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[eng] This thesis has been developed in the framework of the European FoodSmartphone project with the objective to develop user-friendly smartphone-connected electrochemical immunosensors for pesticide residue detection in different food matrices. The target pesticides selected were atrazine, paraquat, bromopropylate and chlorpyrifos, based on their significant impact in the field of food safety. In order to achieve this objective, first the performance of the immunoreagents necessary for the detection of the selected target pesticides (atrazine, chlorpyrifos, bromopropylate and paraquat) was evaluated by Enzyme-linked immunosorbent assays (ELISA). Afterwards, several different typologies of carbon-based screen printed electrodes (SPEs) were produced, modified and characterized. The modification of the electrodes was carried out with the nanomaterial carbon black and the electrode with the best electrochemical properties was used as a platform for the development of different electrochemical immunosensors. The direct use of the SPE’s surface was proven to be successful in the detection of the herbicide atrazine in buffer and in orange juice, achieving limit of detection (LOD) values of 2.09 (0.45 µg L-1) and 2.47 nM (0.53 µg L-1) respectively. An electrochemical immunosensor was also developed for the detection of the insecticide chlorpyrifos in wheat flour samples achieving LOD values around 5 µg kg-1. The feasibility of the developed sensor as a screening method for food safety monitoring was confirmed by the analysis of real samples and their validation by ELISA and a chromatographic reference method (GC-MS). Furthermore, electrochemical immunosensors were developed in buffer for the detection of the pesticides paraquat and bromopropylate, achieving LOD values of 0.24 µg L-1 and 4.32 µg L-1 respectively. All of the achieved LOD values were well below the maximum residue limits (MRLs) established by the European Commission. Finally, the multiplexation capabilities of the developed individual immunosensors were demonstrated with a proof-of-concept study of a smartphone-connected multiplexed sensor. The developed sensor has the potential to be integrated in an easy-to-use and affordable device, which could be used by farmers and inspectors (e.g. at borders) for at-line measurements in order to ensure food safety and quality in the coming years.

Nowadays there is a high demand for cost-effective and user-friendly on-site screening tools in the food safety industry. Electrochemical sensors are the perfect candidates for this purpose since they combine the qualities of being miniaturized and relatively cheap at the same time. The use of carbon-based screen-printed electrodes (SPEs) is particularly ideal for on-site analysis, because of their well known low production cost, which drastically decreases the costs of the analysis. Furthermore, these SPEs can easily be modified with nanomaterials, which can result in a significant increase of their performance. In this study a characterization of in-house SPEs modified with CB and their application for the detection of different pesticides is described. Different materials have been investigated during the printing process and the working electrode has been modified with nanoparticles directly in the ink or by dropcasting either manually or using the Biodot dispenser. After an electrochemical characterization, the best performing SPE has been selected and its performance has been evaluated by using it either directly as a platform for the indirect competitive immunoassay or just as a transducer when the assay was performed using magnetic beads (MBs) as a platform for an Enzyme-Linked-Immunomagnetic-Electrochemical (ELIME) format. Both of the approaches have shown similar LOD and comparable sensitivity despite the fact that different enzymes (horseradish peroxidase and alkaline phosphatase) and different electrochemical techniques (Chronamperometry and Differential Pulse Voltammetry respectively) were applied, from which the latter approach also allows for multiplexation. Thus, the described system is a promising candidate for the development of a portable smartphone-connected device for on-site analysis.