Nuevos avances en sensores voltamétricos nanoestructurados y miniaturizados. Aplicación en una lengua electrónica en el sector alimentario

Resumo

The present Thesis entitled: "New Advances in Nanostructured and Miniaturized Voltammetric Sensors. The Application of an Electronic Tongue for the Food Industry" is framed within a research line focused on the electronic tongues, developed in the Group of Sensors in the Physic Chemistry and Inorganic Chemistry Department of the University of Valladolid. This thesis is presented to obtain the degree of Doctor by the University of Valladolid with an International Mention, and for this reason it is written in two languages: English and Spanish. In addition, the dissertation is structured according to the modality named "article compendium", thus, seven articles published in international journals are attached in the following chapters. Although the apparent productivity, still at least two more papers are expected to be sent to international journals as regular papers. This thesis tackles the development of arrays of voltammetric sensors modified with electroactive materials to employ them as the sensitive part of an electronic tongue devoted to the analysis of different foods or beverages (mainly wines) or compounds of interest in the food industry such as antioxidants. The first works presented here, were carried out using the electronic tongue that was developed by our research group before my incorporation to the team. This system based on carbon paste electrodes, had been successfully used to the analysis of wines with different organoleptic characteristics (variety of grape, monitoring of the ageing, etc). In this Thesis, the system was applied to the study of more complex wine samples than those studied in previous works. In this sense, the system was used to detect the use of alternative methods of ageing and to evaluate the oxidation state of wines. Good correlations between the signals provided by the sensors and the data obtained by means of traditional chemical analysis and a human panel of experts have been obtained. On the other hand, new types of voltammetric sensors have been developed. In this way, new miniaturized screen printed electrodes (SPE) and nanostructured sensors have been developed and investigated as sensing units of electronic tongues. The performance of miniaturized electrodes (SPE) was compared with that of traditional carbon paste electrodes. The responses were similar in terms of intensity and reversibility. The small size of SPE devices makes possible their portability as well as the industrialization. Finally, a novel nanostructured sensor based on lutetium bisphthalocyanine has been developed. It has been prepared by means of electrophoretic deposition technique (EPD). The characterization of their morphology as well as its structure is presented in this work accompanied with the appropriate discussion and justification. The electrochemical behavior has been compared with that observed when Langmuir-Blodgett (LB) films of the same material are used as working electrodes. The main advantage is that the preparation time of EPD nanowires is much shorter than that of LB films (seconds vs. hours) The good success of these nanowire based electrodes lead us to extend the study to other bisphthalocyanines and to construct an electronic tongue formed by an array of three nanostructured electrodes. For this purpose, three bisphthalocyanines (lutetium, gadolinium and dysprosium bisphthalocyanines) have been successfully electrodeposited and investigated as voltammetric sensors. The three electrodes showed a similar behavior, however, differences in the potential values of the redox processes related to the central metal were observed. The array formed by the three EPD sensors has been applied to the study of different phenolic antioxidants present in a wide variety of food products. This array of EPD sensors has shown a good capability to detect and discriminate the antioxidants according to their structure (number and position of the hydroxyl groups in the aromatic ring). The novel type of voltammetric sensor developed has shown to be competitive with the classical LB sensors.