Artificial neural networks for the resolution of dopamine and serotonin complex mixtures using a graphene-modified carbon electrode

Marta Bonet-San-Emeterio thanks to AGAUR, Generalitat de Catalunya and to European Social Fund, European Union for FI fellowship. Manel del Valle thanks the support from program ICREA Academia.This work explores an electrode modified with electrochemically reduced graphene oxide (ERGO) for the voltammetric resolution of mixtures of neurotransmitters and its most common interferents. This enhanced sensitivity device coupled with advanced chemometric tools, such as artificial neural networks (ANNs), is able to resolve and quantify complex mixtures with overlapped signals. In this case, it has been applied to dopamine (DA), serotonin (5-hydroxytryptamine, 5-HT) and its main physiologic interferents, ascorbic acid (AA) and uric acid (UA), which play a relevant role in human body. The results obtained for individual analysis make evident a higher sensitivity of the developed sensor than the unmodified electrode. Furthermore, it has been attained an ANN response model with good correlation ability allowing the separation and quantification of each compound with comparison slope of predicted vs. expected concentrations with correlation better than 0.974. In short, the developed ERGO-modified sensor not only improved the signal but it also permitted resolving and quantifying each compound in complex mixtures when the proper chemometric treatment was used

Modification of electrodes with N-and S-doped carbon dots. Evaluation of the electrochemical response

Altres ajuts: MdV thanks the support from program ICREA Academia. MBSE thanks to la Secretaria d'Universitats i Recerca del Departament d'Empreses i Coneixement de la Generalitat de Catalunya and to European Social Fund, European Union for a FI fellowship.Nitrogen and sulphur-doped Carbons Dots (N-CDs and S-CDs) were synthesized by a hydrothermal method and incorporated as surface electrode modifiers to evaluate their properties for electrochemical sensing. The first task was to characterize the synthesized materials, for which different spectroscopies, scanning microscopes, mass spectrometry and elementary analysis were performed. Next, a glassy carbon electrode (GCE) was surface-modified with the doped CDs and applied to check the electrochemical signal of different organic compounds corresponding to different families. Water solubility of the doped carbon dots forced us to incorporate them in a graphite-polystyrene ink to complete the modification of electrodes. This modification needed a first activation to obtain a properly conductive surface. The organic compounds examined were salicylic acid, cysteine and ascorbic acid. The modified GCEs exhibited an enhanced sensitivity, probably caused by the increase of active surface, but in addition, signals of salicylic acid were shifted ca. 200 mV to lower potentials, what is a proof of the increase of the heterogeneous electron transfer rate, and a demonstration of an enhanced catalytic response

Voltammetric electronic tongue based on carbon paste electrodes modified with biochar for phenolic compounds stripping detection

Altres ajuts: Marta Bonet-San-Emeterio thanks to AGAUR, Generalitat de Catalunya and to European Social Fund, European Union for FI fellowship. Manel del Valle thanks the support from program ICREA Academia.Biochar is a charcoal produced from the biomass pyrolysis process that presents a highly porous and functionalized surface. In the present work an array of carbon paste electrodes (CPE) made of different forms of carbon (graphite, carbon nanotubes and activated biochar) was evaluated in the development of an electronic tongue for discrimination and stripping voltammetric determination of catechol (CAT), 4-ethylcatechol (4-EC) and 4-ethylguaiacol (4-EG) phenolic compounds. Morphological characterization of carbon materials and electrodes surfaces was performed by scanning electron microscopy (SEM) and semi-quantitative elemental composition by energy dispersive spectroscopy (EDS). Electrochemical Impedance Spectroscopy (EIS) measurements were used for electrochemical characterization of electrodes. Cyclic voltammetry measurements were performed for the phenolic compounds evaluated using different concentrations. Principal component analysis (PCA) was performed to evaluate the qualitative analysis. Quantitative data modeling was done using artificial neural networks (ANN). The proposed sensor array presented analytical potentiality allowing the distinction and determination of CAT, 4-EC and 4-EG by using chemometric processing. The method showed sensibility, reproducibility and a good linearity (R2>0.9940) for three compounds evaluated. Spontaneous preconcentration of three compounds was possible using all three sensors, which can allow the application of these as passive samplers for remote determinations of phenolic compounds in wine and food samples

Progresses in new carbon platforms : graphene and carbon dots

En els últims anys s'han desenvolupat diferents estratègies per l'anàlisi eficaç i ràpid de múltiples mostres. Per tal de millorar les propostes actuals, els investigadors tracten el problema des de diferents punts de vista. Dos exemples són els que s'han seguit en la present tesi doctoral, la integració de nous materials que confereixen propietats úniques als sensors, i l'ús d'eines matemàtiques avançades. Concretament, en aquest projecte s'ha inclòs en sensors voltamètrics, no només nous nanomaterials com el grafè i els punts de carboni, sinó també biomolècules com els enzims. A posteriori, aquests sensors s'han aplicat en el marc de les llengües electròniques, una tàctica que consisteix en l'ús de la quimiometria per tal d'obtenir models qualitatius o quantitatius. Per tant, aquesta investigació uneix diferents camps de la química com són la ciència dels nanomaterials, l'ús de sensors electroquímics, i finalment la quimiometria amb l'objectiu de millorar i, doncs, superar, problemes presentats en mètodes d'un caire més clàssic. El treball es divideix en dues seccions, primer se centra en l'ús del grafè, i després en la integració de punts de carboni, i punts de carboni modificats com a material clau en les plataformes de sensat. En el primer cas, el grafè, concretament l'òxid de grafè reduït electroquímicament s'ha dipositat en un elèctrode construït en base d'un compòsit de grafit i resina epòxid. Un cop caracteritzat l'elèctrode aquest s'utilitza per a la resolució d'una mescla complexa d'àcid ascòrbic, àcid úric, serotonina i dopamina. En aquest cas, s'aconsegueix la resolució de la mescla i la quantificació de no només la serotonina i la dopamina, sinó també dels seus dos interferents. Un cop establert aquest elèctrode, es fa ús de la mateixa com a base de la creació de dos biosensors enzimàtics, utilitzant com a element de reconeixement la lacasa i la tirosinasa. Amb el biosensor de lacasa es presenta un estudi de la cinètica de l'enzim, la qual s'usa per a la detecció indirecta de contaminants emergents. Finalment, s'inclouen els dos biosensors, juntament amb la plataforma de grafè, en el conjunt d'elèctrodes per l'anàlisi multivariable del caràcter Brett en vi rosat. Per altra banda, es presenta un primer treball basat en la incorporació dels punts de carboni i els punts de carboni modificats amb N i S, per separat, en elèctrodes de carboni vitri. En aquest treball es mostra una primera provatura de l'ús dels punts de carboni com a catalitzadors electroquímics. Els quals en treballs futurs presenten característiques ideals per ser emprats com a modificadors per elèctrodes en el marc de les llengües electròniques.En los últimos años se han desarrollado distintas estrategias para el análisis eficaz y rápido de múltiples muestras. Para mejorar las propuestas actuales, los investigadores tratan el problema desde distintos puntos de vista. Dos ejemplos son los que se han seguido en la presente tesis doctoral, la integración de nuevos materiales que confieren propiedades únicas a los sensores y el uso de herramientas matemáticas avanzadas. Concretamente, en este proyecto se ha incluido en sensores voltamétricos, no sólo nuevos nanomateriales como el grafeno y los puntos de carbono, sino también biomoléculas como las enzimas. A posteriori estos sensores se han aplicado en el marco de las lenguas electrónicas, una táctica que consiste en el uso de la quimiometría para obtener modelos cualitativos o cuantitativos. Por tanto, esta investigación une diferentes campos de la química como son la ciencia de los nanomateriales, el uso de sensores electroquímicos, y finalmente la quimiometría con el objetivo de mejorar y, pues, superar, problemas presentados en métodos más clásico. El trabajo se divide en dos secciones, primero se centra en el uso del grafeno, y después en la integración de puntos de carbono, y puntos de carbono modificados como material clave en las plataformas de sensato. En el primer caso, el grafeno, concretamente el óxido de grafeno reducido electroquímicamente se ha depositado en un electrodo construido en base a un composite de grafito y resina epóxido. Una vez caracterizado el electrodo éste se utiliza para la resolución de una mezcla compleja de ácido ascórbico, ácido úrico, serotonina y dopamina. En este caso, se logra la resolución de la mezcla y la cuantificación de no sólo la serotonina y la dopamina, sino también de sus dos interferentes. Una vez establecido el protocolo para la modificación del electrodo, se hace uso de este como base de la creación de dos biosensores enzimáticos, utilizando como elemento de reconocimiento la lacasa y la tirosinasa. Con el biosensor de lacasa se presenta un estudio de la cinética de la enzima, que se usa para la detección indirecta de contaminantes emergentes. Por último, se incluyen los dos biosensores, junto con la plataforma de grafeno, en el conjunto de electrodos por el análisis multivariable del carácter Brett en vino rosado. Por otro lado, se presenta un primer trabajo basado en la incorporación de los puntos de carbono y los puntos de carbono modificados con N y S, por separado, en electrodos de carbono vítreo. En este trabajo se muestra una primera probatura del uso de los puntos de carbono como catalizadores electroquímicos. Los que en trabajos futuros presentan características ideales para ser empleados como modificadores por electrodos en el marco de las lenguas electrónicas.In the last few years, different strategies have been developed for the efficient and rapid analysis of numerous samples. In order to improve the current proposals, researchers address the problem from different points of view. Two examples are those that have been followed in this doctoral thesis, the integration of new materials that confer unique properties to the sensors and the use of advanced mathematical tools. Specifically, this project has included in the voltametric sensors, not only new nanomaterials such as graphene and carbon dots, but also biomolecules such as enzymes. A posteriori these sensors have been applied in the framework of electronic tongues, a practice that consists in the use of chemometrics to obtain qualitative or quantitative models. Therefore, this research joins different fields of chemistry such as the science of nanomaterials, the use of electrochemical sensors, and finally, chemometrics, with the aim of improving and, therefore, overcoming problems presented in more classical methods. The work is divided into two sections, starting with the use of graphene, and then focusing on the integration of carbon dots and modified carbon dots as a key material in sensing platforms. In the first case, graphene, specifically electrochemically reduced graphene oxide has been deposited on an electrode constructed based on a composite of graphite and epoxide resin. Once the electrode is characterized, it is used for the resolution of a complex mixture of ascorbic acid, uric acid, serotonin, and dopamine. In this case, resolution of the mixture and quantification of not only serotonin and dopamine, but also of their two interferents is achieved. Once this electrode is established, it is used as the basis for the creation of two enzymatic biosensors, using laccase and tyrosinase as recognition elements. With the house biosensor, a study of the enzyme kinetics is presented, which is used for the indirect detection of emerging contaminants. Finally, the two biosensors, together with the graphene platform, are included in the electrode array for the multivariate analysis of Brett character in rosé wine. On the other hand, is presented a first work, based on the incorporation of carbon dots and carbon dots modified with N and S, separately. In this work a first test of the use of carbon dots as electrochemical catalysts is shown. This work shows a first attempt of the use of carbon dots as electrochemical catalysts, which present ideal characteristics to be used as electrode modifiers in the framework of electronic tongues

Graphene for the Building of Electroanalytical Enzyme-Based Biosensors : application to the Inhibitory Detection of Emerging Pollutants

Graphene and its derivates offer a wide range of possibilities in the electroanalysis field, mainly owing to their biocompatibility, low-cost, and easy tuning. This work reports the development of an enzymatic biosensor using reduced graphene oxide (RGO) as a key nanomaterial for the detection of contaminants of emerging concern (CECs). RGO was obtained from the electrochemical reduction of graphene oxide (GO), an intermediate previously synthesized in the laboratory by a wet chemistry top-down approach. The extensive characterization of this material was carried out to evaluate its proper inclusion in the biosensor arrangement. The results demonstrated the presence of GO or RGO and their correct integration on the sensor surface. The detection of CECs was carried out by modifying the graphene platform with a laccase enzyme, turning the sensor into a more selective and sensitive device. Laccase was linked covalently to RGO using the remaining carboxylic groups of the reduction step and the carbodiimide reaction. After the calibration and characterization of the biosensor versus catechol, a standard laccase substrate, EDTA and benzoic acid were detected satisfactorily as inhibiting agents of the enzyme catalysis obtaining inhibition constants for EDTA and benzoic acid of 25 and 17 mmol·L−1, respectively, and a maximum inhibition percentage of the 25% for the EDTA and 60% for the benzoic acid

Experiences in the detection of drugs of abuse in smuggling seizures and forensic samples using electronic tongue principles

The application of voltammetric sensors to the analysis of illicit drugs in combination with different chemometric tools to achieve their identification and quantification is explored herein. The aim is to process the whole voltammograms obtained from different sensors as a unique profile, and analyze those with the aid of pattern recognition methods that allow the extraction of a characteristic fingerprint, rather than focusing on the oxidation peaks associated to each of the drugs. To this aim, different arrays of electrodes were prepared to analyzed samples employing square wave voltammetry (SWV). Next, identification of different drugs was achieved by means of principal component analysis (PCA) and linear discriminant analysis (LDA), while their quantification was attained by partial least squares (PLS) modelling

Methanol, Ethanol, and Glycerol Oxidation by Graphite-Epoxy Composite Electrodes with Graphene-Anchored Nickel Oxyhydroxide Nanoparticles

In this work, a graphite-epoxy electrode with cyclic voltammetry electrodeposited reduced graphene oxide and nickel oxyhydroxide nanoparticles was prepared by decomposition in NaOH alkaline solution of cyclic voltammetry electrodeposited nickel hexacyanoferrate. FE-SEM studies were performed to confirm the NiOOH nanoparticle; the average size of the NiOOH nanoparticles was 61 ± 16 nm and EDX was applied to analyze chemical composition. To verify the performance of the prepared electrode, it was used in the electrooxidation of alcohols in alkaline medium by cyclic voltammetry. By performing different calibration experiments of methanol, ethanol, and glycerol, it was possible to extract some information about the electrode in the presence of alcohols. The LOD for methanol, ethanol, and glycerol were 2.16 mM, 2.73 mM and 0.09 mM, respectively, with sensitivity values of 1.32 µA mM−1, 1.80 µA mM−1 and 24.60 µA mM−1, respectively. Multivariate inspection of the data using Principal Component Analysis (performed with the ClustVis online tool) demonstrated the potential ability to discriminate between the different alcohols, whereas the explained variance with the first two components was as high as 89.7%