Fabrication of a Multi-Walled Nanotube (MWNT) Ionic Liquid Electrode and Its Application for Sensing Phenolics in Red Wines

A multi-walled nanotube (MWNT) ionic liquid was prepared by the immobilization of 1-butylimidazole bromide onto an epoxy group on a poly(glycidyl methacrylate)-grafted MWNT, which was synthesized by radiation-induced graft polymerization of glycidyl methacrylate onto MWNT in an aqueous solution. Subsequently, a MWNT ionic liquid electrode was fabricated by hand-casting MWNT ionic liquid, tyrosinase, and chitosan solution as a binder on indium tin oxide (ITO) glass. The sensing ranges of the MWNT ionic liquid electrode with immobilized tyrosinase was in the range of 0.01-0.08 mM in a phosphate buffer solution. The optimal conditions such as pH, temperature, and effects of different phenolic compounds were determined. The total phenolic compounds of three commercial red wines were also determined on the tyrosinase-immobilized biosensor

Fabrication of a Microbial Biosensor Based on QD-MWNT Supports by a One-Step Radiation Reaction and Detection of Phenolic Compounds in Red Wines

An Acaligense sp.-immobilized biosensor was fabricated based on QD-MWNT composites as an electron transfer mediator and a microbe immobilization support by a one-step radiation reaction and used for sensing phenolic compounds in commercial red wines. First, a quantum dot-modified multi-wall carbon nanotube (QD-MWNT) composite was prepared in the presence of MWNT by a one-step radiation reaction in an aqueous solution at room temperature. The successful preparation of the QD-MWNT composite was confirmed by XPS, TEM, and elemental analysis. Second, the microbial biosensor was fabricated by immobilization of Acaligense sp. on the surface of the composite thin film of a glassy carbon (GC) electrode, which was prepared by a hand casting method with a mixture of the previously obtained composite and Nafion solution. The sensing ranges of the microbial biosensor based on CdS-MWNT and Cu2S-MWNT supports were 0.5–5.0 mM and 0.7–10 mM for phenol in a phosphate buffer solution, respectively. Total concentration of phenolic compounds contained in commercial red wines was also determined using the prepared microbial immobilized biosensor

Fabrication of Nonenzymatic Glucose Sensors Based on Multiwalled Carbon Nanotubes with Bimetallic Pt-M (M = Ru and Sn) Catalysts by Radiolytic Deposition

Nonenzymatic glucose sensors employing multiwalled carbon nanotubes (MWNTs) with highly dispersed Pt-M (M = Ru and Sn) nanoparticles (Pt-M@PVP-MWNTs) were fabricated by radiolytic deposition. The Pt-M nanoparticles on the MWNTs were characterized by transmittance electron microscopy, elemental analysis, and X-ray diffraction. They were found to be well dispersed and to exhibit alloy properties on the MWNT support. Electrochemical testing showed that these nonenzymatic sensors had larger currents (mA) than that of a bare glassy carbon (GC) electrode and one modified with MWNTs. The sensitivity (A mM−1), linear range (mM), and detection limit (mM) (S/N = 3) of the glucose sensor with the Pt-Ru catalyst in NaOH electrolyte were determined as 18.0, 1.0–2.5, 0.7, respectively. The corresponding data of the sensor with Pt-Sn catalyst were 889.0, 1.00–3.00, and 0.3, respectively. In addition, these non-enzymatic sensors can effectively avoid interference arising from the oxidation of the common interfering species ascorbic acid and uric acid in NaOH electrolyte. The experimental results show that such sensors can be applied in the detection of glucose in commercial red wine samples

Applications and immobilization strategies of the copper-centred laccase enzyme : a review

DATA AVAILABILITY STATEMENT: No data was used for the research described in the article.Laccase is a multi-copper enzyme widely expressed in fungi, higher plants, and bacteria which facilitates the direct reduction of molecular oxygen to water (without hydrogen peroxide production) accompanied by the oxidation of an electron donor. Laccase has attracted attention in biotechnological applications due to its non-specificity and use of molecular oxygen as secondary substrate. This review discusses different applications of laccase in various sectors of food, paper and pulp, waste water treatment, pharmaceuticals, sensors, and fuel cells. Despite the many advantages of laccase, challenges such as high cost due to its non-reusability, instability in harsh environmental conditions, and proteolysis are often encountered in its application. One of the approaches used to minimize these challenges is immobilization. The various methods used to immobilize laccase and the different supports used are further extensively discussed in this review.The National Research Foundation (NRF) of South Africa.https://www.cell.com/heliyonChemical Engineerin

Electrochemical sensors and biosensors: new horizons and challenges in their integration in multisensor systems for food industry applications

La presente Tesis doctoral, plantea el desarrollo de sensores y biosensores para el análisis de alimentos, empleando diferentes materiales y nanomateriales sensibles. Se trata de sensores y biosensores electroquímicos que permiten detectar compuestos de interés en alimentos líquidos tales como leches o vinos. Los sensores se han diseñado empleado diferentes materiales sensibles y tecnologías relacionadas con la Nanociencia, con el propósito de mejorar parámetros analíticos como son: selectividad, sensibilidad, reproducibilidad y repetitividad. Los sensores y biosensores se han utilizado para desarrollar redes de sensores que forman lenguas electrónicas y bioelectrónicas. La preparación y caracterización de los sensores y biosensores desarrollados, así como sus respuestas electroquímicas y su funcionamiento como parte de lenguas electrónicas, se discuten mediante los artículos científicos, indexados en revistas internacionales, incluidos en esta Tesis Doctoral.Departamento de Química Física y Química InorgánicaDoctorado en Físic

Development of electrochemical-based methods for antioxidant activity evaluation

Tese de doutoramento em Ciências (área de especialização em Química)In the last decades researchers have been studying the importance of antioxidants and in order to do that they have developed methods to evaluate antioxidants capacity / activity as they are of major importance for health and food industry The application of electrochemical techniques for the characterization of antioxidants can bring numerous advantages related to the use of less reagents and the miniaturization of the analytical systems. The present methods for the evaluation of antioxidants capacity / activity are classified according to the type of reaction of the assay, as electron transfer reactions (ET) or hydrogen atom transfer reactions (HAT). In both types of assays, antioxidants are tested in reactions with reactants or radicals that are added or generated in-situ using specific reagents. The characterisation of antioxidants by voltammetric techniques has attracted a growing number of researchers that have demonstrated that electrochemical data provides similar information to the classical ET methods concerning the antioxidants reducing power. The possibility of developing further approaches for the characterization of antioxidants based on electrochemical methods has driven to the present work. In what concerns the characterization of antioxidants by ET-based assays two methodologies are proposed based on direct electron transfer reactions with an anode. The first, denominated by RACE (Reducing Antioxidant Capacity Evaluated by Electrolysis), is based on a coulometric assay. The second consists in the chronoamperometric analysis of antioxidants using microchannel band electrodes devices operating under thin-layer regime. Both methods have the advantage of allowing to characterize antioxidants capacity by the amount of charge that species are able to transfer without the need of calibration steps. The second methodology has further advantages related to the use of small sample volumes and to the short time of analysis. Regarding the characterization of antioxidants by HAT-based assays, it is proposed and demonstrated the suitability of electrogenerated HO radical for this aim. Although the electrogenerated HO radicals by the oxidation of water are well known in the scope of wastewater treatment using anodes as BDD (boron doped diamond), their use in antioxidant assays was not reported. With this purpose it is demonstrated that using a Pt anode it is possible to carry out hydroxylation reactions in galvanostatic electrolysis, as with BDD anodes, although the reactions rates are lower and sensitive to the reactivity of the organics. The possibility of carrying out reactions between electrogenerated HO radicals and electroactive compounds was analysed and the proportion between the rates of the direct oxidation and the mediated by HO radicals was shown to be controlled by means of the electrolyses charge density. The apparent rate constant of consumption of organics by the HO radicals was shown to be related to the species reactivity despite their electroactive nature. A kinetic model that allows the evaluation of the rate constants of reactions between organics and electrogenerated HO radicals is proposed and tested in different circumstances, namely for single species and for mixtures of two organic compounds. The possibility of applying the developed methodology in natural samples was also demonstrated using a commercial green tea-based beverage.A importância dos antioxidantes tem vindo a ser estudada nas últimas décadas com a finalidade de desenvolver métodos que avaliem a capacidade / atividade dos antioxidantes devido ao papel fulcral que desempenham na saúde e na indústria alimentar. A aplicação de técnicas electroquímicas para a caracterização de antioxidantes pode trazer inúmeras vantagens em relação à menor necessidade de utilizar reagentes e à possibilidade de miniaturização dos sistemas analíticos. Os atuais métodos para a avaliação da capacidade / atividade de antioxidantes são classificados de acordo com o tipo de reação de ensaio , tal como as reações de transferência de electrões (ET) ou reações de transferência de um átomo de hidrogénio (HAT). Em ambos os tipos de ensaios , os antioxidantes são testados em reações com reagentes ou radicais que são adicionados ou gerados in situ, utilizando par isso reagentes específicos. A caracterização de antioxidantes por técnicas voltamétricas tem atraído um número crescente de investigadores que demonstraram que os dados electroquímicos fornecem informações semelhantes aos métodos ET clássicos no que diz respeito à capacidade redutora dos antioxidantes. O presente trabalho surge com a finalidade de criar uma nova abordagem baseada em métodos eletroquímicos para avaliarem e caraterizarem a atividade / capacidade antioxidante. Relativamente à caraterização de antioxidantes baseada em ensaios ET são propostas duas metodologias que se baseiam na transferência electrónica com o ânodo. A primeira, denominada por RACE (Reducing Antioxidant Capacity Evaluated by Electrolysis), é baseada num ensaio coulométrico. A segunda consiste na análise cronoamperométrica de antioxidantes usando um dispositivo de microcanais de bandas de elétrodos que operam sob um regime de camada fina. Ambos os métodos têm a vantagem de permitir caracterizar a capacidade antioxidantes pela quantidade de carga que a espécie é capaz de transferir, sem a necessidade de recorrer a curvas de calibração. O segundo método proporciona ainda vantagens relacionadas com a utilização de volumes pequenos de amostra e ao tempo curto de análise. Relativamente à caracterização de antioxidantes baseada em ensaios HAT, propõe-se o uso de radicais hidroxilo gerados electroquimicamente e demonstra-se a sua aplicabilidade. Apesar de os radicais hidroxilo eletrogerados, como produto da oxidação da água, serem utilizados no âmbito do tratamento de águas residuais usando ânodos como o BDD (boron doped diamond), a utilização destes radicais HO eletrogerados em ensaios de avaliação da atividade antioxidante não foi reportada. Com este objectivo é demonstrado que utilizando um ânodo de Pt é possível realizar reações de hidroxilação em electrólises galvanostáticas, como acontece com os ânodos de BDD, embora as velocidades de consumo serem mais baixas e sensíveis à reatividade dos compostos orgânicos. A possibilidade de levar a cabo reações entre os radicais HO eletrogerados e compostos eletroativos foi analisada e a proporção entre as velocidades de oxidação direta e a mediada por radicais HO foi controlada pela densidade de carga da electrólise. A constante de velocidade aparente relativa ao consumo dos compostos orgânicos por reação com os radicais HO relaciona-se com a reatividade das espécies independentemente da sua natureza eletroativa . Foi proposto e testado um modelo cinético, que permite avaliar as constantes de velocidade das reações entre os compostos orgânicos e os radicais HO eletrogerados. Este modelo foi testado em compostos orgânicos e em misturas de dois compostos orgânicos. A possibilidade de aplicar a metodologia desenvolvida em amostras naturais também foi demonstrada utilizando uma bebida comercial à base de chá verde

Nanomaterials-based electrochemical biosensors for food analysis

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química Analítica, leída el 20-02-2020El análisis de alimentos es una rama muy importante de la Química Analítica, capaz de aportar información relativa a la composición química, procesamiento, control de calidad y contaminación de los productos alimentarios, garantizando la seguridad y protegiendo la salud pública, así como asegurando el cumplimiento de la normativa y las regulaciones del mercado nacional e internacional. Actualmente, el análisis de alimentos se realiza principalmente en laboratorios, mediante el empleo de ensayos de Química Analítica y microbiológicos. Sin embargo, estos ensayos requieren habitualmente un tiempo considerado y una amplia experiencia para realizarlos, y no se pueden reproducir de forma sencilla en análisis de campo. En este contexto, los biosensores electroquímicos son una alternativa prometedora frente a métodos tradicionales para el análisis de alimentos. Estos biosensores permiten la determinación de los componentes y contaminantes de los alimentos en el lugar de muestreo, de una forma rápida, sensible, selectiva, simple y económica, mediante el uso de instrumentos portátiles y sensores miniaturizados. Asimismo, el rendimiento analítico de estos dispositivos electroquímicos puede ser mejorado notablemente mediante el empleo de nanomateriales avanzados como elementos de transducción, señalización o captura...Food analysis is a very important branch of Analytical Chemistry, able to provide information about chemical composition, processing, quality control and contamination of food stuffs, ensuring safety and protection of public health, but also guaranteeing compliance with international and national standards and market regulations. Nowadays, food analysis is mainly performed at lab environments by using Analytical Chemistry and microbiological tests. However, these tests often take considerable time and expertise to execute, and cannot be replicated easily in the field. In this context, electrochemical biosensors are promising alternatives to traditional methods for food analysis. These biosensors allow fast, sensitive, selective, simple and cost-effective determination of food components and contaminants at the place of sampling, by using portable instruments and miniaturized sensors. In addition, the analytical performance of these electrochemical devices can be significantly improved by using advanced nanomaterials as transduction, signaling or capturing elements...Fac. de Ciencias QuímicasTRUEunpu