OPTIMISATION OF BIOSENSORS FOR THE BIOMARKERS’ DETECTION

The purpose of my thesis is to optimize and test a partially developed microfluidic platform with Organic Electrochemical Transistor (OECT) devices in order to detect specific biomarkers: tetracycline antibiotics and angiopoietin-2 (Ang2) protein. The protein detection is linked with the Digital tEchnology For Lung Cancer Treatment (DEFLeCT) project, targeting a biosensor for early diagnosis and treatment of lung cancer, through the detection of tumour biomarkers. The antibiotic detection instead has been funded by the Food Drug Free project, aiming at the detection of antibiotic traces in food samples, to fight the increasing issue of antibiotic resistance. Based on the technical improvements matured in these projects, this sensor will find an application in the new project, LoCNeuro, dedicated to the development of a lab-on-chip for monitoring neurodegenerative disorders associated with Covid-19 infection. The main goal is to increase the stability and sensitivity of the device. This thesis is conducted at ChiLab and the Nanoscience Laboratory of Department of Applied Science and Technology (DISAT), Politecnico di Torino. The device is composed of a microfluidic platform which contains gold electrodes, an OECT biosensor, PDMS microfluidic channels, bottom PMMA holder and a 3D printed top holder with spring pins for the electrical contact between biosensor and measuring unit. Poly[3-(5-carboxypentyl)thiophene] (P3CPT) is the exploited organic semiconductor polymer. Au gates are functionalized in order to form a specific probe-target layer that will change the gate voltage drop, thus modulating the drain current of the transistors. For Ang2 detection, the functionalization is performed using the Ang2 antibody. In the case of tetracycline detection, a functionalization with aptamers has been used. The microfluidic channels are designed to inject the target molecules only on the sensing gate electrode, thus not contaminating the organic semiconductor and the reference gate. Device testing is therefore performed by measuring the transfer-characteristics of the transistors with both gates and comparing different figures of merit before and after analyte injection. The main issue with such configuration was the instability of the current. There are four main introduced novelties in order to improve the stability of the device: 1. Deposition of the organic semiconductor 2. Gate patterning. 3. New measurements setup 4. New measurement protocol While the tetracycline detection was carried out before the implementation of all these novelties with limited success, the final configuration allowed the detection of Ang2 in the range of interest for biomedical applications. Concentration of Ang2 in blood higher than 50 pM is indeed considered as a possible marker of tumor onset. The achieved limit of detection in diluted phosphate buffer for the developed platform corresponds to 10 pM, therefore demonstrating the ability of the device to discriminate between pathological and non-pathological conditions in an artificial sample. This paves the way for future research involving the analysis of real samples, where different analytes will be detected by a proper specific gate electrodes functionalization.