the concentrations determined in bulk solutions. Sampling of ammonium ion using zeolite-DGT was consistent over the pH 3 to 8 range and the 0.001 to 10 mM ionic strength range. The method also performs predictably in natural waters containing various metal ions. The technique is considered to be a viable passive tool for sampling ammonium from aqueous solutions.
Schematic representation of the principle of DGT and the determination of mass accumulated on the binding gel.