BIOSENSOR PLATFORM INTEGRATING ORGANIC ELECTROCHEMICAL TRANSITORS FOR IN-VITRO CONTINUOUS MONITORING

In recent years, organic electrochemical transistors (OECTs) have attracted interest in the field of organic bioelectronics thanks to their distinctive properties. In these devices, the channel consists of an organic semiconducting polymer which is in contact with an electrolyte. The gate electrode, immersed in the electrolyte, regulates the conductivity of the channel. Biocompatibility, ease of fabrication, low cost, high ionic sensitivity and low-voltage operation are among the properties that make this class of devices suitable for a wide range of applications, such as biosensing, in-vitro monitoring, and wearable and implantable devices. The purpose of this thesis, which is part of the Cobalt project, is the fabrication of an OECT-based device capable of continuously monitoring the behaviour of the endothelial barrier. In-vitro monitoring, i.e. the possibility to analyse and study the behaviour of cell cultures outside of the living organisms, is of great importance because it allows a precise control of the experimental conditions, reduces the costs, and permits to study how cells respond to specifically induced stimuli. Moreover, the continuous collection of data over long periods of time is critical to understand the time evolution of certain biological processes and to identify any sudden changes in the behaviour of the biological sample under investigation. The endothelial barrier, situated on the surface of blood vessels, regulates the exchange of substances between the bloodstream and the adjacent tissues. The analysis of its behaviour is crucial to understand its permeability to certain therapeutic molecules and its implication in the dynamics of specific diseases. This work intends to give an overview of the device design and the processes involved in its fabrication. The device comprises a Top and a Bottom structure, each consisting of three branches. Each branch houses an OECT with a p-type poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) channel. The three OECTs of the Bottom structure are placed at the base of three wells of a multi-well plate, while the three OECTs of the Top structure are inserted in three well inserts, at the bottom of which a layer of endothelial cells is grown. This design, that implements one OECT at each side of the membrane, opens the possibility for a wider set of analyses, depending on the input settings. The device fabrication starts with the creation of the OECTs gold electrodes through traditional subtractive photolithography techniques. The device is then cut with a CO2 laser and the Top and Bottom structures are bonded thanks to oxygen plasma bonding. Contacts between the device and an external ribbon cable are formed using a silver conductive paste and then passivated with an epoxy resin. The device is then electrically characterised and its biocompatibility is tested in an incubator.