Electrolyte-gated organic field-effect transistors integrated into a microfluidic platform: Towards point of care testing

Abstract

Discoveries in immunology are correlating the levels of some biomolecules present in bodily fluids with the type, subtype, and sub-state of illnesses. Monitoring these biomarkers can facilitate early diagnosis of diseases and the assessment of potential risk for each patient. Thus, empowering the administration of individualised treatments. The deployment of such medicine requires the availability of high throughput, reliable portable molecular detection systems. This thesis aimed to address to this demand for point of care devices, by focusing on the development and study of a printed electronic microfluidic molecular detection platform. The building block is an array of Organic Field-Effect Transistors (OFETs) gated through an electrolyte called Electrolyte-Gated OFET (EGOFET). It is designed for multiplex detection of biomarkers in parallel. Initially, OFETs gated with a droplet of water were investigated to benchmark three organic semiconductors, namely 2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene, indacenodithiophene-co-benzothiadiazole and diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (DPPDTT) based polymers. The purpose is to study the electronic behaviour of these semiconductors and to choose the best performing material for the development of a reliable microfluidic integrated EGOFET. Devices based on DPPDTT displayed the highest mobility (~0.18 cm^2/(V.s)) and good on-off current ratio (~3 x 10^3), comparable to the state-of-the-art performance reported to date in EGOFET. Hence, DPPDTT was selected for further investigation. Microfabrication and fast prototyping technologies were combined to engineer arrays of microfluidic integrated DPPDTT based EGOFETs. The device has a network of 4 fluidic channels in each of which there are 4 EGOFET. By functionalisation of individual gates in the array with self-assembled-monolayer of capturing deoxyribonucleic acid (DNA), in operando and specific detection of the hybridization of DNA in ~30 s with errors on the measured figures below 15% was demonstrated. This is faster that related DNA Enzyme-linked Immunosorbent assay (ELISA) kits (~1h) with similar reproducibility. Finally, the transfer of the technology to printable electronics was assessed by developing an EGOFET with a printed DPPDTT. Reproducible average mobility and on-to-off current ratio were respectively ~0.13 cm^2/(V.s) and ~10^2 in printed devices. This EGOFET operated with minimal change in performance for up to 40 minutes under flowing electrolyte with 11%, 8% and 18% changes in transconductance, on-state drain current and threshold voltage. Overall these results suggest that reliable and reproducible technologies based on EGOFET can be developed for high throughput point of need testing and at low cost with en masse facile fabrication techniques.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Turner (Supervisor) & Michelle Webb (Supervisor)