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Histamine, a biogenic amine, is abundant in fermented foods and beverages, notably wine. A high intake of this monoamine may produce adverse reactions in humans, which may be severe in individuals with a reduced capacity to catabolise extrinsic histamine. Thus, control of histamine concentration during wine production and before distribution is advisable. Simple, rapid, point-of-use bioanalytical platforms are needed because traditional methods for the detection and quantification of histamine are expensive and time-consuming. This work applies the lateral flow immunoassay technique to histamine detection. Superparamagnetic particle labels, and an inductive sensor designed to read the test line in the immunoassay, enable magnetic quantification of the molecule. The system is calibrated with histamine standards in the interval of interest for wine production. A commercial optical strip reader is used for comparison measurements. The lateral flow system has a limit of detection of 1.2 and 1.5 mg/L for the inductive and optical readers, respectively. The capability of the inductive system for histamine quantification is demonstrated for wine samples at different processing points (at the end of alcoholic fermentation, at the end of malolactic fermentation, in freshly bottled wine, and in reserve wine). The results are validated by ultra-high-performance liquid chromatography. [Figure not available: see fulltext.]., This work was financially supported by the Spanish Ministry of Economy and Competitiveness under projects MAT2017-84959-C2-1-R, MAT2016-81955-REDT, and AGL2016-78708-R; the Council of Gijón-IUTA under grant SV-18-GIJON-1-27; and the Principality of Asturias under project IDI/2018/000185.

Superparamagnetic iron oxide nanoflowers coated by a black carbon layer (Fe3O4@C) were studied as labels in lateral flow immunoassays. They were synthesized by a one-pot solvothermal route, and they were characterized (size, morphology, chemical composition, and magnetic properties). They consist of several superparamagnetic cores embedded in a carbon coating holding carboxylic groups adequate for bioconjugation. Their multi-core structure is especially efficient for magnetic separation while keeping suitable magnetic properties and appropriate size for immunoassay reporters. Their functionality was tested with a model system based on the biotin&ndash, neutravidin interaction. For this, the nanoparticles were conjugated to neutravidin using the carbodiimide chemistry, and the lateral flow immunoassay was carried out with a biotin test line. Quantification was achieved with both an inductive magnetic sensor and a reflectance reader. In order to further investigate the quantifying capacity of the Fe3O4@C nanoflowers, the magnetic lateral flow immunoassay was tested as a detection system for extracellular vesicles (EVs), a novel source of biomarkers with interest for liquid biopsy. A clear correlation between the extracellular vesicle concentration and the signal proved the potential of the nanoflowers as quantifying labels. The limit of detection in a rapid test for EVs was lower than the values reported before for other magnetic nanoparticle labels in the working range 0&ndash, 3 &times, 107 EVs/&mu, L. The method showed a reproducibility (RSD) of 3% (n = 3). The lateral flow immunoassay (LFIA) rapid test developed in this work yielded to satisfactory results for EVs quantification by using a precipitation kit and also directly in plasma samples. Besides, these Fe3O4@C nanoparticles are easy to concentrate by means of a magnet, and this feature makes them promising candidates to further reduce the limit of detection.

A new generation of magnetic lateral flow immunoassays is emerging as powerful tool for diagnostics. They rely on the use of magnetic nanoparticles (MNP) as detecting label, replacing conventional gold or latex beads. MNPs can be sensed and quantified by means of external devices, allowing the development of immunochromatographic tests with a quantitative capability. Moreover, they have an added advantage because they can be used for immunomagnetic separation (IMS), with improvements in selectivity and sensitivity. In this paper, we have reviewed the current knowledge on magnetic-lateral flow immunoassay (LFIA), coupled with both research and commercially available instruments. The work in the literature has been classified in two categories: optical and magnetic sensing. We have analysed the type of magnetic nanoparticles used in each case, their size, coating, crystal structure and the functional groups for their conjugation with biomolecules. We have also taken into account the analytical characteristics and the type of transduction. Magnetic LFIA have been used for the determination of biomarkers, pathogens, toxins, allergens and drugs. Nanocomposites have been developed as alternative to MNP with the purpose of sensitivity enhancement. Moreover, IMS in combination with other detection principles could also improve sensitivity and limit of detection. The critical analysis in this review could have an impact for the future development of magnetic LFIA in fields requiring both rapid separation and quantification.

Lateral flow assays may be used by minimally trained personnel for fast and inexpensive bioanalyses in decentralized non-exigent environments. Their extension to a broader catalog of applications depends on improvements in their quantification and their sensitivity. We report a strategy that combines nanomagnetic tagging of the analyte of interest with radiofrequency inductive sensing, easy to achieve in friendly and portable format. To optimize nanotag performance, we investigated the influences of their magnetic core size and agglomeration. Iron oxide nanoparticles, with sizes from 5 to 23 nm, were synthesized by thermal decomposition and then coated with dimercaptosuccinic acid and functionalized with neutravidin protein. We tested the system by immobilizing biotin in lateral flow membrane strips. When a sample containing the particles flows along the membrane, the biotin captures the neutravidin together with the magnetic nanotags, which are detected by the inductive sensor. The optimal nanotag core size is the critical threshold for superparamagnetic behavior, which maximizes both the initial magnetic permeability and the saturation magnetization. Controlled agglomeration of the nanotags increases the magnetic mass captured in the test line and further amplifies the signal.

This work describes the fabrication and evaluation of an electroanalytical paper-based platform based on the combination of both, reusable and disposable materials in order to generate simple, versatile and low-cost microfluidic devices. With this aim, a holder containing metal wires that act as reusable reference and counter electrodes has been developed. The gold-sputtered paper electrode is disposable and easily interchangeable, meanwhile the platform that includes reference and counter electrodes can be reused. The detection zone in the paper is delimited by drawing a hydrophobic line with an inexpensive permanent marker. The effect of experimental variables such as adding solutions through the face where the gold was sputtered (upwards) or through the opposite one (downwards) as well as of other working parameters were studied by cyclic and differential pulse voltammetry with potassium ferrocyanide as a common redox probe and indicator species for enzymatic, immune and DNA biosensing. Enzymatic determination of glucose in real food samples prove the feasibility of the developed system for the construction of electrochemical biosensors.

This work describes the development and evaluation of a new electrochemical platform based on the sustainable generation of gold-nanoparticles on paper-based gold-sputtered electrodes. The disposable porous paper electrode is combined with screen-printed electrodes for ensuring a precise electrogeneration of nanoparticles and also for the evaluation of these simple, versatile and low-cost microfluidic devices. Two types of chromatographic paper with different thicknesses have been evaluated. Paper gold working electrodes modified with gold nanoparticles were characterized by scanning electron microscopy and cyclic voltammetry using potassium ferrocyanide as a common redox probe, showing an improved electrochemical performance when compared to bare gold electrodes. The platform has been applied to the non-enzymatic determination of glucose, molecule of enormous interest. The porous gold structure made by sputtering on paper, modified with electrogenerated nanoparticles allowed precise and accurate determination of the analyte in beverages at low potential, This work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under projects CTQ2011-25814 and CTQ2014-58826-R. Estefania Núnez-Bajo thanks MINECO for the award of Ph.D. grant BES-2012-056713

This paper describes the development of simple, sustainable, and low-cost strategies for signal enhancement on paper-based carbon platforms through gold nanoparticles electrogenerated from small volumes of tetrachloroauric (III) acid solutions. Carbon ink is deposited on a hydrophilic working area of the paper delimited with hydrophobic wax. This maskless procedure is fast and cuts down ink waste. The connection of this working electrode to the potentiostat is ensured with the use of screen-printed electrodes (SPEs). Close contact of the whole area of both carbon electrodes improves the precision of the nanostructuration. Resulting gold-modified paper-based carbon working electrodes (AuNPs-PCWEs) were characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and electron dispersion X-ray spectrometry (SEM/EDX). This methodology was applied for the first time to the inorganic arsenic determination in commercial white wines by chronoamperometric stripping of the electrodeposited As(0). In an optimized system, As(III) was reduced and deposited as As(0) on the nanostructured surface by applying a potential of −0.3 V during 180 s. Then, anodic stripping chronoamperometry was performed at +0.4 V. The analytical signal was the current recorded at 30 s. On the other hand, As(V) was chemically reduced to As(III) with 0.2 M KI, and total determination of arsenic could be carried out. As(V) was determined as the difference between total As and As(III).Then, this fast, simple and low-cost method can be employed for speciation purposes. Limits of detection for As(III) and total arsenic (in the presence of KI) are 2.2 μg L−1 and 2.4 μg L−1, respectively, and indicate that this method is suitable for regulated quality control., This work has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under Projects CTQ2011-25814 and CTQ2014-58826-R. E. Nunez-Bajo thanks MINECO for the award of a Ph.D. Grant BES-2012- 056713. Authors thank Prof. E. Blanco-Gonzalez, Prof. M. Montes-Bayon, and J. García-Fernández from the Departamento de Quimica Física y Analí tica, Universidad de Oviedo, for kindly determining the total arsenic concentration in white wines by ICP-MS.

In this work, we report a simple and yet efficient stencil-printed electrochemical platform that can be integrated into the caps of sample containers and thus, allows in-field quantification of Cd(II) and Pb(II) in river water samples. The device exploits the low-cost features of carbon (as electrode material) and paper/polyester transparency sheets (as substrate). Electrochemical analysis of the working electrodes prepared on different substrates (polyester transparency sheets, chromatographic, tracing and office papers) with hexaammineruthenium(III) showed that their electroactive area and electron transfer kinetics are highly affected by the porosity of the material. Electrodes prepared on transparency substrates showed the best electroanalytical performance for the simultaneous determination of Cd(II) and Pb(II) by square-wave anodic stripping voltammetry. Interestingly, the temperature and time at which the carbon ink was cured had significant effect on the electrochemical response, especially the capacitive current. The amount of Cd and Pb on the electrode surface can be increased about 20% by in situ electrodeposition of bismuth. The electrochemical platform showed a linear range comprised between 1 and 200 mg/L for both metals, sensitivity of analysis of 0.22 and 0.087 mA/ppb and limits of detection of 0.2 and 0.3 mg/L for Cd(II) and Pb(II), respectively. The analysis of river water samples was done directly in the container where the sample was collected, which simplifies the procedure and approaches field analysis. The developed point-of-need detection system allowed simultaneous determination of Cd(II) and Pb(II) in those samples using the standard addition method with precise and accurate results, This work has been supported by the FC-15-GRUPIN-021 project from the Asturias Regional Government and the CTQ2014-58826-R project from the Spanish Ministry of Economy and Competitiveness (MINECO). Daniel Martín-Yerga thanks the MINECO for the award of a FPI grant (BES-2012-054408). Isabel Alvarez-Martos acknowledges the EU's support under H2020-MSCA-IF-2014 grant agreement 660339 (eADAM).

Stable and easily-handled synthetic materials mimicking natural enzymes activity would find important biotechnological applications. This article describes the synthesis and characterization of magnetic molecularly imprinted catalytic polymers that exhibit peroxidase-like activity towards 5-hydroxyindole-3-acetic acid (5-HIAA) oxidation. This multifunctional material is obtained from highly crystalline magnetite nuclei coated with a silica layer to protect the iron nucleus from oxidation and to provide anchoring for hydroxyl surface groups. After acrylic functionalization via sol–gel process, a molecularly imprinted polymer with hemin as catalytic center and 5-HIAA as template has been successfully attached to the structure. The resulting hybrid composite is magnetically separable and possesses excellent catalytic ability for the selective oxidation of the indoleamine metabolite tumor marker, showing Michaelis–Menten kinetics with this molecule but not towards other structural analogs. Therefore, it can be considered an artificial peroxidase enzyme.

Biological molecules (e.g., antibodies, enzymes and receptors) have been widely used as specific recognition elements in analytical assays, from homogeneous assays to biosensors, for applications in healthcare, environmental monitoring and industrial-process control. Limited stability, and difficulty and high cost of production are their main drawbacks. Artificial receptors and catalysts prepared by molecular imprinting technology are valuable in replacing biomolecules for molecular recognition in these kinds of assay. In this review, we describe the most recent developments in non-covalent molecularly-imprinted polymers (MIPs) to replace natural receptors in ligand-binding assays and biosensors. A key factor underpinning the most significant advances in this field is obtaining materials that improve the specific recognition and, at the same time, favor transduction. Composites of MIPs and carbon nanostructures or inorganic nanoparticles combine the recognition properties of MIPs with the electrical, optical or magnetic properties of the nanomaterials, resulting in new imprinted nanoreceptors with great potential as sensing materials. We summarize various methods to blend MIPs with different nanomaterials and highlight their application in biomimetic assays. Electropolymerized MIPs (E-MIPs) offer an option for integrating the recognition elements as nanofilms on the surface of different transducers. We discuss recent advances in the use of E-MIPs for analytical applications. MIPs mimicking natural enzymes are also among these new functional materials. We present the approaches to prepare catalytic non-covalent MIPs along with recent analytical applications and challenges for future developments.

Acrylic polymers with catalytic activity for the oxidative degradation of 2,4,6-trichlorophenol (TCP) were developed. In order to mimic the active site of chloroperoxidase (CPO), chloro-iron(III)-protoporphyrin IX was used as the catalytic centre, and methacrylamide (MA) and 4-vinylpyridine (VPY) were used as the monomers that build up the active sites. Taking as basis 3:1 (w/w) acid:basic aminoacidic composition of CPO, three MA:VPY combinations were tested: one keeping the same ratio (3:1) i.e. 25% VPY in the functional monomer mixture, one with lower content of the basic monomer (9:1) i.e. 10% VPY, and one with higher concentration of it (1:1) i.e. 50% VPY. Polymers synthesized with the lowest VPY content exhibited the highest catalytic efficiency, which was improved by the creation of specific TCP binding sites through molecular imprinting technology. In these way, synthetic enzymes with useful properties for analytical and bioremediation applications were obtained.

A method for the rational design of molecularly imprinted polymers with catalytic activity (MICs) that mimic hemeproteins is described. Density Functional Theory calculations applied to the pre-polymerization adduct and to a possible reaction intermediate allow to choose the best functional monomer that builds up the active sites. This functional monomer should stabilize both relevant stages, the first one in an adequate porogenic solvent and the second one in the aqueous reaction medium. In this work, a MIC was synthesized to catalyze the oxidation of 2,4,6-trichlorophenol (TCP), the substrate and template molecule. A hemin molecule was used as the catalytic centre and four functional monomers and six solvents were tested. According to the theoretical predictions, methacrylamide and 4-vinylpyridine MIPs successfully mimic the recently discovered ability of Chloroperoxidase (CPO) to catalyze the oxidative dechlorination of TCP in batch analysis. They exhibit good catalytic properties and substrate selectivity.

This article describes the synthesis and characterization of a catalytic 2,4,6-trichlorophenol molecularly imprinted microgel that could replace a natural chloroperoxidase to develop electrochemical sensors. This polymer exhibits an apparent mean particle size of 1–4 µm and high porosity, and mimics the dehalogenative function of the natural enzyme chloroperoxidase for p-halophenols. Two strategies were explored: a carbon paste modified with the polymer and the drop-coating of screen-printed electrodes with powder suspensions of the polymer and carbon nanotubes. With this last design, TCP concentrations above 25 µM could be detected. The sensor developed this way could be used for environmental waste screening.

A sigmoidal behaviour of chloroperoxidase for the oxidative dehalogenation of 2,4,6-trichlorophenol is reported for the first time. Kinetic data were adjusted to the Hill equation and the kinetic parameters were obtained: n = 1.7 ± 0.2, v max = ( 8.8 ± 0.3 ) × 10 − 5 M mi n − 1 , the pseudo-Michaelis constant Ks* = (8.6 ± 0.5) × 10−5 M, kcat = 677 ± 84 min−1 and the catalytic efficiency = (8.9 ± 0.6) × 106 M−1 min−1. The sigmoidal curve could be related to the cooperative binding of the substrate to the enzyme, so that the binding of the first substrate molecule may help the binding of the second one. Further, both substrate molecules could establish Π–Π interactions between them, which would confer more stability to the system.

The synthesis, characterization and evaluation of the catalytic properties of a hemin–methacrylamide–ethylene glycol dimethacrylate copolymer are described. This polymer catalyzes the oxidative dechlorination of 2,4,6-trichlorophenol (TCP) in the presence of hydrogen peroxide, yielding 2,6-dichloro-1,4-benzoquinone as the main reaction product. This low-cost material allows the complete removal of TCP from water at concentration level of 20 mg L −1 in less than 30 min.

A carbon paste-poly(o-phenylendiamine)-modified electrode to be used as amperometric biosensor for 2,4,6-trichlorophenol (TCP) is described. The enzyme chloroperoxidase (EC 1.11.1.10) from Caldariomyces fumago is immobilized through dispersion in a graphite paraffin oil carbon paste covered by an electrogenerated poly(o-phenylendiamine) (PPD) layer. The main enzymatic dehalogenation product, 2,6-dichloro-1,4-benzoquinone (DCQ) is characterized by liquid chromatography-mass spectrometry and cyclic voltammetry. This product is electrochemically active and can be detected amperometrically at +150 mV vs. Ag|AgCl|KCl (3 M). The biosensor exhibits a response time of 4 min, a detection limit of 10−7 M, and a dynamic linear range between 10−7 and 10−6 M. Selectivity as well as operating and storage stability were evaluated.

A molecularly imprinted polymer for diclofenac (DCF) was prepared by thermal polymerization over silica beads using 2-(dimethylamino)ethyl-methacrylate as functional monomer. After silica elimination by HF treatment, the polymer was applied to the selective solid-phase extraction of the drug from urine followed by its quantification by adsorptive differential pulse voltammetry. Results indicate that the drug could be selectively extracted from the sample and quantified at clinically relevant concentrations (μg/mL).

The voltammetric characteristics of catecholamines: epinephrine (E) and norepinephrine (NE) and related compounds: isoproterenol, metanephrine, L-dopa, methyldopa, vanillylmandelic acid (VMA), and homovanillic acid (HVA) at unmodified and in situ surfactant- modified carbon paste electrodes were comparatively evaluated. For the basic and amphoteric compounds the modification of the electrode surface with submicellar concentrations of anionic surfactants (sodium dodecylsulfate, sodium decylsulfate or sodium dodecylsulfonate) produce an important current enhancement in its oxidation and reduction peak current together with the improvement in the reversibility of the processes. These effects were explained in basis on electrostatic and hydrophobic interactions. On the other hand, the oxidation of acidic metabolites, HVA and VMA, was studied at electrodes modified in situ with cationic surfactants. Under certain conditions the surfactant could stabilise some of the electrochemical reaction intermediates, thus explaining the different voltammetric behaviour of HVA and VMA.

The electrochemical behavior of diclofenac (DCF) at graphite electrodes was investigated. The drug is irreversibly oxidized at 0.84 V (pH 1), giving rise to some products, which exhibit two reversible process with formal potential of 0.39 and 0.63 V. Carbon composite electrodes of different nature [polytetrafluoroethylene‐graphite (PTFE‐G), epoxy‐graphite (EG), epoxy‐carbon black (E‐CB)] were also investigated for voltammetric detection of DCF. A similar electrochemical behavior was observed on these electrodes although graphite was preferred over carbon black as conducting phase, and both PTFE and epoxy could act as agglomerant. Electrodes constructed with these materials could be modified with molecularly imprinted polymers (MIPs), and allowed detection of DCF after incubation in an acetonitrile solution of the drug.

A voltammetric sensor for the determination of diclofenac was developed, based on the molecular recognition of the analyte by molecularly imprinted methacrylate-ethyleneglycol dimethacrylate co-polymers. Pre-polymerisation solutions were deposited onto the surface of a glassy carbon electrode and a polymer film was obtained after spin coating control of thickness and in situ thermal polymerisation. After the template extraction from the resultant film, re-binding of diclofenac is performed from acetonitrile solutions containing the analyte. The amount of bonded diclofenac was then evaluated by differential pulse voltammetry in different electrolytes. The best results were obtained in 0.025 M citrate solution pH 6 containing 10% of acetonitrile. This medium favours the release of diclofenac from the polymer binding sites. In this way, the voltammetric transduction of the molecular recognition event is achieved. Voltammetric selectivity measurements revealed negligible interferences from diclofenac family of anti-inflammatory drugs, such as niflumic or meclofenamic acids.

This chapter summarizes the major advances in the development of electrochemical sensors based on molecularly imprinted polymers as recognition element. A comprehensive and critical analysis of such chemical sensors, grouped around the different types of transduction is presented. The relevance of the type of transduction in defining the requirements for the design of MIPs and the different strategies for coupling MIPs to potentiometric, conductometric, impedimetric, voltammetric, and amperometric sensors are presented. The analytical characteristics of the different sensors are compiled in tables for easy comparison.

A methodology based on density functional theory calculations for the design of molecularly imprinted polymers (MIPs) is described. The method allows the rational choice of the most suitable monomer and polymerization solvent among a set of chemicals traditionally used in MIP formulations for the molecular imprinting of a given template. It is based on the comparison of the stabilization energies of the prepolymerization adducts between the template and different functional monomers. The effect of the polymerization solvent is included using the polarizable continuum model. A voltammetric sensor for homovanillic acid was constructed using different MIPs as recognition element, confirming that the solvent (toluene) and functional monomer (methacrylic acid) selected according to the theoretical predictions lead to the most efficient molecular recognition sensing phase. With the voltammetric sensor prepared using the MIP designed according to the theoretical predictions, a linear response for concentrations of homovanillic acid between 5 x 10(-8) and 1 x 10(-5) M can be obtained. The limit of detection is 7 x 10(-9) M. The selectivity obtained for homovanillic acid over other structurally related compounds buttresses the validity of this strategy of design.

Density Functional Theory calculations have been used to select, among a set of chemicals traditionally used in the formulation of non-covalent molecularly imprinted polymers (MIPs), the best functional monomer and porogenic solvent for the construction of a recognition element for the dopamine metabolite homovanillic acid (HVA). Theoretical predictions were confirmed through batch binding assays and voltammetric detection. The computational method predicts that trifluoromethacrylic acid and toluene are the monomer and solvent rendering the highest stabilization energy for the pre-polymerization adducts. HVA-MIP prepared using this formulation gives rise to a binding isotherm that is accurately modelled by the Freundlich isotherm. The binding properties of this polymer were estimated using affinity distribution analysis. An apparent number of sites of 13 micromol g(-1) with an average affinity constant of 2 x 10(4) M(-1) was obtained in the concentration window studied.

Vanillin is a natural compound easily extracted from plants. It has neuroprotective, anti-carcinogenic, antioxidant, antimicrobial, and anti-biofilm properties. It also presents high volatility, high hydrophilicity, and low bioavailability. Nanomaterials can be used to improve pharmacodynamics, solubility, and stability and to enhance pharmacokinetics. In this work, non-ionic surfactant vesicles were synthesized as vanillin carriers: neutral niosomes formed by Span60 and cholesterol, positive charged niosomes formulated with cetyltrimethylammonium bromide (CTAB), and negatively charged niosomes formulated with sodium dodecyl sulfate (SDS). Niosomes synthesis was carried out with two commonly used methods: thin film hydration (TFH) and ethanol injection method (EIM). The niosomes synthesized were used to prepare two different materials: (i) a powder containing the lyophilized noisome with vanillin systems and (ii) a gelatin matrix film containing niosomes with vanillin. Lyophilization was carried out using maltodextrin as a cryoprotectant. The lyophilization of colloidal structures allows for storage at room temperature for long periods of time, keeping their organoleptic characteristics invariable. Niosomes were characterized before and after the lyophilization process in terms of morphological characterization, size, polydispersity index (PDI), and zeta potential. Moreover, niosomes cargo was evaluated by calculating the encapsulation efficiency (EE) and loading capacity (LC). Results showed that the use of the TFH method allowed us to obtain niosomes of 255 nm with high EE (up to 40%) and LC values higher than EIM. The lyophilization process decreased the LC of the vesicles prepared, but this decrease was mitigated by up to 20% when ionic surfactants were used on the membrane bilayer. Gelatin films are biodegradable materials suitable for food packing applications. The incorporation of a natural compound with antimicrobial activity would be a clear advantage for such an application. The films prepared were characterized in terms of morphology, water solubility, color, and transparency. Niosomes synthesized by thin film hydration had better chemical and physical properties to load vanillin. Especially in the case of application in films, niosomes with a negative charge, formed by SDS, and vanillin loaded gave better mechanical and chemical characteristics to the film.