Development of conductive and printable filaments for electrochemical sensors applied to environmental, pharmaceutical, food and biological analyses

Abstract

Chemical sensors have been widely developed in response to the growing demand for the monitoring of analytes in environmental, biological, forensic and food samples. Among them, electrochemical sensors stand out for translating chemical information into measurable electrical signals and for offering advantages such as good selectivity, sensitivity, low limit of detection, ease of miniaturisation and versatility for both materials and designs. In this context, these devices have grown together with advances in new manufacturing technologies, especially additive manufacturing, which has emerged as a promising approach for the production of electrochemical sensors. In parallel, new conductive filaments have been developed to improve electrochemical responses, expand possibilities for new applications and incorporate sustainability perspective. However, as this is still a relatively recent field, challenges remain in regard to the achievement of improved electrochemical responses, better printability and the use of new polymers to broaden applications. Thus, this Thesis aimed to explore the fabrication and application of new alternative filaments produced in the laboratory for the monitoring of paracetamol, ascorbic acid, dopamine, uric acid, nitrite and carbendazim, demonstrating the versatility of these devices in environmental, biological and food samples. Divided into six chapters, the work presents: general introduction, filaments modified with carbon nanodiamonds and functionalised nanodiamonds, demonstrating the possibility of modifying and improving electrochemical responses; filaments with the addition of edible oils as plasticisers, with a focus on sustainability and demonstrating, for the first time, the influence of specific plasticisers on sensor responses; alternative thermoplastic polyurethane (TPU)-based filaments, used both as sensors obtained from the direct use of the filament itself and as printed electrodes which, compared with polylactic acid (PLA), show greater flexibility without loss of analytical performance, in addition to biocompatibility, thereby expanding the potential for application in wearable sensors; and, finally, more sustainable filaments produced from high-density polyethylene recycled (rHDPE) from cleaning-product packaging, with emphasis on greater chemical resistance and durability when compared with other polymers. All materials were extensively characterised, and the electroanalytical devices were evaluated against the proposed applications. The results expand the possibilities for the development and optimisation of electrochemical sensors, highlighting efficient, versatile, low-cost materials with low waste generation.