Development and characterization of an Electrolytic-Gated Organic Field-Effect Transistor for biosensing applications

In the last decades Electrolyte-Gated Organic Field-Effect Transistors (EGOFETs) have gained attention for fast and disposable sensors development thanks to low-voltage operation, high sensitivity, and easy and low cost fabrication. This thesis is focused on the testing and electrical characterization of a sensor for biological molecules detection, based on an EGOFET device. The purpose of the work is to deepen the operation of the transistor, testing it in several conditions in order to evaluate the performance and the prospect of use. The measurement setup comprises a probe station and a microfluidic system, which allows a continuous flow of aqueous solution inside the EGOFET chamber. In this configuration the target solution flows in the system and reaches the surface previously functionalized, that may be either the gate electrode or the polymer surface. Being the EGOFET highly sensitive to surface changes, the binding between the target and the recognition element results in a current signal change. Moreover, the setup allows real time current measurements at a fixed voltage operating point during the entire period of the protocol. This is a distinctive choice with respect to the most common test typology, that just compares the device characterizations before and after target exposure. The most used target during this work has been Angiopoietin-2, but the sensor has proved to be versatile, responding to several different molecules. Depending on the target, different types of surface functionalization have been performed and tested. In EGOFET fabrication one of the most crucial element is the organic material, and in this project it has been used and investigated the poly(3-carboxypenthylthiophene) (P3CPT), a derivative of poly(3-hexylthiophene) (P3HT). Despite the latter is widely used and studied in literature, P3CPT has the advantage to expose carboxyl groups in the lateral chains, which allows a direct functionalization of the material. The obtained results showed that it was not possible to obtain specific sensing by a direct functionalization of the polymer. Instead, the most promising result has been achieved with the gold gate functionalized with Anti-Angiopoietin-2 antibodies, and bare P3CPenT. The fact that the specific sensing has been reached with the gate functionalization and not with the polymer functionalization, could mean that in this configuration the gate capacitance dominates over the polymer one