Polymeric foams as the matrix of voltammetric sensors for the detection of catechol, hydroquinone, and their mixtures

Producción CientíficaPorous electrodes based on polymethylmethacrylate and graphite foams (PMMA_G_F) have been developed and characterized. Such devices have been successfully used as voltammetric sensors to analyze catechol, hydroquinone, and their mixtures. The presence of pores induces important changes in the oxidation/reduction mechanism of catechol and hydroquinone with respect to the sensing properties observed in nonfoamed PMMA_graphite electrodes (PMMA_G). The electropolymerization processes of catechol or hydroquinone at the electrode surface observed using PMMA_G do not occur at the surface of the foamed PMM_G_F. In addition, the limits of detection observed in foamed electrodes are one order of magnitude lower than the observed in the nonfoamed electrodes. Moreover, foamed electrodes can be used to detect simultaneously both isomers and a remarkable increase in the electrocatalytic properties shown by the foamed samples, produces a decrease in the oxidation potential peak of catechol in presence of hydroquinone, from +0.7 V to +0.3 V. Peak currents increased linearly with concentration of catechol in presence of hydroquinone over the range of 0.37·10−3 M to 1.69·10−3 M with a limit of detection (LOD) of 0.27 mM. These effects demonstrate the advantages obtained by increasing the active surface by means of porous structures.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project AGL2015-67482-R)Junta de Castilla y Leon - Fondo Europeo de Desarrollo Regional (project VA-011U16

Molecularly imprinted polypyrrole based electrochemical sensor for selective determination of 4-ethylphenol

This work describes the development of an electrochemical sensor based on a molecularly imprinted polymer (MIP) for sensitive and selective determination of 4-ethylphenol in wine. The sensor has been built by means of the electrosynthesis of the MIP on a glassy carbon electrode surface using cyclic voltammetry. The electropolymerization has been performed in the presence of 4-ethylphenol and pyrrole as template molecule and functional monomer, respectively. The influence of the molar ratios of template molecules to functional pyrrole monomers and the time needed to remove the template have been optimized taking into account the differential pulse voltammetric response of 4-ethylphenol. Under the optimal experimental conditions the developed MIP/GCE sensor shows good capability of detection (0.2 μM, α = β = 0.05) and reproducibility (3.0%) in the concentration range from 0.2 to 34.8 μM. The influence of possible interfering species in the analytical response has been studied and the sensor has successfully been applied to the determination of 4-ethylphenol in different wine samples.Junta de Castilla y León (BU018G19

The advantages of disposable screen-printed biosensors in a bioelectronic tongue for the analysis of grapes

Producción CientíficaDisposable screen-printed sensors have been modified with enzymes and used to form a bioelectronic tongue dedicated to the discrimination between different grape varieties. The multisensory system combined serigraphied electrodes modified with carbon, platinum, gold, graphene, Prussian blue and nickel oxide nanoparticles (M-SPE) covered with glucose oxidase (M-GOX-SPE) or tyrosinase (M-Tyr-SPE). The M-GOX-SPE and M-Tyr-SPE sensors produced a variety of responses due to the different behavior of the electron mediators of the six screen-printed materials used for the electro-catalysis of the glucose and phenols by means of glucose oxidase and tyrosinase. This variety of responses, together with the capability of the sensors to detect glucose or phenols, allowed the bioelectronic tongue developed here to discriminate between the juices obtained from different varieties of grape. Partial least-squares (PLS-1) multivariate calibration of electrochemical data has been successfully applied to the simultaneous determination of glucose and polyphenols in musts. The discrimination capability shown by this array of cheap and single-use sensors was similar to that found in other complex bioelectronic tongues. The lower price, ease of use and portability of the modified screen-printed electrode system makes the bioelectronic tongue developed here an alternative tool that can be used in situ in the vineyard block.Ministerio de Economía, Industria y Competitividad – FEDER (Grant CICYT AGL2012-33535)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA-032U13)University of Valladolid (PIF-UVa

Carbon Black Functionalized with Naturally Occurring Compounds in Water Phase for Electrochemical Sensing of Antioxidant Compounds

A new sustainable route to nanodispersed and functionalized carbon black in water phase (W-CB) is proposed. The sonochemical strategy exploits ultrasounds to disaggregate the CB, while two selected functional naturally derived compounds, sodium cholate (SC) and rosmarinic acid (RA), act as stabilizing agents ensuring dispersibility in water adhering onto the CB nanoparticles' surface. Strategically, the CB-RA compound is used to drive the AuNPs self-assembling at room temperature, resulting in a CB surface that is nanodecorated; further, this is achieved without the need for additional reagents. Electrochemical sensors based on the proposed nanomaterials are realized and characterized both morphologically and electrochemically. The W-CBs' electroanalytical potential is proved in the anodic and cathodic window using caffeic acid (CF) and hydroquinone (HQ), two antioxidant compounds that are significant for food and the environment. For both antioxidants, repeatable (RSD <= 3.3%; n = 10) and reproducible (RSD <= 3.8%; n = 3) electroanalysis results were obtained, achieving nanomolar detection limits (CF: 29 nM; HQ: 44 nM). CF and HQ are successfully determined in food and environmental samples (recoveries 97-113%), and also in the presence of other phenolic classes and HQ structural isomers. The water dispersibility of the proposed materials can be an opportunity for (bio) sensor fabrication and sustainable device realization

Amperometric detection of triclosan with screen-printed carbon nanotube electrodes modified with Guinea Grass (Panicum maximum) peroxidase

Triclosan is a compound with antimicrobial activity broadly used in consumer products. Because of its well documented toxicity, the amount of triclosan present in different products needs to be tightly controlled. This paper outlines a new amperometric sensor for triclosan detection consisting of a screen-printed carbon nanotube electrode (SPCNE) modified w ith Guinea grass peroxidase (GGP). The GGP-modified S PCNE was a ble t o d etect an enhanced electrochemical response of triclosan, unlike the bare SPCNE. The cyclic voltammograms of the GGP-modified SPCNE in a solution of potassium ferrocyanide showed an increase in the current values and linearity between scan rates and oxidation peak currents, suggesting a surface controlled process. The GGP-modified SPCNEs howed an excellent electrocatalytic activity to triclosan oxidation, at a redox potential of 370 mV, in the presence of hydrogen peroxide, exhibiting a linear response between 20 mM to 80 mM and a detection limit of 3 µM. This new amperometry system, based on carbon nanotubes integrated with GGP, becomes a potential tool for environmental analysis and food quality control.Fil: Orduz Navas, Angie Estefany. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Universidad Industrial Santander; ColombiaFil: Gutiérrez, Jorge Andres. Universidad Industrial Santander; ColombiaFil: Blanco, Sergio Ismael. Universidad Industrial Santander; ColombiaFil: Castillo, John. Universidad Industrial Santander; Colombi

Microwave-assisted pyrolysis for biomass recovery and applications

A pressing environmental concern, agricultural waste demands sustainable solutions. This study explores converting agro-industrial waste into energy and innovative applications through microwave-assisted pyrolysis. It assesses waste-to-energy potential and introduces novel electrochemical sensors for biomedical and nitrite detection

Novel nanomaterials for lab on chip devices development: application to food system and their effect on the oxidative stress in cell cultures

This Doctoral Thesis has been formed in two well-defined areas within the field of design and development of electrochemical sensors, using nanomaterials with high analytical performance in terms of sensitivity, selectivity and reproducibility. On the one hand, the properties of transition metal chalcogenides as new nanomaterials were explored with the aim of developing new high-performance electrochemical sensors. The transition metal chalcogenides are formed by triatomic sheets with the general formula MX2, where M is a transition metal and X is a chalcogenide (S, Se or Te) and where, in turn, M is arranged in a plane surrounded by two others of X linked by covalent bonds. Each of these sheets is held by Van der Waarls forces, facilitating their exfoliation in individual layers by simple methods. First, the ultrasound-assisted exfoliation of transition metals of group VI (MoS2, WS2, MoSe2 and WSe2) was carried out. Subsequently, they were characterized by scanning electron microscopy, Raman spectroscopy, and electrochemical techniques. Next, the electrocatalytic properties of these nanomaterials in the oxidation of polyphenolic compounds, chosen for this purpose for their high antioxidant capacity, were studied. These nanomaterials demonstrated excellent resistance to sensor passivation, one of the limiting factors in the application of electrochemical techniques in the analysis of complex samples. Ultimately, its analytical application to the determination of endogenous polyphenolic compounds in complex food matrices was demonstrated. On the other hand, electrochemical sensors were developed for the in-situ detection of hydrogen peroxide in cell cultures as a marker of oxidative stress. To this end, electrodes based on high-performance nanomaterials were designed and developed aimed at electrochemical sensitivity and selectivity (Carbon Black and Prussian Blue) for the selective detection and quantification of hydrogen peroxide in a cellular model of Parkison's disease. Likewise, an on-chip platform with similar analytical performance was developed to develop cell cultures, detect hydrogen peroxide under conditions of oxidative stress, as well as evaluate the antioxidant effect of exogenous polyphenolic compounds on oxidative stress levels

Novel nanomaterials for lab on chip devices development: application to food system and their effect on the oxidative stress in cell cultures

Esta Tesis Doctoral se ha configurado en dos áreas bien definidas dentro del ámbito del diseño y desarrollo de sensores electroquímicos, empleando nanomateriales con altas prestaciones analíticas en términos de sensibilidad, selectividad y reproducibilidad. Por una parte, se exploraron las propiedades de los calcogenuros de metales de transición como nuevos nanomateriales con el objetivo de desarrollar nuevos sensores electroquímicos de altas prestaciones. Los calcogenuros de metales de transición están formados por láminas triatómicas con fórmula general MX2, donde M es un metal de transición y X un calcogenuro (S, Se o Te) y donde a su vez M se dispone en un plano rodeado por otros dos de X unidos mediante enlaces covalentes. Cada una de estas láminas se encuentran unidas mediante fuerzas de Van der Waarls, facilitando su exfoliación en capas individuales mediante métodos sencillos. En primer lugar, se llevó a cabo la exfoliación asistida por ultrasonidos de metales de transición del grupo VI (MoS2, WS2, MoSe2 y WSe2). Posteriormente, se caracterizaron mediante microscopía electrónica de barrido, espectroscopía Raman y técnicas electroquímicas. Seguidamente, se estudiaron las capacidades electrocatalíticas de estos nanomateriales en la oxidación de compuestos polifenólicos, elegidos para tal fin por su elevada capacidad antioxidante. Estos nanomateriales, demostraron una excelente resistencia a la pasivación del sensor, uno de los factores limitantes de la aplicación de las técnicas electroquímicas en el análisis de muestras complejas, constituyendo este hallazgo uno de los resultados más relevantes obtenidos. En último término, se demostró su aplicación analítica a la determinación de compuestos polifenólicos endógenos en matrices complejas de alimentos. Por otra parte, se desarrollaron sensores electroquímicos para la detección in-situ de peróxido de hidrógeno en cultivos celulares como marcador de estrés oxidativo. Para ello, se diseñaron y desarrollaron electrodos basados en nanomateriales de altas prestaciones dirigidos a la sensibilidad y selectividad electroquímicas (Carbon Black y Prussian Blue) para la detección y cuantificación selectiva de peróxido de hidrógeno en un modelo celular de enfermedad de Parkison. Asimismo, se desarrolló una plataforma on-chip con prestaciones analíticas similares para desarrollar cultivos celulares, detectar peróxido de hidrógeno en condiciones de estrés oxidativo, así como evaluar el efecto antioxidante de compuestos polifenólicos exógenos en los niveles de estrés oxidativo

Microextraction of Xenobiotics and Biomolecules from Different Matrices on Nano Structures

Sample preparation is the backbone of any analytical procedure; it involves extraction and pre-concentration of the desired analytes; often at trace levels. The present article describes the applications of nanomaterials (carbon based inorganic and polymeric materials) in miniaturized extraction such as solid phase micro-extraction, stir-bar sorptive extraction, liquid phase micro-extraction, and dispersive liquid phase micro-extraction in the analyses of aqueous samples. The nanoparticles used for micro-extractions are discussed on the basis of their chemical natures. The synthetic route and the preparation of nanomaterials are described along with the optimization strategies for micro-extraction. A comparison between the conventional materials and nanomaterials for micro-extraction is proposed. The key roles of the nanomaterials for the micro-extraction of different analytes such as drugs, pesticides, polycyclic aromatic hydrocarbons, proteins and peptides from aqueous samples are reported. The use of nanomaterials, combined with miniaturized micro-extraction techniques, proved to be highly promising for sample preparation of various matrices with analytes at trace levels