Boosting Electrochemical Sensing Performances Using Molecularly Imprinted Nanoparticles

Nanoparticles of molecularly imprinted polymers (nanoMIPs) combine the excellent recognition ability of imprinted polymers with specific properties related to the nanosize, such as a high surface-to-volume ratio, resulting in highly performing recognition elements with surface-exposed binding sites that promote the interaction with the target and, in turn, binding kinetics. Different synthetic strategies are currently available to produce nanoMIPs, with the possibility to select specific conditions in relation to the nature of monomers/templates and, importantly, to tune the nanoparticle size. The excellent sensing properties, combined with the size, tunability, and flexibility of synthetic protocols applicable to different targets, have enabled the widespread use of nanoMIPs in several applications, including sensors, imaging, and drug delivery. The present review summarizes nanoMIPs applications in sensors, specifically focusing on electrochemical detection, for which nanoMIPs have been mostly applied. After a general survey of the most widely adopted nanoMIP synthetic approaches, the integration of imprinted nanoparticles with electrochemical transducers will be discussed, representing a key step for enabling a reliable and stable sensor response. The mechanisms for electrochemical signal generation will also be compared, followed by an illustration of nanoMIP-based electrochemical sensor employment in several application fields. The high potentialities of nanoMIP-based electrochemical sensors are presented, and possible reasons that still limit their commercialization and issues to be resolved for coupling electrochemical sensing and nanoMIPs in an increasingly widespread daily-use technology are discussed.

Molecular imprinted polymer-based potentiometric approach for the assay of the co-formulated tetracycline HCl, metronidazole and bismuth subcitrate in capsules and spiked human plasma

BACKGROUND

An anti-H-pylori co-formulated mixture of tetracycline HCl (TET), metronidazole (MET), and bismuth subcitrate (BSC) is recently available. Only two chromatographic and spectrophotometric methods are reported for determining those drugs simultaneously where the effect of impurities that could be present as well as the biological fluids matrix influence do not be taken into consideration. There is a need to develop an easy-to-use potentiometric technique for analysis of TET, MET, and BSC in their co-formulated capsules, in presence of some official impurities and in spiked human plasma.

RESULTS

Three carbon paste electrodes (CPEs) were fabricated for this purpose. Being a solid contact ion-selective electrode, CPE suffers from the creation of a water layer affecting its stability and reproducibility. Besides, it has a common problem in differentiation between two drugs carrying the same charge (positively charged TET and MET). Water layer formation was prevented through inserting polyaniline nanoparticles (≈10.0 nm diameter) between solid contact and ion-sensing membrane in the three proposed sensors. TET and MET interference was overcome by synthesizing a corresponding molecular imprinted polymer (MIP) for each drug. The synthesized MIPs were inserted in equivalent sensing membranes and characterized using several techniques. The suggested MIPs have a noticeable enhanced sensitivity in potentiometric determination. The obtained LODs were 5.88 × 10-8, 5.19 × 10-7, and 1.73 × 10-6 M for TET, MET and BSC proposed CPEs, respectively, with corresponding slopes of 57.37, 56.20, and -57.40 mV decade-1.

SIGNIFICANCE

The proposed potentiometric method makes the detection of the three cited drugs simple, fast, and feasible. This approach is the first for determining three drugs potentiometrically in one combined formulation. The obtained results were compared favorably with previously reported potentiometric methods.

Molecularly Imprinted Polymers Specific towards 4-Borono-L-phenylalanine-Synthesis Optimization, Theoretical Analysis, Morphology Investigation, Cytotoxicity, and Release Studies

The aim of this study was to create molecularly imprinted polymers (MIPs) that are specific towards 4-borono-L-phenylalanine (BPA) to serve as boron compound carriers. The honeycomb-like MIPs were characterized in the matter of adsorption properties, morphology, structure, and cytotoxicity towards A549 and V79-4 cell lines. The honeycomb-like MIP composed from methacrylic acid and ethylene glycol dimethacrylate was characterized by a binding capacity of 330.4 ± 4.6 ng g^-1 and an imprinting factor of 2.04, and its ordered, porous morphology was confirmed with scanning electron microscopy. The theoretical analysis revealed that the coexistence of different anionic forms of the analyte in basic solution might lower the binding capacity of the MIP towards BPA. The release profiles from the model phosphate buffer saline showed that only 0 to 4.81% of BPA was released from the MIP within the time frame of two hours, furthermore, the obtained material was considered non-cytotoxic towards tested cell lines. The results prove that MIPs can be considered as effective BPA delivery systems for biomedical applications and should be investigated in further studies.

Synthesis of Mesoporous Silica Imprinted Salbutamol with Two TEOS/MTES Ratio Compositions through the Direct Incorporation Method for Salbutamol Separation

Molecularly imprinted mesoporous silica (MIPMS) is one of the methods to improve site accessibility molecule target on molecularly imprinted polymer (MIP) for application in solid-phase extraction (SPE). The MIPMS was prepared using salbutamol sulfate as template molecule, cetyltrimethylammonium bromide as a directing agent, and tetraethyl orthosilicate and methyltriethoxysilane were used as silica precursor and organosilane. In this study, two TEOS : MTES ratios were used. The MIPMS-2 with 3 : 1 ratio of TEOS : MTES has better analytical performance than the MIPMS-1 with 2 : 1 ratio of TEOS : MTES. The adsorption capacity of MIPMS-2 was about 0.0934 mg/g, and it was 0.0407 mg/g for NIPMS-2. The extraction ability of MIPMS-2 was good, with a recovery of about 104.79% ± 1.01% of salbutamol in spiked serum. The imprinting factor (IF) value obtained is 1.2. When serum was spiked with salbutamol and terbutaline, the ability of NIPMS-2 to recognize salbutamol increased. Therefore, optimizing the conditions for the MIPMS synthesis is necessary to produce a sorbent with better selectivity.

EGDMA- and TRIM-Based Microparticles Imprinted with 5-Fluorouracil for Prolonged Drug Delivery

Imprinted materials possess designed cavities capable of forming selective interactions with molecules used in the imprinting process. In this work, we report the synthesis of 5-fluorouracil (5-FU)-imprinted microparticles and their application in prolonged drug delivery. The materials were synthesized using either ethylene glycol dimethacrylate (EGDMA) or trimethylolpropane trimethacrylate (TRIM) cross-linkers. For both types of polymers, methacrylic acid was used as a functional monomer, whereas 2-hydroxyethyl methacrylate was applied to increase the final materials’ hydrophilicity. Adsorption isotherms and adsorption kinetics were investigated to characterize the interactions that occur between the materials and 5-FU. The microparticles synthesized using the TRIM cross-linker showed higher adsorption properties towards 5-FU than those with EGDMA. The release kinetics was highly dependent upon the cross-linker and pH of the release medium. The highest cumulative release was obtained for TRIM-based microparticles at pH 7.4. The IC₅₀ values proved that 5-FU-loaded TRIM-based microparticles possess cytotoxic activity against HeLa cell lines similar to pure 5-FU, whereas their toxicity towards normal HDF cell lines was ca. three times lower than for 5-FU.

Nano-molecularly imprinted polymers (nanoMIPs) as a novel approach to targeted drug delivery in nanomedicine

Molecularly imprinted polymers - MIPs - denote synthetic polymeric structures that selectively recognize the molecule of interest against which MIPs are templated. A number of works have demonstrated that MIPs can exceed the affinity and selectivity of natural antibodies, yet operating by the same principle of "lock and key". In contrast to antibodies, which have certain limitations related to the minimal size of the antigen, nanoMIPs can be fabricated against almost any target molecule irrespective of its size and low immunogenicity. Furthermore, the cost of MIP production is much lower compared to the cost of antibody production. Excitingly, MIPs can be used as nanocontainers for specific delivery of therapeutics both in vitro and in vivo. The adoption of the solid phase synthesis rendered MIPs precise reproducible characteristics and, as a consequence, improved the controlled release of therapeutic payloads. These major breakthroughs paved the way for applicability of MIPs in medicine as a novel class of therapeutics. In this review, we highlight recent advances in the fabrication of MIPs, mechanisms of controlled release from the MIPs, and their applicability in biomedical research.

Biotinylated magnetic molecularly imprinted polymer nanoparticles for cancer cell targeting and controlled drug delivery

Here, multivalent functions have been successfully integrated on a single core-shell type nanostructure, for remote-controlled and receptor-targeted intracellular delivery of doxorubicin (DOX) to breast cancer cells that overexpress biotin receptors.

Synthesis, characterization, and evaluation of selective molecularly imprinted polymers for the fast determination of synthetic cathinones

As a kind of new psychoactive substance (NPS), synthetic cathinones have drawn great worldwide attention. In this study, molecularly imprinted polymers (MIPs), as adsorbents for the extraction and determination of 4-methyldimethcathinone (4-MDMC), were first synthesized by coprecipitation polymerization. The physicochemical analyses of MIPs were successfully performed by XRD, FTIR, FESEM and TGA techniques. Furthermore, rebinding properties of temperature and pH dependence, and selectivity and reusability tests for MIPs and non-imprinted polymers (NIPs) were performed using an ultraviolet-visible spectrometer (UV-vis). The obtained results indicate that the imprinting efficiency has strong dependence on temperature and pH, and the optimal adsorption for targets is achieved under the condition of 318 K and pH = 6.0. This means that the combination between the polymers and 4-MDMC is a strong spontaneous and endothermic process. Compared with NIPs, MIPs exhibit prominent adsorption capacity (Q_e = 9.77 mg g⁻¹, 318 K). The selectivity coefficients (k) of MIPs for 4-MDMC, methylenedioxypentedrone (βk-MBDP), 4-ethylmethcathinone (4-EMC), methoxetamine (MXE) and tetrahydrofuranylfentanyl (THF-F) were found to be 1.70, 3.49, 7.14 and 5.82, respectively. Moreover, it was found that the adsorption equilibrium was achieved within 30 min. The aim of this work is the simple synthesis of MIPs and the optimal performance of the molecular recognition of 4-MDMC. Moreover, the synthesized MIPs can be easily regenerated and repeatedly used with negligible loss of efficiency (only 9.94% loss after six times adsorption–desorption tests). Satisfying recoveries in the range of 69.3–78.9% indicate that MIPs have good applicability for analyte removal from urine samples. Ultimately, this material shows great promise for the rapid extraction and separation of synthetic cathinones, which are dissolved in the liquid for the field of criminal sciences.

Molecularly imprinted polymers, as an adsorbent for extraction and selective recognition of 4-methyldimethcathinone, were firstly synthesized through coprecipitation polymerization.

The influence of cross-linking agent onto adsorption properties, release behavior and cytotoxicity of doxorubicin-imprinted microparticles

Molecularly imprinted polymers (MIPs) are synthetic polymers that possess cavities selective towards their molecular templates and have found many applications in separation science, drug delivery, and catalysis. Here, we report the synthesis of doxorubicin-imprinted microparticles cross-linked with two different compounds (ethylene glycol dimethacrylate or trimethylolpropane trimethacrylate) and examination of their physicochemical properties. During the synthesis methacrylic acid was used as functional monomer and 2-hydroxyethyl methacrylate was added into polymerization mixture to increase hydrophilicity of the obtained materials and therefore improve interactions with aqueous release medium. The influence of initial concentration and contact time onto doxorubicin adsorption by obtained MIPs microparticles have been investigated. The microparticles obtained using ethylene glycol dimethacrylate as a cross-linker showed 3 times higher adsorption properties towards doxorubicin, than the ones obtained using trimethylolpropane trimethacrylate cross-linker. The release kinetics of doxorubicin from drug-loaded MIPs microparticles has been proven to be dependent upon cross-linker used and pH of the release medium. For drug-loaded MIPs microparticles obtained using both cross-linkers the IC₅₀ values measured for cancer cell were comparable to the ones measured for pure doxorubicin, whereas the cytotoxicity towards normal HDF cell lines was lower.

Small-Molecule Dengue Virus Co-imprinting and Its Application as an Electrochemical Sensor

Polymers can be synthesized to recognize small molecules. This is achieved by introducing the target molecule during monomer self-assembly, where they can be incorporated during cross-linking polymerization. Following additional pre-processing, the material obtained can then be applied as a sensing layer for these molecules in many applications. The sensitivity of the polymers depends on the "active sites" imprinted on the surface. Increasing the number of active sites on the polymers surface can be achieved by using nanoparticles as a platform to support and concentrate the molecules for imprinting. In this work, we report the first use of dengue virus as a supporting nanoparticle to make for a more effective polymer composite sensor for the detection of bisphenol A (BPA), which is an environmental contaminant. The dengue virus has a nanoparticle size of around 100 nm and its surface provides regions where lipids and hydrophobic compounds can bind, making it an ideal support. The mixing of BPA with dengue prior to monomer self-assembly led to imprinted polymer surfaces with much higher density BPA binding sites and a limit of detection of 0.1 pm. We demonstrate that a BPA-dengue co-imprinting polymer composite sensor shows a very high sensitivity for BPA, but with lower production costs and technical requirements than other comparable methods.

Molecularly imprinted polymers as selective adsorbents for ambient plasma mass spectrometry

The application of molecularly imprinted polymers (MIPs) as molecular scavengers for ambient plasma ionization mass spectrometry has been reported for the first time. MIPs were synthesized using methacrylic acid as functional monomer; nicotine, propyphenazone, or methylparaben as templates; ethylene glycol dimethacrylate as a cross-linker; and 2,2′-azobisisobutyronitrile as polymerization initiator. To perform ambient plasma ionization experiments, a setup consisting of the heated crucible, a flowing atmospheric-pressure afterglow (FAPA) plasma ion source, and a quadrupole ion trap mass spectrometer has been used. The heated crucible with programmable temperature allows for desorption of the analytes from MIPs structure which results in their direct introduction into the ion stream. Limits of detection, linearity of the proposed analytical procedure, and selectivities have been determined for three analytes: nicotine, propyphenazone, and methylparaben. The analytes used were chosen from various classes of organic compounds to show the feasibility of the analytical procedure. The limits of detections (LODs) were 10 nM, 10, and 0.5 μM for nicotine, propyphenazone, and methylparaben, respectively. In comparison with the measurements performed for the non-imprinted polymers, the values of LODs were improved for at least one order of magnitude due to preconcentration of the sample and reduction of background noise, contributing to signal suppression. The described procedure has shown linearity in a broad range of concentrations. The overall time of single analysis is short and requires ca. 5 min. The developed technique was applied for the determination of nicotine, propyphenazone, and methylparaben in spiked real-life samples, with recovery of 94.6–98.4%. The proposed method is rapid, sensitive, and accurate which provides a new option for the detection of small organic compounds in various samples.

Graphical abstract

Highly efficient electrochemical recognition and quantification of amine enantiomers based on a guest-free homochiral MOF

A novel homochiral MOF was facilely synthesized, its nanocrystals exhibit rapid discrimination of α-methylbenzylamine enantiomers and quantitative determination of enantiomeric excess.

The combination of adsorption by functionalized halloysite nanotubes and encapsulation by polyelectrolyte coatings for sustained drug delivery

A novel organic–inorganic hybrid nanocomposite was established for the sustained release of an analgesic.

Synthesis of a nano molecularly imprinted polymeric sorbent for solid phase extraction and determination of phenytoin in plasma, urine, and wastewater by HPLC

In this work a nano polymeric sorbent for phenytoin was synthesized by non-covalent molecularly imprinted polymerization approach.

Application of Ni:ZnS nanoparticles loaded on magnetic multi-walled carbon nanotubes as a sorbent for dispersive micro-solid phase extraction of phenobarbital and phenytoin prior to HPLC analysis: experimental design

Ni:ZnSNPs loaded on magnetic MWCNTs are introduced for dispersive micro-solid phase extraction for the first time.

A core–shell CdTe quantum dots molecularly imprinted polymer for recognizing and detecting p-nitrophenol based on computer simulation

A novel molecular imprinting technology, combined with computer simulation and QDs, was used to detect 4-NP.

Preparation of temperature sensitive molecularly imprinted polymer coatings on nickel foam for determination of ofloxacin in Yellow River water by solid-phase microextraction

A new ofloxacin-templated MIP on nickel foam was investigated for the determination of antibiotics in river water.