Development and characterization of Organic Electrochemical Transistor-based sensors for applications in wearable devices for glucose monitoring

Wearable sensors and flexible electronics are closely intertwined technologies that are revolutionizing various fields, particularly health monitoring, and are essential to the realization of personalized medicine through continuously monitoring an individual’s state of health. Especially, this thesis focus on Organic Electrochemical Transistors (OECTs), which have recently emerged as a highly promising technology in the area of biosensing and flexible electronics. This thesis work is part of an industrial project commissioned and funded by Umana Medical “Vita” Project and is the result of a partnership between ChiLab-Materials and Microsystems Laboratory (Politecnico di Torino) in Chivasso and the Institute of Materials for Electronics and Magnetism (IMEM) at the National Research Council (CNR) in Parma. Therefore, specific details about the device and data collected during the project can be protected to ensure non-disclosure of results. The aim of this thesis is to develop an innovative OECT-based sensor for a flexible wearable device capable of non-invasively detecting glucose levels in diabetic patients through sweat sampling. Sweat is a promising biofluid toward non-invasive, continuous monitoring applications due to its distinct advantages, such as its easy availability and its rich composition of physiologically significant electrolytes and metabolites that vary in response to the state of health, including glucose. Organic Electrochemical Transistors (OECTs), are employed as sensors due to their unique properties that make them well-suited for applications in healthcare and diagnostics, such as high transconductance (on the order of mS), biocompatibility, low voltage operations (< 1V) and amplification capability. In addition, the synthetic tunability, facile deposition and low cost of organic materials make OECTs particularly suitable for application in biosensing. The device is characterized by polydimethylsiloxane (PDMS)-based microfluidic to combat evaporation and absorbent filter paper to enable sweat absorption even in low sweat secretion conditions. The microfluidic geometry proposed is radial scheme to allow sweat absorption and convergence to eight separate chambers where the OECT sensors are placed. The OECT consists of gold source and drain electrodes deposited on a Kapton substrate, a poly-(3,4-ethylene-dioxythiophene):poly-(styrenesulfonate) (PEDOT:PSS) channel and a platinum gate functionalized with the enzyme glucose oxidase (GOx). The system consists of a thin, flexible, circular patch with a diameter of 33.17mm, that can be coated and affixed to the skin, so it is directly interfaced with the liquid electrolyte, the sweat. The device shows a stable and reproducible current modulation and has been demonstrated to be very effective for electrochemical sensing of glucose concentration in sweat. However, more measurements need to be done in order to accurately correlate the channel current modulations with glucose concentrations in sweat and demonstrate the selectivity against interferences. Despite the exponential progress in the field, several key challenges remain, including sweat collection, glucose detection sensitivity, establishing a reliable correlation to gold standard blood glucose meters and a variable rate of sweat production, which appears to be quite low during sedentary activities (&#8776;1 nL/min/mm2).