A disposable edoxaban sensor chip using carbon paste electrode grafted with molecularly imprinted polymer.

Although direct oral anticoagulants (DOACs) are generally safe and TDM is not required, blood levels of the drug are important information for response decisions in emergency care. In this study, an attempt was made to develop a disposable sensor chip for the rapid detection of edoxaban in blood, a type of DOAC. Molecularly imprinted polymers with edoxaban tosilate as a template and sodium p-styrene sulfonate as a functional monomer were grafted onto the surface of graphite particles, mixed with silicon oil dissolved in ferrocene to form a paste, and filled onto a substrate made of plastic film. Sensor chips were fabricated. The current obtained from this sensor by voltammetry within 150 s depended on the edoxaban concentration. Sensitivity to edoxaban was also confirmed in bovine whole blood. The potential of disposable sensors to rapidly detect edoxaban in whole blood was demonstrated in this study, although selectivity, reproducibility, and sensitivity need to be improved for practical use.

Disposable Sensor Chips with Molecularly Imprinted Carbon Paste Electrodes for Monitoring Anti-Epileptic Drugs.

Epilepsy is a neurological disorder that affects millions of people worldwide. Anti-epileptic drugs (AEDs) are critical for their management. However, the therapeutic window is narrow, and traditional laboratory-based therapeutic drug monitoring (TDM) methods can be time consuming and unsuitable for point-of-care testing. To address this issue, we developed a disposable sensor chip based on molecularly imprinted polymer-modified carbon paste electrodes (MIP-CPs) for the TDM of AEDs such as phenobarbital (PB), carbamazepine (CBZ), and levetiracetam (LEV). In this work, functional monomers (methacrylic acid) and crosslinking monomers (methylene bisacrylamide and ethylene glycol dimethacrylate) were copolymerized in the presence of the AED template and grafted on the graphite particles by simple radical photopolymerization. The grafted particles were mixed with silicon oil, dissolving ferrocene as a redox marker to make the MIP-carbon paste (CP). Disposable sensor chips were fabricated by packing the MIP-CP into the base made of poly (ethylene glycol terephthalate) (PET) film. The sensor's sensitivity was determined using differential pulse voltammetry (DPV), carried out on a single sensor chip for each operation. Linearity was obtained from 0-60 µg/mL in PB and LEV and 0-12 µg/mL in CBZ, covering their respective therapeutic range. The time taken for each measurement was around 2 min. The experiment using whole bovine blood and bovine plasma indicated that the existence of species that interfered had a negligible effect on the test's sensitivity. This disposable MIP sensor provides a promising approach for point-of-care testing and facilitating the management of epilepsy. Compared with existing tests, this sensor offers a faster and more accurate way to monitor AEDs, which is crucial for optimizing therapy and improving patient outcomes. Overall, the proposed disposable sensor chip based on MIP-CPs represents a significant advancement in AED monitoring, with the potential for rapid, accurate, and convenient point-of-care testing.

Synthesis of fluorescent Molecularly Imprinted Polymer Nanoparticles Sensing Small Neurotransmitters with High Selectivity Using Immobilized Templates with Regulated Surface Density.

To develop nanosensors to probe neurotransmitters, we synthesized fluorescent-functionalized molecularly imprinted polymeric nanoparticles (fMIP-NPs) using monoamine neurotransmitters (serotonin and dopamine) immobilized on glass beads as templates. The size and fluorescence intensity of the fMIP-NPs synthesized with blended silane couplers increased with the presence of the target but were insensitive to the target analogs (L-tryptophan and L-dopa, respectively). However, when the template is anchored by a pure silane agent, both the fluorescence intensity and particle size of the fMIP-NPs were sensitive to the structural analog of the template. Another fMIP-NP was synthesized in the presence of poly([2-(methacryloyloxy)ethyl] trimethylammonium chloride (METMAC)-co-methacrylamide) grafted onto glass beads as a dummy template for acetylcholine. Acetylcholine increased the diameter and fluorescence intensity of the fMIP-NP, but choline had no effect. When the homopolymer of METMAC was used as a template, the fluorescence intensity and size of the resulting nanoparticles were not responsive to either acetylcholine or choline. The principle of increased fluorescence intensity due to specific interaction with the target substance is probably due to the increased distance between the fluorescent functional groups and decreased self-quenching due to the swelling caused by the specific interaction with the template. The results also indicate that MIP nanoparticles prepared by solid-phase synthesis can be used for targeting small molecules, such as the neurotransmitters addressed in this study, by adjusting the surface density of the template.

A Disposable Sensor Chip Using a Paste Electrode with Surface-Imprinted Graphite Particles for Rapid and Reagentless Monitoring of Theophylline.

This work focuses on a carbon-based imprinted polymer composite, employed as a molecular recognition and sensing interface in fabricating a disposable electrochemical sensor. The carbon-paste electrode was made of a molecularly imprinted polymer comprising a copolymer of methacrylic acid as the functional monomer and blended crosslinking monomers of N,N'-methylenebisacrylamide, and ethylene glycol dimethacrylate, with theophylline as the template. The analytical properties of the proposed theophylline sensor were investigated, and the findings revealed an increase in differential pulse voltammetric current compared to the non-imprinted electrode. Under optimized conditions, the sensor has shown high sensitivity, high selectivity, lower detection limit (2.5 µg/mL), and satisfactory long-term stability. Further, the sensor was tested in whole bovine blood and validated without any matrix effect and cross-reactivity. Additionally, chronoamperometry of the sensor chip supported a rapid determination of THO with a short response time of 3 s. This carbon-paste electrode is highly specific for theophylline and may be applied as a drug sensor for clinical use.

Reagentless Sensing of Vancomycin Using an Indium Tin Oxide Electrode Grafted with Molecularly Imprinted Polymer including Ferrocenyl Group.

Vancomycin (VCM) is a first-line antimicrobial agent against methicillin-resistant Staphylococcus aureus, a cause of nosocomial infections. Therapeutic drug monitoring is strongly recommended for VCM-based chemotherapy. The authors attempted to develop a simple VCM sensor based on molecularly imprinted polymer (MIP), which can be used with simple operations. Methacrylic acid (MAA), acrylamide, methylenebisacrylamide, and allylamine carboxypropionate-3-ferrocene (ACPF) were copolymerized in the presence of VCM and grafted from the surface of indium-tin oxide (ITO) to obtain MIP-coated electrodes. The MIP-grafted ITO electrode was used for differential pulse voltammetry (DPV) measurements in a buffer solution containing VCM or whole bovine blood. The obtained current depends on the VCM concentration with high linearity. The dynamic range covered the therapeutic range (20-40 µg/mL) of the VCM but was almost insensitive to teicoplanin, which has a similar structure to VCM. The ITO electrodes grafted by the same procedure except for omitting either VCM or APCF were not sensitive to VCM. The sensitivity of the MIP electrodes to VCM in whole blood and buffered saline, but the background current in blood was higher than that in saline. This high background current was also seen in the deproteinized plasma. Thus, the current is probably originated from the oxidation of low molecular weight reducing agents in the blood. The MIP-grafted ITO electrode using ACPF as a functional monomer would be a promising highly selective sensor for real-time monitoring of VCM with proper correction of the background current.

A "Single-Use" Ceramic-Based Electrochemical Sensor Chip Using Molecularly Imprinted Carbon Paste Electrode.

An inexpensive disposable electrochemical drug sensor for the detection of drugs (vancomycin, meropenem, theophylline, and phenobarbital) is described. Molecularly imprinted polymer (MIP) templated with the target drugs was immobilized on the surface of graphite particles using a simple radical polymerization method and packed into the working electrode of a three-electrode ceramic-based chip sensor. Differential pulse voltammetry (DPV) was used to determine the relationship between the response current and the concentration of the targeted drug while using one sensor chip for one single operation. The time required for each DPV measurement was less than 2 min. Concentrations corresponding to the therapeutic range of these drugs in plasma were taken into account while performing DPV. In all the cases, the single-used MIP sensor showed higher sensitivity and linearity than non-imprinted polymer. The selectivity test in drugs with a structure similar to that of the target drugs was performed, and it was found that MIP-based sensors were more selective than the untreated ones. Additionally, the test in whole blood showed that the presence of interfering species had an insignificant effect on the diagnostic responses of the sensor. These results demonstrate that the disposable MIP-sensor is promising for quick and straightforward therapeutic drug monitoring to prevent the toxic side effects and the insufficient therapeutic effect due to the overdose and underdose, respectively.

Erratum: Yoshimi, Y., et al. Size of Heparin-Imprinted Nanoparticles Reflects the Matched Interactions with the Target Molecule. Sensors 2019, 19, 2415.

The authors wish to make the following erratum to this paper [...].

Size of Heparin-Imprinted Nanoparticles Reflects the Matched Interactions with the Target Molecule.

It has been shown that the faradic current at an electrode grafted with molecularly imprinted polymer (MIP) is sensitive to the specific target molecule used as the template. This phenomenon is applicable to sensors with very high selectivity, but the sensing mechanism is still a black box. We investigated the size sensitivity of nanoparticles of molecularly imprinted polymers (MIP-NPs) to a specific interaction for determination of the mechanism of the gate effect and its feasibility for new applications. Nanoparticles of poly(methacryloxy ethyl trimethylammonium chloride-co-acrylamide-co-methylenebisacrylamide) imprinted with heparin immobilized on glass beads were synthesized. The diameter of the MIP-NPs of heparin was increased by the presence of the heparin template but was insensitive to chondroitin sulfate C (CSC), the analogue of heparin. The high selectivity of the MIP-NPs was consistent with the selectivity of electrodes grafted with a heparin-imprinted polymer in our previous studies. The quartz crystal microbalance probes immobilizing heparin or CSC were sensitive to MIP-NPs, which indicates that the binding ability of MIP-NP does not discriminate between the template and other glycosaminoglycans. These results indicate that the size of the MIP-NP is sensitive to the matched binding with the template through the imprinted cavity.

Heparin molecularly imprinted polymer thin flm on gold electrode by plasma-induced graft polymerization for label-free biosensor.

Heparin, a highly sulfated glycosaminoglycan, is an important biomaterial having biological and therapeutic functionalities such as anticoagulation, regeneration, and protein stabilization. This study addresses a label-free quartz crystal microbalance (QCM) biosensor for heparin detection based on a macromolecularly imprinted polymer (MIP) as an artificial recognition element. We demonstrate the novel strategy for MIP in the form of thin film on a gold (Au) electrode with the plasma-induced graft polymerization (PIP) technique. The procedure of PIP is as follows: (i) Hexamethyldisiloxane plasma-polymerized thin film (PPF) as a pre-coating scaffold of active species for PIP (post-polymerization) is deposited on an Au electrode. (ii) The PPF/Au electrode is soaked in an water solution containing heparin (template), (2-(methacryloxy)-ethyl)trimethylammonium chloride acrylamide (functional monomer), acrylamide, and N,N-methylenebisacrylamide (crosslinker). Double bonds of monomer and crosslinker attacked by residually active species in pre-coating PPF cause radical chain reaction. Consequently, a growing polymer network of 20 nm thickness of PIP-MIP thin film is formed and grafted on the PPF/Au surface. (iii) The PIP-MIP/PPF/Au is washed by sodium chloride solution so as to remove the template. Non-imprinted polymer (NIP) is carried out like the same procedure without a template. The AFM, XPS, and QCM measurements show that the PIP process facilitates macromolecularly surface imprinting of template heparin where the template is easily removed and is rapidly rebound to PIP-MIP without a diffusional barrier. The heparin-PIP-MIP specifically binds to heparin compared with heparin analog chondroitin sulfate C (selective factor: 4.0) and a detectable range of heparin in the presence of CS (0.1 wt%) was 0.001-0.1 wt%. The PIP-NIP does not show selectivity between them. The evaluated binding kinetics are association (ka = 350 ±â€¯100 M-1 s-1), dissociation (kd = (5.0 ±â€¯2.0) × 10-4 s-1), and binding (KD = 1.3 ±â€¯0.6 µM) constants, demonstrating that the PIP-MIP as a synthetic antibody can be applied to analytical chemistry.

Improved gate effect enantioselectivity of phenylalanine-imprinted polymers in water by blending crosslinkers.

In this work, the anodic current at an electrode grafted with a molecularly imprinted polymer (MIP) crosslinked via a combination of hydrophobic ethyleneglycol dimethacrylate (EDMA) and hydrophilic methylene bisacrylamide (MBAA) was found to exhibit enantioselective sensitivity to the phenylalanine template in aqueous solution. An MIP-grafted electrode crosslinked with a 2:1 mixture of EDMA and MBAA was observed to respond to the template with the highest enantioselectivity, such that the change in current induced by the imprinted template was more than four times that induced by the enantiomer of the template. The contact angle of a water droplet on an MIP-coated electrode prepared using the optimal crosslinker blending ratio was also sensitive to the template and again exhibited chiral selectivity. The change in the contact angle induced by the template was more than twice as large as that obtained from the template's enantiomer. Atomic force microscopy showed that the surface of the MIP layer fabricated using a mixture of crosslinkers was rougher than that made with a single crosslinking agent, although there was no apparent correlation between the roughness and the enantioselectivity of the layer. These results indicate that the appropriate combination of crosslinkers enables the chiral-selective gate effect by modulating the flexibility and hydrophilicity of the MIP layer. The approach described herein therefore represents a new means of improving the selectivity of MIPs by blending crosslinkers having different chemical properties.

Application of the 'gate effect' of a molecularly imprinted polymer grafted on an electrode for the real-time sensing of heparin in blood.

Heparin is the most important anticoagulant drug used during surgeries and extracorporeal therapies. Although the blood levels of heparin should be monitored continuously during the procedure to ensure the safety of the patient, there is currently no technique for measuring heparin in real time. This study describes the use of a molecularly imprinted polymer (MIP) as a recognition element in the development of a heparin sensor for real-time monitoring. An indium tin oxide (ITO) electrode grafted with a heparin-specific MIP was used as a working electrode to perform cyclic voltammetry of ferrocyanide. The anodic current was found to be dependent on heparin concentration, probably due to the "gate effect", which is a change in the accessibility of the MIP-modified electrode to ferrocyanide, triggered by specific interaction between MIP and heparin. The kinetics of heparin interaction with the MIP-grafted electrode was evaluated using potentiostatic chronoamperometry of ferrocyanide in an electrochemical flow cell. The response time to stepwise changes in heparin concentration between 0 and 0.04 units per mL was estimated at 20 s, which is remarkably shorter than that achieved using conventional methods for monitoring heparin. The MIP-grafted electrode demonstrated exceptional sensitivity and could detect heparin in whole blood samples (0-6 units per mL) diluted 100-fold with physiological saline containing ferrocyanide. Therefore, the MIP-grafted electrode is suitable for real-time monitoring of heparin in blood. Another advantage is that a very small volume of blood is needed, which is very important, especially when regular measurements are required.

Influence of the solvent on nature of gate effect in molecularly imprinted membrane.

The solute diffusive permeability in a thin layer of a molecularly imprinted polymer (MIP) is affected by specific binding of the MIP with a template. This phenomenon, termed the "gate effect," would be widely applicable for the development of novel biomimetic sensors. However, the mechanism underlying the gate effect is not totally understood. We present here investigation of the role of specific adsorption of a template and solution content in MIPs on the gate effect. A molecularly imprinted self-supporting membrane was formed by copolymerization of methacrylic acid, 2-vinylpyridine, and triethyleneglycol dimethacrylate in the presence of L- (or D-) phenylalanine as a template. The template adsorbed by membrane with degree of enantio-selectivity in a mixed solvent of methanol and water. The amount of adsorption and binding selectivity showed little sensitivity to the solvent composition. The solution content in the membrane increased with increasing the methanol concentration of the solvent following a sigmoid curve with an inflection point at methanol concentration of 20 wt.%. The content increased in the presence of the template at methanol concentrations higher than the inflection point, and decreased at lower methanol concentrations. The creatinine permeability across the membrane estimated by batchwise dialysis increased in the presence of the template at 50 wt.% methanol in the solvent, and did not change at 20 wt.%. There was no permeability for creatinine in the pure water solvent. Both the solution content and the permeability were not affected by the presence of the enantiomer of the template. The results show that the choice of solvent controls more strongly the nature of the gate effect than the specific binding of the template.

Development of an enzyme-free glucose sensor using the gate effect of a molecularly imprinted polymer.

The instability of enzymatic glucose sensors has prevented the development of a practical artificial pancreas for diabetic patients. We therefore developed an enzyme-free glucose sensor using the gate effect of a molecularly imprinted polymer (MIP). This sensor has the advantages of improved stability and a simplified manufacturing procedure. An adduct of glucose and 4-vinylphenylboronic acid (VPBA) was synthesized by esterification and was then purified. The copolymer of the glucose/VPBA adduct and methylene bisacrylamide was grafted onto an indium tin oxide electrode surface. Glucose was washed out from the copolymer to obtain an MIP layer. Cyclic voltammetry of ferrocyanide in aqueous solution was performed using an MIP-grafted electrode, and the effect of glucose on the anodic current intensity was evaluated. The anodic current intensity was sensitive to the glucose concentration, and the dynamic range (0-900 mg/dl) covered the typical range of diabetic blood glucose levels. The response time of the MIP-grafted electrode to a stepwise change in the glucose concentration was approximately 3-5 min. Thus, we can conclude that, by taking advantage of its gate effect, it is feasible to use an MIP-grafted electrode as a glucose sensor for monitoring blood sugar in diabetic patients.

In situ control of cell adhesion using photoresponsive culture surface.

A photoresponsive culture surface (PRCS) allowing photocontrol of cell adhesion was prepared with a novel polymer material composed of poly(N-isopropylacrylamide) having spiropyran chromophores as side chains. Cell adhesion of the surface was drastically enhanced by the irradiation with ultraviolet (UV) light (wavelength: 365 nm); after subsequent cooling and washing on ice, many cells remained in the irradiated region, whereas most cells were removed from the nonirradiated region. The cell adhesion of the PRCS, which had been enhanced by previous UV irradiation, was reset by the visible light irradiation (wavelength 400-440 nm) and the annealing at 37 degrees C for 2 h. Also it was confirmed that the regional control of cell adhesion was induced several times by repeating the same series of operations. Further, living cell patterning with the 200 microm line width was produced readily by projecting UV light along a micropattern on the PRCS on which the living cells had been seeded uniformly in advance. By using a fluorescent probe that stains living cells only, it was confirmed that the cells maintained sufficient viability even after UV light irradiation followed by cooling and washing.

Development of an artificial synapse using an electrochemical micropump.

Improving the resolution of artificial sensory organs requires an interface that receives external information from electronic circuits and stimulates appropriate neurons individually in response to that information. The method of electric stimulation in available artificial sensory organs is fairly nonselective; therefore, we developed a method of chemical stimulation of neurons using a neurotransmitter containing an electrochemical micropump powered by the bubbling that occurs during water electrolysis. The micropump contains a glass nozzle with a tip 10 microm in diameter. Two blackened platinum electrodes for the electrolysis were inserted into the body of the pump, which was filled with neurotransmitter solution. The distance between a neuron of the gastropod Aplysia and the tip of the nozzle was adjusted to about 100 microm. A potential difference of 3.0 V was applied to the electrodes to propel the solution toward the neuron while its membrane potential was monitored. Administration of 1-mM acetylcholine to a resting neuron caused neural firing only when the voltage was applied for 0.5 s and without a time lag. During administration of 50-mM gamma-aminobutyric acid to spontaneously firing neurons, the firing disappeared with a time lag of 1 s after application of 3.0 V. We concluded that an electrochemical micropump can be applied for rapid neurotransmitter administration to control the excitation and inhibition of neurons. This simple pump can be miniaturized to create "synapses" in artificial sensory organs.