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Saygin, GULSEREN DENIZ, (2023)  - Dispositivi microfluidici integrati in biosensori di elettronica organica  - , Tesi di dottorato - (, , Universitą degli studi di Modena e Reggio Emilia ) - pagg. -

Abstract: The electrolyte-gated organic field effect transistors (EGOFET) are commonly used in biosensing applications due to the ultrasensitive sensing mechanism. The potential of the gate electrode is sensitive to antigen binding at surface bound recognition sites, which is capacitively coupled to the transistor channel. Even the low amount target biomolecules can cause a shift of the gate electrode workfunction, inducing a change in the Electrical Double Layers (EDLs) near the semiconductorelectrolyte interface.In this PhD thesis, I present applications of multi gate EGOFET architectures integrated with microfluidic devices exploiting diffusion in laminar flow mixer. The gradient of concentration affects the EGOFET electrical characteristics, providing an insight of the kinetics of surface functionalization reactions, oligonucleotide probe-target hybridization or antigen-protein binding reactions. The reported results indicate that multi gate EGOFET can be used as an electroanalytical tool for monitoring self-assembly monolayers (SAM) on top of gold thin electrodes sputtered on flexible polymeric substrates. The possibility to control the self-assembled monolayer formation is achieved by means of the diffusion interface within the microfluidic streams. For this purpose, we integrate the microfluidic mixer with EGOFET device by means of an electrolyte bridge. The mixer performance is validated with UV Spectroscopy with different biomolecules. The diffusion interface between concurrent streams of solutions generates a concentration gradient along the H-mixer main channel, which affects the kinetics of thiols self-assembly upon the array of electrodes patterned on the lower boundary of the microfluidics. The study was pursued with four short chain alkanethiol moieties (3-mercapto-1-propanol, 6-mercapto-1-hexanol, 8-mercapto-1- octanol, 9-mercapto-1-nonanol) at flow rates ranging from 2 µl/min to 50 µl/min. The drain-source current was recorded in the nA to µA range, showing a decrease correlated with the axial position of the gate electrode along the microfluidic channel. The initial gate electrodes in the array kept the same transfer curves as immersed in the PBS electrolyte, while those along the stream were influenced by thiol diffusion, leading to drain-source current lower than 50%. Multi gate EGOFET architecture with microfluidic chamber has been used to perform biorecognition with oligonucleotides probe-target pairs, showing high sensitivity response. MicroRNAs (miRNA) are classified as important biomarkers for cancer such as glioblastoma, lung and breast cancers. The device allows one to measure the differential response with respect to a sensing gate and a reference gate electrode, both immersed in the electrolyte above the transistor channel. Hybridization with oligonucleotide in the picomolar regime induced a reduction of the current flowing through the transistor channel. The device response signal is reported at various gate voltages, being the sensitivity of the biosensor maximized in the sublinear regime, with a limit of detection as low as 35 pM. We describe the dose curves with an analytical function derived from a thermodynamic model of the reaction equilibria relevant in our experiment and device configuration and we show that the apparent Hill dependence on analyte concentration with exponent between 0.5 and 1 emerges from the interplay of the different equilibria. The binding free energy characteristic of the hybridization on the device surface is found to be approximately 20% lower with respect to the reaction in solution, hinting to partially inhibiting effect of the surface and presence of competing reactions.