Tailor-made chemical sensing platforms for decentralized healthcare and wellbeing

Resumen

The main motivation of this doctoral thesis is the development of affordable and user-friendly tools for the digitalization of the chemical analysis in different scenarios, with the main goal of improving the quality of life of people by facilitating the decision-making process. The digital revolution, together with many other technological advances, have boosted the development of sensors with ability to monitor several physical parameters in our daily life. These type of sensors has been implemented in cars, homes, hospitals, in the form of embedded or wearable devices, etc. offering the ability to generate a plethora of information in order to perform real-time decisions. However, nowadays there is still a technology gap in the digitalization of the chemical information required to address pressing social needs in healthcare, wellbeing, environmental monitoring and threat assessments, among many others. Although the advances in these fields are also progressing quickly, its implementation in real scenarios is being very slow mostly for the complexity and scalability of these systems. Hence, huge efforts in the scientific community have fostered the progress of analytical devices, particularly in the development and application of portable and low-cost tools for the decentralization of the chemical analysis. This technological revolution will result in an improvement of our wellbeing, an optimization of the healthcare costs, control of pollution and improved security and surveillance, which are some of the main current issues that concern society. In order to address these challenges, the overall goal of this thesis is the exploration and development of novel, intuitive and affordable (bio)chemical sensors that can pave the way to the construction of affordable, robust, scalable, user-friendly and simple platforms for decentralized settings. The main added value of this thesis is the introduction of new electrochemical sensors integrated in different types of affordable and tailor-made platforms, which can be used for several applications from personalized healthcare as well as the monitoring of chemical compounds in the environment. In addition, this thesis remarks the necessity of the development of chemical sensors as an instrument for helping society and improving the healthcare system and wellbeing at all levels. The work has been focussed in two main issues. In the first part of this thesis, wearable and embedded electrochemical sensors based on resistant materials that address the problems related to the user interface are described. In the second part, a new detection strategy for the fabrication of enzymatic sensors with potentiometric detection showing an excellent example of the whole analytical process -from fundamental to applications- is presented. The thesis has been structured in 10 different chapters, each one containing the following information: Chapter 1 provides a general overview of current social needs and challenges in healthcare and wellbeing. The chapter explains how the technological advances could help and improve the current system. It makes emphasis in the joint development of mobile health and point of care technologies as a solution to these challenges. Chapter 2 describes the foundational aspects of the different electrochemical techniques used in this thesis. Moreover, general definitions and conventions about the main components and working principles of the electrochemical sensors developed during the thesis are detailed. Definitions about analytical parameters used for the characterization are also discussed. Chapter 3 corresponds to the experimental section, where the main materials, procedures and instrumentation common throughout all the work are described. Chapter 4 describes the development of a wearable multi-ion potentiometric sensor in a commodity material such as textile. The analytical performance of this sensor under different types of mechanical stress is discussed. The integration of this sensor with common textiles opens new opportunities for using wearable chemical sensing in different fields such as: diagnostics, healthcare and sport. Chapter 5 presents the integration of an electrochemical sensor in a user-friendly platform such as rubber balloons. The sensor based on resilient nanocomposited inks is able to monitor explosive compounds. This is a clear example of decentralization of the environmental analysis beyond the most common topic of decentralization of healthcare. Chapter 6 this chapter together with the following two explore a novel approach to develop potentiometric biosensors with enhanced sensitivity. This chapter is focussed on the understanding of the mechanism involved in the detection of hydrogen peroxide by a platinum electrode coated with a Nafion membrane. Chapter 7 describes the development of a paper-based enzymatic electrode for determination of glucose in biological samples. It is presented as an interesting alternative for the development of simple and affordable devices for decentralized settings. Chapter 8 responds to the goal pursued during the last two chapters presenting a novel low-cost, compact and sensitive paper-based platform for the accurate monitoring of glucose in biological fluids. This low-cost analytical device opens up new prospects for rapid diagnostic results in non-laboratory settings. Chapter 9 provides some alternative modifications in order to improve the outcomes of potentiometric biosensors. In first place, making the device more affordable by developing alternative redox substrates; and in second place, using a different polyelectrolyte coating that confers more interesting features to the biosensor. Chapter 10 outlines the main conclusions derived from experimental work as well as reflects on next steps in order to continue with the improvement of these devices in the field. Along this thesis a successful development of tailor-made and low cost sensors for their use in decentralized chemical analysis has been achieved. Moreover, the manufacturing of affordable, simple and robust devices has been exemplified. Besides, the adaptability of these sensors onto commodity substrates (textile, rubber and filter paper) as well as their simplicity in construction make them an optimal tool for the use in decentralized scenarios. Furthermore, these types of sensors built with commodity materials allows to decrease the manufacturing costs thus enabling the development of disposable sensor. In this way, the electrochemical sensors developed throughout this thesis play a crucial role in improving the social and healthcare system. Of course, further studies regarding the stability and storage of these sensors must be carried out to drive these tools as a final and real applicable product. The main goal, the exploration and development of novel, intuitive and affordable sensors, has been successfully accomplished. Along the work, it has been demonstrated that the content of the thesis can pave the way to the construction of robust, simple and cost-effective platforms for decentralized chemical and biochemical analysis. The thesis has been focused in the research of low-cost detection methods for embedded and point of care (POC) applications. Tailored substrates able to endure daily mechanical stress (such as bending, stretching or wrinkling) without compromising their analytical performance have been developed. Advanced materials that are able to overcome high mechanical deformations as well as provide a suitable platform for the development of an electrochemical sensor has been achieved. Furthermore, the sensors have been successfully implemented into commodity substrates to address social needs in different scenarios such as healthcare and wellbeing, environmental monitoring or threat assessment. The work performed in this thesis has been looking for solutions for the optimization of current processes such as healthcare by providing prototypes for mHealth tools. Huge efforts have been fulfilled in order to develop potentiometric enzyme-based sensors for biomolecules monitoring. A novel, low-cost, compact and sensitive paper-based platform for the accurate monitoring of glucose in biological fluids has been developed. All in all, the basis of the novel electrochemical sensors has been applied in this doctoral thesis with promising results for its implementation in the market in a near future.